Thread: Well... here was the culprit

BEN i wanted to go off your theory that you were talking about. i just recently but bc stage 2 on my turbo bb. running stock boost stock t25 and after the instal it seemed like it ran a little bit slower off the lower rpms then before. could your theory be the reason why?? of course i have to put my timing back to 15 degress because i have no idea what my timing looks like since my timing light broke. so im thinking A my timing is way off or B your theory. what do you think

The phenomenon I described isn't a theory, it's fact. If you have an engine A that flows poorly and an engine B that flows much better and you put the same turbo on them and run the same boost pressure, you're going to be in two completely different parts of the compressor map and flow two completely different amounts of air, and make two completely different horsepower levels.

By adding the BC stage 2 cams to your motor the T25 is riding a different curve up and across the compressor map. You're going to be farther right on the compressor map than you used to be. I'm pretty sure the problem you're having at lower rpm isn't a deficiency in the turbo or a problem related to the added flow of the cams at high rpm. It could be the cam's fault, but not related to their higher high rpm flow over stock. Their high overlap might be causing the problems at low rpm, or their poor flow in general at low rpm (I haven't ever seen a N/A comparison between BC stage 2 cams and stock so I'm really just guessing here).

The problem could be that you're too far to the right on the T25 compressor map, but to get too far to the right at low rpm is a considerable feat. I do think those T25s are too small though, I've never liked them at all. From 1990 on, stock size turbos tend to leave no room for improvement, and you've gone and added cams... =]

You might also think it feels less powerful at low rpm because you're undoubtedly making a lot more power at higher rpm.

cool. i knew that you lose low end power with the bc 2's so i knew it had to do with the bigger cams but upon reading your post i started to think. i mean its was a pretty noticible lost in the lower rpm. but it does have a better kick up top. i already have a t28 sitting next to me that i will be putting on soon. so that and putting my timing to the proper place should help with the lower rpms