Factory Cast Iron Exhaust Manifold Effect On Power Levels

[Wreckless Warren]

I was curious if there is any data on the effects the various factory FE cast iron exhaust manifolds have on power output. We are all familiar with the shorty and long tube cast iron exhaust manifolds. But it seems starting in 65 with the new Galaxie chassis and the unibodies of the Mustangs & Fairlanes the factory manifolds became more restrictive (except the 65-67 427 manifolds in the Galaxie).  Yet factory power ratings didn't seem to suffer?

Case in point is the 64-65 330 hp rated 390 Police Interceptor engine. I believe both engines are mechanically identical with the exception of the exhaust manifolds. The 64 used the shorty Hi-Po manifolds where the 65 used the same log (pancake) manifolds found on the 300hp 390 and the 250hp 352 (the shorty manifolds do not clear the 65 chassis configuration).

How could both engines have the same power output?

I was wondering if Jay (or anyone) had any data on this or had entertained doing some dyno comparisons of the various factory exhaust manifolds. ww

[jayb]

Don't you have a copy of my book, Warren?  There's a whole chapter on FE exhaust testing, where I ran log manifolds, 390 GT manifolds, 428CJ manifolds, 427 Fairlane manifolds, plus the long and short cast iron headers, and a bunch of different tube headers.  Bottom line for the cast iron stuff is that the long headers are best, shorties are second, and they kind of go down from there.  The 390 GT manifolds are hardly any better than the log manifolds...

[Wreckless Warren]

Yes I do, talk about brain fade on my part! Sorry for wasting space on the forum Jay, now back to reading. But wouldn't you agree somethings wonky about the factory 64-65 390PI hp numbers? ww