I usually ran 60 or 65%. No more than 70 and add shims until it doesn't blow glow plugs or knock.  I think 45 to 50 is a better range. Much past that the performance vs headache ratio goes up too much to be worth it.  With current tech and rules the best bang for the buck is running a tuned muffler like a Jett or a Nelson.  I think some of the Thunder Tigers were a 1000 to 1500 rpm gain just by bolting on a Nelson muffler. 

Sorry I don't know any actual number on compression ratio, maybe reach out to Burt Brokaw or Eric Conley. They are pretty knowledgeable on the current Nelson related stuff specific to carrier. Better yet call Henry or Mike Langois(current producer of Nelson engines). Mike used to mess with high nitro/high performance stuff.

how did you calculate compression ratio?

Like many other thing the principle is simple, but getting the numbers is not so easy.

Swept volume is the part of the displacement with all the ports shut. (SV)
Combustion chamber is the volume with the piston at TDC. (CC)

So compression ratio would be (SV + CC) / (CC)

Measuring the combustion chamber volume of a tiny engine would be quite a chore unless it's a cone or a simple hemisphere.  Maybe filling it with a liquid would suffice.

On that note:  If a muffler prevents the exhaust from fully exiting the engine, the gas will be somewhat compressed to begin with, thus increasing the effective compression ratio.  This might HELP and undercompressed engine or KILL an engine that was overcompressed to begin with.

I just kept adding head shims until I stopped blowing plugs. Some motors like the old Super Tigre .35 blew a plug a flight.

Would motoring the engines through with compression gauge in place of glow plug be a repeatable measure of where you are as far as cyl pressure/compression ratio limits when running heavier loads of nitro. When getting close to/ into  detonation I found success with the use of Toluene when percentages of nitro of 60% and higher are used. In some cases replacing the methanol with straight toluene as the co-solvent.

What motor are you talking about?

Which model of Super Tigre 35?

Thanks