I am with Ty on his Idea of what "vintage" is .. I use 1960 as my "cut off date" .. or things no longer made.. mainly when selling on the Bay.. it is key search word...  like "old" .. "antique" .. "out of production"... "early" ..."obsolete" or "old time"... it's all relative to ones age ...

The practical rpm as related to model engines refers to what is common and ordinary in everyday day use.. what an engine was designed to do within the limit of the "practical rpms" .. some people try to "ask" an engine to do more than it was designed to do.. I have run 25% nitro in a old OS 15... man, it was running... then... bam.. the rod snapped.. I was flying RC . You can also take an 1/8th" piece of plywood, 6"x1" and put it on a Cox .049... and that poor engine seems to turn 30,000 rpms ... what a sound it makes.. these are examples of going beyond the "practical rpms". 

The muffler will work well within the manufactures specifications.. for idle and the high rpms.. anything more and cooling can be a problem or the engine dies from being unable to burn the fuel quick enough. .. when an engine hits a peak in rpms... there is a place where "useful" power begins to drop and goes beyond what the engine was designed to do... thus the practical rpms is a "safety net" so the engine won't be damaged.

Jim

I keep seeing "Vintage" on e-b and thinking "Stupid *ss that's a modern engine". Then I realise it's 40 years old! 

That is what happened in the case I saw. It is for an AP Wasp .061 which are still being made and one can buy new from distributors. This one listed the RPMs at 3,000-14,800 so I looked at the MFG page and got the correct numbers. The listing also says it has dual ball bearings and that too is wrong.

As for the word vintage, it is overused, and almost always misused so I don't pay attention to it much either.

The reason I was asking about the practical has been answered now as well and I agree but the numbers Larry Renger has posted have been pretty short of 25K.

Thanks for all the replies guys!

Robert