My findings from porting well over 18 sets of of 6X heads over the years with a spread of about 70% of them being -4 and the rest -8 is that the port shapes are the same within casting tolerances.
It's the 6H casting that they had to resort to making the chamber deeper to get up to 124 or so CCs where in the port shapes / depths where shortened.
Due to where the chambers where carved out more in the -8 heads they are a little less shrouded then the -4s, but this added air flow only shows up when the Intake side of the heads are ported a great amount and valve lifts above .600" are used.
All low compression heads that do not use the RA4 type chamber from 71 and up if using 2.11"valves and ported to flow 230 cfm and up could make good use of having the chamber unshrouded as in this photo.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!
1) 1940s 100% silver 4 cup tea server set.
Two dry rotted 14 x 10 Micky Thompson slicks.
1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.
Education is what your left with once you forget things!
Last edited by steve25; 10-14-2021 at 11:41 AM.
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