2JZ won't make more than 5psi

[Dirgle]

Car:
1987 Supra
Stock Aristo 2JZ mated to a R154
2.5" intake pipe with DM FMIC
3" Exhaust with a 50mm restrictor plate



The problem I'm dealing with is that the turbos won't push past 4.5~5 psi of pressure. The engine will turn all the way to redline without a problem, abit with a lack of power, but it's smooth all the way. There are no codes. And I get a little dip in the pressure at around 3800 rpm. Then it's right back to 4.5 psi.

I have checked all the piping and tightened all the T-clamps. I don't believe there is a boost leak in the intake piping. I have also disconnected the wastgate vacuum line to see if there would be any change, there wasn't.

The restrictor plate is used to control the boost since the JDM wastgate is to small. But 50mm -52mm seems to be the standard that people use to see 16 psi. I would be surprised if my restrictor plate was keeping it down at 5psi. I'm going to enlarge it this weekend to see if there is any change. But I would like to see if anybody else has any ideas before I do. Also the exhaust 3" mandrel all the way back to a straight through muffler. If this doesn't have an effect I'm going to do a temp TTC mod for further diagnosis.

One oddity I noticed is if I do a 4th to 2nd down shift with a rev match at anywhere above 3400 rpm the boost falls off to 0psi after a couple hundred RPM. If I let the clutch bring the revs up to that range then the boost stays at 5psi.

Any ideas?

 

[tissimo]

Restrictor?


Sounds to me like you have a dead turbo though.

 

[ahmed]

dead turbo OR
leakin at exhaust manifold either cracked somewhere or leakin gasket.

 

[89turbotoy]

stuck open wg or massive boost leak

 

[Dirgle]

Restrictor?


Sounds to me like you have a dead turbo though.

Hope not. The first turbo sounds healthy. I can hear it spool, and there is no metal on metal sound. And at the point the second turbo comes on line I don't hear the infamous death whine. And before I put the engine in I checked for shaft play, and it's well within TSRM spec. It's possible, but they sound good.

As for the restrictor, does the question mark mean that you think it might be a culprit or because your not sure why I have it?

dead turbo OR
leakin at exhaust manifold either cracked somewhere or leakin gasket.

That's an idea. I'll look around tomorrow.

stuck open wg or massive boost leak

It spools pretty quick. I see positive manifold pressure at 1500 rpm, and the 5psi just before 2000 rpm. So I doubt it would be the wastgate. But I'm going to keep looking for a boost leak.

 

[mkiiichip]

isn't whole idea of "twin turbo" was that both turbos were supposed to spool together?

 

[ahmed]

isn't whole idea of "twin turbo" was that both turbos were supposed to spool together?

no. im just gettin into these cars but from what i hear on the 2jz 1 spools then the other one starts makin boost at higher rpm. but there is a mod to make them both work the the same time.

 

[Dirgle]

no. im just gettin into these cars but from what i hear on the 2jz 1 spools then the other one starts makin boost at higher rpm. but there is a mod to make them both work the the same time.

Correct. The 2JZ uses a sequential turbo system. It uses all the exhaust energy from the engine to spool one turbo in the lower end of the rpm range. Then in the 3300-3600rpm range, as the engine is producing more exhaust energy, a small amount of exhaust gas is used to pre-spool the second turbo. With the second turbo coming fully online and joining the first turbo in powering the engine at 3800 rpm. This type of setup gives good power down low, where most driving is done.

This is of course is different from the twin turbo 1JZ's which use a true twin turbo setup. With both turbo's running at the same time. There is a way to do a TTC(True Twin Conversion) with the 2JZ. I haven't done this yet but from what I'm told the boost comes on a few hundred RPM's later, but the torque curve is smoother.