RX-Ben

iTrader: (7)

Let's be sure we are comparing apples-apples here-
seems like the people advising against the GT42 have used it as a front mount - whereas the rear mount changes the equation quite a bit.
Does anyone have any rear-mount experience with this turbo?--- that is the key question here.

Ben

RealQuick

iTrader: (14)

Thast been my point all along...

FastCashDave

Well one thing about it, if it don't work I can always go bigger.
And you know what they say Bigger is Better, I just won't tell my wife that

VINCE

iTrader: (1)

Ok let's hear from all the rear mount experts since there is a HUGE difference per some.

NA$TY-TA

iTrader: (21)

That’s what I was thinking... if anything you would think it would be less efficient...

2000 Tran Zam

iTrader: (2)

X2.

The reason they say its innefficient is due to more lag.

So the only thing that I can think of is if it creates more lag, maybe it wont bottle neck as easy since there is more room to hold the charge (IE. long *** piping?)

RealQuick

iTrader: (14)

Most people would agree that a T70 p trim turbo is too small for a 346ci LSX motor. Lets just use Purevil's old setup for conversation sake.

At 6krpm and 346ci his airflow requirement @ 14psi would be roughly 68lb/min from here:

http://www.forcedinductions.com/consumption346.htm

Now, when you look at a compessor map for a T70 and look up 68lb/min @ 14psi the turbo would have been off the edge of the compressor map showing a very inefficient setup:

http://www.forcedinductions.com/Tseries.htm

Now, he made 700rwhp @ 14psi wit his rearmount setup ... and I do not know of one single front mount turbo lsx with a T70 to match those numbers. Allthat I have seen have fallen short... and most only achieve those numebrs with a T76. My point is perhaps the turbo on the rear will alter output and blanket statements may not be totally correct.

Just food for thought.

Zombie

iTrader: (2)

I don't have a gt42-76, but I have a Innovative T76 R trim turbine .81 housing. I have problems making more than 16psi of boost on my 370 motor. Backpressure gets really high after 5500 rpms, as in 3:1 Below that it hangs out around 2:1. I'm sure insulating the piping would help the back pressure issue some. Swapping from the .70 divided I had on there to combat lag when I had headers to the .81 netted me a 50 rwhp gain on the dyno.

Hoping to go mid 10's @ 130 tonight on 15psi.

I've been able to get over 15psi before but the car has slowed down (this was on the .70 divided housing). Haven't been able to get over 16psi with the .81 housing and don't know if it will make more power even if I do.

Mustang dyno numbers with .81 housing ended up being (th400, 91 octane/meth)

470 SAE @ 10psi
520 SAE @ 15psi

Uncorrected numbers were about 40rwhp lower.

RealQuick

iTrader: (14)

I would think the 408 shouldnt have too much problem spooling the big A/r GT42-76mm. So you didnt have enough motor to get 15psi with a T76 and .81 A/r...

2000 Tran Zam

iTrader: (2)

I think he mentioned the backpressure would be too great since a 76 ran into those issues on a 370...

Zombie

iTrader: (2)

I don't understand what you are asking. I make 15-16psi, just can't seem to get any more out of it though.

Backpressure through a 408 and a rear mounted gt42-76 is probably going to be way higher than what you would like.

Stupid Boost

iTrader: (1)

I agree I would go bigger at least on the turbine side. Also ask the best guys in the business, either Jose or Jason at FI or Corky Bell at Bell IC's. They will tell you what you need to know. The boards are great for conversation, but everyone is just giving you an opinion. You need to talk to folks who build and design turbos.

FastCashDave

I know your right about conversation.
And I love it, I have learned so much in the past three years here and the Corvette forum. That is why when I start a new project I always go to these two boards.
Dave

Slowhawk

iTrader: (12)

Backpressure is a big thing,but we were told the T4 flange88mm on a 408 wouldn't work and it does very well

I say try the Turbo you got and go from there.

2MUCHBOOST

iTrader: (4)

Is that a mid frame turbo or large???? Its looks huge

VINCE

iTrader: (1)

Dave is looking for advice from people that know what they are talking about. I still see a bunch of guesses. It is also easy to use another car as an example because as we know all cars are made exactly the same and will respond exactly the same as the next car with the exact same mods. I am using a 76mm turbo on my Supra. 3.0L motor guys. Look at Daves supporting mods. This engine should breathe like a **** and when that 76mm hits full boost it will run out of steam quick. Hell even Supra owners are running bigger turbos on their smaller motors for drag applications.. It's easier for Dave to play around with the A/R than to keep swapping turbos..

RealQuick

iTrader: (14)

Whats nice with the GT42 is he can upgrade like Kyle did and not change the hotparts. I say start with the GT42 and put all the guessing to a stop. Check the dyno curves and decide where you want to go from there. Turbos get more expensive the bigger you go... might as welll try what you got. You can always upgrade to the S series stuff from Jose...

FastCashDave

The physical size of this thing is larger that my T88.
This thing is a monster.

Pro Stock John

iTrader: (34)

I get all the names and numbers mixed, up so Dave you have a T6 flanged 76mm turbo there? Based on what I've read, it's too small for your engine, but if you already own the turbo put it on and max it out. Maxing it out means you will only make a certain amount of boost, and beyond that it will just make the same power and more heat.

smokinHawk

iTrader: (48)

did you guys ever measure the back pressure with that yet?
how high are you reving it?
also what were they highest dyno numbers on his set up, i think i missed it.