De-Stroke or Stroke

OK there is a Bare LT1 Block 2Bolt on my stand I have a GM-6 Turbocharger from a GM Diesel and I have created all neccesarry things to do it. But here's what I'm wondering, ,

Straight line performance is Minimal I hate drag racing I like Road Courses so I want to Know if De-Stroking to a 327 and Turbocharging at about 4PSI would be better? I'm thinking more along the lines of a high revving driving machine as opposed to a Big Displacement torquer. Or do I just stay with a 350? Has anyone done anything like this? Seems like the 327 would be a "quicker" motor. I think I need a new Crank anyway Beacaue (if you read My Sqeaking Thread) the Rod Bearings for #'s 7 and 8 spun and sorta ground down the crank :) so Now starts my bottom-end Build-Up!

No, the 350 is the best place to start on a turbo small block.

Don't destroke a engine and spend money at it unless you are going for more RPM at the same displacement with a larger bore.

Bret

agreed.youd think youd want to stroke even further for a road coarse, but i may be wrong

I'm dooing the same thing right now but without the turbo. this will be the second engine I've de-stroked to a 327 would'nt think twice about it.
the first onewas aboutthe best chevy engine i've ever built
they can handle the revs and make awsome power

I'm dooing the same thing right now but without the turbo. this will be the second engine I've de-stroked to a 327 would'nt think twice about it.
the first onewas aboutthe best chevy engine i've ever built
they can handle the revs and make awsome power

Was this a Gen II block you did this with and if so what hind of RWHP did you make Plus keep in mind the T56 I thinkl my crank is trashed so I'll need to make a decision also what Crank did/are you using?

youd need some really big bores to make destroking worth it

Revs for revs sake isn't logical. If you have the same heads and an optimized cam with the same bore, the longer stroke/larger displacement motor will make about the same peak hp but will make more torque. IOW, it will be a faster combo.

Rich

While the early 327's were good in their day, engine technology has far surpassed these older motors.

Since you are RPM limited w/ the LT1 to 7K due to the computer lmitation, there is no need to try to destroke. A decently built 350 should be capable of this RPM anyway. Cubes tend to rule in every aspect except mileage. Any gain you achieve in peak HP due to the reduced frictional losses of the shorter stroke, you will likely lose in torque at lower RPM. Torque will generally rule on the street & the strip. Road courses generally favor torque as well, with the HP numbers helping only on the long straights. To flow the same air as a 350 at 6500, you need to rev the 327 to 7k. Keep in mind that you are not onto a new idea to build a 327..... the reason there aren't more of these is they generally are not worth doing. Personally any time I buy a crank & pistons for a performance build, (class rules permitting) they are to build a 383.

Your turbo idea must be thoroughly researched as there are many turbo specs to take into consideration to be sure it will work properly on your engine. 4# boost is not going to make it a powerhouse anyway, so be careful of your parts combination as you may spend a ton of fabrication labor to build a economical low boost turbo motor that gets outrun by a N/A 383.
If you are insistant on doing this, buy a used LT1 crank & use it. They are easy to find & will live at 4# boost all day.

I don't mean to be negative, but only want you to keep from wasting your money.

Thanks for the info I think I will stay at 350 now. As far as Turbo, where do I find out more technical inf The GM turbo I have came off of a 6.0 Diesel and the limited research I have says that @ 4000 RPMs one side (Exhaust) will provide about 4# of boost

are you going to run the turbo off one side or both, That disel isnt going to have the same amount of exhaust running threw it
so i have no idea on boost

I have seen 4,500fps as a guideline for maximum average piston speed in a street/strip or amatuer race motor. This assumes the use of high quality "sportsman racer" or better type components and (needless to say) careful engine assembly. If you accept this, approximate max rpm is as listed below.

stroke rpm
3.25" ~8,300
3.48" ~7,800
3.75" ~7,200
3.875" ~7,000
4.00" ~6,750

Interestingly, a 325ci motor at 8,000rpm and a 400ci at 6,500 each move ~775cfm. So, if they were optimized in other respects they would make about the same hp. This doesn't change the basic limitations of rev range though. If you optimize a traditonal 2V OHV V-8 to run up to 8,000rpm, it won't be much fun at 2,000!

Rich

I've seen a few relatively big CID motors turning some pretty high RPM recently. How about a 428cid Gen3 motor spinning up past 8200? Or even a 514cid BBC spinning up to 9000? You mainly need very good flowing heads.

Revs for revs sake isn't logical. If you have the same heads and an optimized cam with the same bore, the longer stroke/larger displacement motor will make about the same peak hp but will make more torque. IOW, it will be a faster combo.

Rich



hm.. i might disagree... but a bit only, because i follow your logic and i embrace it, hence why i went with the 383 and didn't stay 350... But it got me thinking...thought: isn't it easier to handle and get the best performance out of a high revving engine with less torque and same HP than a higher torque engine?

Wouldn't you spin the tires a lot easier?? i thought that was what GM did with the 346, hence why the new Z06 and its 7L will have 345s on the rear tires...

The viper engine was being talked to go down from 8.3L to 6.9L on a v10. would it be to reduce the torque, up the revs and get same or more power so its easier to handle and get the performance out of it?

too much torque= spinning tires!

This is silly, the stroke or destroke thing is purely going to depend on the type of driving. torque is good on the street because you use power in all rpms, it wont matter at the track with your 5000rpm stall and trans brake. That is why supras with a very limited power band can go so fast. Overall i would go stroker same top end but you have bunches more torque. Why would i want to rev the crap out of my car on the street to make power. i have rode 2strokes before no power on the bottom crazy to end = not practical at all. 600 sportbikes are the same way, no torque rolling on the throttle, they dont make power till 9,000 but when your at the track your only out of power for a limited time when you launch. If you have more torque you can launch at lower rpm and keep reliabilty up. The reason F1 rev high is not because thats where the power is at, its because they have very strict limitations and thats the only way. same way with imports no cubes no power. only way to make good torque and keep rpms down is with nitrous. the only reason people rev motors that high is to cover somthing up but If they have the right setup is wont hurt them any at the strip except for reliablity

hm.. i might disagree... but a bit only, because i follow your logic and i embrace it, hence why i went with the 383 and didn't stay 350... But it got me thinking...thought: isn't it easier to handle and get the best performance out of a high revving engine with less torque and same HP than a higher torque engine?

Wouldn't you spin the tires a lot easier?? i thought that was what GM did with the 346, hence why the new Z06 and its 7L will have 345s on the rear tires...

The viper engine was being talked to go down from 8.3L to 6.9L on a v10. would it be to reduce the torque, up the revs and get same or more power so its easier to handle and get the performance out of it?

too much torque= spinning tires!

You have a point, and I know quite a few people who live by that moto. Amongst my friends we have those who choose to build 383's instead of 350's and 400's instead of 377's (destroked 400).

The bottom line is that those who build the larger displacement versions of motors require less stall speed and less gear to accomplish the same (or better) performance as those who choose the smaller displacement versions.
The smaller displacement versions are less streetable, require larger converter stall speeds and steeper gears to do what the larger displacement motors do on low end torque alone.

Here is a perfect example:
I have two friends, similar vehicle weights, similar solid roller sbc setups, one running a 355 and one running a 383.

The guy with the 355 runs a steeper gear and a 5000 stall, whereas the guy with the 383 runs a 3000 stall and a more streetable gear, they run the same 60' times and similar ET's.

Most answers are dealing with a Automatic Trans, Wouldn't a broader RPM Band Help with a M6?? The only thing that got me into this is the GM Gen III 5.3, It's close to a 327 and I think it may be a little "Quicker" than a 350 Granted it was in a Shortbed Single Cab Silverado but it seemed to have a Wide RPM Band

A smaller displacement engine is not going to have a "wider" powerband, it will just be higher in the rpm range.

A smaller displacement engine is not going to have a "wider" powerband, it will just be higher in the rpm range.

"Wider powerband" is probably another way of saying a flat torque curve. This comes from good breathing, correct manifold runner length and cam timing. VVT helps a lot, also.

Recently GM, for one, has been building engines that produce about 90% of their maximum torque from converter stall speed (under 2000 generally) to WOT shift rpm. For example, the 4200 I6 gets about 90% of max from 1900 to 5600. The LS family of truck engines are very similar to this, irrespective of displacement. All of them have about the same rpm range; the bigger ones just have more grunt. Other OEMs are doing the same thing, especially with their premium V6 and V8 engines. It sure makes the cars driveable.

a lot of it is also the fact that they have wide seperation angles. close = death to emissions which is the LAST thing GM wants to do.

Wide powerbands aren't always good, especially in something like drag racing or towing.
Sometimes youd rather have it peak higher at one RPM and you dont care about the rest.

In old Z28 for example, Id launch at about 4000 rpm and shift around 7000 and come back down to around 5ish (i think). Aside from the initial launch, i dont care how good the powerband is from 1000-5000. the whole time i dont care about anything other than 4000-7000.

A flatter curve USUALLY means you "cut off the peak" and distributed it evenly :)

a lot of it is also the fact that they have wide seperation angles. close = death to emissions which is the LAST thing GM wants to do.

Wide powerbands aren't always good, especially in something like drag racing or towing.
Sometimes youd rather have it peak higher at one RPM and you dont care about the rest.

In old Z28 for example, Id launch at about 4000 rpm and shift around 7000 and come back down to around 5ish (i think). Aside from the initial launch, i dont care how good the powerband is from 1000-5000. the whole time i dont care about anything other than 4000-7000.

A flatter curve USUALLY means you "cut off the peak" and distributed it evenly :)

..and that usually means more area under the curve in the rpm band you are using the engine. I think that would be pretty much ideal for towing. Even with a torque converter, it's difficult to keep an tow vehicle in a narrow rpm band, especially with wide ratio spreads and acceleration from a stop to highway speeds.

If course drag racing is a different story from towing. Hey even Nextel Cup engines have different shaped torque (and hp) curves for different tracks. The "plate" engines have a couple hundred rpm band in which they run, and some short tracks have a 3000+ band. The higher speed unrestricted tracks are more like 1500.

Assuming they can get "forward bite", perhaps the Cup engines go for area under the tq and hp curves also. Of course, because traction control can't be used ;), the torque curve could be shaped to reflect available traction.

Recently a big block dirt modified driver was complaining about his car losing traction about half way down the straight when the engine "came up on the cam". He wanted more driveability because lifting slightly in the middle of the straight was not easy for him to do. High peak torque point was slowing him down. The plan may be to flatten out the torque curve and work on forward bite because he will have more grunt at the slowest portion of the corner and a more steady push down the straight.

As an engine builder once said: "Different strokes for different folks." I think he might have meant torque and power curve shape also.

In road racing there are numerous examples where the torque curve interacts in interesting ways with the available traction. Two stroke GP bikes are a prime example. These things are incredibly "peaky" with a very narrow, very steep torque curve. Consequently, there are only a few people in the world capable of driving one to the limit. I used to do some road racing (many years ago) with a 250cc two-stroke, and man, that was something else. You did NOT want it to "come on the pipe" anywhere near the apex of a corner.

For towing, you want a broad and flat torque curve with emphasis on the low and mid rpm range, for sure. Drag engines can be very "peaky" if the vehicle has a high power to weight ratio and enough gears (or a loose converter). Street machines also want a broad, flat torque curve but it can be biased to the mid and upper range as compared to a tow vehicle. In the case of a high power/weight, especially for the street, it may be desirable to decrease the low end to make the car easier to control. Reatrding the cam is one way to do this.

Rich

Isin't interesting the terms that are used for the sudden gain in TQ in the RPM band?

"came up on the cam" & "come on the pipe" just to name a few.

Actually it has a lot to do with both of these, I'm just suprised that "come up on the intake" is not one of them yet.

Basically the rapid gain in TQ is due to camshaft (intake duration and closing point), exhaust tuning length in the headers/pipes and intake manifold tuning lengths. Usually on a race engine all these three things work together to make the motor gain TQ in a certain RPM band. Flattening out the RPM band or getting a higher max RPM so you don't have to drive below the TQ curve and then suddenly jump up on it.

Bret

hey rich that reminds me. why don't you ever hear about loose converter tech? i mean you could spend thousand developing an engine to do what you want all the way across the band, but why not develop a converter that can sit in the right spot? to me all you would need a a pressure guage and solenoid for the fluid, know where you want the rpms to stay at, and some computer to do it for ya.

cause if i step back i see it to be more logical to tighten and loosen the converter than to try to make as much power at say 3000-5000rpms. then you could have different setting. set the converter for fuel economy, or for hp or for tq or for emission, etc.

hey rich that reminds me. why don't you ever hear about loose converter tech? i mean you could spend thousand developing an engine to do what you want all the way across the band, but why not develop a converter that can sit in the right spot? to me all you would need a a pressure guage and solenoid for the fluid, know where you want the rpms to stay at, and some computer to do it for ya.

cause if i step back i see it to be more logical to tighten and loosen the converter than to try to make as much power at say 3000-5000rpms. then you could have different setting. set the converter for fuel economy, or for hp or for tq or for emission, etc.

Well, we do have continuously variable transmissions now. Also, the multispeed, electronically shifted clutch type trannies in F1 keep the motor in a very narrow powerband. A converter could also be made to do this with variable geometry fins/vanes, couldn't it?

Rich

Well, we do have continuously variable transmissions now. Also, the multispeed, electronically shifted clutch type trannies in F1 keep the motor in a very narrow powerband. A converter could also be made to do this with variable geometry fins/vanes, couldn't it?

Rich
i've never heard of one, but if they can do it for turbos...

Well, we do have continuously variable transmissions now. Also, the multispeed, electronically shifted clutch type trannies in F1 keep the motor in a very narrow powerband. A converter could also be made to do this with variable geometry fins/vanes, couldn't it?

Rich

Interesting idea. IMO, the problem with adjusting the converter for slip is the loss of efficiency. Yeah, we could keep the engine on the pipe/cam/intake but lots of the power would just be heating the oil. Imagine a trans cooler a lot bigger than most turbo ICs. :)

Do you remember the variable pitch or "switch-pitch" or SPB ("Switch Pitch Bitch" coined by those who developed it, pehaps) stator in some THM 400s? It had two positions, a high stall ratio position and a low stall ratio position. Obviously the high stall worked for launch and the low stall for cruise. Remember this was before TCC (lockup converters) and before OD automatics. It felt like another gear. It was used mostly in the heavier B-O-C bodies. (Buick-Olds-Cad for you under 50 youngsters). Oh, yeah in high stall (max slip) there wasn't much creep at a stoplight. That was good for us OFs. (you figure out the acronym). Of course I wasn't an OF back then. Shoot, Bret was still 12 years from being born.

I've wondered why, other than mechanical complexity and strength reasons, we haven't tried this in aftermarket street converters. Imagine a 3500+ stall in high pitch and a 1700 rpm stall in low pitch. Or maybe 4000 and 2000.
Yee-ha! Now add a TCC (lockup) to this, and computer control the whole thing. It sounds like a transmission engineer's worst nightmare. I wouldn't doubt it a bit that some OEM has tried (and rejected) it. Six or seven gears sounds like a better idea.

CVT is cool, but currently limited to torque/hp values we tend to laugh at. Even steel chains can only push so much power/heat.

FWIW, if the rpm-determied-by-exhaust-sound technology used by TV media can be believed, some F1 engines pull from below 12k to 19k, which is equivalent to maybe 4500-7000 or 6000-9500 both of which we see in other race series. Hmmm. Variable inlet geometry (length or diameter)?

Yeah, I remember those "SPB" converters. I like your idea of combining that with a lockup clutch. Surprising no one is doing it.

Rich

I wouldn't be suprised to see a car with "everything" variable coming out in the next 10 years.

CVT, valvetrain, suspension, displacement etc etc.

But then again, the Saleen S7 has showed the world of OEM production (well for exotics anway): simpler is better. I wonder if ferrari is bitter :D

Well, I built a 377 for my c10 pickup truck that weighs 3400lbs. THis motor has 10.73:1 compression, comp cam magnum 480H, perfomer rpm intake, 400 smal block bored .40 over , 350 crank, 750 double pumper, crane cam aluminum roller rockers, edelbrock performer rpm heads ( 2.02 intake, 1.6 exhaust, 170 intake runners, 60 exhaust) msd 6A box, msd pro billet distributor, msd 8mm plug wires, champion 12rc-yc plugs, meiling high volume oil pump. Sorry for being a little long but i want every to know. I love this motor, greatest motor ive ever had. Ive had 350, 327, 400 and all of these were built. I know that my 377 would beat all of them. The power kicks in at about 3500 and pulls hard till about 7500-8000. Yes i know my cam and intake are not rated for that high rpm but it still has hard pulling power. You just need to drive a vehicle with a perfectl set up 377. I love my 377 if you dont beleive me race me.

if you want to get technical a 400 with .040 bore with 3.48 stroke its a 379 ci

The idea that there is some "magic" bore/stroke may actually have some validity, but probably not as applied to a typical SBC. The case of a displacement limited racing class is where it might apply. Something like F1, where displacement is limited and there are megabucks available to truly optimize EVERYTHING about the engine within the rules of the class. Even basic technical info such as B/S numbers aren't readily available, but the specs I have seen do indicate that they are all pretty close. The rules mandate a V-10, and all of the engines except the Renault have 72 degree V. The Renault is 110 degrees. They end up very, very similar in basic architecture.

It would be with engines that highly developed that things like conecting rod length and other subtleties make a measurable difference. It's nutty to spend much time discussing things like that for a street or street/strip motor. Small differences are just not going to matter. The power advantage is going to go to the engine with more displacement, better heads and induction system, better exhaust, and an optimized cam.

Rich

well, so far anybody where i live i have raced and beat. Mustang with 406, and was built beat him. 88 pickup 383 built, beat him too. Im not tring to brag but the 377 is just a motor that is underestimated.

The idea that there is some "magic" bore/stroke may actually have some validity, but probably not as applied to a typical SBC. The case of a displacement limited racing class is where it might apply. Something like F1, where displacement is limited and there are megabucks available to truly optimize EVERYTHING about the engine within the rules of the class. Even basic technical info such as B/S numbers aren't readily available, but the specs I have seen do indicate that they are all pretty close. The rules mandate a V-10, and all of the engines except the Renault have 72 degree V. The Renault is 110 degrees. They end up very, very similar in basic architecture.

It would be with engines that highly developed that things like conecting rod length and other subtleties make a measurable difference. It's nutty to spend much time discussing things like that for a street or street/strip motor. Small differences are just not going to matter. The power advantage is going to go to the engine with more displacement, better heads and induction system, better exhaust, and an optimized cam.

Rich

There is no "magic number" as you said, but diaplacement per cylinder and operating rpm and all its limitations may push a design toward certain numbers.

Late in 2003 BMW published some performance specs for their 2003 F1 engine. From these, if they were true, some interesting dimensional specs can be calculated.

BMW said 19,200 max rpm, 10,000g max piston acceleration and 25 m/s (4921 ft/min) average piston speed. With some calculation a stroke of 39.065 mm (1.538 in.) results, and a bore of 98.75 mm (3.888 in.) gives about 3.0L. The piston gs allow one to calculate rod length also, which I got to be about 80.25 mm (3.159 in.), and a rod/stroke ratio of 2.05. None of these numbers seemed out of line with other things I've read, and the relatively sane average piston speed surprised me. My guess is that the rod was about the shortest they could fit into an engine with that stroke and large piston diameter.I'll bet it's titanium and VERY light!

V-angles of F1 engines seem very strange to me. Renault gave up the wide angle in 2004, I believe, and 72 to maybe 90 degrees is used. Personally I don't care for "odd-fire" v-angles like 90 on a V6 or V10, but that's evidently less important than other things like packaging in F1.



My $.02

well i was thinking about this in class today. and can you image how crappy this would make motorsport? engines wouldn't rev, they would just have the same hum. and for spectators hearing that it would get dull. not to mention various teams would be trying to find the max hp/tq at the exact rpm. like making 675.45hp @ 6547.547 rpms
and alot of the smaller teams probably wouldn't be able to afford the changes in research.

There is no "magic number" as you said, but diaplacement per cylinder and operating rpm and all its limitations may push a design toward certain numbers.

Late in 2003 BMW published some performance specs for their 2003 F1 engine. From these, if they were true, some interesting dimensional specs can be calculated.

BMW said 19,200 max rpm, 10,000g max piston acceleration and 25 m/s (4921 ft/min) average piston speed. With some calculation a stroke of 39.065 mm (1.538 in.) results, and a bore of 98.75 mm (3.888 in.) gives about 3.0L. The piston gs allow one to calculate rod length also, which I got to be about 80.25 mm (3.159 in.), and a rod/stroke ratio of 2.05. None of these numbers seemed out of line with other things I've read, and the relatively sane average piston speed surprised me. My guess is that the rod was about the shortest they could fit into an engine with that stroke and large piston diameter.I'll bet it's titanium and VERY light!

V-angles of F1 engines seem very strange to me. Renault gave up the wide angle in 2004, I believe, and 72 to maybe 90 degrees is used. Personally I don't care for "odd-fire" v-angles like 90 on a V6 or V10, but that's evidently less important than other things like packaging in F1.



My $.02

That avg. piston speed surprises me as well. I have been using 4,500fps for the amateur level drag race and street/stip engines I'm involved with. And these aren't using anything exotic in terms of materials.

Rich

That avg. piston speed surprises me as well. I have been using 4,500fps for the amateur level drag race and street/stip engines I'm involved with. And these aren't using anything exotic in terms of materials.

Rich

About the shortest legal stroke in s 358 Cup engine is 3.25 or maybe 3.27. That gives the same avg. piston speed as the F1 BMW at about 9100 rpm, and we are seeing 9500+ on telemetry. That's approaching 5200 ft/min for an endurance engine. Hey, that's only 5000 piston gs. Piece of cake!

Cup shortblocks see practice, qualifying and the race. That's a lot of revs in anger (10^6 minimum). Next year that will decrease maybe 10-15% in about half the races with Sat qualifying and no happy hour. Won't save much money, IMO.