Ok I posted this at the bottom of some insignificant thread and I guess nobody noticed but I think it's really important and would be beneficial to everybody on the boards, especially those less-knowledgeable, like me . Anyways, here goes:

"How should one know what size primaries (and for that matter, exhaust system) to use without being too big or too small? It would be awesome if you experienced guys could make a chart that corresponded engine output to recommended header primaries and exhaust system size. What do you think? It would really help out those newbies like me!"

What do you guys think?

 

I'm no expert, but I'll try.

Someone posted a chart a while back from some company.

1 5/8 primaries are good for about up to 400 hp, and I believe 3'' single exhaust is good for a little over 400hp but not much IIRC.

Dual 2.25'' exhaust is pretty much equivalent to single 3''.

 

Mark, do you mean that they can support up to 400hp before becoming a restriction or what?

 

HP-------Single----Dual
200-300----3"------2.25"
300-400---3.5"-----2.5"
375-450----4"-------3"
450-550---4.5"-----3.5"
550-650----5"------3.5"
650-800-------------4"
800-1000-----------4.5"
1000+---------------5"

 

hmm, didn't realize single 3'' was restrictive for a little over 300 hp, where did you get that chart?

 

Hmm, I know someone with a 800+hp 347 Mustang GT and they have dual 3" exhaust.

 

ok, nothing strange about that, if that above chart is correct, then he'd make more power with dual 4.5''

 

That chart is actually used by Dynomax and Hooker for sizing exhaust for HP.

 

Cool, I didn't realize it was that low.

 

these are suggested pipe sizes for street performance. "this information is provided merely as a guideline to flowmaster muffler inlet size selection for peak performance at full throttle levels. for vehicles that are street driven on a daily basis, consider using the next smaller pipe diameter for best results."

for 300-350 ci:
250 hp- 3" single or 2.25" duals
300 hp- 3" single or 2.5" duals

for 350-450 ci:
300 hp- 3" single or 2.5" duals
350 hp- 3.5" single or 2.5" duals
400 hp- 4" single or 3" duals

if youre pushing more horsepower than that, you can figure out what size pipes because you should know what youre doing when you have that much power. theres more listed like pipe sizes for racing applications, and theres stuff listed for smaller engines, but i figured this is most likely what you guys are looking for.