OK ... two separate references list the first long branch manifolds coming out in 1963. They remained relatively unchanged through 1969. They were used more extensively in production cars starting in 1965, being a dealer option or parts-counter product until that time.
Today, there are the orignals, and there are reproducitons. The reproductions come from at least three companies, and the "better" ones come from R.A.R.E. and are available in two styles: Standard reproduction (2.3" collector) and a larger 3" collector version. These are almost out on the market. Other reproductions have been available for some time.
Thanks for the info. How much differance in performance between the 2.3" and 3.0" collectors? Did the RA exhaust manifolds from the RA 69 firebirds have 3.0" collectors? Thanks.
As far as I know, no Pontiac ever came from the factory with 3" exhaust. The 3" long branch are being produced to help out the guys with monster motor 455s in their Birds to keep the "stock" look. I am willing to bet there is a large difference between them ans the 2.3". From what I have read, there is already going to be a large difference in the basic flow between stock and the R.A.R.E. pieces to begin with. The internal designs are supposedly much improved.
The RARE large manifolds are available in roundport. It's the D ports that are almost available. RARE has what appears to be some pretty firm production dates.
From everything I've read, the 3" (Super Long Branch) manifolds will only net you an improvement if you're running a monster motor as Q referred to. For that configuration you might net 20-30 HP over standard RA manifolds (based on extrapolation from data I've seen). With a stock or mild 455 or smaller, you probably won't net any HP increase over standard RA manifolds.
