camaroturbo

i have a 383 sbc dart pro 1 heads 600liftcam 114lsa 8.5 comp turbo is a gt4788 88mm top wheel a/r .69 and a 3.5 exh wheel with1.32 it had a .96 and i went to a 1.32 and it did help forsure but after 6000rpm its making to much back psi and lossing power. down pipe is 5" for 1 foot than in gos down to 4" and dumps under the pass seat should i go up to a 5" wheel and 1.08 exh housing ??????? it has a 2.5 crossover to the turbo thx for the help everyone

So.jerZ-28

iTrader: (20)

valve spring pressure? size primaries?duration of cam int/exh?
1.32 definitly way too big,
I would say a .81-.96 should work well.

camaroturbo

i had the .96 housing and it was to small i dont have any prob spooling the 1.32 at all am have a top end prob i can make 15psi on the trans brake in 1.5sec primaries are 1 5/8 and the springs r setup for the cam i dont have my paper work with me right now but i will get it on asap but my bigs prob is to much back psi its more than double my boost. boost is at 14psi right now

OUTLAWZ RACING

iTrader: (9)

What size flange?

355TurboLT1

iTrader: (11)

Bet its a T4........Is it a Precision unit or a garrett? The 1.08 and bigger are T6 thats what I have.

camaroturbo

T6 garrett

veee8

iTrader: (40)

If interested we have a 1.08 a/r housing if you want to trade for the 1.32.

camaroturbo

no thx I have a .96 1.08 and the 1.32 lol but even with the 1.32 am haveing a back psi prob thx tho and 1 ? wut size headers do you have and cross over? do you have that meet be my prob

black98ws6ta

iTrader: (77)

That turbo is known for not being the best on a larger motor. Are you having actual problems from the backpressure or just worried that it is a large number? 2:1 isnt horrible.

camaroturbo

just back pressure becuse the car make power up to 5000rpm than just falls off and that's with 13 psi so I pulled the muffler of and now it pull good to 5900 rpm than falls off at 13 psi it picked up 100 hp just by pulling the muffler

DrTurbo

iTrader: (3)

GT47's will have backpressure problems period...... on these larger motors. We have tons of data from these units on V8's. Great turbo up to 900-1000rwhp...above that the backpressure goes through the roof. Is the power falling off at the top end badly or boost falling?? Typically you will see a trend on these motors with that turbo that the HP will drop on the dyno above 6K with a GT47 as the backpressure elevates above 2:1. Slap on a GT55 and it will keep climbing up to the redline as long as the motor doesn't go above 400ci. You can bandaid it with a larger A/R, but your still having to flow through that turbine wheel.

camaroturbo

the boost don't fall of just power and do I have the bigs exh housing for this turbo (1.32) and if I put a GT55 with exh housing should I run on that thx

DrTurbo

iTrader: (3)

1.12A/R is what we tested and works excellent on that size motor. Response it VERY good and easily will make 1000rwhp without breaking a sweat. Give us a shout, we carry the GT55's in 91 and 94's in the journal bearing versions as well.

camaroturbo

ok 1st my boss is going to try and put the lil biger exh wheel in and a 1.60 exh housing do you think that will help any and how much do thay run in the 91 journal

DrTurbo

iTrader: (3)

Which turbine wheel are you going with?

camaroturbo

its a 4" 102mm off a c15 cat turbo I have to get a housing milled out to fit I can mill out a 1.08 1.23 1.60 and a 1.8 wut wut would be my best bet and the the one I got on the car is a 92mm

355TurboLT1

iTrader: (11)

Too bad you dont have the Precision GT4788. Vee8 made 1200hp if im not mistaken and didn't have any backpressure issues. Granted he was running a 370 if I remember correctly. Also I would think it would be in your best interest to run the 5 inch DP alone and see if you gain anything more. Do the easy stuff first. I'm finding it hard to believe you are having backpressure issues at 13 psi even on a larger 383.

camaroturbo

yea am doing a 5" down pipe asap and vee8 said he did have some backpsi but at higher boost idk y my setup is doing it at 13psi and only made 650rwhp at 5900rpm and falls of fast

355TurboLT1

iTrader: (11)

Ok cool. Vee8 has been working on another members car(they call it the cookie monster) and it has the Precision GT4788 on it and made 1000+rwhp and no mention of backpressure issues. The Precision unit is more efficient than the garrett although I think the exhaust housings are the same. Keep in mind that this car has a 370ci motor but I dont see you having issues even with a 383 at 13psi. That isnt ****. I just think you have alot more going on than the turbo. It should make good power past 13psi. Granted it will hit a point where it will be expected on your setup to fall off due to backpressure. Let us know if you get any improvement out of the straight 5 inch DP.

camaroturbo

yea its a all new setup so its prob not all the turbo am just try to find the prob ill be trying to get that 5" DP and the new exh wheel and see wut happens mybe my log stly headers r do something to am not sure