engineermike

This man speaks the truth. I knowingly decided to go from 363 up to 388 cid with my T76GTS simply because I wanted max power at a lowish pump-gas boost level. If I was looking for max power, I would have de-stroked down to 290 - 330 cid and cranked the boost way up on race gas.

germeezy1

Ok you just sealed my direction that I am going, granted I have a C5 so it won't launch as good but 9's is plenty fast enough for me. I would assume that you do regular rebuilds at that level or with the turbos is it an easy streetable combo? What other mods do you have? Stand alone ECU? Meth Injection? Sheet metal intake?

engineermike

A smaller motor will have a better backpressure/boost ratio on any given turbo. Most of us are stuck using a small-frame turbo since we don't want to do major frame surgery on the car. So, with a small-frame turbo, smaller cubes can make more power, providing you're willing to run 20++ psi boost.

You guys heard of Brent on turbomustangs.com? He's running a 302 Ford with a T4 flanged T88. At 28 ish psi, he's making 1177 rwhp on the puny F-cam (226/226). He hasn't measured it, but I bet his backpressure/boost ratio is 1:1 or less.

Mike

LTLHOMER

iTrader: (10)

Go with big stuff 3. No fancy intake needed. Meth probably needed if you want to run pump gas but racegas for the track days is no big deal. You won't be able to use most of that power on the street so you can turn it down and run 93 and still spin your tires all over the place on low boost.

We cruised Gratiot on 93 octane regularly.

germeezy1

The car will go sideways now on the spray at 60 mph so I would imagine that 600 RWHP is plenty enough on the street.

cablebandit

iTrader: (37)

Lynch is in the 6s with 2-88s and twice the cubes of Brent....they went to bigger cubes becuase its much easier on parts....especially the valvetrain...do you really think they would do better with a 302 and 2-88s?

engineermike

Brent = 302 cid and 1 x 88mm turbo.

Lynch = 604 cid and 2 x 88mm turbos.

Sounds to me like they're on the same plan.

Also, if Lynch increased cubes to be easier on parts, then he did it for the exact same reason I did. I was tired of replacing pistons, running 24 psi boost. So, I stroked it for more cubes and turned the boost down to 17 psi, knowing I'd lose ultimate power potential. I haven't broken a piston since!

Mike

bboyferal

iTrader: (9)

This introduction of pressure cons from which the smaller motors don't suffer does make alot of sense... One question though,

What about all these BIG BBC's being built with big twins? What's their pressure like because they are certainly big and they do push the boost?

Okay, nothing to do with power now, but another thing: smaller bore = stronger motor makes sense, but why do so many claim more reliable motors and parts with big bore/big stroke combinations?

kp

iTrader: (34)

Once again it boils down to money, reliability and being practical.

There is a big difference between 4000lb land barges that are street driven and dedicated race cars. There is no doubt in my mind a 408 with a T88 would be more tractable in a 4000lb car then a 347 and a T88. Even if the 347 at higher RPM could make horsepower the 408 car is going to be more fun to drive. Even at the track the torque is going to help a heavy car in the first 100' where it matters for ET, a lightweight dedicated drag car doesnt need the torque and works in a very narrow RPM range. I fully understand the concept of the pressure ratio, but it really depends what your goals are. I find it hard just to say 'smaller is better' or bigger is better' because its just not the case everytime.

engineermike

Because you can run less boost to make the same amount of power. In my experience, the reliability gained by reducing boost by 7 psi is far greater than the reliability lost by boring or stroking.

bboyferal

iTrader: (9)

Makes good sense. Thanks.

engineermike

Well. . . each turbo only has to support 250 - 300 cid. So, it really is a "small" motor when you have twins. The backpressure/boost ratio can be quite good on large cid if you have large enough turbo's.

germeezy1

The bigger the bore the increased risk of detonation and cylinder distortion at high boost levels. But then again having to run less boost would more than make up for the inherent problems on a big bore motor. What power level does a forged 346 start causing huge reliability problems?

DrTurbo

iTrader: (3)

They are not 88's

DrTurbo

iTrader: (3)

Once again I will say......optimum is 1:1. If your really good you can get below 1:1. , and the turbo becomes a scavenge pump . Their is a reason why companies contact Jose for turbo info as well. Jose told me what gave Lynch away is they used the same compressor cover from the GT47, but you can't hide a extra blade on the compressor wheel....lol.

bboyferal

iTrader: (9)

That sounds right, but then it leads us back to earlier statements made in this thread about bigger being better for max-effort turbo applications. On our LS1's, this just may not be true... If there's one thing I'm learning here, it's that you should always have more turbo than motor (regarding size, only of course... Motor needs to be TOUGH!).

Shinobi'sZ

Kind of funny that you have Formula 1 cars using 90 cid motors making 1400bhp.

I only made close to 1000bhp on my little 346cid.

bboyferal

iTrader: (9)

^ Yeah, but this our problem right here:

I've never read a good answer to this... Most experience head lifting before approaching engine size limitations on 346 LS1's.

germeezy1

Where did you get the setup that was in your 97, you had alot of the same mods that I have.

Pro Stock John

iTrader: (34)

There is a simple formula that captures all the variables when spec'ing a turbo setup:

Money + Physical space constraints + Max RPM + octane of fuel + weight of vehicle + usage of vehicle + Performance/ ET/ Dyno goals

Pretty simple eh?