Hi I have a 57 belair with a 540 blower motor it make about a 1000 hp need new header's and would like to go with fenderwall type I;m told I need 2 1/4 to 2 1/2 primary tube's and 4 inch collector's any idea,s does anyone make these?
Never seen any with primaries that large, and not sure how they could get a 2.5" primary to match up with the largest ports on a BBC? Are your ports on the heads large enough to be 2.25"-2.5" openings? If not then making the tubes much larger than the ports wont work, and they'll still restrict flow.
Largest I've seen available were 2.125" tubes and 3.5" collectors.
The largest street long tube header is 2.25 at the flange and 4.0 at the collector. To get any larger you may have to go to a step header. Our Willys we built back in the late nineties had a 600 inch Hemi and the heads were raised port with very large ports. These heads were designed for running a Super charger and was made to scavenge lots of exhaust.
What heads are you running on your big block ? Also consider wether your running more street then track. Large primary and collector work best at hi rpm so you may want to consider what your going to be doing most.