Just wondering. From my experience in CL combat and racing, the fit of the piston(ABC) is the #1 difference between a good engine and a great engine. But what is Henry and Dubb doing that OS or ST aren't or can't? I know also from experience that the big handling difference between the cheapy engines and the OS's is the carb. I put an OS carb on my Tower Hobbies 46 and it became a totally different engine. It had the same easy characteristics that all my OS's have had. It it possible that OS can make the engines but don't because of warranty problems. When you push an engine as hard as the Nelsons and Jetts are you have to have the strength to take it. Would an OS 46 setup with the same timing numbers and compression put out the same as a Jett or Nelson?
We got into this discussion at the LHS when looking over a new Rossi.
So, What's the difference?
later,,, basmntdweller

I have a Jett 46 sport engine on a Shrike. It does everything right, idles well and hauls ass. Drinks fuel like crazy. It is like riding a road racing two-stroke motorcycle. A lot of top end power, with a lot of RPM. A friend at the local RC field can and has made an OS 46 run as fast as a Jett 46. But the problem it is very short lived. I think the rod and bearings went. Destroyed the engine case along the way. Lasted about six flights. He also uses ducted fan engines that last longer, K&B and OS. The quality of the materials of the Jett is evident, it is a hand made engine. The Jett is not an engine for everyone, as the price reflects the quality. One of the best parts about the Jett is the support, and knowledge that Dubb Jett provides. Can Rossi, OS, or others do this?

That longevity question is one of the things I was wondering about. An OS can go that fast, it just won't for long! I agree that none of the big companies are going to have the support that guys like Henry and Dubb can give. When I was driving race cars the company owner for my carb gave me his cell phone number so he could help getting it set up right at the track! That's service!
,,,basmntdweller

I have a rossi .12 for my RC10 GT that does 35,000 rpm and makes over 1 HP. Not too shabby...

I have also raced gas r/c cars. Yes they can do 35,000+ RPM, but they couldn't do it for an entire tank of gas, every time. I would like to get a 10-20 sized plane for a Force .12 that I still have since I sold my cars. Figure I'd cut down the head and fix the carb, ought to go like hell.

Not only do Nelson and Jett engines have superior piston to sleeve fits, they have 3 other very important things going for them as well:
1. 17mm crankshafts (2mm bigger than your average .40)
2. Tuned mufflers.
3. Very high compression ratios (15:1 measured full stroke)

The only other .40 size engines I know of that have 17mm cranks are the Rossi (the first to do so) and the K&B .48. But they have less compression and more conservative port timing.

Does anyone remember when the Rossi .40 first came out in 1986? It changed everything. It's 17mm crank, relatively high compression (about 11:1 full stroke), and sorta tuned muffler paved the way for the Nelson .40. Henry Nelson took all those ideas and pushed them to the limit when he released his Q-500 engine in 1991.

The other important thing is that Jett and Nelson are building small production runs where they can hold very tight tolerances with a lot of measurement of components and quality checks. It isn't worth it for OS to play that game because of the small number of engines sold to that market. That's what Mr. Nelson said.

Is the quality that you get when you buy one of those engines,the best materials with a good design. the O.S. engines can not compete with this engines because of durability.the nickel on the cylinder wear out and the bearings on the crankshaft can`take the strain of high rpm. for sport flying the O.S. engines are good.