Quote:
Originally Posted by George Wright
An IHRA crate motor can use any duration, they only check the lift. Not sure why, but the IHRA tech sheet wanted the duration. They probably use the same form for pure stock specs. Did you use any kind of modeling software for your header design? I used the recomendations from Pipemax and came up with:
1- 5/8" tube for 8 inches
1- 3/4" tube for 8 inches
1- 7/8" tube for 16 inches
3- 1/2" collector
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Not yet, I was going by an admittedly softer, lower rpm engine. Running ported stock heads on street/bracket stuff I found sbf like 1 1/2" to add torque, especially when the majority is below 6000. With a 4000 converter I guess I don't need to worry about anything below that. My tube bender doesn't have 1 5/8, but I do have 1 1/2 and1 3/4.
Your total of 32" makes more sense due to the higher rpm of this combo. Perhaps 1 1/2" is too small, period? If that's the case maybe I'll run;
1-3/4 X 32" or
1-3/4 X 16" and 1 7/8" X 16"
3 1/2" collector (12" to start)
Header design has always been a facination to me but with mud trucks/street/bracket stuff, I've always concentrated on smaller dia to keep the flow around 300fps and fairly long for lower rpm torque.
(I see 2" pri on a sbc and think "What the....."???) Obviously I've got to rethink some stuff...
Excellent point on the 3 step, never thought of it but with limited lift you do need the pull from scavenging on the back of the valve as long as possible.