I think you can still search Ted's archives for his dyno testing on a 312 and see the differences the different exhaust manifolds and headers made on that engine.  I would think 15 hp would be a minimum increase on a fairly stock engine with good exhaust system.  Joe-JDC

JDC

Here’s the link I have to the exhaust test. The FPA’s are several pages in.

http://forums.y-blocksforever.com/Topic55379.aspx

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

I have the FPA headers on order. Looking at July delivery and I ordered them last week.