MrWS6

Hey guys,
I am considering going with a turbo set up on my forged 422 ci and before I make the call to place the order I just wanted to see your guys thoughts. I was thinking of going with LS1 motorsports for their turbo system. Should I go with the T-76 upgrade do to the large displacement of the motor? My comp. ratio is are 10:1. Also should I change my cam, I am using the S1 cam from MTI. I dont want to go super crazy as far as PSI but pretty much as much as I can run safely on the street/strip. What kind of number do you think I could get at the wheels?Thanks
Chris

SuperZ28

I'm new to the F.I. game, but here's my thoughts.

first, if it was me, I'd go with a diff cam. I went with something like the LPE GT2-3, but with more lift. I think your cam has too much duration, but that's just my opinion

second, I would imagine with a good tune, you could safely run 10 to 12 lbs on your CR. I wouldn't be surprised if you hit high 600s/low 700s on proper fuel with that much boost.

I went with a 408 Iron block, I'm running the turbotech T-76. My goal is 18 psi on 8.6:1 CR

I'm sure others with more experience will chime in soon...good luck with everything!

BOO HOO BRIAN

iTrader: (-10)

A nice precision 76 gts with a turbonetics .96 on center exaust housing which might be a little too small or a 1.3 on center which might be a little too big. The biggest exaust housing precision make in on center is an .85.

Earl H

iTrader: (1)

If you can wait about 3 weeks, I'll be installing a pt76 gts on a 422 LS6 motor. It will be on a Z06, but the results should be comarable.

MrWS6

well by there time things get moving on this project I am sure I will get to see the results! anyone else want to chime in.

Pro Stock John

iTrader: (34)

I had an S1 (244/244/112) in my old 422ci and I would not use it for a turbo.

That cam will have too much overlap.

Try bbrannen@compcams.com and see what he says, but I would keep in mind that most cam companies will suggest cams that are comparably smaller than supercharger cams so if it sounds milder it is.

MrWS6

thanks I will email him as far as the cam goes, anyone else know what kinda power I can expect at the wheels.

BOO HOO BRIAN

iTrader: (-10)

Depends on what turbo and what boost level.

MrWS6

I was thinking the t-76 with 10 or so pounds of boost.

Pro Stock John

iTrader: (34)

700-900rwhp depending on your ECU and fuel system.

eviltwins

I've said it before and i'll say it again. On a big motor like a 422 or a 427 a single T4 exhaust housing is going to start to be pretty restrictive for exhaust flow, which can lead to blown header or head gaskets. If I were to do a 400+ inch small block I would run (at least) a small-frame PT88, or a pair of T4 housings turbos. As engine size increases, you need to increase the size of the exhaust housing proportionally.

Earl H

iTrader: (1)

Evil,

I've seen you state this before. Harlan has said the same in different threads. The small frame PT88 is rated at 1,200fwhp vs. the PT76 GTS, which is rated at 1,100fwhp. That doesn't seem like much of a difference. In real world application, the PT76GTS was good for 980rwhp on a pretty "tame" combo'd Supra (recent mag article). I've also been told that the GTS has laid down more than 1,000 rwhp on another application. Now you maybe (probably are) right about your assessment. Can you explain to me why a 422ci LS1 would have problems making at least 650-700rwhp at 12psi given the right supporting hardware? Thanks in advance for entertaining the question. This is turning out to be a great thread.

eviltwins

I'm sure you could easily make 650-700 RWHP on that setup, but I just think you would see a lot lower backpressure with a PT88. The biggest motor i've used a T76 or seen a T76 used on was a bud of mine's Fairmont, with a 418 stroker. He was running a PT76-GTQ .96 A/R tang housing, only spun the motor to 6250 and he was lunching header gaskets left and right. Never actually checked the backpressure, but we switched to a PT88, didn't really slow down spool that much, but we never blew another header or head gasket with the car. I've also seen this, on a larger scale, on big block motors. I helped a friend of mine build a single turbo setup for his 540" 69 camaro last summer, we originally built it for a PT88, and with 12 pounds of boost we were normally seeing 30+ PSI of backpressure. Talked to some people that have done big block turbo setups before, and they all said that when you go big inches, you need to run a much bigger exhaust wheel, so in our case his goal was 1000 RWHP, but we switched to a T94 on the motor, and at 12 psi the backpressure was reduced to around 20 psi @ 12 psi of boost. I know that's not a straight-up, apples to apples comparison because there is a pretty hefty difference in compressors from a T88 to a T94, but the T88 is rated @ 1250 horsepower, and it was choking off the motor that was only making around 700 to the wheels.

I'm not trying to say that it WON'T work, but if I were in your shoes I would run something that would give me more flexibility in the future. If you decide that you want to make more power you pretty much have to reengineer the entire kit and try to fit a TV-frame turbo in there, or rebuild it alltogether.

BOO HOO BRIAN

iTrader: (-10)

Only problem with an 88 is the compressor map. Unless you are willing to run 20 psi + , it doesnt make much more power than a 76. It might even make less power at 10 psi than a 76. I have personally seen t4 exaust housings support over a 1000 hp so im not convinced on the back pressure issue. With turbo cars , cubic inchs are not a factor in the ability to produce hp. A 274 cube motor and a 422 cube motor making a 1000 hp need to move the same amount of air in and out to support the hp.
A gt42 or a 76 gts support 1200 hp. I think that will provide a lot of growth for an ls1 car.

Earl H will show some people what kind of hp a 76 gts will support .

eviltwins

Well, I've seen a PT88 car with a 383 @ 19 psi go 154 through the traps at a 3350 race weight, so I don't think he's going to need to run stupendously high boost to make power with it, IMO. That's Shane from induction motorsports' car that i'm talking about, I don't know if he posts on here.

Like I said, this just just coming from personal experience, I don't really have any scientific evidence to back myself up, but to me it makes sense. It's like running a single T3 exhaust housing on a V8, sure 4banger hondas can make 500+ WHP with a single T3 with fair backpressure levels, but would you want that dinky housing taking the exhaust gas from a 500 RWHP LS1? I think it would be come quite a restriction, even at the same power levels as a honda.

MrWS6

thanks so far guys all the info really helps...

BOO HOO BRIAN

iTrader: (-10)

On the 88 the aerodynamics of the comp wheel causes a completly diffrent map than say a 76. At 10 psi will an 88 move air? Of course. But it will not make good power and the compressor surge will be almost undrivable. You are to far off the compressor map at that boost level .

The t3 exaust housing on a 500 hp 4 cyl and a 500 hp ls1 will see the same backpressure since it still takes the same amount of air and fuel to make 500 hp.