Gearing selection re-re-revisited... :)

Me again, resident LT1 project car boy. :)

I thought I had the gearing question solved. Jordon recommended I keep the 4.10s in my car (assume a 2.97:1 first gear T56) to help with low rpm cam surge by getting the engine into higher rpms quicker at low vehicle speeds. Good plan, but...

After some long hard thought, I've talked to Mark a little and we'll probably have a new cam ground and dial my engine back a bit to make it even more streetable. The power numbers were excellent, but power is useless if you can't put it to the ground. It's also useless if you hate to drive what you've built. We made more than enough power to "sacrifice" some of it, and still end up with too much, when it comes right down to it.

So assuming a more mild solid roller cam, and maybe dropping back to 600-620 horsepower, I think that the 4.10s are probably more of a liability than a benefit. The big horsepower Corvettes with have traction problems even with 3.42s. I know that many F-body owners run 3.73s, but F-body owners also tend to be drag racers in many cases. In building a true street car, I don't think I need the gearing that I would if I intended to run slicks at the drag strip. I need something that will help me get power to the ground with street tires, or at the most, drag radials. I'm not worried about being as close as possible to peak power as I cross the quarter mile, I'm worried about blazing my tires if I even look at the gas pedal too hard. :)

I've pondered Car Test 2000 numbers for a few months now, and have come to the conclusion that Car Test is useless. Not only have I found many glaring inconsistencies (calculated top speeds higher than the possible gear-limited top speed, which indicates no factoring of wind resistance, not to mention other problems) but the numbers reported for even widely differing combinations (2.90s vs. 4.10s, for example) aren't different enough to believe that the results are being calculated correctly. I know for a fact that it's not calculating tire spin properly, generating tire spin only on launch and at the shift, but holding well in excess of 1.0 g of acceleration, even on street tires. No way.

I know from real world results (videos that I've seen of big cube LT1 Camaros, Z07 and built Z06 Corvettes, etc.) that the Corvette, at ~300+ lbs. heavier, has no trouble at all accelerating quickly both from a dead stop and at highway speeds with a 3.42 differential. Add a lot of horsepower, and they have severe traction problems in 1st and 2nd even with a 3.42 diff and P335s in back. Same goes for Camaros, I'm sure... put in a built 396 LT1, for example, and the car wants to blaze its tires all the time in lower gears, especially for those with 3.73s (or higher).

All I'm asking for is confirmation that going in the opposite direction (3.42, 3.23, and maybe even a little lower) is the right way to go for a street car that may see very limited drag strip use, but certainly on nothing more serious than drag radials.

And finally, the Saleen S7 seems to be confirmation of my theory concerning gearing. 550 horsepower @ 6,400 rpm, 520 lb-ft. of torque at 4,000 rpm, and a 7,000 rpm redline from 7.0 liters, and they gave the car a 3.22 differential with a 2.46:1 first gear. If I have a 2.97:1 first gear and more power, in a car that weighs almost the same, wouldn't it stand to reason that I'd pull even harder (or spin more) using a 3.23 differential also? Obviously the 3.23 diff isn't holding the S7 back any in the acceleration department.

I've got a friend assuring me that my car won't pull as hard on the high end if I lose the 4.10s... maybe he's right, but there's not much on the road that will pull as hard as my car would with 3.23s or 3.42s either, and having a car that doesn't hook until 60+ mph and having to pull high speeds to really use your power isn't where I want to be.

Any help would be greatly appreciated, as always. :)

Im in the same boat as you are now in gear selection, yet my car is not making anywhere near mega HP or TQ. IM in between 410s and 373s.

I dont think it is absoultly wrong to step down in gearing for high horsepower cars. Most of the M6 guys running blowers and nitrous are using the 373 gear instead of the 410 in mostly drag cars.

The problem associated with lower gearing in drag cars is the launch. You need enough power/clutch/gear to be able to launch the car without burning your clutch, and without bogging.

The lower (numerically) gear you select, the more wear and tear acts upon the clutch which is something to consider also in high HP aplications. A 500rwhp car and a 3.08 gear would = a very shortened clutch life.

If I were you, for a street only car, as mentioned, i stick with the 342 ratio. If you wouldnt mind running DRs on the street, i would go with the 373. Anything lower than the 342 IMO would be useless (top speed would be 300mph? if it wasnt for air), which is so under geared.

Hope this helps a little
jared

Originally posted by atljar
The lower (numerically) gear you select, the more wear and tear acts upon the clutch which is something to consider also in high HP aplications. A 500rwhp car and a 3.08 gear would = a very shortened clutch life.Can you elaborate on where you heard/learned this? The Viper GTS-R has a 3.07 differential, and many other high powered sports cars (which I'll list in a moment) also have remarkably "tall" differential gearing. I've never heard that gearing had an impact on clutch longevity... only driver abuse and/or exceeding the power handling ability of the unit. :)

If I were you, for a street only car, as mentioned, i stick with the 342 ratio. If you wouldnt mind running DRs on the street, i would go with the 373. Anything lower than the 342 IMO would be useless (top speed would be 300mph? if it wasnt for air), which is so under geared.Also consider that I'm planning to use the 2.97:1 gear set T56 as opposed to the 2.66:1 gear set in the '94-up F-body cars. With a 3.23 differential, the final drive is actually a little higher than 3.42s in a '94-up F-body.

1st gear - 2.97 x 3.23 = 9.59:1
2nd gear - 2.07 x 3.23 = 6.69:1
3rd gear - 1.43 x 3.23 = 4.62:1
4th gear - 1.00 x 3.23 = 3.23:1
5th gear - 0.80 x 3.23 = 2.58:1
6th gear - 0.62 x 3.23 = 2.00:1

1st gear - 2.66 x 3.42 = 9.10:1
2nd gear - 1.78 x 3.42 = 6.09:1
3rd gear - 1.30 x 3.42 = 4.45:1
4th gear - 1.00 x 3.42 = 3.42:1
5th gear - 0.74 x 3.42 = 2.53:1
6th gear - 0.50 x 3.42 = 1.71:1

Here are a few other cars with incredibly tall differential gearing...

Viper GTS-R
3.07:1 differential
2.66:1 first gear
8.16:1 final drive

Ferrari F40
2.90:1 differential
2.77:1 first gear
8.03:1 final drive

Saleen S7
3.22:1 differential
2.46:1 first gear
7.92:1 final drive

McLaren F1
2.37:1 differential (?!?)
3.23:1 first gear
7.66:1 final drive

Lamborghini Murcielago
2.53:1 differential
2.94:1 first gear
7.44:1 final drive (and that's a 3,600 lb. car!!!)

All are high powered sports cars, some more so than others. All have plenty of torque. Most are fairly lightweight, with the McLaren and S7 coming in at right around where I'll be (~2,700-2,750 lbs.) and the F40 at about 150 lbs. heavier. The Viper weighs in the 3,300 lb. range, and the Murcielago is 3,600, as mentioned above. Yet all the manufacturers of these cars (built for street and open road course use) geared them this way, so they must have had some reason, and the pattern is too obvious to ignore. By comparison, even with the 2.66:1 first gear T56, with the 4.10 differential, my final drive is at 10.91:1 in first gear. No wonder the guys with 3.73s and 4.10s can't get any traction on the street. :)

Does anyone know how car manufacturers select their gear ratios? My Z06 has the same 2.97:1 first gear and 3.42s, and weighs 3,117 lbs. Someone at GM must have felt that the 2.97 gear set gave an advantage over the standard 2.66:1 gear set with the 3.42s, and they're right. To a point... when you slap that MTI Z07 422 in the car, suddenly it's got a little too much gear in 1st and 2nd. At that point, if GM were issuing the car with, say, 580-600 horsepower, I wonder what they would have selected for gearing for street use.

Anyway, I need to make a decision, since if I'm going to have a custom ring and pinion cut, I'll need some lead time so it doesn't add further delays to finishing my car. I've decided to stick with the stock housing, so my only option lower than a 3.90 is to have the gears made to order, unfortunately. Still, that's far better than ending up with a car that's completely useless below 60-70+ mph because it has way too much gear for the street.

Also, I've only found one 18" drag radial, and it's a P305/45-18, which is a big tire. ~28.8" tall compared to the stock P225/50-16 (~24.86" tall) or the fairly common aftermarket options of P275/40-17 and P285/35-18 (~25.66" and ~25.85"). I doubt I can fit the P305 under the back anyway, so I think drag radials are out unless I want to stick with 17" rims. I was planning on moving up to 18s.

Hope this helps a little
jared Thanks!

Originally posted by jimlab
Can you elaborate on where you heard/learned this? The Viper GTS-R has a 3.07 differential, and many other high powered sports cars (which I'll list in a moment) also have remarkably "tall" differential gearing. I've never heard that gearing had an impact on clutch longevity... only driver abuse and/or exceeding the power handling ability of the unit. :)


All are high powered sports cars, some more so than others. All have plenty of torque. Most are fairly lightweight, with the McLaren and S7 coming in at right around where I'll be (~2,700-2,750 lbs.) and the F40 at about 150 lbs. heavier. The Viper weighs in the 3,300 lb. range, and the Murcielago is 3,600, as mentioned above. Yet all the manufacturers of these cars (built for street and open road course use) geared them this way, so they must have had some reason, and the pattern is too obvious to ignore. By comparison, even with the 2.66:1 first gear T56, with the 4.10 differential, my final drive is at 10.91:1 in first gear. No wonder the guys with 3.73s and 4.10s can't get any traction on the street. :)

Does anyone know how car manufacturers select their gear ratios? My Z06 has the same 2.97:1 first gear and 3.42s, and weighs 3,117 lbs. Someone at GM must have felt that the 2.97 gear set gave an advantage over the standard 2.66:1 gear set with the 3.42s, and they're right. To a point... when you slap that MTI Z07 422 in the car, suddenly it's got a little too much gear in 1st and 2nd. At that point, if GM were issuing the car with, say, 580-600 horsepower, I wonder what they would have selected for gearing for street use.


Thanks!

OEM gear ratios are selected for all around performance and driveability. As you pointed out, it's difficult to drive a car that has gobs of torque AND lots of gear and can fry the tires through 1st and maybe 2nd gear. It takes a very skillful driver to control that. Even Winston Cup guys have that trouble on the shorter tracks, and most of them have very educated right feet! That may be why there have been so many rumors of traction control in WC.

ZO6 is a good example. The steeper 1st on the Z06 went along with the larger, sticker rear tire to better launch the car. I also think they were looking to get sub 4 second 0-60 times on absolutely stock Z06. If it went to 500+ lb-ft, bigger tires still would be needed, and ASR would probably be the only way to get better launches, especially for magazine test guys, who almost always turn it off. It's a balanced system. Throw gobs more torque at it and the scale tips.

When you jack up the low-mid range torque significantly, you need to increase the traction to go along with it or the car not only is more difficult and less satisfying to drive, but it can be slower if you are always going up in smoke.

Big cams often put a big hole in the low-mid range torque curve which makes the car even more difficult to launch. If the engine then "comes up on the cam" with a huge torque spike at say 4000-5000, poof goes the traction again. Smoke isn't fast.

IMO, if you want a quick street car with the kind of torque/weight ratio you have, you need an engine that has a fairly flat torque curve, and pulls from the low 2000's at part to full throttle. It's hard to do that and make 500+ hp (NA), but many of the cars you mentioned do just that. 250 degree (@.050) cams in a Chevy won't make it happen. I don't know about your engine, but I've seen a 6 L SBC pull over 520 lb-ft and over 550 hp on the dyno with cam durations below 230 degrees on 92 octane. It was a very aggressive roller with lots of lift and had great heads. It also idled below 900 with no lope. 85% of max torque was available from 3000 to power peak at 6300.

With that kind of a torque curve, and the car weight and tires you have, 3.23-3.42's should be easier to drive, be very fast, and not buzz the engine during cruise. You'll still have trouble getting it all down w/o slicks, but you should be able to control it with your right foot and not your left (slipping clutch).

The key, IMO, is to build a driveable engine to fit the chassis, not build a killer motor (from 5000 to 7000+) with a huge hole in the low end torque curve, and try to get it to launch on street tires or DR's with less than 50% of the weight on the 2 driving wheels.

IMO, with this killer type of engine, and low gears (3.07's etc.) you have to slip the clutch during launch to keep the engine above 2500-3000 because it dies or even stalls under full throttle in those ranges. That's not much fun in my book, and it's SLOW!

I think you are on the right track with a milder cam, and mid 3's gearing.

Sorry to drone on so long. My $.02.

To compose an intelligent response, we need to know how your motor is set up. IOW, what rev range do you plan to use, and what is your redline? I use 3.42's because I have a low rev setup (6,000rpm redline, peak hp at 5,500). Works great at the track, where I just touch the rev limiter through the traps, and on the street where I can cruise at 75mph at less than 2,000rpm. That's the beauty of the M6! I am contemplating a TH400, but really think the M6 is the better choice beacuse of the wide gear range except for extreme duty track use.

Rich Krause

Interesting gear ratio combo. Looks like something more useful in a street motor with a wide torque band than a 600-620hp street-race motor. Thats alot of power to try to drive it around too much. The only reason to get a higher gear, to me, would be because of the trans ratio. I would go 3.73:1. Yeah 3.42's are gonna give a little more 'running room' in 1st but then again, wouldnt 3.73's make the car hit the tires quicker?

Originally posted by jimlab
Can you elaborate on where you heard/learned this? The Viper GTS-R has a 3.07 differential, and many other high powered sports cars (which I'll list in a moment) also have remarkably "tall" differential gearing. I've never heard that gearing had an impact on clutch longevity... only driver abuse and/or exceeding the power handling ability of the unit. :)

Also consider that I'm planning to use the 2.97:1 gear set T56 as opposed to the 2.66:1 gear set in the '94-up F-body cars. With a 3.23 differential, the final drive is actually a little higher than 3.42s in a '94-up F-body.


Maybe i shouldnt have used the phrase "very shortened clutch life", but with a numerically lower gear more time will be spent slipping the clutch getting the car started from stops, which equals more wear and tear on the clutch. Seems to me as that would shorten the lifespan of the clutch?

Correct me if anyone knows other wise, but i always thought a lower numerical gear is easier on the rear, harder on the clutch. A higher numerical gear is easier on the clutch, harder on the rear.

Originally posted by rskrause
To compose an intelligent response, we need to know how your motor is set up. IOW, what rev range do you plan to use, and what is your redline? I use 3.42's because I have a low rev setup (6,000rpm redline, peak hp at 5,500). Works great at the track, where I just touch the rev limiter through the traps, and on the street where I can cruise at 75mph at less than 2,000rpm. That's the beauty of the M6! I am contemplating a TH400, but really think the M6 is the better choice beacuse of the wide gear range except for extreme duty track use.My redline is an arbitrary 7,500 rpm. In its current iteration, the engine is still making nearly 640 horsepower at 7,400 rpm, but it is starting to fall off, and peak power is around 6,900-7,000 rpm. If we re-cam the engine for better drivability, I am sure that my peak will fall a bit, and that I'll be shifting a little sooner, but still over 7,000 rpm.

Horsepower looks like this... (my engine dyno numbers compared to converted RWHP figures for a stock '93-'95 RX-7 TT and a fully modified "360 RWHP" RX-7 with stock twins)
http://home.earthlink.net/~jimlab/pics/rx7/Horsepower.jpg

And torque looks like this...
http://home.earthlink.net/~jimlab/pics/rx7/Torque.jpg

396 LT1, 215cc raised runner heads, 2.10/1.65 valves, Hogan intake, 1,300 cfm monoblade, Crower ultralight crankshaft, Crower maxi-light rods, custom JE pistons @ ~12.5:1 static compression, Cam Motion solid roller in the 26x/26x range with over 0.650" lift and a 112 lsa, I believe.

The car will weigh in the 2,700-2,750 lb. range and was 50/50 balanced and should be pretty close even with the V8. The widest tire I can probably put under the back would be a P285 or P295.

Quick question... is there any correlation between the number of teeth on the ring and/or pinion gear and strength? I'm assuming that the lower the number of teeth, the better off you are?

The reason I ask is because I can achieve a 3.23:1 ratio with a 42-tooth ring gear and a 13-tooth pinion gear (3.231:1), but I could make a nearly identical 3.27:1 ratio with a ring gear with only 36 teeth, and a pinion gear with only 11 (3.273:1), which I assume would be quite a bit stronger. 6 less teeth on the ring gear and 2 less on the pinion have to count for something, right?

My stock gears are a 41-tooth ring gear and a 10-tooth pinion gear.

Originally posted by jimlab
Quick question... is there any correlation between the number of teeth on the ring and/or pinion gear and strength? I'm assuming that the lower the number of teeth, the better off you are?

The reason I ask is because I can achieve a 3.23:1 ratio with a 42-tooth ring gear and a 13-tooth pinion gear (3.231:1), but I could make a nearly identical 3.27:1 ratio with a ring gear with only 36 teeth, and a pinion gear with only 11 (3.273:1), which I assume would be quite a bit stronger. 6 less teeth on the ring gear and 2 less on the pinion have to count for something, right?

My stock gears are a 41-tooth ring gear and a 10-tooth pinion gear.

While it's true the teeth are larger on the 36:11. you are putting the same amount of torque through fewer teeth, so each one has to take more of the load. The finer pitch 42:13 with more teeth in contact spreads the load out more and might be stronger. The quality of the steel, machining and heat treatment are probably as important however.

With your tire limitations, I doubt rear end strength will be a problem, unless it's the original RX7.

Originally posted by jimlab
My redline is an arbitrary 7,500 rpm. In its current iteration, the engine is still making nearly 640 horsepower at 7,400 rpm, but it is starting to fall off, and peak power is around 6,900-7,000 rpm. If we re-cam the engine for better drivability, I am sure that my peak will fall a bit, and that I'll be shifting a little sooner, but still over 7,000 rpm.

Horsepower looks like this... (my engine dyno numbers compared to converted RWHP figures for a stock '93-'95 RX-7 TT and a fully modified "360 RWHP" RX-7 with stock twins)
http://home.earthlink.net/~jimlab/pics/rx7/Horsepower.jpg

And torque looks like this...
http://home.earthlink.net/~jimlab/pics/rx7/Torque.jpg

396 LT1, 215cc raised runner heads, 2.10/1.65 valves, Hogan intake, 1,300 cfm monoblade, Crower ultralight crankshaft, Crower maxi-light rods, custom JE pistons @ ~12.5:1 static compression, Cam Motion solid roller in the 26x/26x range with over 0.650" lift and a 112 lsa, I believe.

The car will weigh in the 2,700-2,750 lb. range and was 50/50 balanced and should be pretty close even with the V8. The widest tire I can probably put under the back would be a P285 or P295.


You were able to pull 400 lb-ft @2000 rpm at full load on an engine dyno with the 26x/26x (@.050) cam? That's a torque curve to die for! 400 lb ft @ 2000 and still at 8000! That's one dyno run I'd like to observe.

With that kind of torque curve, why are you worried about gearing and driveability? Just let the clutch out about 2 grand and control the wheelspin with your right foot.

I'm also very impressed that 215 cc heads will pull that kind of hp at 8000 on a 396. What kind of flow numbers?

Originally posted by jimlab
My redline is an arbitrary 7,500 rpm. In its current iteration, the engine is still making nearly 640 horsepower at 7,400 rpm, but it is starting to fall off, and peak power is around 6,900-7,000 rpm. If we re-cam the engine for better drivability, I am sure that my peak will fall a bit, and that I'll be shifting a little sooner, but still over 7,000 rpm.

Horsepower looks like this... (my engine dyno numbers compared to converted RWHP figures for a stock '93-'95 RX-7 TT and a fully modified "360 RWHP" RX-7 with stock twins)
http://home.earthlink.net/~jimlab/pics/rx7/Horsepower.jpg

And torque looks like this...
http://home.earthlink.net/~jimlab/pics/rx7/Torque.jpg

396 LT1, 215cc raised runner heads, 2.10/1.65 valves, Hogan intake, 1,300 cfm monoblade, Crower ultralight crankshaft, Crower maxi-light rods, custom JE pistons @ ~12.5:1 static compression, Cam Motion solid roller in the 26x/26x range with over 0.650" lift and a 112 lsa, I believe.

The car will weigh in the 2,700-2,750 lb. range and was 50/50 balanced and should be pretty close even with the V8. The widest tire I can probably put under the back would be a P285 or P295.

Jim: I remember you posting on a related matter a while back. There was a lot of discussion then re: gearing for traction. This doesn't make much sense to me in your case. I assume that this isn't going to be a drag car, right? If you aren't going to have a DR suspension and a huge set of slicks on it, there is no way you will be able to launch it hard no matter what your rear gear is. You have have to use the traction control device known as your right foot! Most likely you won't be able to use full throttle on a 295 street tire in first or second gears, and maybe third as well no matter what gear you select!

When you come right down to it, you don't need a T56 six speed at all with your TQ curve and a curb weight of less than 3,000lbs. If you go with 3.2x:1 like you are talking about, sixth gear will be useful from maybe 120mph and up! IOW, the spread of ratios is more than you need. I would go for a gear that allows me to use 1-4 as normal driving gears, 5 as an OD, and never figure on using 6th. This would be maybe a 3.73, I'd have to do a little calculating to be sure. Alternatively, you could gear it to use 2-6 and never use 1st except in a parking lot or traffic jam. That would entail a 4.11 or more. The advantage here is that you would never use 1st gear under high throttle, which might protect the transmission. Of course, I think you will have no problem with transmission or rear end longevity no matter what - you will just spin the rear wheels long before anything breaks.

Rich Krause

Originally posted by OldSStroker
While it's true the teeth are larger on the 36:11. you are putting the same amount of torque through fewer teeth, so each one has to take more of the load. The finer pitch 42:13 with more teeth in contact spreads the load out more and might be stronger. The quality of the steel, machining and heat treatment are probably as important however.

With your tire limitations, I doubt rear end strength will be a problem, unless it's the original RX7. Good point, and thanks for bringing that up. I had forgotten that more splines are usually better on the input shaft and output shaft of a transmission (as well as increased diameter) to spread the load further, so the same must also apply to ring and pinion gear teeth. Thanks!

Originally posted by OldSStroker
With that kind of torque curve, why are you worried about gearing and driveability? Just let the clutch out about 2 grand and control the wheelspin with your right foot.I expect that a 2,000 rpm launch would result in horrendous tire spin, regardless of what gearing I have, as Rich pointed out. I'm not looking to launch all that hard, but I am looking for some sort of advantage in being able to use "more" of my throttle pedal without fear of breaking the rear tires loose.

I'm already horribly well aware that even with a 3.42:1 differential, that with the 2.97:1 T56 or even the 2.66:1 T56 that I'll have a hell of a time in 1st and 2nd if I get happy with my right foot. I know that the MTI Z07 converted Corvettes have incredible traction problems in 1st and 2nd, even with P335s in the back, if you're not careful with the throttle. I expect to have to "tip in" the throttle, but it'll be a lot easier, I suspect, with a 3.xx gear ratio as opposed to some drag racing 4.10s in the back. :)

The only reason the car had 4.10s in the first place is because the rotary (obviously) makes almost no low end power. :)

The current plan is to step the cam down some and try to make the engine a little more docile. In Mark's words "it's streetable, but it's definitely a popcorn popper". :)

I'm also very impressed that 215 cc heads will pull that kind of hp at 8000 on a 396. What kind of flow numbers? ~34x cfm on the intake @ 0.700", 2.10" valve.

The best pull on the base maps had a big dip in the curve through peak power, but made a very promising 640.8 @ 6,400 before the dip, and 636.7 @ 7,400 after the dip. We're still waiting on the modified front cover (cam sensor) for the eDist, so I don't even know what kind of numbers it would have made tuned if I left the cam as-is, but they saw 647 on one pull, on the base maps, and peak power should have been in the 6,900-7,000 rpm range. It's down to ~622 at 7,600 and falling off, so I was planning on using 7,500 as the "redline".

Originally posted by rskrause
Most likely you won't be able to use full throttle on a 295 street tire in first or second gears, and maybe third as well no matter what gear you select!Yep. But it would be a lot worse with 4.10s, probably. :)

When you come right down to it, you don't need a T56 six speed at all with your TQ curve and a curb weight of less than 3,000lbs. If you go with 3.2x:1 like you are talking about, sixth gear will be useful from maybe 120mph and up! IOW, the spread of ratios is more than you need. I would go for a gear that allows me to use 1-4 as normal driving gears, 5 as an OD, and never figure on using 6th.I've sort of figured that, although it galls me to haul around an "extra" gear I might rarely use.

Alternatively, you could gear it to use 2-6 and never use 1st except in a parking lot or traffic jam. That would entail a 4.11 or more. The advantage here is that you would never use 1st gear under high throttle, which might protect the transmission. Of course, I think you will have no problem with transmission or rear end longevity no matter what - you will just spin the rear wheels long before anything breaks.It's been suggested by a couple people to keep the 4.10s and start in 2nd gear... but that has to be hard on the transmission and clutch. The alternative is to start in 1st and *really* short shift 1st gear and travel around a gear higher than I normally would. I'd rather have a more "normal" arrangement, if possible.

I was leaning towards the G92 T56 (2.97:1) because they're less expensive (brand new) than the '94-up T56 (2.66:1). Mark said the 400 lb-ft. rating wasn't anything to be concerned about. The 5th and 6th gear ratios are better, although 1st through 4th would be equivalent to my Z06 (3.42 diff) and I know for a fact that it's already hard to launch "aggressively" without spinning, even without the low end power of a stroker engine. :)

An ideal gear set would be 1st through 4th from a '94-up T56 with 5th and 6th from the G92, (0.80, 0.62) I think. The 0.62:1 6th gear puts me at ~1,930 rpm @ 70 mph, which is just about right.

Man you'd better make some videos of this... thing... after your finished with it. I was actually planning on an LT1 3rd gen swap, if you couldnt tell from the name, but decided it was too much of a hassle so I bought an F-body, oh well. Good luck....

Originally posted by rskrause
If you go with 3.2x:1 like you are talking about, sixth gear will be useful from maybe 120mph and up!

Well I guess that depends on what you consider "useable". With the 93 T56 and its .62 6th gear 3.23's are very usable IMO. With that combo my car would pull in 6th gear as low as 50mph. Granted you werent going to win any races that way it had enough grunt such that downshifting wasn't nessecary. With lots more torque and considerably less weight to carry around I dont think Jim will have any problems making use of 6th gear.

Jim: If think you're on the right track with something like a 3.23 or 3.42 gear ratio. I run 3.42's now on my 93 T56 and I wouldnt want anything higher. Partly beacuse I'm lazy and I dont want to shift any more often than I need to, and partly beacuse it would push my crusing RPM @70mph higher than I would like.

My $.02 :cool:

Thanks Jason. Looks like I'll be going with 3.42s, since although I'd like just a little less gear, I can get my gears more cheaply if I can interest other people in going in on a group purchase. :)

Honestly I want to see the actual dyno printout scanned in.

12.5:1? Why do that on pump gas in a car? You better run high octane (100) or run it really cold.

Please post the flow numbers at all lifts too, not just 3xxcfm numbers. BTW who did these heads? and how are they still 215cc's?

Bret

Originally posted by SStrokerAce
Honestly I want to see the actual dyno printout scanned in.I only have the numbers that Mark Montalvo sent me, he apparently has pictures of the dyno monitor during the dyno session(s) and video, but I haven't seen either. He simply sent me a quick write up of what happened, and you can see that here...

http://home.earthlink.net/~jimlab/images/dyno1.jpg

12.5:1? Why do that on pump gas in a car? You better run high octane (100) or run it really cold. It might actually be closer to 12.2:1. Mark had custom pistons made and we sold the ones that I sent him, so I'm not sure where it ended up, but it is in the 12.2-12.5:1 range, static. With a 26x/26x @ 0.050" solid roller cam, obviously dynamic compression is lower. It is a pump gas engine, and the car is not intended to be a daily driver.

Please post the flow numbers at all lifts too, not just 3xxcfm numbers. BTW who did these heads? and how are they still 215cc's?B&B Performance did the heads under Mark's guidance. They were custom cast AFR 215cc raised runner heads with reverse cooling revision. 2.10"/1.65" valves. I was specifically asked not to publish the flow figures, however.

http://www.c-zone.net/markm/JimLaBreck/heads/bare/DCP_0373.jpg
http://www.c-zone.net/markm/JimLaBreck/heads/bare/DCP_0379.JPG
http://www.c-zone.net/markm/JimLaBreck/heads/bare/DCP_0383.JPG
http://www.c-zone.net/markm/JimLaBreck/heads/completed/P1020025.JPG
http://www.c-zone.net/markm/JimLaBreck/heads/completed/P1020031.JPG
http://www.c-zone.net/markm/JimLaBreck/heads/completed/P1020032.JPG
http://www.c-zone.net/markm/JimLaBreck/engine/completed/P1190035.JPG
http://www.c-zone.net/markm/JimLaBreck/predyno/P1010114.JPG
http://www.c-zone.net/markm/JimLaBreck/dyno/P4260021.JPG

Bret, if you are at all in doubt of the power my engine made, you're more than welcome to contact Mark directly and ask him about it. :)

We're going forward with having 3.42 gear sets made, thanks to everyone for all of your help!

Sorry to resurrect such an old topic... If you have compared the z06 to a camaro you see how well the z06 mm12 was chosen... the 5th gear falls to around 5000+ after running a hard 4th which makes the car INCREDIBLY FAST! for the HP up top till 150...

One of the reasons I chose the 4.11 was because I wanted that 5th gear... 2 options: have the pinions and replace them (expensive and a lot of work) would still keep the 3.42 (just as you mentioned before) or put a 3.90 wich would make it very comparable...

The 4.11 made my car very nasty till 150 which is where I finish all my runs...

with a 26.1" tire like the firestone is a CRAPY combination for the track because I have to end at 118 in 4th and then run 5th... but I gained .4s launching on second gear which is what I do.. I dont run on slicks, but If I did I would go with 28" slicks which is better for traction and will equate to a 130mph 4th gear speed... (I think)

I would love that GM had a tranny with such a combo as I would change mine in a heartbeat...

Heare's a calculator which I find useful:

http://murray.faithweb.com/formulas.htm#find_rear

Your speed should change with the ratio of the tire diameters:

28/26.1 x 118 = 126+ @ 6250

BTW, I ended up going with an M29 T56; 2.97, 2.07, 1.43, 1.00, 0.80, 0.62. Same 1st through 4th as the Z06, but with better 5th and 6th gear ratios. In the back, I went with a custom fabricated mount for an '03 Cobra 8.8" IRS with 3.55s. I'll also be using RaceLogic's traction control system to help out.

Somebody did a bracket for the camaro for the corvette IRS! the gig costed 750..

Where did you get the transmision???

I like the 5th and 6th of the corvette z06....
why didn't you go with the 3.73? 150.6mph in 5th? that is a good number

just letting you know i didn't read through this thread and dont plan too, my opinion:

get the damn car together and get a BASELINE LOL

it isn't too hard/expensive to change gears

Originally posted by The Highlander
Where did you get the transmision???Sallee Chevrolet, $1,700 + shipping.

why didn't you go with the 3.73? 150.6mph in 5th? that is a good numberToo much gear in 1st and 2nd for a street tire, and I'm not building a drag car.

Not to mention the fact that I'll be able to hit 150+ mph in 4th... 25.7" tall tires, 3.55s, and an arbitrary 7,500 rpm redline. :)

1st - 2.97:1 (10.54:1 final) - 54 mph, gear limited
2nd - 2.07:1 (7.35:1) - 78 mph
3rd - 1.43:1 (5.08:1) - 113 mph
4th - 1.00:1 (3.55:1) - 162 mph
5th - 0.80:1 (2.84:1) - 202 mph
6th - 0.62:1 (2.20:1) - 220+ mph, drag limited

Originally posted by 89ProchargedROC
get the damn car together and get a BASELINE LOL

it isn't too hard/expensive to change gearsYou have to start somewhere, and when you're building from scratch, you might as well make the effort to come up with the right combination the first time.

Originally posted by jimlab


You have to start somewhere, and when you're building from scratch, you might as well make the effort to come up with the right combination the first time.

not to be the one here with the bad point of me view but in my experience, the right combination is usually not the first one

*shrug*

Originally posted by jimlab
Sallee Chevrolet, $1,700 + shipping.

Too much gear in 1st and 2nd for a street tire, and I'm not building a drag car.

Not to mention the fact that I'll be able to hit 150+ mph in 4th... 25.7" tall tires, 3.55s, and an arbitrary 7,500 rpm redline. :)

1st - 2.97:1 (10.54:1 final) - 54 mph, gear limited
2nd - 2.07:1 (7.35:1) - 78 mph
3rd - 1.43:1 (5.08:1) - 113 mph
4th - 1.00:1 (3.55:1) - 162 mph
5th - 0.80:1 (2.84:1) - 202 mph
6th - 0.62:1 (2.20:1) - 220+ mph, drag limited

You have to start somewhere, and when you're building from scratch, you might as well make the effort to come up with the right combination the first time.

but why 150 mph in 4th?????? Unless you plan on hitting 200mph I think its not worth it... You should have 135 in 4th and 150-155 in 5th.. that is just my opinion... good price on the trans ;)

Originally posted by The Highlander
but why 150 mph in 4th?????? Unless you plan on hitting 200mph I think its not worth it... You should have 135 in 4th and 150-155 in 5th.Why? I think the top speeds in each gear are throwing you off a little. :)

The gearing I chose is comparable to a standard T56 (2.66:1 1st) with 4.10s with the exception of 4th gear, so the gearing is fairly short as it is for a street car. The only reason I will be able to attain such high speeds in each gear is the ~7,500 rpm redline and tire size, and that's sort of a side effect, not a deliberate act.

My goal was to smooth the solid roller out as much as possible at low speeds with the relatively short gearing (10.54:1 final in first), while still maintaining a reasonable freeway cruising rpm. ~2,000 rpm @ 70 mph in 6th is pretty good. Simulation also showed that my trap speeds would likely be highest with the 3.55s, since I wouldn't be shifting right at the end of the quarter, not that I'll be drag racing much.

Just because the car has 200+ mph capability doesn't mean that I've compromised the other gears. This is a ~2,700 lb. car with the equivalent of 4.10s and an ultralight rotating assembly in a 650+ horsepower stroker that we're talking about... not a car that I put 2.73s in to try to claim high speeds in each gear. :)

BTW, like my speedo?
http://home.earthlink.net/~jimlab/pics/rx7/Gauges_new_lit.jpg

Originally posted by 89ProchargedROC
not to be the one here with the bad point of me view but in my experience, the right combination is usually not the first one

*shrug* Agreed, but that doesn't mean you can't take your best shot at getting it right the first time. I picked a configuration that I can easily go up (3.73) or down (3.27) if need be, fairly inexpensively. I don't know what else you expected.

When you're still in the process of designing the car, you can endlessly debate which gears to go with. Eventually, though, you have to make a decision and buy the parts. Decision made.

Originally posted by jimlab
BTW, like my speedo?
http://home.earthlink.net/~jimlab/pics/rx7/Gauges_new_lit.jpg
Yes yes we all hate you Jimbo. :p

BTW i like your choice on trans & gearing :)

Wicked...

The thing is that i would have still chosen the 4.11 gears... but this is just theoritacally but here it goes...

You would have
46 in first
66
95
136
170

I guess that would be an awesome gearing for a car that revs a lot... you will "let it rev" with a 4.11. In terms of top speed per gear I would still choose the 4.11.

But now to the practical view. the thing is that the multiplication in first is :12.21 and second 8.51 and 5.88 in third.. which means that in a 2700lbs car you will be burning first second and third... which you would need a slick to drive around and it will feel like a honda in 6th gear... 60mph@2000rpm ??? damn no...

I dont know.. too much rpm???

With the 3.55 you keep what you are saying but I find it that you will be shifting at 5300 after each gear (more or less).... What do you think? how much torque are you making at 5300?

Originally posted by The Highlander
But now to the practical view. the thing is that the multiplication in first is :12.21 and second 8.51 and 5.88 in third.. which means that in a 2700lbs car you will be burning first second and third... which you would need a slick to drive around and it will feel like a honda in 6th gear... 60mph@2000rpm ??? damn no...Yep, 4.10s are way too much gear for a street car/tire with a 2.97:1 1st gear. It's borderline as it is with the 3.55s, but should be fairly usable, especially with traction control.

On street radials, more gear wouldn't have bought me more acceleration, in my opinion. It would only have increased the probability that the RaceLogic system would have to step in, and reduced the input "granularity" of the throttle even more.

60 mph in 6th should be about 1,725 rpm, by the way. I don't know that you'd want to drop much lower with a cam as big as mine... the ride might get a little jerky, if you know what I mean. :)

With the 3.55 you keep what you are saying but I find it that you will be shifting at 5300 after each gear (more or less).... What do you think? how much torque are you making at 5300? 563 lb-ft. :)

Originally posted by kmook
Yes yes we all hate you Jimbo. :p

BTW i like your choice on trans & gearing :) Thanks. :)

Yes after thinking about it.. its the best choice.. actually.. its the choice I wanted, but... No M29 available... and I am not about to spend 1700 bucks on a trans right now...

But I will... :D

Originally posted by The Highlander
No M29 available... and I am not about to spend 1700 bucks on a trans right now...

But I will... :D Well, Sallee Chevrolet has them waiting when you're ready... :)

http://www.torquecentral.com/attachment.php?s=&postid=71897

Isn't it a better idea to change just the 5th gear on the tranny rather than buying? or what are you risking if you do?

How much for the racelogic?

The reason I bought an M29 was because my car (obviously) didn't come with a T56, and I wasn't willing to put an "unknown" used T56 in that I'd possibly have to pull back out for a rebuild soon after. The M29 is also the cheapest new T56 available from Chevrolet, with the fringe benefit of having the gear ratios that I wanted. Obviously, with a pre-existing T56, it would be cheaper to send it off to D&D or someone else and have them work it over and throw in the 5th and 6th gear ratios you wanted at the same time.

The RaceLogic system for a V8 with ABS and launch control is normally $1,300, with the full throttle shift option available for another $175. I helped pull together a group purchase with the RX-7 and Supra communities that sold over 100 units, but the best price break was reached at only 20. After the 30% discount, I paid $910 (I passed on the full throttle shift) and everyone in the group purchase got the dash mount control thrown in free of charge.

http://www.racelogic.co.uk/traction.htm
http://www.racelogic.co.uk/adjuster.htm

Ya the racelogic stuff rocks, thats what I am using for my 68.

A friend of mine with a 700hp Talon has their system and loves it. I drove the car a few times and I was impressed enough to buy it too.

Gearing selection blows....i just started doing that and its frusstrating, but looks like I will be going with a similar selection of gears, but with a higher rear gear, 3.23 most likely.

good luck man, i know how long and involved projects are....

Hunter

Why is the trans cheaper?? I always wondered that?? is it softer? will it break if ridden hard.. I remember that was the point..

Since the first is so steep it broke first gear or something.. anyways.. i dont launch with slicks...

Wow Jim that racelogic stuff looks great from the info on their site.

But im curious for input on an unbiased source. Have you ever been in a car that has it? Or did you just drop the money on it hoping that it is good?

I was playing a bit with excel and liked the 0.84 5th of the z06 better than the 0.8... of course.. that's for MY application ;)

How much would D&D charge to replace it??

Originally posted by jimlab
Yep, 4.10s are way too much gear for a street car/tire with a 2.97:1 1st gear.
I disagree and I'm using a 3.06 first gear :p However I'm not making anywhere NEAR the same power or torque from my stock LT1 shifting at 5500 :( Those gears and my Vigilatne were good enough to get my 2 ton boat to the 60ft mark in 1.82 seconds though :D

Originally posted by AdioSS
I disagree and I'm using a 3.06 first gear :pI guess I should have specified that I was talking about my car only. :)

Well... i have a 2.66 first and the 4.11 and on first and second... there is not much I can do...

On the track.. i gained .5s launching on 2nd gear... (this is with fireston ez50ep)

Originally posted by kmook
Wow Jim that racelogic stuff looks great from the info on their site.

But im curious for input on an unbiased source. Have you ever been in a car that has it? Or did you just drop the money on it hoping that it is good? I've never ridden in a car that had it, but there are a number of well-respected RX-7 community people who have it and give it rave reviews, as well as some in the Supra community. The Blitz Supra which was used to set the sub-8 minute (7 min. 49 sec.) Nurburgring record for a tuned road car was also using RaceLogic's traction control system.

I sat on the fence for quite some time before I was convinced, but as far as I can tell, it's the least invasive traction control system the average consumer can buy. It's supposed to be nearly seemless in the way it cuts power, unlike the Supra's stock system, which slams a throttle blade closed and cuts air to the engine resulting in an almost complete bog. The Corvette's system is a little better, but still cuts power so heavily that it often results in a bog. This system cuts power but keeps the wheels moving at the set amount of allowed tire slip, so you're still making forward progress at the limit of traction.

Everyone who I've talked to who has used the unit says it's the best thing they've ever done to their car, next to making more power. :)

Originally posted by The Highlander
Why is the trans cheaper?? I always wondered that?? is it softer? will it break if ridden hard.. I remember that was the point...Not sure why it's cheaper. It was rated at 400 lb-ft. of torque as opposed to the 450 lb-ft. of the 2.66:1 T56s, but Borg Warner specified that those ratings were for 24 hour continuous power handling, IIRC. I've never heard of anyone breaking one, and if anyone has, it was probably in a situation where a 2.66:1 version would have been at risk also. :)

Originally posted by jimlab
I guess I should have specified that I was talking about my car only. :)
I should also tell you that I'm cheating on the street and running 29" tall tires.;)

Damn those are very big tires!!!! they should weigh a lot.. which tires are theese?

Originally posted by jimlab
Everyone who I've talked to who has used the unit says it's the best thing they've ever done to their car, next to making more power. :)

Dammit now i want one :) Do you know offhand who has the best price on one?

Originally posted by kmook
Dammit now i want one :) Do you know offhand who has the best price on one? Matrix Engineering in Portland, OR is the only authorized RaceLogic dealer in the United States, so there's no price shopping to be done, unfortunately. I helped organize the last group purchase, and that's your best bet for saving some money on the system and extra features.

If there's enough interest, they can certainly start another group buy, assuming they become a forum sponsor. In the previous group purchase I urged Matrix Engineering to become a sponsor on both forums involved, and there was no problem with that. I'm sure they'd do the same here.

Standard price for the V8 system is as follows:

Racelogic Adjustable TC w/ ABS (Max 12cyl) - $995
Racelogic Adjustable TC w/ Launch Control & ABS (8cyl) - $1300
Racelogic Adjustable TC w/ LC, Data Logging & ABS (4/6/8cyl) - $1595
Full Throttle Shift option - $175

The full throttle shift option must be purchased at the same time as the system. It's not something you can easily or cheaply add later, if you change your mind.

Here's the contact information for Matrix Engineering. Jeremy Williams is the contact for RaceLogic systems.

Matrix Engineering Inc.
4060 SW Macadam Ave.
Portland, OR 97239
503.443.1141 Tech
503.443.1142 Fax
888.249.0013 Orders
jeremy@matrixengineering.cc
www.matrixengineering.cc

What is the launch control??? the rev limiter at 3000 or whatever rpm I desire??? if I have an MSD all I need is a 2 step...

Originally posted by The Highlander
What is the launch control??? the rev limiter at 3000 or whatever rpm I desire???http://www.racelogic.co.uk/launch.htm

I think its cheaper to do it with the MSD and its the same thing...

Originally posted by The Highlander
I think its cheaper to do it with the MSD and its the same thing... As only a two-step rev limiter, sure... as traction control tied into the rev limiter? No.

RaceLogic's version allows you to hold an rpm that would normally result in tire smoke and the traction control system then controls the inevitable wheelspin during the launch. With the MSD, you can only launch at an rpm that's limited by tire type and available traction, and all it does is allow you to keep the throttle floored without over-revving so you can concentrate on the tree. No help with traction whatsoever.

Furthermore, it makes sense to get both the rev limiter and traction control in one package if you don't already have a two-step, doesn't it?

Please explain further more...

If you have a 2 step (I already have the MSD) you put a rev limiter to what you know the trac control will help... As I see it.. it works exactly the same way...

Highlander, it looks like Jim explained the Racelogic system quite well. Instead of keeping this topic going off in left field lets try to get it back on track. Maybe if you need further explination of the system, either contact Racelogic themselves, or send Jim a PM.

Thanks.

Originally posted by The Highlander
Damn those are very big tires!!!! they should weigh a lot.. which tires are theese?
Only 235/75R15s on some cop car rims (for now.) They aren't lightweights, but I think they weigh less than my 255/50ZR17s on impala rims. I think the extra height of the front tires helped my ET a bit too ;)

I am considering getting some lightweight rims to put these on to shave several pounds.

I'm also considering putting some 295/65R15 BFG drag radials on the back :D

Thought some of you might be interested in seeing how this turned out. I finally found the time to finish my Cobra 8.8" IRS conversion. :)

The finished components (http://home.gci.net/~jimlab/images/Cobra/PB120004.jpg) (close-up (http://home.gci.net/~jimlab/images/Cobra/PB120005.jpg)) after powder coating, including my engine cradle. The Driveshaft Shop (http://www.driveshaftshop.com/) made the hybrid ('03+ Cobra inner spline, '93-'95 RX-7 outer spline) 300M chromemoly center shafts to my specifications. Here's a picture of the completed axle assemblies (http://home.gci.net/~jimlab/images/Cobra/PC080013.jpg).

So this (http://home.gci.net/~jimlab/images/Cobra/P8210035.jpg) finally became this (http://home.gci.net/~jimlab/images/Cobra/PC080019.jpg). A close-up of the suspension (http://home.gci.net/~jimlab/images/Cobra/PC080022.jpg) (polished), and the rear mounting bracket (http://home.gci.net/~jimlab/images/Cobra/PC080024.jpg) which ties into the stock differential mounting tabs.

I ended up going with a Zexel T-2R Torsen differential and 3.55:1 Ford Motorsports gears to start with. I didn't want to drop too much in the upper gears, and with the 2.97:1 first, I've got a final drive (10.54:1) almost equivalent to a standard T56 (2.66:1 first) with 4.10s (10.90:1 final drive). In other words, plenty of gear. :)

BTW, other 3rd gen. RX-7 owners liked the setup so much that I've already sold several copies (http://home.gci.net/~jimlab/images/Cobra/P8210014.jpg) and will be having another 5 or 6 made soon. Here's another picture (http://home.gci.net/~jimlab/images/Cobra/P8210015.jpg) of the "clones".

ok i'm not sure if this has been said, but i'm too tired to read it all now. Im just taking a break from nascar o5 on x-box. (stupid roomate walked in front of TV durring qualifying, now i'm starting 32nd in a short race :mad: )
its also 11:45pm :o

this may sound a bit counter intuitive but it is easier to launch on a steeper gear than a shallow one.

for example, T-56 on 3.23 vs 4.11
at a 2200mph roll out
you are making you tires go 0-20mph instantly (off the line once the clutch is engaged) vs 0-15 instantly. obviously the clutch slips a bit but you get the idea.


if you try to launch at a high rpm with shallow gears 1 of 2 things will happen.

1. tires will spin because they cant go 0-45mph instantly.
2. engine will bogg to half the rpm and you will launch way below your powerband, slowly get into your powerband (due to being outside it) and fight the tall gear to do so.

now you sound like you have enough to roast them at any rpm in 1st, but i hope you see what i'm saying.

Its why people do high stalls AND high gears


Also FYI;
the saleen s7 road car orignally had a taller 1st gear ratio which was cut down to a steeper one due to the fact that drivers/owners complained about the jerky launches. with a mclaud (spelling anyone?) clutch as grippy as that, a tire that GRABS HARD and a motor that WONT bog down - it was a problem because they "idled" at 11mph!


edit: all the above also implies that your foot isn't an on off switch!
using shallow gears to launch easier is traction control for dummies :p

Jim.... money always calls money ;)

I'm glad you finally put it together.. it simply looks great and awesome...
I would have thought you would have gone with the c5 rear.... but still... nice nice setup man ;)

we have more or less the same gears as i have a 94+ with 4.10 and a strange diff.

I'm glad you finally put it together.. it simply looks great and awesome...
I would have thought you would have gone with the c5 rear.... but still... nice nice setup man ;)Thanks!

The C5 has an 8.25" ring gear vs. the Ford's 8.8", and the differential case would have presented some mounting issues that the Ford case didn't, but I did consider it. Basically, we mounted the diff in much the same way that Factory Five Racing does in their Cobra replicas. Why reinvent the wheel? Oops, never mind... :)

The inner CV joints on the '03+ Cobra axles are also identical in construction to the RX-7's, which made making a hybrid axle as easy as possible. I cut the tripod end off a Cobra axle, milled out the center (I bought a milling machine a year or so ago) so that the RX-7 axle center shaft would fit into it, and drilled and tapped 3 holes to use bolts to hold it in place for mock-up on the car. I used the "Frankenaxle" to determine the length I needed for the new center shafts, then welded it in place. The result looked like this (http://home.gci.net/~jimlab/images/Cobra/RX-7%20Cobra%20Axle%202.jpg). Some people actually thought I was going to use that axle on my car. :D

With all the knowledge on this board I'm almost in shock that no one has posted some very basic track tuning tips

If it was me....... I'd gear for a conservative rpm passing through the traps at what speed you expect. Period.

To get traction, you need to retard the lower rpm's timing until it hooks up.

With all the knowledge on this board I'm almost in shock that no one has posted some very basic track tuning tips

If it was me....... I'd gear for a conservative rpm passing through the traps at what speed you expect. Period.

To get traction, you need to retard the lower rpm's timing until it hooks up.
There is no modifier vs speed or gear to the timing tables...

With all the knowledge on this board I'm almost in shock that no one has posted some very basic track tuning tips

If it was me....... I'd gear for a conservative rpm passing through the traps at what speed you expect. Period.

To get traction, you need to retard the lower rpm's timing until it hooks up.
I don't believe "Jimlab" is all that interested in drag racing.... hence his basis for gear selection might not be based on trap speeds.

I don't believe "Jimlab" is all that interested in drag racing.... hence his basis for gear selection might not be based on trap speeds.


Ya well that makes it even harder. I'd try and find some road race guys and get their opinions. That's a whole other ball park where I've never played ball.

If you're a street racer, then the drag race tuning stuff is still the same only tune it for a rolling punch on the street.

Got traction control? Why do you think it's illegal in Pro Stock?? Get the drift?

Trust me, if too much power was my problem, I'd re-educate the right foot first and if that didn't work...... go to intended use tires and suspension tuning way before I'd get hung up on real high gearing.

I mean...... why did you do the engine?? To give um hell right! Then do it!

With the money you got tied up and the rpm capability, I'd try 3.90 gears, tires, suspension, timing and if it still doesn't work..... then bump down the gearing. Them gears ain't all that expensive compared to what you got in that engine and you can easily pull 3.42's but I wouldn't, if I didn't have too..

Have fun and good luck. Just wish I had your problem to worry about. But then again, I've got a pretty educated right foot who just loves being challenged.

Kinda like the way "give um hell" rolls off my lips. Ya, I like that idea. Give um hell guy!

jim, it sounds as you have built quite a monster, could you please post some pics if you don't mind :D

If you're a street racer, then the drag race tuning stuff is still the same only tune it for a rolling punch on the street.I based my decision primarily on 40-140 acceleration simulations. Trap speed was secondary, but the car should trap in the high 130s anyway.

Got traction control?RaceLogic with launch control.

With the money you got tied up and the rpm capability, I'd try 3.90 gears, tires, suspension, timing and if it still doesn't work..... then bump down the gearing. Them gears ain't all that expensive compared to what you got in that engine and you can easily pull 3.42's but I wouldn't, if I didn't have too.As I said, I have a 3.55:1 ring and pinion. With my M29 T56, my gearing is comparable to a standard T56 with 4.10s, except for 4th. I've got plenty of gear for a 2,750 lb. car. If it's too much, I'll drop down to a 3.27:1 or lower. 3.73s, 3.90s, or 4.10s would be way too much gear.

2.97:1 x 3.55:1 = 10.54:1
2.07:1 x 3.55:1 = 7.35:1
1.43:1 x 3.55:1 = 5.08:1
1.00:1 x 3.55:1 = 3.55:1
0.80:1 x 3.55:1 = 2.84:1
0.62:1 x 3.55:1 = 2.20:1

2.66:1 x 4.10:1 = 10.90:1
1.78:1 x 4.10:1 = 7.30:1
1.30:1 x 4.10:1 = 5:33:1
1.00:1 x 4.10:1 = 4.10:1
0.74:1 x 4.10:1 = 3.03:1
0.50:1 x 4.10:1 = 2.05:1

jim, it sounds as you have built quite a monster, could you please post some pics if you don't mind :DIt's still very much in progress, but this should give you a general idea...

http://home.gci.net/~jimlab/images/Engine/Delivered/PA030002.JPG
http://home.gci.net/~jimlab/images/Misc/P8080013.jpg

Wow, that motor is a thing of beauty!! That is gonna hall arse when you get it done!

It's still very much in progress, but this should give you a general idea...

http://home.gci.net/~jimlab/images/Engine/Delivered/PA030002.JPG
http://home.gci.net/~jimlab/images/Misc/P8080013.jpg

:eek:

That is NICE, bro. :)

Mike

Jim
how long have you been working on this project? how close are you to putting it on the road?

Nice to see you're still around Jim :)

The differential mount/rear subframe looks freakin sweet. Tough as nails too I'm sure! The T2R is a great diff too. It is THE one to have if you want to put power down in turns.

Keep up the great work, once its finished there will be nothing else like it on the streets :eek:

Jim
how long have you been working on this project?Consecutively or chronologically?

I pulled the engine subframe to start the V8 swap in October of 1999. However, the car has been sitting for most of the intervening time, since I've had other cars (1994 Supra turbo, 2002 Z06) that I've been "distracted by" since. I do a little here and a little there when I feel like it, which really isn't very often. Some times weeks and months go by without even touching it.

A lot of my lack of interest is due to the crap I've had to put up with during the project. I had one a**hole set me back a couple years while I waited on conversion pieces (subframe, trans brace, etc.) that never really materialized, and another a**hole who set me back a year or more on my engine, stole a bunch of parts and $$$ from me, and basically got away with it. It's a long story. :D

how close are you to putting it on the road?Not that far where parts are concerned, but probably another year where interest and free time are concerned. I really don't care any more, but it's sort of a point of pride to eventually finish it. :)

Nice to see you're still around Jim :)

The differential mount/rear subframe looks freakin sweet. Tough as nails too I'm sure! The T2R is a great diff too. It is THE one to have if you want to put power down in turns.

Keep up the great work, once its finished there will be nothing else like it on the streets :eek:Thanks Jason. I still haven't fixed all the problems Mark caused me, but I'm getting there. :)

I have a new front cover that I welded in cover plates for the Opti and water pump drive holes for and had polished, but now it's at the powder coater's with a bunch of other parts (including my intake) getting a coat of "near chrome" (decided I didn't want the upkeep). I've got new gaskets and a new 242/248 solid roller from Comp Cams waiting to go in. I've got the right MSD crank trigger, the MSD cam sync stub, and 2 sets (don't ask) of LS1 coils for the ignition setup, so I need to get all that stuff on the engine too. The valve covers Mark got for the engine don't fit in the car, so I need to get new covers and have them modified for the coil brackets, and the list goes on... :D