I installed a 3" cat and exhaust to match my downpipe. That replaced a 2.5" exhaust and likely clogged cat. Next thing I know, my normally steady 15 psi of boost heads right for 20 psi. The higher the RPM, the higher the boost. I started simple and eventually eliminated everything that could affect boost. In the end, I had to remove my manifold and cut off the pipes for the external wastegate. Once I did that, it was painfully clear that I had designed the orafices for the wastegate pipes too small. Embarassing as it is to admit, I calculated a radius and drilled it as a diameter. At higher exhaust flows, I was overwhelming the holes and continuing to spool the turbo. The wastegate was wide open, but the flow just wasn't getting to it. The weird part is that I have been using this manifold, turbo, and wastegate for years without issue. After drilling the holes out and welding the pipes back together, I have my rock steady boost back. I'm still working on getting my pride back.

Corbin
'95 ESI-T

Now with more power and fewer leaks



Humble servant of the Wiki

HOw small did you drill the holes?

It looks like I drilled two 13mm holes for a single 36mm inlet (38mm nominal wastegate). Clearly, I left my brain brain at home that day. I was aiming to match the area. I didn't bother to match the actual flow characteristics. I hogged each of the two holes out to 26-27mm and it works fine now. I just can't believe it didn't present itself until I put in the new exhaust in. I'm sure the 30F weather added to the problem.

Corbin
'95 ESI-T

Now with more power and fewer leaks



Humble servant of the Wiki