ORIGINAL: blw
It all depends on the engine, the prop, and what you want to get out of it. Xjet hit it right about propping for the power curve.
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And I am not saying otherwise.
Most folks acknowledge that if you want all-out speed from a model airplane, you will end up using a two-stroke engine. How many of us can explain in engineering parlance WHY this is true, without referring to the years of experience they have under their belt? Even many of the acknowledged experts in our forums would be at a loss to explain this commonly known truth in verifiable, scientific, easily repeatable and verifiable terms. Does this mean that their opinions have no merit? Of course not. Experience coupled with proper observation and analyzing habits can yield a terrific amount of information. Yet, we have some folks, especially since the advent of the internet, that always use the "show me in demonstrable terms or reliable information sources" argument in an attempt to put down other folks' opinions with which they do not agree.
Let's put an end to this type of argument. The goal is transparent and has nothing to do with furthering our knowledge on any topic.
From the second paragraph on, this was not referring to you, Barry. And I do not mean it as a put down to anyone in particular. As far as I'm concerned, we are all friends here.