I have been doing some looking into doing a conversion on a yamaha YG4 apex FI snowmobile engine. I have found a lot of older discussion on some other forums on using them in Highlanders but am wondering if there are any zenith builders who have successfully done this conversion? On a CH750 STOL in particular. I believe there is a integrated gearbox available that is out there for there engines from a company called skytrax that is supposed to handle around 200hp. Is this worth looking into further or am I wasting my time? It seems like it would be a pretty good fit to me but I would like some opinions and information from a few folks who have been at the experimental aviation game longer than my 2 months. Thanks in advance for your replies.



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It could be done for shure

I beleive the adapter uses a rotax geaebox

Price should be reasonable

Performance shoild be great

The question is how muxh time is it going to add to your build

You will have to customize the firewall forward,

Engine mount, cowling , radiator,  fuel system.

Firsr step would be to figure  out weight and balance.

Then you can determine how far from the firewall the enginw should sit.

Look at hiw long the ul motor mounts are.

Thanks Fred. It sounds like the Highlander installs are saying around that 180# mark for the engine, gearbox and accessories. I think the UL350 is around that 180# neck of the woods. Do most builders do their own mounts or 3rd party them out for design and construction? How does a person test them for load if you do it yourself?

I’m slowly putting an Apex into my 601xlb. I have the engine and half the mount that bolts to the engine. Still need to order the gearbox and do the math to weld up a mount. After seeing one of these engines in a flying plane you will be sold. They are a beast. But no doubt will add a lot more work and time to the project.


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