Looking at the O.S. 91 engine, for example, there are many different designations or model types for this engine. Surpass II with pump and without, ringed, fx, etc... Did a check on the comparison link but still find it confusing apart from the obvious (2 stroke vice 4,etc...). How does one tell what engine they require and is there a site that can explain the evolution and differences of an engine type over the years. What is the difference between a O.S. of 10 years ago compared to now? Hear the new O.S. are kind of quiet...love the sound of my four stroke Saito 80. Looking to build a Sig Four Star 60 or Goldberg Tiger and trying to determine a good engine (and the proper designation). Any help would be appreciated!
Thanks.

The OS 91 Surpass II pumped/nonpumped is almost the standard engine of the Senior Pattern Association.

A sport type airplane like a Four Star loves a four stroke engine.

Theres not much difference in the way the OS 91 Surpass I & II runs. The Surpass I came out in the early 90's. The Surpass II came out in late 2001. Before that there was the 90 four stroke and it didn't have as much power but still enough for a Four Star.

The Four Star flies great with any two stroke from 60 up through 91. It doesn't make much difference. They also work fine with the four strokes from 65 up trough 110

I think the Tiger was intended for a 60/61 two stroke. The current OS91FX two stroke has the same external dimensions and is a fine engine.

Some planes originally designed for 60/61 two strokes do not have enough room up front nor will they balance easily with a four stroke engine.

The OS .91 four cycles and the .91FX (two cycle) both have a ringed piston. They are not available without a ringed piston.

One of the big differences between the .91 Surpass I and Surpass II is the carburetor. Both versions run like an OS -dependable and easy to operate- but in my opinion the carb on the Surpass II is marginally better, if only because it seems the low end needle is easier to set. Your mileage may vary here, and others may not agree, that's just what I've experienced. That said, I wouldn't turn my nose up at a Surpass I if I had an extra to put on a plane.

Also, the pumped version of the Surpass II seems to be the best idling engine I've ever run.

The .91FX was introduced sometime in the late 90's, and I don't think it has been changed since then, except for the needle valve mount.

I have flown a Four Star 60 with both the .91 Surpass II and the .91FX and I much prefer the characteristics of the plane with the FX on the nose. It was the same plane with only an engine swap, and while it flew well with either power plant, I liked the performance better with the two cycle.

I have a page on my site the explains the [link=http://www.hooked-on-rc-airplanes.com/nitro-rc-engines.html]differences in glow engines[/link] in general.

I don't really have any thing on the evolution of engines, but this page will give you a better understanding of ringed vs ABC, bearings vs. bushes etc.


Hope this helps...

Wings thanks for the link. Thanks guys for your responses.

here is the OS history pages there is the timeline for development of there engines http://www.osengines.com/history/ostimeline01.html

Neat! I'd never seen some of those engines on there.

Those dates are likely the dates when they began producing those engines in Japan, but not when they began importing them into the US. That page shows the .91 Surpass II and 1.20 Surpass III as debuting in 1996. I am positive they did not appear here until late 1999 or early 2000.

Get the Goldberg Tiger 60 and stick a 90 size 2 stroke on it and you won't be disappointed.

I tried an OS 61 2 stroke, an OS 91 surpass 4 stroke and a Super Tigre 90 on mine and I like the Super Tigre 90 2 stroke the best.

The Tiger 60 is a smoothe flying plane and flies like it's on rails.

Have fun and good luck.

Hungry...how was the build process on the Tiger 60? This'll be my first build and i don't want it to be too complicated. How many hours did it take you and what is your experience level?
Many thanks.

I know there is an explanation on here somewer but cant seem to find it....Im building a hangar 9 cessna 182 40 size and have the opportunity to get a o.s. .46 fx. I was wanting an .46ax but the fx will come as part of a trade. I checked out the os website and found out that the ax is the newer version of the .46 fx. Is this still a good engine???

I prefer the .46FX to the AX.

The AX puts out more torque at lower RPM to spin a bigger prop for 3D, but the FX spins up faster with a smaller prop for speed. Both are good engines.

sweet thats what i wanted to hear!!!! lol

Actually, my tiger 60 is the ARF version. If you click on the link below in "Kit Building" for the goldberg tiger 60 you will find a lot of helpful information. I started building and flying in 1973 and I converted mine into the tail dragger version. As far as how long will it take for you to build depends on how many hours per day you work on it. You could have it done in a week if you worked a lot each day on it. Me, I take my time when I build a kit and enjoy the process. Probably take me at least a month or two taking my time working little by little on it.

http://www.rcuniverse.com/forum/sear...D&sortMethod=d

Here is a tiger 60 build thread..... http://www.rcuniverse.com/forum/m_49...2ctiger/tm.htm

good luck with yours

Thanks for the info...still haven't decided...maybe a Sig Four Star 60, or the Pulse XT 60. Decisions, decisions.