A few weeks ago, I went from stock DP + Random Tech HFC + stock cat back to a stock DP + 100 cps HFC + RRE Stealth exhaust. I thought that with the stock DP, I wouldn't see much improvement in engine efficiency, but I was surprised to find that it took way less tension on the wastegate to maintain the same boost levels. I'm still thinking about how to best explain this effect, but I think its safe to say that the free flowing exhaust setup is resulting in a much greater pressure differential across the turbine making it work much more efficiently. Anyhow, I installed a 3" DP this morning (Helix v2), and wasn't expecting much more of an improvement, but there was a reasonably good improvement. The required tension on the wastegate was even less, and the boost still went beyond the target values.

Another interesting effect here is the complete elimination of all knock at high rpm after installing the components. I figure that I can easily dial in another 2 deg of timing at the top end and get at least another 10 whp. Probably more with AFR tuning.

Anyhow, just another tidbit showing that the DP, cat, and cat-back all contribute significantly to improved performance.

stock exhaust with Random Tech 2.5" HFC



stock DP + 100 cps cat + RRE Stealth



Helix v2 DP + 100 cps cat + RRE Stealth