I just got a RC Super Tiger G-21 that has 40 stamped on the side. It has a baffled piston and twin ball bearings. Will this make a stunt motor and if so what do I need. It came without a muffler but did have one at one time as it has the tabs for one that show signs of use. It has great compression and is really smooth when you spin the prop.

Thanks Randy It came only with a RC carb but I scored an original venturie on ebay still in the package.

Ijust looked and your right rustler ican see the piston skirt com up a little in to the exaust. Any cure for that or get a muffler for a 46?

Well I"m going to give it a try in a plane and see what it does. I got it free so anything but being a pig it should be alright for somthing.

Well I"m going to give it a try in a plane and see what it does. I got it free so anything but being a pig it should be alright for somthing.

Go for it Mike. I didn't mean anything I said to imply it's a bad engine. We used them in the early days of rat quite succesfully, and if you fit a muff. it could well prove to be a pleasant useable motor. I'm a great admirer of S.T. engines.

 Throw a .46 piston / liner in if its got muffler ears . And the head .

When the first Van Loo version of SIG's Chipmunk kit was still new, I built one for a G21-40.  Van Loo had used that engine, but I kept trying to run it in a classic breaking run, and it kept "running away".  I pulled the 40, and used a 46 instead, but then the fuel mileage was much worse, so I planned to cut into it to swap tanks (hadn't left the bottom part of the firewall off to allow the tank to slide in and out).  I never modified it, and in fact never completed the entire finish (I test flew it in monotone, single color - metallic blue).

I swapped away the 40 for a backup 46, built a Skylark (always loved those), and the Chip became my hangar queen.  Interestingly, I ran across someone running their G21-40 in a wet two stroke, and getting excellent performance, but one difference was fuel.  I had been using Ritch's Brew 5 % Nitro, 22 % oil, partly castor, mostly synthetic.  Whoever (and blame my age for forgetting any face or name to match) had that other 40 used SIG 5 % all castor fuel -- 25 % oil, I think.  If I ever have another G21-40, I'll be using more oil in the fuel, and less of it will be synthetic. 

As Bill Little says a blind hog gets lucky sometimes.

Personally, I'm not enough of an iron engine expert to recall, although the Tigre 40 was also a Rat Racing favorite, in both front and rear intake versions.  I believe that some 40s shared the Perry Porting and flat top pistons from the G21-35s, while others had the same baffle piston style as the 46.  The reason I have for adding a comment is because I listened to a discussion with George Aldrich and two others about the ST 40 as a stunt engine, and he wasn't too thrilled with them, the way I recall, but one particular alteration that was discussed was really dismissed strongly. 

Apparently, some people were grinding as much as 1/16" from the top of the Tigre piston's baffle, for some reason (maybe someone here, such as Randy, may recall what that was supposed to be good for).  In George's opinion, that was worse than merely useless, it created negative results.