No additional boost after BPU - Whats wrong?

[Guest pokaichip]

Hello,

I recently went BPU on my Jspec expecting to get some extra boost. But to my surprise I am still sitting at about 10 psi (factory) boost after going BPU.

 

What I modified:

- New Apexi n1 exhaust system including 1st and 2nd decats.

- Fitted 2" restrictor ring after the 2nd decat

- HKS FCD

- HKS Speed delimiter

 

What I need to do still (although my mechanic says these shouldn't impact my boost pressure):

- Upgrade fuel pump to Walbro GSS342

- Upgrade spark plugs

 

My mechanic said maybe because the wastegate spring is capped at 10 psi. So no matter what the maximum I would get is 10. But I didn't see any evidence on the forums to back his claim.

Any advice would be much appreciated.

Thanks in advance!

[ellis]

Did you fit a boost controller?

[Guest pokaichip]

I have not. I was under the impression the jspec doesn't require a boost controller for BPU. I was thinking of getting one but wanted to see what kind of boost I'm getting with just the decats.

[tony tt]

Rule of thumb is the restricter ring to go between the decats bud. Boost controller and raise it. What size of r ring did you use? Some cars won't raise boost themselves. Some need a little help with the BC.

[Guest pokaichip]

Interesting. My restrictor ring is 2" does this need to be bigger? Also what kind of material are most guys using for the restrictor ring. Mine is basically some thin sheet metal, so I put it behind the second decat just in case it gets too hot or something.

Perhaps I will try to relocate it to between the 1st and 2nd decat and see if that makes a difference.

[ScottC]

The restrictor ring lowers the boost back down to a safe limit, you then use a BC to raise the boost up to your required level. A boost controller can only raise boost, not lower it. If you don't have a boost controller fitted try removing the restrictor ring and see what happens, but keep an eye on your boost pressure in case you over boost.

[tony tt]

It will be better positioned in the middle of the decats to allow back pressure to the turbos. When I was bpu I had a 1bar restricter ring and raised boost to 1.2 with the BC.

[Paul Whiffin]

This is probably your issue, collapsed turbo air intake pipes, they are all doing it and this will restrict your boost.

We do our own replacement fluro lined silicon hoses or genuine Toyota, I bet this is your problem.

 

 

[Guest pokaichip]

Thanks for the detailed pics! I'll try moving the restrictor ring first...

Thanks

[mac79]

I think those are mine that paul changed for me.

[Ian C]

As has been said, take the ring out first and see what you get Each ring needs to be fettled to an individual car to some degree.