Pumping up a 912ul

[shortfielder]

I am mostly interested in a -4 as long as there is enough room in it for me. Hopefully, I will be finding out soon.

So, while I am waiting, I have lots of time to think about stuff.

It seems that a lot of -4 have the ul engine. I am pretty sure that I will want more power, and have asked about doing the conversion from a ul to a uls.

Another thing I had wondered about was changing the pistons on the ul to get more power.

I read the following on another site, thought that the guy brought up some good/interesting points.

Hadn't seen it discussed here, so thought I would share. Hope I'm not repeasting stuff.

Re: [RansS7Courier] 912XTRA


Wally,

Vendor offers a set of aftermarket high compression pistons for the 80 HP Rotax 912 that raises its' CR from 9.0 to 10.5 . Price for the piston set is $850.00 The claim is made that the 10.5 CR gives 15 additional HP at full power, making the "re-pistoned" engine equivalent to a 912S.

This is not exactly true. The 912S has higher compression ratio, but also larger bore (84 mm versus 79.5 mm ) and a slightly different cam profile which, taken together, provide slightly more top end performance than the 80 HP 912. The 912S also has a beefier gearset and clutch assembly, plus a bigger starter unit to handle the engine's higher compression.

If you were already performing a top end overhaul on your 80HP 912 you could consider putting in higher compression pistons. You would probably get some additional HP at the top end, but at the expense of easy starting, smooth operation, and the ability to use regular (87 octane) mogas.

I would not break into a healthy engine to replace anything.

Dave

Gary

[Av8r3400]

Why not surf around Bully Hawk Performance for a bit.

Transforming a UL to a ULS is probably not a fair or accurate statement. Boosting the performance of a UL with hard parts is possible, however. I'm sure Rotax and their service shops don't like this because it takes money from them and also lessens some of the mysterious stigma about tuning and working on a 900 series motor. Rotax has everyone so snowed with all of their bulletins and requirements (some good some pure BS) that people even argue about the goop put on their sparkplug threads...

I've seen some of these modifications run and run very reliably.

[shortfielder]

I don't know anything about any of the Rotax engines. But I want to. So this is how I find out. By posing questions to those that do, and watching for points of agreement

I do know what I am looking for in performance.

And am just looking for the safest, most efficient($$'s), way to get there.

Gary

[shortfielder]

Forgot the part about Bullyhawk. Hadn't heard of them before, but will check it out.

Thanks Gary