i have a big block in my 85 chevy. th emotor is out of an 83 chevy C3500. I bought some flowtech headers off ebay about 6 months ago. finally got around to putting them on here recently and i ran into a problem. My motor has square exaust ports, where my headers have round. I searched summit motors and ebay for some square port big block headers but find none. Whats the problem here? They actually seal up pretty good, but i dont see how its possible to put round to square and have a tight seal.

Any suggestions/ideas

is the round tube lager in diameter than the square port? if so, than there is no issue, a flat surface is a flat surface no matter what shape hole is in it.

if not, you will have some seal of flow issues. tubes to small the square corners may exceede the gasket area of the header. the tube will also cause air flow issues.

I will check on it for sure.. so what gasket would you suggest using? the round or square?

thats on you, you are just going have to hold them up to the port and the tube and find the best combo.

thanks for your help!

The header ports on my 454 were round (Heddman) and I used an aluminum multi layer gasket. Works great, highly recommend it.

Pretty much all BBC headers are going to have round ports. You need to use round gaskets or they'll never seal. I know this because I went through many, many gaskets before someone told me. I have Flowtechs on my truck and they work ok, but the pass. side collector rubs on the front driveshaft.