Help! Rb25 Boost Drop, Won't Hold Gt3076 .86

[DriftSquad]

Okay so sorry it's been so long.

I had an old post from a few months ago explaining my issues with my rb25 not holding boost to redline. I can't find it anymore so I have to start a new one.

Problem is it hits full boost then drops of to 11/12

Psi by the end of the rpm. Originally it was thought there were leaks and the rear housing was to small (.63)

So fixed the boost leaks! And slapped a brand new gt3076r .86 rear on

And I still have the same problem. I thought maybe the boost controller was doing it.. So wile on the dyno we adjusted the spring to 16psi and ran no boost controller and the result is the same! With no boost controller it still drops passed the waste gate spring pressure?

I give up! Anyone had this problem?

Mods

Gt3076 .86 high mount (genuine)

Stainless high mount

Pro boost wastegate 50mm

880cc injectors

Greddy plenum

Intercooler

Blitz duel solenoid boost controller

Microtech lt12s

[Blackkers]

Hey mate, this is by no means abnormal.

What boost controller were you using?

An electronic boost controller will have an option to hold boost after it peaks.

I use a GFB ge-force 2 and the setting is called sensitivity or SENS. it works flawlessly, I could hold 20psi to redline if I wanted. I think it was about $280 from MRT in Sydney on special

[Ben C34]

Is that an eBay stainless manifold? Maybe it's a poor design.

[KiwiRS4T]

How hard would it be to swap in another wastegate to try?

[Ben C34]

Just had a look at pro boost. I would be getting g a decent gate on there asap. That pro boost one doesn't inspire much confidence.

Edited September 18, 2014 by Ben C34

[Ben C34]

And if your manifold is a pro boost one it looks more likely to have boost spikinh control issues due to the wastegate location.

I'm certain it's the poxy gate.

[DriftSquad]

The stainless manifold seems to be build well. That's not saying it's not the

Problem. The wastegate port comes from both sides of the manifold then joins to 1 pipe.

The wastegate could be the issue. I only used it because a Friend had one on his vl making 500hp and seemed to work well.

Maybe the wastegate is 2 big?

As for the boost controller I'm not clear on its operation as the tuner set it up this is the model controler

[Dose Pipe Sutututu]

how have you plumbed the vac lines on the gate?

I prefer this setup for good boost control (remember to set your EBC for external gate or else it won't work):

[KiwiRS4T]

The stainless manifold seems to be build well. That's not saying it's not the

Problem. The wastegate port comes from both sides of the manifold then joins to 1 pipe.

The wastegate could be the issue. I only used it because a Friend had one on his vl making 500hp and seemed to work well.

Maybe the wastegate is 2 big?

As for the boost controller I'm not clear on its operation as the tuner set it up this is the model controler

The wastegate is bigger than you need but that shoudn't be the problem -its how well it works. In my opinion its essential that everyone learns how their wastegate and boost controller works. I must say I am a slow learner and it took me a fair while but often everyone will assume that someone else knows what they are doing or has set everything up right. Do a lot of Googling and find out just how your boost controller works and how it should be set up so that you can eliminate problems.

[skylinecouple]

As Bob said. Research. I cannot tell you how many times I had so called experts tune or set-up my car and fail miserably.

[DriftSquad]

Thanks for your help, iv tried looking up my issues and if I could bring up my old post from early this year you would see all the things iv tried now to hold boost. Iv hit a dead end. The only thing left sounds like new exhaust manifold and wastegate. I would have thought my sbc boost controller would be able to make it hold. But even if the gate is set to

16 pound the boost drops below that.

[GTSBoy]

Are you using the forum's search engine or are you using google to search the site? Because you know that in-built forum serach engines suck balls and google rocks at site specific search, don't you?