Here's a before/after for an SCCA ITS car. No porting allowed (well, 1" past the gasket only, where it hurts the m20). This was done only with seat angles, back cuts, valve shape, and most importantly, starting with an untouched head that already flowed well for stock...
Lift" CFM before/after
.1" 29/34
.2" 59/60
.3" 114/118
.4" 171/181
.5" 174/185
Lift" CFM before/after
.1" 29/34
.2" 59/60
.3" 114/118
.4" 171/181
.5" 174/185
Comment