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I am looking for pipe sizes (length and diameter) for the various brands of header available for the 300. I want to make my own and have access to pipe benders and can weld them together myself
IIRC, the Hedmans are 1.625x34. FWIW, you can't build a set of headers for what you can buy them for. The Hedmans are like $135. The only time it's worth it is if there isn't anything available for your vehicle.
If I had the patience and money, I would gladly make my own set of headers just to have a decent flange system. AFAIK, all of the standard headers have a semi-machined pile of weld around the ports for sealing surface. I know this is supposed to be like an o-ring, but I think it just promotes warpage. I would rather have a completely machine-flat cylinder head flange surface and an overall thicker flange.
Hedman headers from Jegs, Summitt Racing, PAW (Performance Automotive Wharehouse) probably the most common/least expensive (Approx $140. + shipping) Hooker headers, most performance oriented, also most expensive, same sources listed above. Pacesetter/Dynomax headers Jegs, & JCWhitney. E-bay, type in ford 300 under car/truck parts/exhaust, used pop up from time to time (good ones though usually go for close to new prices when shipping is figured in, so you have to be carefull) And you already know about Clifford. There might be one or two others out there that I don't know about. So will leave to others to reply. Happy Hunting.
I just bought a new set of Thorley headers on Ebay. $97 delivered. The seller is listing more. I know the Thorley name, but can find nobody to say how they will fit on the I-6. I don't have them on the engine yet, as I am looking for an intake and carb to make the package complete. John