RX-Ben

iTrader: (7)

I'm considering a rear mount turbo for my LS1, but the rear mount is a bit different than the normal manifold turbo that I'm used to. Anyone have any idea how this will affect sizing? My guess is that the A/R should be decreased- but how much?
FWIW- I'm looking at a GT40R (w/1.06 exhaust A/R) and GT42R (w/a 1.01 A/R).
I'm looking for the smoothest throttle response (least lag possible), as I'll be doing road racing with this setup.

Thanks
Ben

GR33N GoblinM6

iTrader: (14)

what are the HP goals you require? a 60-1 .81 A/R is common for quick spool.. if you want a bigger turbo.. you can look at a GT67 with .81 or .96 A/R

that 1.06 is going to be very laggy..

longrange4u

iTrader: (2)

I am going with a PT-88 in my custom build but it still has a .96AR. If you are stock cubes I would not consider going larger then a 76GTS... if you want minimal lag and your ok with ~550RWHP I would reccoment the GT67 Goblin spoke of.

I would not consider going larger then a .96 AR for a rearmount setup.

RX-Ben

iTrader: (7)

I'm shooting for 650-750hp.

The sizing on the GT wheels are a bit different than the T series - are you taking this into account? I mean, the A/R is just a ratio (not a pure size)- the turbine wheel sizing and aerodynamics are compeletely different from a T series to the GTxxR series.

Unfortunately I don't think there are any turbine maps for the old T series, so it is hard to compare flow rates from the GT series A/R to the old T series A/R.

In any case, what I'm hearing is that with stock bore/stroke, lag is an issue with the rear mount up to around 550hp? What about with a 402?

From the dyno graphs on the STS site- it looks like there is no sign of lag with their LS1 setup- as there curve is nothing approaching the typical "waterfall" shape that I normally see as boost comes on. The analog to that turbo (making 500hp @ 8psi) seems to be the GT40R.

Thanks for the responses,
Ben


Ben

chuntington101

well i have heard of someone on here running a T70 and pushing 700rwhp! it was pushing the turbo to its limits but it did work!

for a 750 bhp tops, why not go for a T76 on a 383 or 402?? should be a very nice comob

thanks Chris.

chuntington101

PS the GT42 is very similar to the T76, but thanks to the dual ball bearings and better turbine design they should spool quicker!

speaking of spool, i have seen a 2.0ltr Evo spool one of these by 4500rpm! these things are really nice! but you do pay for them!

thanks chris!

GR33N GoblinM6

iTrader: (14)

750rwhp... go with a GT70 .96 A/R and use meth... you will definately need a front mount to cool that charge off..

or you can also use the more expensive GT76 or its big brother GTS76..

RX-Ben

iTrader: (7)

Well, I'm really trying to limit my choices to something the the GTxxR line - like the GT40R that ATP has a GT42R wheel, and a GT40R exhaust (GT4094R). I'm under the impression the GT turbos are a bit better than the T series, and twin ball bearing setup is better as well.

I guess my main question is- how much does the rear mount kill response?
I did see a dyno graph on the STS page from a GTO w/a T76- looks pretty decent.
Also- I saw a guy name Dave Martis who runs a GT76 w/.81 A/R on the exhaust in a lim green mustang road racing car (AIX) - though he uses a 4.6L Ford DOHC engine.
(http://www.ststurbo.com/dave_martis_mustang)
Seems like a 5.7L LS1 should have at least similar flow to that engine.

So- from what I'm seeing- the rear mount seems pretty viable. And the other thing- the LS1 is so torquey down low that a little lag may actually not be a bad thing for keeping the car on the track.

The big question I have now is converting between the old T series- specifcally that GT76 that I mentioned above and the GT series. I'm guessing the GT4094R (the GT40R/42R hybrid) should be a pretty close approximation.

I'll inevitably have some more questions in the future about heads, cams, intake, and intercoolers, but I'll be doing a bit of searching - now that the rear mount seems viable.

Thanks again
Ben

longrange4u

iTrader: (2)

You will never fit a GT42 under the back of the car, its a large frame turbo... I have a mid frame turbo (PT-88) and it gave us hell... If your looking for 750 RWHP on a 400+ Cube block... I would reccomend the 76GTS

RX-Ben

iTrader: (7)

Good observation. The GT40 (as is the GT4094R) is a mid-frame from what I can tell, it is just slightly larger than a GT30R or GT35R.
And if worse comes to worse, I can mount it in the back like Martis did in his Mustang.

Ben

chuntington101

i thought the GT42R, the ones that the EVOs are running was a mid frame and simlar in size to the 76??? where am i going wrong here??

Chris.

RX-Ben

iTrader: (7)

The GT42R is huge, I'd be surprised to see that on anything other than a pure drag Evo (with a bump in displacement) - like this:
http://www.amsperformance.com/amsdragevo.php
http://www.amsperformance.com/chrisevo.php

Here are the GT42 dimensions-
http://www.atpturbo.com/root/turbopi...ns/gt42dim.htm

and here are the GT40 dimensions-
http://www.atpturbo.com/root/turbopi...ns/gt40dim.htm

I guess the GT42 is still a midframe (I'm not sure exactly what qualifies as a midframe) - and at first look it is bigger than the GT40, but the dimensions given for the 40 and the 42 are not measuring the consistent (the 42 dimensions are for the full width, while the GT40 dimensions are just for the width of the compressor/turbine)
So you are right, sorry about that.


Most guys stick with GT35R -
http://www.amsperformance.com/roadraceevo.php

The last car is sick- it kicked serious butt in last year's One Lap race.

I'm building an RX7 (FD) for that race with a swapped LS1, or LS2, or L92...and really thinking about going turbo.
I currently have an head/cam/headers RX7 (FC) with about 430hp...but I'm already feeling the need for more.

Ben