Can anyone offer any experiences or recommendations for using a stock ST G21/40 in stunt?  Props, fuel, venturi, etc.?  It came out in a number of different versions.  Is one better for stunt than another?

Thanks in advance!

Philly Flyers???  I have heard of them.

hi David,

All of my experience (so far!) has been with the ST .46.  BUT!  I have a couple of good ST G.21/40s now and will be using one in a Classic model.  I plan on using a 10 1/2" to 11" prop with 5-6 pitch, and possibly a 10"-6p 3 blade.  I know Billy Werwage flew his USA-1 first on a ST G.21/40 but quickly went to a ST .46.  So, for my size model the .40 should work real well.  I understand they are very similar to the .46 in run characteristics.  I haven't heard a word on whether or not one "series" of the G21/40 is better than another for stunt.  One of mine is a Big Jim Greenaway Hemi, the other is stock but both seem to match each other as far as the "parts".  Either way I have a couple of the "small case" (.29) G.21/46 that run great if needed.

Big Bear

Thanks everyone for the input.  Best thing I think is just to give it a try with a variety of props, venturis, etc.   My sense is it probably won't do the magical ST46 4-2-4 or it would now be in wider use.  But, the engine could be good for a reliable 2-2-2 with a flat pitch prop. 

I do recall that Jim Silhavy used an ST G21/40 in his orginal Gypsy. So, there may be some potential here.

Cheers - David

Hi David,

The ST G21/4r0 should do just about, if not as good as the .46 for the 4-2 waltz.  No reason for it not to!   I would definitely say the reason it hasn't had the popularity in recent years is that it is not as strong as the .46 yet bolts up in the same holes.  The Tim Tanner approach!

Big Bear

In comparing the ST G21/40 with the ST G21/46, I find that in the .40 the piston skirt rises above the exhaust port. It is not much but very visible. This would imply that we have a bit of sub piston admission here. Would this influence the performance in our muffler-on age?
I have enormous difficulties in getting the engine to run , I am not even mentioning attempts to make it go 4-2-4.