I would think more, 1 hp/cid is easy with bolt-ons nowadays, even in our old pushrod engines. For the kind of exhaust discussed here (2" primary on a 351) I'd say more like 1.4hp/cid would be considered serious enough to warrant the big headers on that engine. You need to consider displacement and expected rpm needed to fill a 2" pipe, not just hp/cid. A 200 cid 6-cylinder can make over 200 hp but it doesn't need 2" headers to do it. Most new cars easily produce well over 1hp/cid. No 2" headers there either. Thanks to the advances in cylinder heads and cams 1+hp/cid is common (almost expected) now.
Here is what I have on the table as of now. 351w block, balanced steel 10:1 rotating assembly from ohio crankshaft 408 cid, Jegs/Kaase heads,244/253@.050@624/640lift roller cam,victor Jr intake, annular 825 mighty demon
Yup, that sounds serious. So it's not a 351 anymore. How do you like those heads? I've heard they can be a pain to set up the valvetrain correctly.
Hope you the best with the 2 inchers. Thats alot of header. my 12.5 comp 377 cube dart headed NOS assisted motor works fine with the 1 3/4 headers if you cant find anything. But if you do find somthing please share. I would try them
with the size cam and low comp pistions i am using there have been no issues in setup at all. It pretty much bolts together as is.
