bbc drag race header size

[gnicholson]

i have a 505 inch bbc that makes 860 hp. the 70 chevelle has 2.125 primaries with merge collectors thar go from 3.25 to 4 inches with 12 inches of collector length. im considering building a 565. my question is how much power will these headers cost over an optimised setup . this is a throttle stop set up so torque from 4k is important

[prairiehotrodder]

i went from 2" hooker headers to 2.25" lemons headers on a 750 hp 540 BBC and gained absolutely nothing. I have no dyno numbers. Just race track timeslips.

[gnicholson]

ive experimented with 2 inch to 2 1/8 on my old drag race 454 that made enough steam to run high 9s and also gained nothing. my guess is i would be down 25 hp on a 565.

[engineguyBill]

Actual primary tube diameter is not absolutely critical on a maximum effort race-only engine. This sort of engine should have a step larger section of primary tube, the same distance from the exhaust port for each cylinder. More important is to have short primary tube lengths in conjunction with early-opening exhaust valve in order to use cylinder blow-down in order to help overcome pumping losses at high RPM. Collector length is also an important consideration on maximum effort race-only high RPM application.

[gnicholson]

thanks for the response bill. getting short equal length primary tubes in a full chassis chevelle will be a challenge. would it be a good idea to try dynoing some of these 1st to give me some idea? i plan on building whatever i decide on myself out of 321 stainless

[MadBill]

With that kind of investment in time an money looming, I'd suggest starting with the most effective and inexpensive PipeMax sizing program. It's invaluable for optimizing exhaust dimensions and many other engine specs as well as for general knowledge. Also, sourcing your SS materials from Burns will get you free precise design specs as a bonus: http://www.burnsstainless.com/x-design.aspx