sbc 383 with gt4788 help with exh housing
#1
sbc 383 with gt4788 help with exh housing
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
#3
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
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#8
#10
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
#11
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
#13
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.
#15
#16
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
#17
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.
#19
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.
#20
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