I’ve flown the UMS 77cc nitro 7cyl in a large scale model of the Lockheed Sirius, 100 inch WS I think, and it was good. The engine takes forever to break in properly and has a very weak glow system. The cylinders are vulnerable to plugs stripping out because they are cast aluminum. You can get the cylinders upgraded with inserts for the plugs and an ignition system but by then you should just buy a Moki. We had issues with the battery pack for the glow system and no issues with the plugs as of yet. It is a very fuel efficient engine and messy with glow fuel plus exhaust residue but it sounds cool and looks nice in a round cowl.
The Saito 90 is very good and I’ve used it in a large Mr Mulligan with great results. Again scratch built large scale model and it hauled it around with authority. If the engine is broken in on a bench and adjusted accordingly it should run great in the model like we have experienced. The FG84 was a mixed experience because we sent it out for an upgrade service after break in and then it failed on its maiden flight. Subsequent flights have resulted in less performance over time so that engine has been installed in a Gilmore scale race plane project. I’m planning on lapping the valve seats to increase compression on that engine.
From the YouTube videos I’ve seen of the FG90 in these TopRC warbirds it seems it is the best choice of the 4 stroke radials other than a Moki. Some have said it’s the minimum engine choice and it flies scale like, aka underpowered.
Now, there are NEW UMS gas radials I’ve never seen in person that might be better than anything we’re talking about,
https://www.morrisminimotors.com/eng...s-engines.html
There are several engines to choose from, no idea what fits and how they work, etc.
If anyone has experience with 90cc and up engines let’s see