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Turbocharger Engineer
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751 Posts
Discussion Starter #1
He guys I'm helping a buddy of mine with his 95 Supra TT, for some reason we can not keep the boost up. He can launch and in 1st gear it will hit ~15-16psi, then hit 2nd and it will go to 19psi where it should stay, but by 5K rpms the boost drops back down to 13-14psi? It continues this in the next 2 gear......will go to 19-20psi, then fall to 13-14psi. Why is the boost creeping back down? Does he need a stronger spring in the wastegate? Or does he just need a boost controller? Thanks for any help.


Jose
 

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boost is good
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772 Posts
might be a boost leak. if its the stock bov, there could be a chance that it could be leaking under high boost too.
 

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Turbocharger Engineer
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751 Posts
Discussion Starter #5
All he has is downpipe, cat back exhaust, K&N drop in filter in stock airbox, and the boost is rigged for 19-20psi, not sure how he has the vacuum lines routed. Thats about it.....

Jose
 

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JZ 97 SS 1500 said:
All he has is downpipe, cat back exhaust, K&N drop in filter in stock airbox, and the boost is rigged for 19-20psi, not sure how he has the vacuum lines routed. Thats about it.....

Jose
Sounds like he may be using the Bleeder 'T' to raise boost, I had that mod for a bit and it did the same thing, it's a bad way to control boost IMO and doesn't hold the boost well.
 

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you might not have a problem at all, all stock turbos have a hard time keeping up and will start to fall after a certain rmp.
 

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Ok, Ok , I’m the mysterious guy with the boost problem. Jose is a good friend helping me out but the answers we have received so far are the same I received over a year ago. So let me give a few more details. I had talked to many people then until I decided it was up to me to figure out the problem. Boost leaks, no… BOV, no the only solutions I could come up with is wasted gate was too weak. No one would accept that possibility so I had to prove it. Well the problem came about after Majestic Turbo in FL rebuilt my turbos, I would only make 14PSI :( with the hoses to waste gate unplugged where before I made 17-20psi, 21psi in od. I have heard over and over the turbos will only flow 17-20psi. Well maybe, but I took the simplest fix I could think of. Which was to take a one way air valve to pull a vacuum on the waste gate at idle and hold it there under boost. The boost spiked to 24psi. Well after seeing 24psi and hearing a few pings and had visions of engine parts laying on the road. I quickly unhook the vacuum line and found a spring to hook to the waste gate. The results varied but kept the boost up around 17-20psi but would roll back to 14 psi at the top of each gear. Well it was close enough to drive and only slowed me by a tenth or two. With the vacuum line hooked up it would hold 20psi but would spike way too high and 20 was a tad more then i wanted on pump gas.

With just the spring the boost dropping off in each gear also killed the top end charge that the supra is known for and after having a stock LS1 camaro stay with me it’s time to get back what was taken.
(note: This LS1 runs 8.4 in 1/8, my best was 8.1 and now i run 8.3 on a good night)

So guys, I know if I find the right spring and put a BC on the car that my problem would be solved but then it would be rigged. I don’t want it rigged anymore then it already is, I just want to work on it once and be done with it. I want to hold 18 or 19 psi all the way. I need to know if you can replace the spring or replace the waste gate on the car without pulling everything apart. If so, what do I need and how much do I have to pull apart to get it done.

Thanks for all your help :D
Jimmy
1994 Auto
[email protected]


http://hiwaay.net/~dimos


 
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