My 454 will have a pretty good cam, Comp XE274, along with around 10:1 cr with around 510hp. should I get the 1 3/4", 1 7/8" or 2" primary headers?

 

I'd go with the 1.75" primaries. They'll be planty, and give you better clearances. The big primary tubes can get pretty darn tight when they all come together on the way to the collector, which often results in binding at the steering column, or hitting the starter, crossmember, etc.

 

yeah thats what i was thinking, either the 1 3/4" or 1 7/8" what size are yours Vall?
also do you think I should stick with my 2.5" exhaust pipes or go with 3"?

 

I had 1 7/8" on my '69,had to ding one tube a little next to the steering box.
Your 2 1/2" exhaust should be fine.

 

Been so long since I bought mine I had to go get the calipers and measure them! They're 1.75" diameter, and 2.5" exhaust all the way back.

 

If you decide to go larger I can tell you these worked well for me with no clearance issues. Noticed under the applications tab that these do not work with stock a/c or manual shift on column.

http://www.summitracing.com/parts/HE...n/?prefilter=1