so correct me if im wrong, but from what ive seen, 1 5/8 inch headers support up until 300 horsepower. after that, 1 3/4 should be used for after that. so what im wondering is if i swap the 1 3/4 inch headers into my 1991 305 tpi, would they be too big? i dont wanna buy to sets of headers once my 350 build is done :/

all criticism accepted

 

Yeah 1 3/4 is pretty big for a 305. It won't hurt anything to run them but you will lose some low end power. My brother put 1 3/4 long tubes on his 302 Mustang and it lost some low end power but pulled hard at the top end of the revs. If the 350 is in the near future why not just leave the 305 exhaust stock and worry about it when you have your hands on the 350.

 

there is also another way to look at this. And there is no formula set in stone as to what diamter is good to xxx HP

Anyway, for example, you purchase the Hedman shorties and install them on the 305. Later, you buy a 350, rebuild it and modify it. Compare the stock exhaust manifolds of the 350 to the hedman headers, which are better............................................................................

 

I had hedman 1 5/8 shorties on my 383.
On the dyno NA is 377rwhp, about 485crank hp.

Yes I could have been better with long tubes but shorties will support way more than 300hp!