boost dropping after peaking at approx 5,500 rpms
 

Ok I performed the obligatory search and didn’t find anything conclusive. There doesn’t seem to be any feedback indicating that any of the tips given resulted in a solution . Perhaps they worked but the originator of the threads never responded to indicate they were successful.

Anyway here is my problem. My boost is trailing off once it peaks after around 5,500 rpms.. It will drop from around 0.95 kg/cm^2 to 0.75 kg/cm^2 or less.

I am running a 35r and a Tial wastegate with a 0.8 bar spring. I have used both the PFC and a Profec Spec II to control the boost, both with the same results. I have boosted a couple of times without any boost controller and it seems to hold at spring pressure. However I have not performed those runs (with no boost controller) runs more than once in a row. I am under the impression that the more times I boost consecutively the boost tends to trail off more.

My boost was rock solid up to 17 psi until a couple of weeks ago. I sent the wastegate back to Tial and they tucked the diaphragm and pressure tested it. When I received the wastegate from Tial, I pressure tested the bottom port. It was leaking air from around the valve guide, once the valve opened up. Tial assured me that this was normal.

I have read several threads where individuals had a very similar problem. What was the fix? Did anyone actually find a boost leak?

what size turbine housing?

Thanks for the response.

The turbine is 1.06. I had previously ran close to 17 psi to 7,000 rpms with very little drop off.

I’m embarrassed to say, my boost issue is resolved. I removed, repositioned and tightened the couplers.

hehe i was assuming we had the couplers and clamps covered :)

glad you got it figured out though