Exhaust port flow vs. header size

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Exhaust port flow vs. header size

Post  glenevans on November 5th 2015, 6:01 pm

After reading responses to HorsinAround's question regarding headers, I think my car is in a similar situation. So the question of header diameter comes up quite a bit on performance engines,  I have a 545 (4.50" stroke) with the P-51 heads in the engine bay of my 1969 mustang, using the crites 2" swap headers that point down soon after leaving the port exit. Keeping in mind I run the car at 4300 ft. elevation, losing 12-13% of horsepower, but still pushing 545" of air.         Would bigger headers benefit this engine in its performance, even if they have to point down to fit engine bay configuration ??????  (545 cubes, .760 lift, 275* duration I, 284* exhaust, 14:1 compression, 1150 carb, 8'' converter)   thanks. Or asked another way, do p-51 heads flow enough exhaust in this configuration to benefit from larger headers

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Re: Exhaust port flow vs. header size

Post  dfree383 on November 5th 2015, 7:31 pm

Bigger headers will gain you a whole lot on that combo

The crites stuff it street material

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Re: Exhaust port flow vs. header size

Post  maverick on November 5th 2015, 7:32 pm

If you're looking to optimize power by swapping headers, you might consider notching those shock towers first. That nasty downturn from the exhaust port is probably a bigger power killer than wrong primary tube sizes.
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Re: Exhaust port flow vs. header size

Post  glenevans on November 5th 2015, 8:08 pm

I do have the shock towers notched back 2 to 2 1/2 inches, so would a BBC 2 1/8 camaro header work with the adapters (moving a couple pipes maybe)?? Or are we talking home made (this is the "dfree motor" - since he was always telling me to get into roller cams, modern heads, ha ha, leave my old flat tappet - dove heads behind)

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Re: Exhaust port flow vs. header size

Post  dfree383 on November 5th 2015, 8:11 pm

Laughing Laughing Laughing

I'd just get the right headers to start with
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Re: Exhaust port flow vs. header size

Post  maverick on November 5th 2015, 8:15 pm

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Re: Exhaust port flow vs. header size

Post  glenevans on November 5th 2015, 9:20 pm

Ok, so is it best to try header kits, or have them made by a shop? 2 1/8" be close? Thinking 6800-7000 rpm

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Re: Exhaust port flow vs. header size

Post  dfree383 on November 5th 2015, 11:08 pm

glenevans wrote:Ok, so is it best to try header kits,  or have them made by a shop?  2 1/8" be close?   Thinking 6800-7000 rpm

2 1/4 or a 2 1/8-2 1/4 step with a 4" collector
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Re: Exhaust port flow vs. header size

Post  Super Snake Steve on November 5th 2015, 11:59 pm

What about ford Powertrain application headers I have no experience With these headers just asking what you professionals Think about his design for this Application

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Re: Exhaust port flow vs. header size

Post  gt350hr on November 6th 2015, 12:24 pm

Glen ,
        Follow Dave's suggestion of 2-1/4" primaries and 4" collector. 36-38"s of primary and 12-20"s of collector. You'll be glad you did.
  Randy

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Re: Exhaust port flow vs. header size

Post  glenevans on November 6th 2015, 12:45 pm

Ok, thanks a bunch for the help. Appreciate it.

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