I have been told by some shop owners that if I upgrade my headers to a bigger size that I will lose some power at low to mid rpm, but I will gain power in the high rpm range.
True or False? Any advice would be appreciated.

Unless the cams have been replaced & the compression raised to 11to1, increasing the headers size won't give a boost in power.

Your shop is correct to an extent, but not really. Increasing the size of your exhaust will do that, less low end torque but more torque at higher RPM's. This is what I have, since I have a 3" exhaust pipe from the headers to the tail pipe. However the 2.5 headers are not that much larger than than 2.3 headers. The main reason to switch to Euro 2.5 headers would be that they have no pre-cats. So you will see an increase of power over the entire RPM range due to that. If it wasn't for that upgrading 2.3 headers to 2.5 would be basically pointless, for the little size difference.


------------------
Adrian Eckenrod
MBCA, PCA, BMWCCA & SCCA* member
86 190 2.3-16
83 944 ITS Racer