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best 100 HP auto/motorcycle engine conversion?

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rv7charlie

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They're really squishy for certified a/c engines, too. Claimed weight for Lyc 360s ranges from ~265 lbs (yeah, right...) to 335 lbs. Pretty big spread. Likely reality is 295-320 for parallel valve versions, and pretty much 335 for the angle valve engines.

Given the age of the tech in a Corvair (only a few years newer than an O200), I'd be surprised if it came in any lighter than an O200, especially if looking at installed, FWF weights.
 

tallank

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Nothing new under the sea. Err...sun.
Axial engine - Wikipedia
1st one I read about was the DynaCam, back in the 1960s, but they've ben around a lot longer than that. Powered some torpedos.
I saw a couple of demos / presentations of this engine at my EAA chapter. The problem with this engine is that the crank turns half the RPM of the basic engine. Result is a very slow turning engine with lots of torque. At 200 hp you would need a ten foot diameter prop. Can't be used in a motorvehicle because the gearbox would be humongous due to the torque.
 

Brünner

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I saw a couple of demos / presentations of this engine at my EAA chapter. The problem with this engine is that the crank turns half the RPM of the basic engine. Result is a very slow turning engine with lots of torque. At 200 hp you would need a ten foot diameter prop. Can't be used in a motorvehicle because the gearbox would be humongous due to the torque.
Would it be possible to pair it with a multiplicator gear to increase the prop RPM? Sounds like a rather interesting engine.
 

rv7charlie

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I don't remember the rpm being that problematically low; the Dyna-Cam version actually flew for several years. According to Kitplanes, shaft rpm at 200 HP was 2000, which is lower than typical Lyc operating rpm but well within usable prop dia requirements for a typical plane using 200 HP. I have friends that have operated Wankels with 2.85-1 reductions & controllable props that run sub-2000 rpm in cruise (best BSFC @ ~5200 rpm/2.85).

A typical piston engine conversion to a/c use needs a reduction of somewhere between 1.4 & 2.5 to make decent power and get prop rpm in a usable range, so the Dyna/etc engines sound about right for a direct drive prop.
 

cblink.007

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Have you gotten an honest 'fighting weight' for the R1200? Would the Yamaha RX1/Apex/etc be in the same ballpark? There are already at least two vendors offering drives for the Yamaha 4cyl engines, and Air Trikes says that it will be the next engine they build for. There seem to be a *lot* of them flying here in the USA on STOL a/c and trikes, and I haven't read anything negative from anyone who's installed one.

The Yamahas make more HP than you're looking for, but if they're light enough (and they're really light), you might be able to just let the engine 'loaf'. Another option would be the 3 cyl version; only a little lighter than the 4cyl but might be enough to matter in your case.

Charlie
Having done a BMW R1200GS and recently, a Yamaha Apex conversion, I am here to say the Yamaha beats the BMW across the board...hands down. Lighter, simpler, less expensive, more efficient.....and more reliable, among other advantages, such as more power and way better throttle response. Also easier to get official maintenance manuals and parts for the Yamaha, and an R1 bike guru (the Apex's internals are from an R1) did the rebuild for us at the local Yamaha dealer. BMW flatly refused to give advice or do service due to insurance reasons, and we were stuck with using bootlegged manuals, as only certified repair centers can have the latest & greatest.

The expensive BMW experiment of ours a few years ago ended with a failure of the integral gearbox on the dyno during a simulated max power climbout...about 45 seconds into it to be exact. Total time on overhauled/modded engine? 1.3 hours. The cause of the failure was insufficient lubrication in the gearbox as a result of the lube system modifications. We were in about $5,800 at the time of failure. On the record, we were not abusing the plant on the dyno at all.

The Yamaha conversion was simple as it could get. Bolt on the SkyTrax box and replace the wire loom & exhaust system. The plant ran like a dream on the dyno, and we have a baseline vibration spectrum profile on the entire system (vibe spectrum analysis is a key part of our test program).

Our Apex YG4i with SkyTrax box is now preserved, but otherwise ready for install on our bird when the time comes!

There is even an advantage in an anticipated lower insurance premium for us with the Apex!
 
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