Exhaust - 101
Transfers - 119 ----- .
Those are about stock numbers more or less .Except as I recall the transfers are at around 20 after the exhaust .
If I remember right the stock piston to head deck clearance is around 45-46 thou which does better at around 23-26 thou .The exhaust set at 96 would give you a little more blow down which you'll need at higher speeds ,Depends on what you have in mind I suppose .
I'm not sure what to do using a flat top but with a pop up the uppers mildly fingered will give you a better sweep ,really makes a difference .Neat older saw model,my favorite of all the Stihls .If they are done right they will scoot .
To tell the truth I never gave using an 064 piston any thought but it sounds like an idea .I opened the windows up on the stock Mahle 038 Mag piston though .
What the hey if you can hold the speed up using a short transfer and a long exhaust you've got a winner .In my case with a domed popup I had to put a D-handle on it because it became a finger snapper .
I'm curious as to how this works out because I've got another 38 mag in the shed I haven't even started on yet.Lots of saws ,no time .
I am a bit worried compression might be a wee bit much, but like I mentioned, a little added exhaust duration, or a thin gasket will help on that.
I've had real good luck with the two port stihls running a bit shorter than normal blowdown. Well see how it works out I suppose....