I am researching using a triple for an ultralight plane. I have narrowed it to a Yamaha 700 or a Cat big triple. Go to the dealer and mention airplane and it gets quiet fast! Will buy a mid to late 90"s sled, lots of mountain sleds around here. Like the triple smoothness and torque, had enough of the rotax twin engines. Any help would be appreciated, still ride borrowed or renters once in a while but long out of touch on the tech side.

Criteria
Bulletproof
Detuned to 5200 rpm, monster torque, is this too conservative rpm for this engine, web says its strrrrrong!
Max power for takeoff 2-3 minutes 75-80% after usually just 2-3 hours per day.
Is this engine oil injected?
Does it compensate for altitude, usually 3000-5500 feet operating.
EFI available?

Thanks Bob

The Yamaha 700 is probably the most reliable triple ever built. You'd need to rejet it for the higher altitude. Yes, they are oil injected.

Thats going to be lower than ideal rpm for the yammy ,or any of our 2 strokes, I would suggest a viper motor because of the single pipe and I would say the cat tripple has weigh alot more especaily with the tripple pipes. what kind of power are you looking for?

I am looking for the equivalent of 70-80 horses. The application will use a Prop Speed Reducer (PSRU) to put the prop at 2500 rpm. The Rotax 582 is detune to 5800 max for thier aircraft line, rotary valve and RAVE, dual ignition.

I looked at the different marine engines but they are not as easy to find here. Also the sled engines are plentiful and much cheaper around Alberta.

Would a properly tuned 700 be reliable at say 6200 for 2-3 minute pulls with a period of easy pull after? I chose that rpm range as a guess.

the 700 viper for example is a single piped tripple with variable exhaust it makes about 80 hp at 6500 and peaks at with 123ish from about 8500-8900 and on a the 2 strokes we run lugging it below peak power at wot can cause detonation, so one way or the other gearing low would be better than gearing it to tall, it also would run better on pump prmuim than 100 LL or maybe prem with 10% 100LL
typicly on sleds we dont even engage the gluch untill about 4-5000 so they usually cruise between 5-6500 so they will survive at that rpm as long as you dont lug the crap out of it and I dont think you will. A good source for yammi info is totallyamaha.com they will explain the difference between the motors if thats the power you are looking for you could use a 700 sx/sxr tripple also which opens up your choice of donor sleds also consider buying a donor sled you could probobly buy a running sled take the motor and have liitle to no money ito it after selling the parts, used motors are expensive compared to what you can buy a sled for

At sea level. That power will be way down when you're high in the sky. Not sure how high you're flying though.

He said 3000-5500 feet either way it would be alot more power than a 582 rotax

Thanks guys, feel it is doable and I have always been a Yamaha fan. There are clutch PSRU's that kick in around 3500 to 4000 rpm. The gear PSRU's really take a beating at low speed due to prop harmonics. Rattles the bearings out of the PSRU. I am also looking at Cat batteryless EFI due to the easy altitude compensation.

How do the automatic compensators, Holtzman I think, perform.

I have used the holtzman tempaflow that compensates for temp but not altitude and I found that it worked from right above idle to 3/4 throttle and didnt do much above that, I will be trying a variflow next year