Help with overboosting problem - 1JZGTE

[Scottywilkes]

the problem im having at the moment is this

With no boost controller fitted, and the gates connected normally if i hold the throttle (wheel spin in first and second ) boost will continue to rise, most ive had it to is 1.4bar, and omfg does it go hard haha.

Ive tested the actuators and they are opening correctly and at 9psi (standard actuator springs) it is fully open.

So the problem i think im having is im maxing out the wastegates?

Ive got a hybrid FMIC, 3 inch mandrel bent stainless twin system as straight as you will get it with no car, and 2 blitz nur mufflers out the back, literally no backpressure

Set of Lews seperated wastegate dump pipes, and when i had the turbos off recently i ported out the exhaust manifolds as the stanadrd cast manifolds are quite restrictive.

IM kicking my self that i didnt open up the wastegates when i had the turbos off and the rear housings apart haha.

Any other ideas? Im toying with the idea of installing a highflow cat which i have in my garage which may create some backpressure and help, but im running out of ideas.

Its a 92 manual soarer reasonably modified but standard turbos. So 1JZGTE with twin CT12a turbos.

Any help would be much appreciated im hoping i dont have to rip the turbos off again to enlarge the wastegates haha

[pandaah]

the vacuum lines going to the actuators are all ok?.. getting vacuum thru them on idle?

[midnight_purple_GA70]

or even see if you can fit a factory cat back exhaust up and see if boost drops if it does then you know your exhaust is too free flowing and putting a high flow cat in might be just enough to make it work...

[Cressid@]

I had similar problem before when I installed a pair of steel wheel ct12a (2nd hand Chinese)
boost keep rising no matter how I tune my boost controller.

My issue was the rear turbo wastegate only can
open half way. The actuator's rod couldn't push it fully back because the water
pipe was in the way.

Make sure nothing obstruct it from open fully. You can use a long screw driver and push it back manually. It's abit hard to get to but that fixed my problem.


Test it just by using a long screw driver and push the actuator see if it open fully

[Pimpin_1JZ]

I can tell you now that your problem won't be your exhaust. With those mods it will be expected that the boost will rise but obviously not 1.4 bar. You should be expecting something like .9 bar.

[Scottywilkes]

i was hitting boost cut with the fmic, and my old catback haha, which is 14 psi,

Since pulling the manifolds off, porting them out, porting the entries to the turbos (exhaust entry) installing the twin dumps, and fabricating the exhaust the boost has skyrocketed so it has to do with the small gates not being able to bleed off enough exhaust gases to keep the turbine at a stable speed.

Anyway, looks like i may be installing a nice GT35R soon as the rear turbo oil seal is on its way out.

SO hello tial 44mm gate, and GT35R

[bungs]

The wastegates on the 1j turbos flow fine, it's nothing to do with that. Check to make sure the flaps aren't staying shut due to obstruction. Maybe they're fouling on the dumps that were installed.

[Scottywilkes]

check all that with a pressure guage, the actuator arms are completely open at 9psi roughly, theres nothing obstructing the actuator or the linkage. The dumps were on the car previous to modifying the turbo manifolds and making the exhaust so dont see a problem there.

Anyway today i plumbed it directly from the actuator to the snail and it seems ok now, still spikes to 1.2bar in 2nd though, but in 4th on the highway sits at 14 psi, hopefully its not a problem in the avcr solenoid haha

[Scottywilkes]

well ended up being overwelmed wastegates, pulled them off, pulled the rear housings off and ported both the gates out 2.5mm each, reasembled the turbos, slapped the turbos back in along with the lews dump took about 5 hours and started her up and took it for a spin, holds .9bar boost perfect now , so i was outflowing the standard wastegates, its nice to hold 20 psi now

[bungs]

First i've heard of such a thing. I still reckon they were stuck closed somehow Good the hear it's all good now