I can't tell you in the performance area, but, when you ask of reliability and ease of tuning, hands down, OS makes one of the best mills out there. The reputation of OS is hard to beat in the tuning and reliability department. I run the OFNA Picco .26 and its a very powerful mill, but tuning is a little rough. The Hyper 8 is also a powerhouse (just a hair less than the picco .26) but is also a LITTLE rough to tune. No bad though. And certainly nothing that will even aggrevate you.
At the end of the day, I think you will find that most any OS user will tell you that they are the best in the tuning department. Even some of your top racers will do OS carb conversions on their mills for that very reason.
Power Output: 1.9 BHP at 30,000 RPM
Practical RPM Range: 3,000-35,000 RPM
I don't want to pick nits over BHP and HP but the 8-port race seems to be the more powerful engine (at least on paper).
I own the Hyper 8-port race. Tuning is har dbut not impossible. The OS 20e carb is rumored to be a direct fit. A friend is going to sell me one of these OS carbs for $20.
here is another possibility for you:
O.S. .21 RZ-V01B
Power Output: 2.4 BHP at 32,000 RPM
Practical RPM Range: 3,000 - 40,000 RPM
It's $250 though.
I love my 8-port race and it's a damn bit bang for the buck (got mine for $172 shipped) even if the needles are a little touchy. Add the replacement OS carb and got one nice setup.
I think RG and RZ is where it changes to the better engine.
I just bught my OS 20e carb for my 8-port race last night. I still have to mount it and tune it. IF I ever get to the track, we have a lot of buggies with a lot of different engines. The guys at the shop and I are very interested how the 8-port race performs against the big boys. I'm sure someone will have the RZ out there. I will come back and tell you guys how the 8p race stacked up.... if the weather ever lets up around here.... sooo annoying...