Greetings . . . I am not a student of the 'more modern' Chevy I6. But as a student of the earlier I6 I prefer the dual pattern grinds that extend the duration of the exhaust valve - and avoid unnecessary overlap on the intake valve events. In the early design Chevy's this part of the Volumetric Efficiency equation was typically neglected by the average hot-rodder who was more concerned with getting fuel/air into the cylinder then assessing the cleanliness of the cylinder when that charge arrived. If exhaust gases remain they asphyxiate/dilute the incoming charge - reducing VE. Moreover, with the right exhaust system treatments I think that there are perhaps scavenging effects to be had by having the exhaust valve open late too . . .
regards,
stock49
