Will just this change from the stock 2.25" system alone change the afr considerably?

 

it might because the boost will be higher.if you can get the boost back to the same level,it should be close to the same.

 

At the moment I'm only running about 8-10psi and when I had the stock system it was also about the same, so the 3" didn't really have any effect on boost, tho it does spool quicker from vac to full boost.

The problem that I'm having is that now with the 3", at top end the car hesitates a lot and the exhaust keeps popping? With the stock system I don't get this problem. I haven't retuned the car yet since this upgrade so I'm wondering if it has something to do with the afr, athough with the afr reading off the Apexi turbo timer seems to be the same/ similar as the stock system...Timing hasn't changed either.