First, is the reason for the length for use as input for computer evaluation ?
I cannot add here what the exact length is or was on a actual factory head. But for conversation I have a copy of a old 'corrected flow data sheet' on a iron head done by Dave Bisschop at SD Performance, on it he lists the intake length as 4.5" and the exhaust as 4.8". I also have a copy from about 15 years ago for the input used on the Performance Trends Engine Analyzer program for one of Jim hands combinations with his iron heads, the program input requires intake length only and it was listed at 5".
A post from years ago by Jim Hand....
My Performance Trends PRO engine analyzer states: "Port length" is the port length of the intake port (down the center of the port) from the intake valve to the end of the head port (the start of the intake manifold runner.)
All stock iron heads I have measured are 5.0", and all stockers I have measured have 153cc volume. And I just remeasured a 6X and it is 5" in lenth. Depending on how centered you can keep the measuring hose/wire and where you terminate the valve end, you could see a slight variation but no more then 1/4". Incidentally, my current 6X-4's measure 171 cc port volume and flow 266 cfm @ .550 @28" pressure with 2.11 valves. Also, you can assume that all 8 are equal length.
Personally I thought my old Performance Trends Engine Analyzer program stated 4.7 inches. But I will assume Jim's information could be more accurate for the use in the EA program.
Last edited by Steve C : 07-16-18 at 12:37PM.