Surely someone has a formula for finding the optimum header primary tube size. I'm not finding it.

 

OK then, how about a general rule of thumb? How much power can be supported by 1-3/4" primary long tubes? How much can be supported by 1-7/8" primaries? We're not talking about a typical street car here.

 

99% of smallblocks use 1 5/8 headers because they increase torque over 1 3/4 headers.

The 1 3/4 will give you some extra hp at the cost of torque but not enough to make a difference.

1 7/8 are for bigblocks.

 

Nononono... HOT (race motors) small blocks can fully utilize 1 7/8 primaries stepped into 2" primaries into 4 or 5 inch collectors. (Stahl headers, Lemons headers, hooker 2322)

400-550 horsepower small blocks 383+ can generally utilize 1 3/4 headers (such as hooker 2210's).

1 5/8 will support more than you think, and almost anything on the street.

HOWEVER, the rules change when you use power adders. Hooker 1 3/4 longtubes will cost you a bit of power if you are supercharging/nitrousing past about 600 horses. Take a look at the Devilray corvette, 600 horsepower N/A with 1 7/8 primaries.


This is a general idea of where things stand, I know someone will post, "I've seen a guy run 9's with 1 5/8 headers." I've seen it too, but how much faster would he have run with a less restrictive header?

 

That's the type of answer I'm looking for. My heads were flowed with a 1-7/8" pipe, but fitting a pair of those on a thirdgen would be costly. My 406 has the best of everything and it's borderline whether to use 1-3/4" or 1-7/8" primaries. 2" primaries are not needed for my application and would kill bottom end too much.

 

What a dumba$$! I can't believe I just did that! Sorry.