Originally Posted by combatpigg

Andy, Dave Shadel at Performance Specialties is the guy who drove this point home with me. Piped engines with high timing are every bit as sensitive to the compression adjustment as a diesel if not more so. You want to use the least amount of compression that will get the job done. In "glow talk"..prop load and nitro content need to be viewed as having the same effects as the chosen compression ratio.
It's possible to find the right combination that gives great performance and decent longevity, but it needs to be done carefully.
Since these engines don't come with compression screws, you've got to start out with a pile of head shims and start subtracting them until you can at least get the engine to bump, then barely run, then barely pre-stage, then possibly hit full song. During these trials, you must be using a ridiculously undersized prop as basically a cooling fan for the engine.
The next step is to begin increasing prop load until the engine shows signs of complaint. Hopefully at this stage you are near what your "Target Prop Size" is for speed. It's helpful to have an educated guess based on pre-existing research. There is not an infinite amount of incrementally sized props to find the best one, so at this point your new hobby has become "Prop Mod Man". The fine line between 195 and 200 mph can be just 5 minutes worth of scraping on any given sized "off the shelf" prop.