.049 vs .051

daviddiag Sat Jun 16, 2012 1:06 pm

Is there much difference in performance between .049 and .051 displacement engines, given same porting and other performance related features? Are there .049 cylinders with same porting as .051 cylinders?
What was purpose of an engine design with .002 cubic inch increase in displacement? Was this a way to run this engine in a different class? What about the Cox .050 that I have heard of? Was that simply a rounding up of .049? Wow! Six questions in one post! Sorry boys! Very Happy

**Admin** Sat Jun 16, 2012 1:55 pm

A TD .049 and a TD .051 are supposed to perform the same. The .049 was to be used in "1/2 A" class events and the .051 was to be used in "A" class events. That is the same for the Killer Bee .049 vs the Killer Bee .051 and so on. Some notice a slight drop in RPM but higher torque (read that in a test article, I'll try to dig that up).

gcb Sat Jun 16, 2012 7:27 pm

daviddiag wrote: ...What was purpose of an engine design with .002 cubic inch increase in displacement? Was this a way to run this engine in a different class? What about the Cox .050 that I have heard of? Was that simply a rounding up of .049? Wow! Six questions in one post! Sorry boys!

This difference was originally done for free flight planes so the engine could be switched to fly in two different classes without making trim changes to the airplane. This process was not exclusive to these sizes, but they were the only ones affected by Cox.

Everything is the same between the .049 and .051 except the piston/cylinder set where the .051 has a slightly larger bore. The .051 piston has a groove cut in the skirt for easy identification. Pistons and cylinders must be a set. They are NOT swappable...that is, an .051 piston must be used in an .051 cylinder, etc.

And yes, the .05 was a rouding up of .049 to differentiate the throttled version from the venturi version.

George

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