Gonna buy an exhaust kit. I would like advice on which size pipe and why. I have a .30 over 455, e heads (out of the box), Comp XE274H cam. Motor will make around of 480ish hp. I believe in the Jim Hand book he used mandral bent 2.5" pipes. He said that 3" is too big. The car is a 68 convert with a 4 spd manual trans. The system will be stainless to rear bumper. I'm looking at a kit from Summit with dual muffs and either a Pypes or Magnaflow mufflers.
Thanks for the help.
Steveo

455 here, E-heads, Doug's headers, 490 hp on the dyno.

Went with a 2.5 inch kit from Pypes. You are going to find the 3 inch is going to be tough to fit down between the rear springs and the inner rear 1/4 panels unless you are not going to follow the factory routing.

There's also the fitment issue going between the vert brace and the floor at mid body unless it comes with oval pipes in that area.

i have a ragtop with a flowmaster 2.5 inch and its fine as far as performance goes. but Firebob is right i cant install my brace. So im going to alter it to fit .

Thanks guys for the input. I didn't even of the convert brace. Also a 2.5 system is cheaper.