The Super Tigre is a main topic on these forums over and over. Mostly because it is unique in its features and is NOT an OS Clone like so many other engines, some of which try to combine OS and ST features, and do neither justice.

I have used ST first for Cl and later RC, since the first one I ever saw, G-35, in Plattsburgh NY, 1961, while TDY there at the USAF base as an Umpire in the Strategic Air Command, 8th AF, bombing compitition. In addition I have used most every brand ever introduced since then up until around 2000+ because I now just stick with my old favorites, where ST is still the top of the list.

When John Maloney, World Engines, sold the IMPORT Rights to OS and ST to Great "Pains" in 1985, things soon began to change. First, GP deleted the carb restrictor which made the 40-51 much easier to tune. For mine and some friends, I still make them. In the search for a few hundred more RPMs the boring out venturis of the carbs has decreased carb. efficiency, thus making the engine less popular among the newer generations that expect everything to be plug and play. Of course then GP can sell you the high-priced spread -- the OS!

When GP bought out ST from the original Italian family and moved the operation to China, well 'nuff said about that. [:'(]

For those that have problems with ST 90 and such, try adding enough Castor Oil to increase your oil content to 20%, or close. I run 5-10% Wildcat syn./castor mix in sport engines. WC 5% comes with 16% oil. Not enough for a ST 90. Add CASTOR. The 10% WC with 18% syn/castor will do for a well run-in 90, however if you wish to lug a BIG prop, better add some castor. Reducing the compression has not yet shown me any real help in the nitro thing for the .90.
Yes when I first started going larger than the .75s (which never gives any problems) to the .90s, I too did the carb thing in all manners. Then after all those years of playing with STs, right here on an RCU forum someone said that the ST.90 does NOT like much nitro. Experiments with added oil, and less nitro proved to be the ticket for the .90. I have several, two in use, and they just do whatever I need.

BTW that ST .45ABC is a real performer. DO NOT use normal break-in procedures on any true ABC. Only a couple runs using a small prop -- I suggest a 9-6 wide blade, like maybe a cut down 11-6 wood -- and fast runs. Then go fly. ABC is a whole 'nother game when comparing to a ringed engine.

BTW, with the current ST muffler, don't push the muffler up to the engine as far as it will go. Too much back presure/blowback on the acceleration from idle to full power. Either hang the muffler far out or better is to cut that pipe so it extends as little as possible into the muffler for your installation. Some I just cut at a 45* and that seems to be fine, especially if the muffler is not up by the engine.

One more BTW: The 40-45- and 51 are all the same case. They fit the same mounts. No diff. in the model fit.

Best of luck in your modeling.