912 High Compression Pistons

[mtgsxr]

Ok im really wanting to do the high compression piston kit in my 912. its a early engine and just turned 30 hrs. lol yep 30. anyhow does anyone have any mid to high times on these pistons? notice any major power gains?

[Av8r3400]

Define early?

By my recent experience with my motor, an early 90's vintage 912 UL, I don't think I would consider the high compression modification without doing some other modifications, first:

1. Over Run clutch in gearbox
2. Updated gear set in gearbox
3. Soft start module
4. HD starter

Just to start with...

[mtgsxr]

I believe its a 1993 engine.

[Av8r3400]

That's about the same vintage as mine.

The power gains from a hc modification are real. In our engines the gear box will not like the "harshness" of the high compression power without the additional mods I listed. Figure an additional $3000 worth of parts to do them.

[Slyfox]

Define early?

By my recent experience with my motor, an early 90's vintage 912 UL, I don't think I would consider the high compression modification without doing some other modifications, first:

1. Over Run clutch in gearbox
2. Updated gear set in gearbox
3. Soft start module
4. HD starter

Just to start with...

don't forget the pins for the rockers. either check them every annual or update.

[WWhunter]

I spoke with Mr. Stockton about this same issue and he reccomended going with the standard Big Bore kit. This kit gives 104 HP on the old 80 HP engines. This is a substanial increase. My engine is a 1996 vintage and am seriously considering doing this since I am not happy with the oil useage it is currently having with the 95HP ExtraPerformance kit.
As Av8r3400 states, the additional expenses incurred with the HC nearly double the investment as a lot more needs to be changed to allow use of the HC kit.

[Av8r3400]

The big bore kit is more money than the hc pistons, but I would agree, in the long run, the big bore would be much less stressful to the rest of the engine and it's systems, requiring fewer additional repairs or modifications. This would make it overall a less costly way to get more power from a 912UL.

As an aside, in about 1995 the gearbox components were updated. The gears were widened and the oiling inside the gearbox flowed differently. This makes the later model gearboxes more robust, in my opinion.

[WWhunter]

Ok, my apologies. I have been following the thread on the Big Bore kit and mistakenly assumed this was what was being asked. I see the error of my thinking. The question was refering to just high compression piston kit. :o

Needing to back track a bit and say that you need to disregard my comments on my previous post.

I will comment on the little I do know about the high compression pistons of standard bore. I bought a plane with these pistons already installed so can not really give an opinion of them over the stock pistons. My plane definitely is not lacking for power and I would be 100% satisfied with it other than its slight oil usage. I have had a difficult time in finding anyone with a lot of time on this conversion but the couple of I have spoken with say this is normal. I think the way it was explained to me was the metal used in these pistons causes a difference in the expanding and conracting of the cylinders/pistons. Supposedly the oil useage I am experiencing is totally acceptible. I am not happy with it and have been looking to either rering the engine or get the big bore kit.
Not a Kitfox, but there is a gentleman in Canada that deals a lot with RANS S-7's and he had stated that there was a considerable performance gain with the high compression piston kit when they were installed in an S-7 that was on floats. He has a couple of sites with a lot of good information on Rotax mods such has thermostats, heaters, etc.

If you want to broswe them:

www.stoneylake.org/pipcom/rans.htm
www.ranss7.com/

[mtgsxr]

Thanks for the input guys

[foxkit3]

I recently installed the high compression pistions in my older 912 with no heavy duty starter no slipper clutch, no soft start. Runs good, nice power increase. the pistions are a work of art when you get them, there so pretty you want to put them in. the extra oil passage for the wrist pin is a nice up grade. I would recemend them.

[KenyaKitfox]

Can anyone clarify whether you need to up-rate your spark plugs with the high compression conversion? The UL is listed using 7E plugs and the ULS 8E.

A tad confused as my 912 has light blue CH covers, not black and not green.

They were apparently supplied with the high Compression conversion done by the previous owner. I can't seem to locate any literature on the kit or the procedures.

Any light to shed?
Many thanks all
Zeke

[Av8r3400]

Yes, you want to run the 8E plugs, same as the 912 ULS.

The blue rocker box covers must have been painted by the previous owner. I had mine powder coated yellow just to be different.

[KenyaKitfox]

Thanks Av8r4300, fast response!

The Rocker covers came that colour with the kit I am told. I've seen a similar shade on some internet searches for this engine type - perhaps it is a French thang?

Can you (anyone) point me at any official documentation for the upgrade that confirms this as my local AMO mechanic is sceptical. I found something called a 912xtra conversion kit - not sure this is the one. It also stipulates 8E (with a 0.22 mm gap!?!), and higher octane fuel, for the 95hp conversion. So I'm leaning toward that as the solution.

Thanks again

[WWhunter]

Zeke,
Are you referring to the Zipper kit or the Extra-Performance piston upgrade?
I originally had the Extra-Performance (High compression) pistons in my my plane. They were already installed in the engine when I purchased it. The instructions did include a change of spark plugs and also required higher octane fuel.
My Zipper High Torque kit, used the same upgraded plugs as used in the Extra kit.
I can't give you any help on the Zipper high compression kit since it is bigger cylinders and higher compression pistons. I just looked at the Zipper webpage quickly, but didn't see any mention of plugs, but I am thinking that there is a change.

Ok, I guess Av8R3400 responded as I was typing.

[KenyaKitfox]

Appreciate Much!
It's a tricky one to get a definitive answer on but this is the third push in the 8E direction I've had - Actually the 4th. The engine has very infrequently given me a feeling that it's not firing right - like a change in pitch on the cruise, not a miss but sort of like that. A drop in power, briefly and then all OK again. It's happened twice in the 80 of hours I've put on her to date. She must have been telling me something! Apparently incorrect plugs can do that. Never had it happen to me before tho.

[Av8r3400]

I can not give you any "official" documentation, only anecdotal information I got from Hal Stockman, the designer of my big bore kit. His advise to me was that any modification beyond the UL specs, in displacement or compression, he recommends the "8" spark plugs. Additionally, on Hal's advise, I run mine at .020 - .022" gap. These are not very powerful ignitions to handle a wider gap.

Mine is the "low" compression kit, so 87 octane is fine. Again he instructed me that any compression above mine requires at least 91 octane.

[KenyaKitfox]

Well that wraps it, Thanks Av8r3400 and WWHunter - you guys have been a great resource ahead of the weekend!

I'll run the 8E's for a bit and see how we go. I can get 95 Octane so will stick to that too.

Very interesting to learn about the Zip Kit.
All the Best
Safe Flying
Zeke