[onefastredsc]

Hi all. With the weather here in western PA being a little too crumby to wrench on my car (no garage, i know.....), I thought i would create a post to start some healthy debate on a topic that recently crossed my mind. I have a 128i with the N52 motor, on which i installed a 3SI manifold from a N51 motor that i procured from a wrecked SULEV 3 series on ebay. I installed the manifold back in December, as i had to remove the manifold anyway to replace a failing starter motor located under the manifold. I have since put about a 1k miles over 2 months of driving with the 3SI installed on the factory tune without any issues. I do realize that i must install some sort of tune eventually to fully realize the benefits of the manifold (OE style 330 tune or aftermarket), but i've been telling myself to hold off until i NEED to tune the car post header installation.

Which brings me to the headers. I also have a set of AA headers i purchased on sale over the holidays, coated by SwainTech to boot, that have been staring me in the face and tempting me to brave the conditions and install. However, i've noticed that some forum members (here and/or in the E90 forums, can't recall which) have reported issues with idle fluctuations and emissions efficiency CELs after installing catless headers, even with the accompanying tune. I've also noticed that the claimed crank HP increase of the 3SI with tune is approximately 30HP, which approximately totals 260, with another 10-15HP provided by the headers with tune to a total of 270-275.

So then my question is whether or not the headers are worth the hassle of risking a CEL and/or idle fluctuation issues for that extra 10-15hp? Do they provide a significant improvement compared to a 3SI with tune all across the rev range, specifically in regions of the RPM where most daily driving occurs (2k-4k rpm)? Or is their contribution mostly felt near the top of the range where the efficiency of equal length exhaust tubes and their scavenging effect really shines? I guess i'm trying to narrow down the contribution of these mods and weigh them against any possible drawbacks.

Thanks in advance for your inputs.