If you have a thin gasket use it - Athena seem to be thick. If compression is too high, detonation comes to visit and mice eat holes in pistons. Make sure that the gasket has 71-72mm bores. Most are up around the 75-76mm size and they encourage detonation in that gap. If you have a spare cylinder head, you could get it machine to take inserts like the ones that VHM sell for race bikes or weld it up and machine a different shape and squish band. Cometic can make you a custom gasket with the right size holes and not too expensive.
Billy Alvarsson's
Bimotion software is a good source for head designs and port dimensions.
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Correct on inlets. They are too low already - BUT the floor typically has a terrible bump/ramp at the liner that hurts flow. A spacer is great because you can clean up the inlet port floors and still have the right port timing. Spacers are available from COMETIC gasket in the US and if you have problems with getting them to ship, I have a couple in stock. I'll have to check the thickness though.
My motor has cleaned up inlets with very short bridge, stock transfers, ported (cleaned up) crankcases, raised and widened inlet ports, and high compression stock shape head, and it's close to 80 HP on stock BS40 carbs. That's a lot of work but not much different to stock. With a spacer and good ports you can get closer to 100 with good individual pipes.
Pipes are the key to performance. Pipe designs not only change the amount of power but the shape of the power curve. The classic example of that were J&R which had a reputation for hitting hard at 4500 and being all done by 6,000. When I entered the J&R dimensions into MOTA simulation software, it showed that same thing. JEMCo, Allspeed and Bassani pipes had very different curves. On teh street I like the Strader 3 into 1. It doesn't make as much power but it sounds great and is really light.
