I have a couple of the G-90 versions of the Super Tigers. There were S-90's with a round machined head that had a sunken radius in the center and had a removable front bearing housing. Then they came out with the S90K and it had a die cast head that was almost square and had tall fins on it. Then they came out with the G-90 which looks somewaht like the S90K but has a single piece crankcase.

The G-90 uses a bigger rear bearing than the 'S' models. Therefore the crankshaft is different too.

There has been considerable talk on here about which propp to use. On the 'S' models everyone always used a prop that equates to the 14-6. But a respected model engine engineer in this country, Dave Gerieke, Did torque measuring on the G-90 and determined that its torque peak is somewhere down around 7500 rpm. Therefore, they should be propped with a big 15-8 to utilize the engine's power down closer to the torque peak.

To run one with this big prop, it's the sickest sounding engine that ever was. It may have more powerthis way? But the engine sounds correctly running a 14-6 type prop on it.

The G-90 is very popular in some of the 60 size warbirds like the P-51, P47, and P40 types.

Both the Super Tiger 90's and the OS 91FX's are almost the same size as their 61 counterparts. They are just a little taller. The motor mounts are the same.

The Super Tiger carb has been a topic of discussion on here in the past. Some people hate it and even change to a ASP/Magnum or an OS carb. Other's think that the ST carb is just fine the way it is. It's a matter of understanding it. There's some threads over in the manufacturer's section that discuss the proper way to set up a ST carb.

The OS 91FX is notorious for having trouble with the remote needle valve. It tends to suck air Some have resolved it with new O-rings while others put a Tower or K&B remote needle valve on it instead.

Good luck and enjoy

Jim