# Rotax 912 Performance upgrades (Turbo, Big Bore, Etc)

Discussion in 'Firewall Forward / Props / Fuel system' started by JayKoit, Aug 27, 2019.

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1. Aug 27, 2019

### JayKoit

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I have a Zenith 601XL-B that's getting close to needing an engine, and since I'm out west in Southern California with family in CO, I'm thinking I need something with some high altitude performance and reliability behind it since I'll be flying over mountains - and of course I'm on a budget (10k?) which means I have to be a little more creative...

I started off by considering:
- 110-120 hp Corvair with super low time
- a low time C-85 stroker with the O-200 crank and high compression pistons (which I've read can be good for about 105-110 hp)
- Viking 130

BUT, then I discovered all these 912 mods out there, and now I'm also considering getting a used 912 UL, and modding it by doing any one of the following:

1 - A Zipper Big Bore kit w/ 1484cc (114hp)
2 - An Edge Performance 912 Turbo/EFI kit (up to 154 hp, but might be too pricey)
3 - A VZ Power 912 turbo kit - which look great and are supposed to be very affordable in addition to being DULV certified in Germany, and they claim 95 are flying reliably. I've emailed for a price list and am waiting to hear back.

I like the Idea of a turbo with a variable pitch prop (and that new Kool variable pitch reversible and featherable prop for $2200 looks amazing). What would you do? Anyone here have any experience with any of these engine modifying companies, or the engines listed above with a Zenith 601/650? Thx! 2. Aug 27, 2019 ### Armilite ### Armilite #### Well-Known Member Joined: Sep 6, 2011 Messages: 3,059 Likes Received: 247 Location: AMES, IA USA 1st What Engine was the Plane Designed for? 2nd Do you have that Engine or No Engine yet? 3rd 10k probably isn't enough unless you go 2 Stroke! A Rotax Rick 670(669cc) is 92hp@6350rpm. Those 670's have been Big Bored to (82.5mm x 70mm) 748.6cc! PSI makes some Billet Race Engines based off Polaris Sled Engines in 900cc to 1200cc to 1800cc range. 900cc/7cc= 128.5hp@6500rpm, a 1200cc/7c= 171.4hp@6500rpm and a 1800cc/7cc= 257.1hp@6500rpm. But PSI Race Engines aren't Cheap either. Since it's a Billet Case made on a CNC Machine and it already is Flat on the Front, it wouldn't be too Hard for them to Add Rotax's Provision 8 Data to the Case Front, or better yet the Billet Gear Drive made for them Suzuki Geo Engines which I'm sure can handle more HP than Rotaxs Gear Drives. I would approach them, it's for an Air Boat (Planes Scare People), and you just want a De-Tuned 9.5cr for 91 Octane turning Max 6500rpm. Skidoo and Arctic Cat have 1000cc 2 Strokes, I don't follow Polaris or Yamaha much, but they probably have one also. Just a Good Core O-200 goes for around$4-$5,000 today, rebuilt$12,000-$14,000, New$24,500. The main upgrades are a CAM, Higher CR Pistons, and I think you can go with a little Bigger Intake Valve and do some Porting. You're probably talking about a 10-25hp upgrade depending on what you all do, unless you turn it Higher Rpm. If you're in the Mountains a Turbo would be nice, also EFI for combating Carb Ice.

A Turbo Setup for O-200/912 probably $5000+. EFI Setup$5000+.

A Good Core 912 $????? A New ROTAX 912 ULS | 100 HP ENGINE from CPS is$18,878.00

ROTAX 914 UL Tubo Engine - 115hp is $30,638.00 Rotax 912UL 80HP Used but Almost New with only 137hrs since new.$12,500 on Trade-A-Plane.

IF, YOU, can Rebuild Engines, and understand these different Upgrades, and want a 4 Stroke 100+hp, I would pick a Continental O-200, and maybe use Bigger Bore Cylinders for even more CI/CC. There is Cheaper EFI & Turbo Options out there, but more hands-on and a little R&D to get them to fit.

Use a program like Desktop Dyno to Input all your Engines Parameters, then you will have a Ball Park HP Number your looking at. If your starting out at Higher Elevation say 3000ft, that 100hp at sea level and Elevation of 3000 feet is 9.00 HP loss. You can run Higher CR's at Alitude to Gain back that hp loss.
http://www.proracingsim.com/desktopdyno.htm

Example: A Stock Skidoo 800HO is 146hp@8000rpm = 96%, 800cc at 96% at 6500rpm = 119hp! I believe it used 12.5cr which you would want to drop to at least 11.5cr for Plane use, so probably around 115-116hp. IF you use the Simple Rule 7cc to make 1hp, 800cc/7cc= 114.2hp. None of the Newer Skidoo/Rotaxs have a Provision 8 Case, but you can still Hang them Upside down with a Belt Drive.

I like this Billet Gear Drive made in FL, not Cheap, but HD! Mount that Baby on a 900cc to 1800cc Billet PSI Engine and you would have an Awesome Engine.

3. Aug 27, 2019

### Armilite

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Example Big CC 2 Strokes:

900c at say 93% at 6500rpm = 128hp@6500rpm
900c at say 93% at 6000rpm = 118hp@6500rpm
900c at say 93% at 5500rpm = 108hp@6500rpm

1000c at say 93% at 6500rpm = 142hp@6500rpm
1000c at say 93% at 6000rpm = 131hp@6500rpm
1000c at say 93% at 5500rpm = 120hp@6500rpm

1100c at say 93% at 6500rpm = 157hp@6500rpm
1100c at say 93% at 6000rpm = 145hp@6500rpm
1100c at say 93% at 5500rpm = 132hp@6500rpm

1200c at say 93% at 6500rpm = 171hp@6500rpm
1200c at say 93% at 6000rpm = 158hp@6500rpm
1200c at say 93% at 5500rpm = 145hp@6500rpm

etc! There up to 1800cc last I knew.

The only Rotax Triple made with a Provision 8 Case was 1993 748, I think it was (72mm x 61mm) 745.3cc. A Big Bore (76mm x 61mm) 830.5cc. Make a Triple 70mm Crank from a 670 and it's Big Bore Cylinder parts, (82.5mm x 70mm) 1123.0cc.

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4. Aug 27, 2019

### pictsidhe

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Turbo normalise it. I'd be leery of increasing the power over stock sea level.

5. Aug 27, 2019

### BJC

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First, I don’t know what a 601XL - B is, but a quick look at the performance specs for the 601XL shows the cruise speed for the straight 912 version to be close to Vne, and the cruise speeds of the 110 and 115 HP versions at Vne. That makes me think the the 115 HP version is capable of exceeding Vne in level flight.

Given the history of the aircraft, I would not equip it with a turbocharged engine, nor would I install more than 100 HP.

BJC

6. Aug 27, 2019

### ToddK

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For the money and simplicity, the Corvair is hard to beat.

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7. Aug 27, 2019

### Victor Bravo

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Which now cheerfully brings us back to the original subject, the Rotax 912 series. Does anyone here know if there are any low-risk upgrades specific to the 912 80 HP engine, to provide a little more oomph, without changing it to the 100HP Rotax ? I'm informed that the "zipper" big bore kit is not available for the smaller engine (and that this zipper upgrade requires some preventive welding on the crankshaft anyway). My interest in this subject is that I have a line on an 80HP 912, and I'm looking at an airframe appropriate for that engine (CH-701), and I'd sure like to know if there are any minor tweaks, bolt-on goodies, or "tuning tricks" specific to the 80 HP 912 that are reasonably safe to do.

8. Aug 28, 2019

### JayKoit

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To answer your questions, the Zenith 601/650 was designed to work with any of these engines, with complete firewall forward installations available...And I don't have an engine yet (however I do have a Continental mount)

In regards to the engines you mentioned That is some serious power to weight ratio right there. And a very interesting idea and intriguing engines/gear drives for sure. But I think for my first build I want to go with an install that's more established, there's so much support for Zenith w/Rotax, Continental, Jabiru, and Corvair (including DVDs that walk you through the whole installation). Plus I did just see a C-85 stroker on Barnstormers last week 0 smoh for $4500 though, so I know they're out there... I just wasn't ready to pull the trigger on a specific engine just yet. Corvairs also lurk around that price range with under 100 hours on them. And occasionally a low-time 912UL will show up for about$7K, and with the turbo kit you're at 12-13k...

9. Aug 28, 2019

### n3puppy

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What is the fuel capacity of your plane? - I see where the CH610XL has 24 gallons in the wing tanks

If you do use eventually decide on a 2 stroke engine, expect significantly more fuel burn than a 4 stroke (BSFC)

Four Stroke Example ( from manuals)
912 ULS 98.6 Hp - 7.1 Gals per hour. .43 BFSC
912 UL 79.9 Hp - 6.3 Gals per hour. .48 BFSC

Two Stroke Example ( from manuals)
447 UL. 39.6Hp 5.3 Gal per hour .8 BFSC.
503 UL. 49.6Hp. 6.6 Gal per hour .8 BFSC
582 UL. 64.4Hp 7.0 Gal per hour. .65 BFSC

About 35 more HP from the 912 - for the same 7 gallons an hour of a 582

Also found a Dyno chart for a Rotax 800 - little less hp than the one referenced above(141 vs 146), but close

Rotax 800 engine - 6500rpm. 105Hp .65bsfc
105Hp x .65 BSFC = 68.25 Lbs fuel per hour.
68.25 lbs / hour = 178 CFM air at 12:1 a/f ratio = 97% VE
68.25 lbs / 6 lbs per Gal = 11.37 Gal per hour
11.37Gal per hour / 7.1 Gal per hour = 1.61 times more fuel per hour
61% more fuel burn than a 912ULS at similar hp output. (105 vs 100)

In real world terms. - that's 3 1/4 hours flight time vs 2 hours (with some reserve in each case)

10. Aug 28, 2019

### TFF

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I dont think you are going to put a turbo on a used 912 and have success. I think it would need a rebuild before I would add a turbo. At least a top if you think the rest is good. Budget be dammed I would pick Continental, Rotax, Corvair in that order. Price dependent, I would look at my money to spend and buy the best I could afford.

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11. Aug 28, 2019

### JayKoit

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When it comes to the 912 80hp, I am definitely interested in finding out more about this:
https://www.912turbokit.com/fly-120hp

It's made for the 912UL 80hp, and they appear to have a decently tested and reliable turbo kit, but I'd of course like to talk to some owners for confirmation. They have about 100 kits flying. It's DULV certified though, which means in Germany any aircraft manufacturer can sell this kit/engine combo as a part of their aircraft as standard installation. TBO 1500 hours and 2 year warranty.

Also, I looked on the Zipper Big Bore site and they do indeed make kits for the 912UL. From their website:
"The 1484cc ZIPPER CYLINDER HIGH POWER KIT will give your Rotax 912uls, 114HP. You can upgrade from a 100HP Rotax or an 80HP Rotax (912 ULS or 912 UL)."

I've seen lots of 701's over the years with the 912UL, seems like a good fit.

12. Aug 28, 2019

### JayKoit

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The Zenith 601 XL-B is the "modified wing" version of the 601 XL. It has a beefed up spar, aileron/bellcrank mods, beefed up attach points, etc.
Per the manufacturer the recommended power range for the plane is 80-140 hp. Plenty of models fly with 130hp vikings and don't fly near Vne - mostly because the published performance specs are very optimistic..

...And based on the history of the 601 XL-B, I'm not worried about a 100+hp engine in the least (since the XL-B hasn't had a single failure to date)

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13. Aug 28, 2019

### JayKoit

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I agree, if I were to turbocharge a 912 I'd want one that's VERY recently overhauled, or I'd put a fresh top end on it.

14. Aug 28, 2019

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