It's something about you don't want to open up the headed, it will decrease the speed of the flow.
The only porting should be done down around the valve pocket and in the divider area.
If you have all the race parts and make big HP then exhaust porting may do some good.
198k, 5/20/12 new ej257 short block, 8/20/11 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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