RE: LOWERING COMPRESSION
Running more nitro in an engine that has not been designed for it will wear it out sooner. Pre-ignition and detonation will occur. The firing timing on glow motors is an interesting subject. Read up on it and you will be amased at the things that affect good running.
The European motors are typically designed for no-nitro use. We are spoiled here in the US that nitro is easy to get.
The main reason that MDS engines have a bad reputation among most US RC pilots is that they are designed for little or no nitro. When run with the almost standard 15% nitro fuel they will overheat and also bang up the conrod bushes. This is because the ignition occurs too early.
Also, in the '80-90's, the Hanno special OS .60 pattern engines were notorious to destroy themselves if the combination of high nitro and tuned pipes were used. We would decrease the compression by adding extra shims under the head. This did not rob any power and the engines lasted.
If you need more horsepower, get a larger engine.
Safe flying!