Thanks Motorman.

All this talk about shims got me thinking about mine. I bought a used NS12 S3 off Ebay. It runs and sounds great but I haven't had it on the track. Anyhow, it has two .012" shims under the head (for a total of .024"). I very carefully used the solder trick to fine my piston/head clearance. I came up with .035"

This sounds like alot more clearance than what people here are saying they have

But my engine sounds good, it idles good, and it looked wickedly fast on a empty parking. I used 20% nitro and what looks like a NovaRossi 6 glow plow (engine came with it).