This problem has stumped me for over 2 months now.

First my setup
D16A1
00 DX manifold with IHI RHB5 flange welded onto manifold
IHI RHB5, Mazda 626
Internal Wastegate
2.25" downpipe
2.25" charge pipes
2.5" exhaust
40 feet elevation
Ported/polished head, stock cams
9.5:1 compression (stock)

Even with the wastegate flapper fully open, the turbo spools to 9 psi at 5500rpm in 4th gear.

My wastegate port is not clogged. I know the wastegate is fully opened as I completley disconnect it from the actautor arm and the exhaust must keep it fully open.

I am thinking two things, #1, wastegate port too small, #2, engine flows too much air for this small turbo, spools like crazy. Any ideas here? I cant get any definitive answres.

Right now my solution to the problem is just run 9 psi , 450ccs with turboedit, but i really wana lower the boost as this car is uncontrollable. Its a 87 CRX btw.

 

Boost creep is a common issue with the Garrett T25 lineup (including the IHI RBH5), and ported turbine housings are often available to cure the problem.

But one thing you did not discuss: What does your downpipe look like? How does the pipe from the wastegate port meet up with the main pipe?

 

I used the stock downpipe/"O2 housing"
. I basically cut it in half, and welded a 2.25" 90 degree bend to the cast iron piece. Then, I simply used a 1.5 foot long 2.25" pipe to mate it up to the exhaust. It basically looks like a stock setup.
I got these pics from HMT
Maybe they will help to explain what I am saying.


I have been thinking of upgrading to a 2.5" downpipe for a while (or maybe even 3"?) But I am worried this will just increase the problem.

 

This ported O2 housing you speak of, can you provide more information, as to where they can be bought, and are the O2 housing all universal for the "T-25 lineup?" Sorry I am new to boost.

If I try to enlarge the wastegate port on my turbo with a die grinder and stone, will it cause it to crack since its cast iron?


Thanks for the help, not even HMT coudl answer my questions.