what size headers?

grumpyvette

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Staff member
" i started building a new exhaust system and i want to swap the headers for some new ones. the old ones are banged up and dented, speed direct has a page with header fitment. so the only header that fits perfect is a heddman with 1 3/4 primaries. all the others like hooker,dynatech with 2" and 2 1/8" primaries just fit with dimples. the headers i run now is a 2" on my 540 Street solid roller BBC. should i go with the 1 3/4 headers or stay with the biggers and dimple them? "




calculations show 2" is a better match than 1 .75" on a 540 big block.
keep in mind the collector length and diam. plus the whole exhaust restriction behind the headers will also effect the headers ability to scavenge the cylinders and help increase volumetric efficiency, drive train gearing compression and cam timing will all be factors in selecting the ideal exhaust header,no header will function well unless matched to a low restriction exhaust behind it! and theres a very significant difference in the power potential between your average commercial header thats randomly matched to a cam, and having selected both the header and cam to work together as a complementary matching pair in a selected rpm range, where the combination fully exploits cylinder scavenging efficiency,gains in excess of 40 hp are common.
header primary length, diameter and collector design are all something that can be fairly accurately calculated, if you know the engines displacement, compression and cylinder head flow and cam timing.


read thru the links and sub linked info

viewtopic.php?f=56&t=185&p=219#p219

viewtopic.php?f=56&t=961

viewtopic.php?f=56&t=1730

viewtopic.php?f=52&t=5321&p=16006&hilit=volumetric#p16006
 
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