Hi Mark . . .
I am a fan of dual-pattern grinds myself. I have fitted one to my hopped up 216 - specs can be found here:
Inliners Post circa Jan '15 I have not put the engine back between the frame rails yet. I am at least two months from the break in run.
The reasons for a DP grind have been discussed in a variety of posts like:
Inliners Post circa June '07 In a nutshell - going for longer duration on the exhaust lobe gives the engine better volumetric efficiency through exhaust scavenging (because the EV remains open longer reducing the likelihood of orphaned exhaust gases remaining in the cylinder at the Intake Valve open event.) Because of the asymmetrical grind the amount of overlap is not significantly increased by the longer duration on the exhaust lobe - for a given LSA. And the overlap will mostly be at low Intake lifts - thereby limiting low RPM reversion.
For a street driven engine I would stick with stock LSA - not to mention it is easier for the re-grinder to work the existing lobe centers on the core.
regards,
stock49
