Originally Posted by LVSBB6

Went to dyno today to tune HKS turbo & Blitz camshafts and noticed some weird unsolved problem which I thought was fixed previously, horsepower power flattens out quickly by 5000rpm and started to dip down right around 6500rpm. We have tried various Mivec setup, while boost is 27psi tapering to 23psi, and A/F 11.9 to 11.1. Tune is good and spools quickly, but for some reason high end power just falls flat to the ground. Looking back at my old tune, this problem has started during the time I was running the FP Green. Originally it pulls all the way up to 7500rpm, but months later when I went back for a retune, the power flattens out at 5000rpm and falls down by 6500rpm. At that time we found there was an exhaust leak and manifold leak which were fixed. I thought that were the issues so when we installed the HKS turbo and made sure there was no leak, we thought the problem went away.

What could be causes for this? I have read a clogged cat would be one scenario but I'm running test pipe. And the fact that my boost is not being withheld doesn't sound like a clogged exhaust syntom? Could it be a pest or something clogging the exhaust? Mind you my NurSpec DT isn't a straight through style system so I can't see whether it is being clogged up or not...

Could it be SST TCU issue? I remember seeing some high horsepower MR which has power dipping issue in the high range as well. But that doesn't explain why I didn't have the problem originally, it happened after a while with the turbo upgrade.