problem? how so?

Just work on sticking you launch (for lower mph through the traps), shifting deep in the rpm band, and HOLD 3rd gear for the final 100 feet or so.

Going to 3.23's means a slower car (since the RPMS drop down), while 4.11's (like I went with) MANDATE that your shift to 4th. Holding 3rd gear is a MUCH better option than shifting gears one more time. if you only have to do it for the final 100 feet or so.

On a good run I'd hold 3rd gear and get decent times stock (14.2 ina convertible TA WITH spare tire/jack and passenger). With tire spin I'd either hold 3rd or shift to 4th and get the same results... about 14.5. I know it sounds crappy but that's how it worked out for me. If you can launch her well, and shift deep you'll be fine.

Once you bump the power or swap to 3.73/4.11's your stuck shifting to 4th every run, no question about it.

 

The trick is to use the 1:1 gear most of the 1/4mile run which is 4th gear for an M6 car. I'm saying this because there is a guy who tested his M6 car in 3rd, 4th and 5th gear on the dyno to check for power losses since he runs in top speed events. He found that 4th gear did dyno higher 10-12% higher than 3rd gear. I found this true because with my 392rwhp car i should have been trapping 115-116mph with my car weight, but instead i was trapping 113-114mph which is around 20-30rwhp less because i didnt use 4th gear that much(last 60-100ft). My car used to trap 111-112mph with the stock cam because i was shifting to 4th gear early down the track since my power band was earlier (6000 RPM instead of 6600RPM with the cam). I hope this clears things up for the guys facing this problem

 

Not necessarily a slower car. Closer to the peak power and not over it in 3rd gear.

It has been proven time and time again that these cars drag race best when using all of 4th gear (while still pulling hard) right before the traps.

 

Using all of the final gear is always a good thing. And yes, steeper gearing can help you do that (that's why we/I usually go for 4.11's once the mods start). If you've driven a 4.11 geared LT1 though, you know it's just NOT a set up GM would ever market for the "average consumer". I'd agree that it's a better option than 3.42's, but not by much.

Here the break down:
3.42's get you to 100 mph at redline (in an LT1),
and and LS1 can get 103 at 6000rpms.
4.11's get you to 105mph at 5800rpms (LT1 redline), even higher in LS1's. Neither car could pull a redline run with these (although its close).

The 4.11 gears are not better than the 3.42s for
using the whole gear". Their inherent torque multiplication is better however. The difference would be more if you didn't hold 3rd while running 3.42's, but if you can get away with only 2 gear shifts instead of 3 you can gain 0.1s or so (which is why people who switch to 3.73's in stock cars rarely see any gains over 3.42's... the acceleration is better, but the extra shift isnt').

4.11's are good for keeping revs high, but the gains of 0.1 second for them just don't outweigh the benefits of a 3.42 gearing while on the highway (to GM at least ). Let's be honest here... GM doesn't sell drag race vehicles, they sell consumer vehicles. That's why the small ET loss was traded for MPG and less shifting. Having driven both setups over the past 100,000 miles that's my take on each, of course your milage may vary.

BTW... my cat-back goes in soon. (no one ever said I quick to mod... just quick to buy ).

 

Just an FYI....best ET is obtained by maximizing the average HP throughout the rpm range in each gear. In short, your optimum shift points are typically 500-800 rpm above peak power - depending upon the actual HP curve, your tranny gearing, and your driving (errr...shifting) style.

 

That's right. You can actually plot this out using your dyno numbers and overall gear ratio. You plot torque at the wheels vs. speed and for each gear the speed at which the torque drops off below what you have in the next gear is your shift point. Did I make that clear? It's easier to graph than to describe. There are also some utilities floating around on the web to do this.

In general, for drag racing, top gear should be 1:1 because that's where the least power loss through the tranny occurs. For heavy cars with a broad torque curve, a 4-speed works well with a manual tranny or a 3-speed for an auto. You chose a rear gear/tire combo that puts you a couple of hundred rpm over peak hp in your 1:1 gear as you go through the traps. With an auto, you have to account for converter slip. So, you can't talk about ideal rear end gear ratios without keeping in mind the weight if the car, the size of the tires, the rpm range of the motor, and the expected trap speeds as well the efficiency of the converter.

Example: my setup uses 3.42's and a TH400. I go through the traps at 6,400rpm using a 27" tire at 141 mph. That would be 6,000rpm with no converter slip. So, the converter is accounting for the extra 400rpm. The power peak is 6,100rpm so the 6,400 that I actually achieve is just about spot on.

That's the kind of reasoning you need to go through to select the best gear for your setup.

Rich Krause

 

http://prestage.com/carmath/dynochart.asp



BTW, you can do similar calculations with the HP curve, and if you have no program to help you, it is actually easier to look at the HP curve vice the tq curve and come up with fairly accurate shift points.

It also bears mentioning that HP and torque are mathematical derivatives of each other - at any given rpm, you cannot change one without changing the other....an increase in one will always produce an increase in the other, and vise-versa.

 

Right, you get essentially the same curves either way.

Rich Krause

 

I go to 4th or I'd be hiting the revlimiter just past the 1k marker. My best run was 13.55, but that was with a bit of wheel spin out of the box. I have to replace the toque arm bushing and maybe I can come up with some better launches. I'm still in the 2.2 60ft range. I'm hoping that the bushing replacement will do something for me.

 

4.10's / 4.11's are the best gear ratios for our cars running with 26" tires IMO (until you start running faster MPH). With the M6, you'll be crossing the line between 5500 - 6000 RPM in 4th gear, and same RPM for an A4, but in 3rd gear.

Running faster than ~110? Raise rev limiter to ~6500 RPM.......good 'til ~120. Running faster than that?? Use 28" tall tires, and you're good 'til over 130!