Anybody want to share some experience (good or bad) about this engine.
With all the threads of people having trouble with the OS91FX, this seems like an option for my next project.....croz

I've got 'em both, I'll take the OS anyday!

Both engines are powerfull but the O.S has a bit more. There is nothing wrong with the ST .90. A friend of mine has a st 90 in a 15lb beechcraft bonanza and it flies it with a 14x6.

Power is not an issue.
I'm interested in a reliable, user friendly engine...croz

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

Here is my .40 size WM P-51 with a G90 and 12/9apc. No problems and about 95mph.

I have my G-90 in a Top Flight Gold Edition P-47. Only problem I have ever had with it was that the rotating slot in the carb was not smoothly machined all the way down, causing a VERY rough/sticky throttle arm movement. No big problem though, I just used a piece of 1500 grit wet/dry sand paper in the edge of a pop-sickle stick to dress the machineing marks out of the slot, and it is now smooth through out it's full range of motion. The engine runs great with the stock muffler and makes very respectable power with a 14 x 6.

Lee

Cyclic Hardover
So what is the problem with your setup ?. Lots of racing around here with the WM P51 and the OS 61FX using 15% fuel. Speeds around 105 (radar gun) aren't that uncommon. ST may be OK if you can get them set up but they sure suck the fuel.... Way out of proportion to the power output IMHO.

Well if you add the approximate 17%loss in power and speed I have here at 5000ft, I should blow right by you down there on the beach (114mph?)

I have a G90 in my UCD 3D. runs great but didn't like the 14x6 prop...very sluggish throttle response...but it did hover easiest with the 14x6...but for everything else a 13x6apc was happier on my engine. Quick throttle response for doing waterfalls or flips etc. I dont think I want any part of the OS91fx from all that I've read even if it does have a little more power..the ST90 is a good bang for the buck IMO. I also have a ST75 that I bought used from a club member that almost blows the doors off my 90. I did make the mistake of buying a Magnum61 fs...I think I'm sending this engine back to HP. Broke it in as suggested and it runs good but has no power, very low compresion. my .2$

Ron

Flatspin,
can you tell me what your RPMs are on the ST90 w/ 14x6, and 13x6 props?


thanks

I have some RPM info on my ST G90:

10% Omega
11,300 RPM with 13x6 MA
10,400 with 14x6 MA
idle @ 2,600

I have not tested the engine with APC props but I expect that there would be an RPM increase over those old black slabs.

JTEC muffler
OS7d carb

By the way, the OS carb greatly improved the midrange transition but max RPM was not significantly affected.

TX