View Full Version : Jet Ski Engines
05-17-2004, 05:59 AM
Has anyone attempted to see if an engine from a Jet Ski would work for a gyro? The new Sea Doo engine has some impressive stats.
Type Supercharged four-stroke, three-cylinder Rotax® SOHC with Intercooler
Bore x Stroke 100mm x 63.4mm
Displacement/hp 1494 cc / 215 hp
Compression ratio 8.5:1
Carburetion / Fuel injection Multi-port fuel injection
Lubrication Dry sump, pressure oil system
Cooling Closed-loop cooling system
Fuel type Regular unleaded
Nice 215 HP and I would figure it doen't weigh to much either but didn't have the stat on that.
Is there something governing the type of engine for gyro's or since they fall under the Experimental catagory anything might go?
05-17-2004, 07:15 AM
Scott, First of all you can put any engine you like in an experimental. As for the Jet Ski engines, it's already been done on a couple of gyro's.
The main problem is cooling for the engine. These were designed to be cooled by large amounts of fresh lake water. So you need to know how much cooling the engine will need so you can install large enough radiator. Plus the necessary adapters, fittings, hoses, etc.
The next problem is finding or designing a reduction unit to slow the prop down to a more manageable RPM.
So, if you have the technical skills and a machine shop to accomplish the above items. Then go ahead and have a go at it.
Ron A. was talking about wanting to convert one of these engines for Gyro use. I'm sure he will have more ideas.
05-17-2004, 07:37 AM
I got ideas, but no means to make them happen. Maybe one day...... Anthony S. in Texas runs a 80 horse Yamaha jet ski engine and he uses a Rotax gearbox and a belt driven water pump and a standard VW Rabbit radiator and he says his system runs almost TOO cool. For someone who has some time money and a lathe and milling machine and knows how to use the stuff... A jet ski engine - especially the new Four strokes - seems like a great gyro engine for the money.
05-17-2004, 12:14 PM
Those Ski-Doo engines really do seem fantastic. Probably pretty difficult to find one right now, but they will start to become available in the next couple years.
I just recently purchased a polaris 700 twin snowmobile engine that I'm going to work on converting. The engine will make 125HP stock at 8000 RPM. I plan to run it derated down to 7000-7100 to get 100-105 HP out of it. I am working with a guy to mate a Rotax C box to it. There are alot of advantages to these engines;
1. Much more modern engineering, Case Reed Valves as opposed to Rotary Valves.
2. Parts are readily available and usually 1/2 to 1/3 the cost of the Rotax Parts
3. Great Horsepower and according to the snowmobile guys, this Polaris 700 is just about bulletproof and should be very reliable running derated at 7000 RPM.
4. Electronic Ignition system that advances and retards automatically with Engine RPM rather than the set timing of the Rotax.
5. All setup, this engine should weigh nearly the same as my Rotax 532 that only makes 65 HP.
05-17-2004, 01:00 PM
I think Russ King used a 670 rotax out of a snowmobile, It was also "derated"
I dont think it lasted over 50 hours. I am sure he can get on here and give you all the details :D Russ
05-17-2004, 04:26 PM
I think this is a Kaw trip
05-17-2004, 04:27 PM
I had a Rotax 670 loved it but it hated my gearbox. maybe if I get a autoflight universal gearbox from NZ it will hold up to the power. I ran it at 6800 about 95 HP and I was a climbing fool. The power band was like a 532 on crack but I like it.
05-17-2004, 04:31 PM
and this is a twin off a jet ski, I think.
05-17-2004, 04:34 PM
and this is houston shot from my Dominator
05-17-2004, 05:25 PM
The bottom one is Anthony Spagnoletti's (sp?) Yamaha Twin from a watercraft I'm pretty sure. I saw it last year at Bensen Days, a very nice machine. Great Picture of the houston skyline.
I've heard the same things about the 670 - Same manufacturer - Same Engineering - Rotax. I would be interested to hear what Russ has to say about it.
05-17-2004, 05:26 PM
What gearbox did you have the 670?
05-17-2004, 05:33 PM
Those are both jet ski engines. I heard Anthony had a engine out with his twin but don't know any more about it if it is even true, but I do know those ARE jet ski engines. Hardest part they told me was making the tuned exhaust system.
05-17-2004, 05:42 PM
Todd it was the MZ gearbox
05-18-2004, 09:12 AM
Todd it was the MZ gearbox
Is that the one with the clutch?
Was it a new one or used?
What happened, like: how many hours did it survive?
Inquiring minds want to know...
I had a Rotax 670 ski doo engine that was set up by R&D Aerosports to run at 7000rpm max and 106hp. It was mated to a Rotax C gearbox. It came on hard at 4500 rpm but was controllable on a two seat gyro. It lasted 29 hrs when it fried the mag end bearings. I learned later that the squish band was too tight and the compression too high. It was the first one that R&D did and I was the guinea pig. I think they learned from their mistake at my expense. I wouldn't let R&D touch my lawn mower.
05-18-2004, 01:38 PM
Good one Russ K.
05-18-2004, 02:05 PM
I haven't heard much good about using the 670. Like the 532, it is very peaky. According to the snowmobile guys I've talked to, the polaris 700 supposedly has a very smooth power band. Let me know if my thinking is all screwed up here. I've looked at the HP graph, the engine will make about 124HP @ 8000 RPM. If I run it derated to a maximum of 7100 (about 90%) of rated HP, it appears from the graph I should see about 105 HP.
Currently with my 532, I can cruise at 65MPH @ 5800 RPM. The 532 is supposed to be 65HP @ 6700 RPM. So I'm guessing that at 5800 RPM this engine is probably putting out between 45-50 HP.
Now, going further, (and only guessing), it seems that the Polaris will probably make the same 45-50 HP @ only 4500 RPM. If thats the case, will I see better fuel economy in cruise flight with this engine running at only 4500 RPM as opposed to the 5800 RPM of the 532?
05-18-2004, 02:56 PM
Russ I was the guinea pig for this MZ gear box. I got the gear new from ASAP in Canada
sent it to R&D and they put it on the 670. And yes it had a clutch but gear oil would work its way back to the clutch and out of sky you come. O ring one lasted 15 hours 2 about the same I sent the package to R&D and got the mz202P. It is OK but not good for two place. No troulbe with this motor yet. I will need to sell it now to get more power so I can train someone.
I think R&D put the box on off center that made the O ring get pulled and that was the end of it. If done right the 670 would be fine. I would not run it over 7000 at all just 90 HP from that small motor is good.
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