How can I make an informed decision choosing between similar engines?

[drseti]

it has a pretty darn good track history!

Well, it certainly has a long history. Which is a mixed blessing. At any rate, $11k more than a Rotax 912 ULS is not a trivial cost.

[Hambone]

it has a pretty darn good track history!

Well, it certainly has a long history. Which is a mixed blessing. At any rate, $11k more than a Rotax 912 ULS is not a trivial cost.

True. Now, if they would only stick a 912 ULS in a Vashon Ranger and knock that $11k off the price...

[fatsportpilot]

I'm not a big fan of Continental engines. If I wanted an older-design direct drive engine then I would buy a Lycoming.

[scoutdsa]

An update on my decision process.

I decided I am going to go AGAINST the ULPower engines after talking with someone who has a lot of experience with them and his website http://www.myulpower.com/ that informed me of some problems that he believes the engines have.

1) Sloppy clearances creating piston slap
2) Cheap third party pistons
3) Extremely rich mixture preset
4) Very small oil capacity causing overheating
5) Cheap voltage regulator (this one is the also true for Rotax's Ducati I hear)
6) 100LL damages exhaust valves

I think I am going to settle either Rotax 912iS or maybe the Edge Performance's aftermarket Rotax mod the EP912STi.

So I am at this exact spot. I am building a Zenith Cruzer and was pretty solid on the UL Power 350i until I ran across the issue with the pistons. The Rotax 912iS was also my second choice, but I am struggling with understanding what the loss of 18 hp will do to the performance. Would you share your final decision and any issues you have run into. Appreciate it.

[3Dreaming]

So I am at this exact spot. I am building a Zenith Cruzer and was pretty solid on the UL Power 350i until I ran across the issue with the pistons. The Rotax 912iS was also my second choice, but I am struggling with understanding what the loss of 18 hp will do to the performance. Would you share your final decision and any issues you have run into. Appreciate it.

There are some things to consider when comparing the horsepower numbers. How does UL power determine their horsepower? Is the Dyno number tested with the stock exhaust or straight pipes? For example a 160 horse Lycoming in a Cessna with the stock exhaust is only around 133 horsepower on the dyno. Lycoming establishes power using straight pipes. I am pretty sure the Rotax numbers are measured with the stock exhaust. So actual power at the propeller might be the same.

Another thing to consider is the Rotax while it turns a higher RPM, the propeller RPM will be considerably lower than the UL Power engine. Slower propeller RMP is more efficient, and allows for a larger diameter propeller. The larger diameter propeller moves a larger column of air.

[drseti]

Just last night I was talking to a Lycoming engineer who told me that the new, injected and turbocharged 140 HP Rotax 915iS actually outperforms the 160 HP Lycoming O320. So there's obviously more to consider than HP.

[jetcat3]

Just last night I was talking to a Lycoming engineer who told me that the new, injected and turbocharged 140 HP Rotax 915iS actually outperforms the 160 HP Lycoming O320. So there's obviously more to consider than HP.

I believe it! It’s technically 145/146 HP at 45” and 5800 RPM on the dyno but Rotax conservatively lists it at 141 HP. I’ve been behind it twice in a TSi with three on board and it’s extremely powerful. It’s hands down the best piston engine in all of GA in my opinion.

[JimParker256]

The other point I would raise is that the Zenith Cruiser performance with the Continental O-200 appears to be very decent. With a lighter, and higher powered Rotax 912ULS or 912iS engine, it should be even better. (O-200's are well known to produce significantly less than the claimed 100 HP – many people claim that the older Continental C-90s are actually more powerful.)

The factory claim of 1000 fpm with the O-200 is plenty good. Ditto for their claimed 100/125 foot takeoff/landing distances with the O-200. Installing a more powerful engine will likely give you better climb performance, but frankly won't make the airplane much faster... That plane is pretty "draggy" based on the aerodynamic induced drag. My buddy who has a 120-HP CH-750 climbs at well over 1200 FPM, but his cruise speed is MAYBE 2-3 mph faster than the 100-HP versions he flies formation with...

If it were me, I'd prefer to have a lighter airplane (more useful load) with still absolutely stellar performance... but maybe I'm crazy.

[drseti]

If it were me, I'd prefer to have a lighter airplane (more useful load) with still absolutely stellar performance... but maybe I'm crazy.

Maybe you are, Jim - but I agree with your preference.

[RBearden56]

Be mindful of what you are focusing on. As a student and low time pilot I would recommend a reliable engine that is simple to maintain and operate. I really like the Rotax 912ULS and would like it more if it had one carb instead of two that need balancing and twice the cost at rebuild time. My current Continental O-200D has a 2400 hour TBO, very simple, and reliable as the day is long. It just feels right. Performance is good, climbs out at 800 FPM and cruises along at102 knots with speed to spare. All maintenance is traditional and it can be done by any LSRM or A&P. The O-200D in my 162 outperformed the 912ULS I had in a lighter Allegro 2000.

Focus on learning to fly, build your skills and gain the experience that will last you a life time. All of that stuff doesn't matter when you are up there enjoying yourself.

Randall Bearden
Sport Pilot
LSRM
Cessna 162 ELSA

[JimParker256]

.... I really like the Rotax 912ULS and would like it more if it had one carb instead of two that need balancing and twice the cost at rebuild time....

While I would agree that one carb is better when it comes to synchronizing carbs, etc., I would challenge the "twice the cost at rebuild time" statement. You can't buy parts for your "real airplane carburetor" at the local motorcycle shop...

All maintenance is traditional and it can be done by any LSRM or A&P. The O-200D in my 162 outperformed the 912ULS I had in a lighter Allegro 2000.

The O-200D is a great engine, and I have no wish to disparage it in any way. For people who are just "uncomfortable" with the geared Rotax, the O-200D is an excellent choice. Cessna chose it largely because they felt their flight schools would be more comfortable owning and maintaining an engine so similar to the other ones they operated.

But there is no really valid way to compare the performance of two different engines when they are mounted in two different airframes. I would assert that it is a physical impossibility for a heavier engine, producing the same horsepower, to "outperform" a lighter engine producing the same horsepower, provided both engines are installed in the same airframe. It's just simple physics and aerodynamics, and has been confirmed (at significant cost) by folks who've tried putting O-200s and other "heavier" ~100 HP engines into a Vans RV-12, only to wind up ripping them back out to use the Rotax again.

And for many of us, useful load is a significant component of enjoying our airplanes. The heavier weight of the O-200D is one of the reasons the Cessna 162 has such a ridiculously low useful load. Admittedly, I'm bigger than the average guy, but with me and full fuel, I could carry a toothbrush and not much else... Same airplane with a Rotax engine and a composite prop would have significantly better useful load.

Focus on learning to fly, build your skills and gain the experience that will last you a life time. All of that stuff doesn't matter when you are up there enjoying yourself.

Randall Bearden
Sport Pilot
LSRM
Cessna 162 ELSA

On that statement, I'm 100% in agreement with Randall. The best "upgrade" you can do on ANY airplane is purchasing more fuel to fly more often!

[fatsportpilot]

.... I really like the Rotax 912ULS and would like it more if it had one carb instead of two that need balancing and twice the cost at rebuild time....

While I would agree that one carb is better when it comes to synchronizing carbs, etc., I would challenge the "twice the cost at rebuild time" statement. You can't buy parts for your "real airplane carburetor" at the local motorcycle shop...

The Jabiru 3300 has a single Bing 94 CV carburetor which is a motorcycle carb just like the Bing 64 that Rotax uses.

[fatsportpilot]

So I am at this exact spot. I am building a Zenith Cruzer and was pretty solid on the UL Power 350i until I ran across the issue with the pistons. The Rotax 912iS was also my second choice, but I am struggling with understanding what the loss of 18 hp will do to the performance. Would you share your final decision and any issues you have run into. Appreciate it.

I haven't finished my decision yet but I'm pretty sure I'll go with either a Rotax 912iS or 915iS if I buy a Bristell, or Jabiru 3300 if I buy the American made Lightning LS-1. This is what I have found out in my research of a bunch of different aviation engines. I am not an expert in aircraft engines but this is what I have concluded. It isn't exhaustive and I've left a lot out of considerations like price, size, and weight but I hope it will help someone or spark discussion or additions. Also I couldn't find any detailed information on Lycoming IO-233-LSA only a bunch of broken links.

Rotax 912iS Sport

URL: https://www.flyrotax.com/produkte/detai ... ort-2.html
Stats: 100hp @ 5800rpm, 1352cc, 10.8:1 CR, 4 cyl, liquid cooled, geared transmission, dry sump, fuel injected, normally aspirated

This is my favorite because they are liquid cooled which means they run at lower temperatures. This has an important effect because it decreases expansion of metals which lets them use much tighter clearances. And because of the reduction drive it lets the engine run at the optimal rpm for the best power curve and I believe Rotax has very well perfected the gearbox's reliability. I like the fuel injected models the best (912iS Sport and 915iS) for the efficiency as well as redundancy (fuel injectors, critical sensors, electric pumps, ECU, generators, and of course ignition systems aka ignition modules, and spark plugs). Component lifetime is increased because the fuel injectors and ignition systems are alternated on every cycle so only one plug+injector fires at a time instead of both together. They also have a very wide support network and iRMT classes let you learn how to do most maintenance yourself. Best of all they are really really light engines and have the best power to weight ratio of them all.

It has a few downsides though like the increased complexity of the gearbox, dry sump, and liquid cooling. Also it doesn't like to run 100LL without extra maintenance. And some of the redundancy is not perfect for example the fuel injected models have the dual generators (or dual magnetos and single generator) are housed in the same stator and are only electrically isolated, not physically isolated. I also don't like the carbureted versions because of the need to sync carbs and if they're going to go the way of more complex designs, why not go all the way and make it fuel injected? Also I've heard that the 914UL turbo has its own set of problems that are not present in the 915iS turbo.

Edge Performance EP912STi

URL: https://www.edgeperformance.no/
Stats: Up to 177hp @ 5800rpm, 1621cc, 11:1 CR, 4 cyl, liquid cooled, geared transmission, dry sump, fuel injected, turbo-normalized

It is an aftermarket mod for Rotax 912ULS which improves horsepower with a performance camshaft, more displacement, and a fuel injection system. The boost in horsepower is huge at almost 177 (instead of 100) although the max continuous power is only 135. But for a similar price I could just get Rotax 915iS which has the same max continuous horsepower even if the WOT power is only 141. And the 915iS has a lot more redundancy for the same price. The EP912STi has almost no redundancy. But I do trust its designer to know what he is doing so I do not think it is a bad aftermarket mod at all. For me the tradeoff for getting the EP instead of the 915iS is that I lose a lot of redundancy as well as factory support but I gain more horsepower at WOT and a much lower weight (about the same weight as the 912ULS or even a little less). It is great if your mission is extreme maximum power for STOL or if you want an adequately high max continuous power of 135hp and don't care about redundancy, but you don't want the extra weight of the Rotax 915iS.

MW Fly B25G-R-155-B

URL: http://www.mwfly.it/engine%20feature%20 ... %202.0.pdf
Stats: 155hp @ 4700rpm, 2549cc, 10.5:1 CR, 4 cyl, liquid cooled, geared transmission, semi-dry sump, fuel injected, normally aspirated

This is a fuel injected Italian engine and it's a little obscure but it has a similar paradigm to Rotax because it opts for liquid cooling and an optional gearbox to reduce weight and improve efficiency at the expense of being more complex. Early MW engines had really bad problems with the gearbox failing and even improvements didn't help a lot but I heard that lately they are using a much better gearbox. I think their gearbox uses a separate oil system from the main oil system for the gearbox so that it can use 100LL without clogging the gears over time. The MW engines pride themselves on using a lot of redundancy and safety features like using gears to reduce the speed of the camshaft chains (there are two) to give them a longer life but to be honest I don't trust them as much as I trust Rotax for reliability especially because they are less well known and tested and because of having dual chain driven camshafts.

ULPower 350iS

URL: https://ulpower.com/en/engines/ul350/ul350is#1-specs
Stats: 130hp @ 3300rpm, 3503cc, 8.7:1 CR, 6 cyl, air cooled, direct drive, wet sump, fuel injected, normally aspirated

They are direct drive fuel injected engines that look great on paper but according to myulpower.com they have a whole lot of problems like piston slap, low quality third party automotive pistons, rich running, and a small oil tank that leads to overheating. They also use solid lifters which not everyone likes. The person who created Edge Performance used to work for ULPower but left because of these issues, I think. I would not recommend this engine for anyone based on all the things I have read.

Jabiru 3300

URL: https://jabiru.net.au/wp-content/upload ... ressed.pdf
Stats: 120hp @ 3300rpm, 3300cc, 8:1 CR, 6 cyl, air cooled, direct drive, wet sump, carbureted, normally aspirated

They aren't fuel injected but they are simple (eg it uses a real rotating distributor instead of a wasted spark ignition system) which makes maintenance easier. The old engines had severe reliability problems with thru-bolt fractures which would destroy the engine and gave them a bad reputation. Gen 4 Jab engines are supposed to have fixed this totally. Other than being less efficient (carbureted) and a bit heavier they look really nice. But the only problem I saw which is a little worrying but is total hearsay is someone on a forum supposedly knows of some problems with the gen 4 pistons or cylinders or something but which he can't talk about. I don't know if it's crappy tolerances or something more sinister.

Continental O-200D

URL: http://www.continental.aero/engines/200.aspx
Stats: 100hp @ 2750rpm, 3292cc, 8.5:1 CR, 4 cyl, air cooled, direct drive, wet sump, carbureted, normally aspirated

I didn't look into them very much at all because I don't like using 100LL and because they are quite heavy for such low horsepower. I've heard stories about them producing less hp in the real world than they are rated for and that their quality control is not the best (that last statement comes from an anonymous person's blog comment claiming to know this from speaking with one of their engineers so take with a big grain of salt). I would never go with O-200D in a modern plane that deserves a modern engine.

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