Quote:
Originally Posted by 25stevem
I don’t know if you folks have ever seen this guide chart for exh header tube size, but I have found it extremely accurate!
The only tempering I add to this is if I need more exh flow then the port is providing in order to get the exh to intake ratio better .
Any exh port I have ever worked with of any make on my flow bench ( and even long ones like Pontiacs ) will pick up 3 to 5 percent more cfm above .350” lift if the header tube that bolts to the exh flange is 1/8” larger in it’s perimeter.
This why especially with a race motor that the exh side is flow tested with at least a 6” long tube in place.
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That chart is proof positive that the long branch exhaust manifolds are not up to the task on a good flowing head. I did not have a chance to flow the CNC ported E-heads on the engine, but I would feel safe saying the exhaust flow around 240 + CFM max and 225 + at my max valve lift. That puts me at around 2" primary tubes as stated in an earlier post. The long branch manifold on the left side that jogs around the starter has areas where I bet the passage is 1" to 1.25" maximum. Unfortunate, but the ease of packaging a manifold vs tube headers is a compromise each user needs to assess for themselves I guess.
I made final pulls last night with manifolds in place again. No changes in set-up. Started pull at 180 degrees and the engine repeated within 1% of best previous pull last week. Don't remember the exact numbers but torque approx. 468 ft Lbs +- @ 4800 rpm and HP 446 @ 5900 rpm. Pulling it off in a few days and getting it ready to install. Once I can get the files off the computer or actually get a printer to work, I will post more details for anyone interested. The ancient computer that runs the dyno has a broken CD drive and no working USB for a flash drive. It's always something.