When I picked up my head from my buddy who did the valves we talked a bit about "gasket matching" and other ways to reduce turbulence in the intake and exhaust passages.
Here is how the intake passages matched up to the insulating spacer before I did any work:
And after some die grinder and dremel work:
I know it looks like the inside surfaces are all full of grinding marks, but they are from a pretty fine sanding drum and are quite smooth to the touch.
I did similar smoothing work on the exhausts, although I didn't do any diameter enlarging on those the way I did on the intakes.
Current Bikes: 2002 XR650L, Nighthawk, 1986 Honda XL600R
, 1988 Hondasuki KLNX250R
, 1988 BMW R100GS (dead)
Previous Bikes: Honda XL250R (2 of them), Honda XL600R, Kawasaki KLR600, BMW K1100LT, BMW R60/6, BMW K75, Husqvarna 430XC
for my Cummins 4BT International Scout build thread www.christianristow.com