More Zipper Discussion

[jiott]

The Zipper kit was mentioned; I am curious, does anyone know what the compression ratio becomes with the Zipper kit on a 912ul and on a 912uls? The Zipper kit increases the bore but not the stroke, right?

[Slyfox]

I fly a 4-1200 912ul on amphib floats with the IVO ULTRALIGHT 3 blade prop and agree the manifold pressure gauge isn't really needed. I also have a Lake Amibian with a constant speed prop, and there the mp guage is absolutely needed. But for some reason or other, the Rotax mp gauge doesn't move as much, so I pretty much never use it.

Rather, I listen to the engine to know if I am overloading or underloading it. I find 5,000 rpm to be a nice speed for my engine overall and find it runs smoothest there. But I believe every 912 has its "sweet spot", so just play around until you determine that with your Kitfox.

I think the 912 and the 4 were a match made in heaven...it's that good. I keep thinking I should replace my 80 hp 912ul with a 100 hp 912s, or maybe just Zipper kit my UL? But even though I'm on heavy amphib floats it does really good with that 80 hp 912 assisted by the IVO IFA. . I even have a spare 100 hp 912s laying around, but just don't know if it will make my plane that much better? So I haven't got real serious about changing it out.

Can anyone that changed their 912ul Model 4 to a 912uls comment on that? Maybe I'm not knowing what I'm missing?

the difference when I changed out mine was OMG.

[Av8r3400]

The Zipper kit was mentioned; I am curious, does anyone know what the compression ratio becomes with the Zipper kit on a 912ul and on a 912uls? The Zipper kit increases the bore but not the stroke, right?

The Zipper (http://zipperbigbore.com) (1484cc) replaces the Pistons and cylinders, increasing the bore only. The bottom end of the engine is not touched.

There are high (11:1) compression and low (9.7:1) compression kits available. The low compression kit allows the continued use of 87 octane fuel to make about 105 hp, where the high compression requires 92 octane, and a hd starter and slipper clutch in the gearbox are recommended, which will produce about 115 hp.

There is also a 1622cc kit which requires some machine work and change of the cam to achieve 125 hp.

[av8rps]

Thanks for the input on going to the higher hp engine on the Model 4.

I guess if it is that obvious it would probably be even more so on my Kitfox since I'm dragging around an additional 200 lbs of floats, not to mention all the additional drag. I'm honestly surprised it is so significant as my plane even on floats is like a ro ketship compared to most other float planes.

Larry, did you install your Zipper kit by yourself? Did you do the 105 or the 115? I really like my 912ul, so I've been hesitant to install a big bore kit in it. But you got me thinking...

87 vs 92 oct fuel shouldn't be a big deal as generally I always buy premium fuel anyhow, as non ethanol 87 octane isn't easy to find.

[Av8r3400]

(I moved these posts out of the other discussion so we don't hijack any further)


My engine is the low compression 105 hp version. I didn't want to upgrade the starter and add the slipper clutch.

Yes, I did the Zipper upgrade myself. Pretty easy, actually. Here's a couple photos.

Here is the engine stripped of the OEM parts.
11297


New Pistons and Cylinders.
11298


Fully assembled long block.
11299

[HighWing]

I talked to a friend today, by coincidence. He has the low compression Zipper kit. I watched as Hal installed it last year and asked him today how he liked it. Big smile. Great! I was mostly interested in issues. None.

[av8rps]

Larry,

First, thanks for moving this off the other thread I was hijacking. All of us here are lucky to have such great moderators!

And 2nd, thanks for the great info. I think I'm gonna do the same thing to mine since everyone is having such good luck with theirs. And my pushrod tubes are leaking a bit anyhow, so I will be able to kill 2 birds with 1 stone.

I can hardly wait now until next year at the fall seaplane fly in where the only planes that can beat me off the water are two Rans S-7's with 100 hp 912's. If I gain 24 hp (or even better 34 hp :eek:) I will literally "Blow them away", as I'm almost able to beat them now. That will be priceless...:D

I will probably do what you did and simplify things by just going 105 hp on my 912ul on my Kitfox. And if I'm as impressed as you are with that Zipper kit mod, later I'll bump my Highlander to the 115 hp as that already has the slipper clutch and HD starter. And honestly, when it's on amphibs it is nearly 100 lbs heavier than my Kitfox (bigger, heavier floats, and my Highlander airframe is 45 lbs heavier), so it could use some extra power.

It truly is amazing how well these 912's work on our planes, and all you can do with them, all while burning very little car gas. I just love these planes...:)

[Russell320]

I'm also looking at the 105 hp version for my 912UL...80HP. One thing that I have to consider is I have the ultra light IVO IFA prop which has a 100HP limit. With the zipper kit being 105HP, a new medium prop would be recommended. I talked to IVO and they agreed that the heavier prop would be best. Sooooo, while the zipper kit would be great on my Speedster, I'm going to stick with what I have......which is really all I need....

Just a thought..

Russ

[Dusty]

Good point regarding the prop,so far the only point against the zipper!
Would 5 hp over the prop limet be a deal breaker?

[Russell320]

IVO seems to think so. But I think it's just lawyer talk.

[av8rps]

I would have the same issue as I run the IVO IFA UL also. But knowing that others have flown hours and hours with the UL blades on a 912S Rotax, I don't think that will stop me from going to the big bore. And honestly, with more HP available, maybe I will just need a fixed pitch prop? In many regards that would be simpler. Av8r3400 has a huge 2 blade Prince on his Zipped up Model 4, and from what he is saying that's probably all a guy needs, because you get a better takeoff and climb, but yet have enough power to cruise efficiently.

[av8rps]

IVO seems to think so. But I think it's just lawyer talk.

We could do like Cub Crafters does and just put a placard on the panel saying something to the effect "Do not exceed 100 Hp". So when applying full throttle you just back it off about an eighth of an inch from the stop :rolleyes:

The biggest issue with the IVO UL blades is that they cavitate on initial throttle application when used on higher HP. But they do work. The 100 hp+ Highlander used in the Dead Stick Takeoff video had an IVO IFA with UL blades, and cavitation was the only issue he ever experienced.