Page 1 of 1

EFI Rotax 9XX conversion

PostPosted: Tue Dec 09, 2014 7:07 pm
by BRS
Engine after conversion
Engine before the conversion
I finally did it. Converted my turbo'd 912 to fuel injection. So I guess it's time I shared this with you all as Ronnie told me there are several folks asking him about this but he has not had the time to work it all out. Converting is really a mixed bag and it all comes down to your goals and how you want your engine to run. I'll try to explain and muddle through an explanation of the system I installed.

Hardware: The computer "ECU" is the heart of an EFI system. All the other parts can be made in a modest shop but I didn't want to make parts that were already available so I purchased a "Kit". The kit I got was from EdgePerformance and is based on the SDSEFI(.com) EM-5 ECU. Since this is the ECU I've been running on my Subaru (EJ22) powered gyroplane for the past 3 years I knew it well and have developed a lot of trust in this computer. This made the choice of this kit easy. The only hard part was deciding to spend the money without justification other than just wanting to. But then again the entire aircraft falls into this category.

Goals: My goals for this were to (1) get rid of the two throttle plates, (2) get rid of carbs, (3) get rid of the uneven fuel flows caused by the uneven rotax intakes, (4) get the engine to run as smooth as I knew it could at ALL settings. Since I was already turbo'd I didn't need to pickup any extra power but I did anyway.

Compromises: This is a single computer ECU that runs just the injectors, the ignition system is unchanged. The compromises in this system is redundancy. Basically I've traded two carbs for a single electronic system with some single point failure points. Sounds like insanity doesn't' it? Well, I consider this as a risk assessment exercise. I'm satisfied, based upon what I know. My thought process goes something like this. This ECU is robust and has a really great track record, most electrical failures are installation errors (poor wiring) though this is an area I'm skilled in. I fly mostly alone and over terrain where and engine out means I'll need a ride home, not to a medical facility.

Physical Description: Included are a few pictures, I'll try to remember to take pictures of the instrument panel later on. Removed items are the two carbs, airbox, one throttle cable, the choke cable. All the 914 TCU sensors are reused except for the carb enrichment solenoid. The low pressure fuel pumps are replaced with high pressure fuel pumps and fuel regulator. The programmer and mixture knob (rheostat) are installed in the panel. It is possible to remove these once things are all fine tuned, but since I like options and information I like them available. Electrical - careful consideration here is very important. There are basically three power items and they all get their own circuit breaker. They are the ECU, fuel pumps, and Injectors. These three (except for one fuel pump) I installed on the Alternator side of the Master relay but on the Master relay side of the Alternator circuit breaker. This comprises my Essential Bus. This is the area where the 914 installation manual installs one of the the fuel pumps. Basically this allows for a main bus failure or an Alternator failure (but not both) and still be able to keep the fan running.

Benefits and Operation: I only have an hour of flight time since the installation so I don't yet know everything about how it is going to workout but I'll share what I know so far. I currently have the idle set to 1200 RPM and it runs very smooth. I'll probably set it to 1000 or 1100 eventually if I can keep it smooth. If you set your idle this low you will likely have to connect the throttle position sensor (TPS) as this is needed at low rpms for the electronic form of accelerator pump to work. On the other hand if you set your idle up near 1700 rpms then this is not needed. So far I have the engine running smooth at all rpms and conditions that I have tested. The fuel tuning is done in steps of 250 rpms. The SDSEFI guys recommend using a air fuel ratio (AFR) meter and an O2 sensor to set the mixture. I had done this on my gyroplane when I first learned this ECU but didn't care for this method. Instead I use engine RPM, EGT, and engine feel (smoothness & response) to fine-tune the ECU. BTW - I received the ECU pre tuned for a 914 which was quite close but I've a slightly different turbo'd 912 so the mapping is not identical. Below 3500 rpm I focused on engine smoothness above all else. Above 3500 rpm I first set max power (highest rpm in that 250 rpm range) then I considered richness and EGT. Most of my EGTs run right about 1400˚F. At lower rpms I kept the mixture relatively lean but near 5000 rpm I moved richer. Above 5500 rpm I am running as rich as possible but no so rich that it get rough. Since I like to tinker this is a good project for me. On takeoff I gained over 200 rpm. which means I now need to adjust my prop as the engine wants to exceed 5800 rpm (I hit 5900+ rpm). In the future I hope to experiment with having the ECU shut off the fuel when the MAP pulls down to some low number like 7". This only happens at idle when the prop is driving the engine in a descent. This ECU has lots of capability for stuff like this.

More later.

Re: EFI Rotax 9XX conversion

PostPosted: Tue Dec 09, 2014 8:45 pm
by kenryan
Great job at paving the way! I have two questions. First, what do you think those extra rpms translate to in terms of horsepower? Second, do you have any feel for improved fuel economy? Again, nice job. Oh, yeah, and what did you use for fuel pumps?

Re: EFI Rotax 9XX conversion

PostPosted: Wed Dec 10, 2014 1:26 am
by BRS
kenryan wrote:Great job at paving the way! I have two questions. First, what do you think those extra rpms translate to in terms of horsepower? Second, do you have any feel for improved fuel economy? Again, nice job. Oh, yeah, and what did you use for fuel pumps?

I don't really know how to estimate what power gain those 200+ extra rpms represent. Figuring it is at the top of the rpm band where prop drag is the most it might be a significant amount. Perhaps someone else on the forum would have a better handle on this.

Fuel gain is reported to be on the order of 10%. That sounds like a lot to me but then again I know from my previous black sooty plugs that I was running excessively rich. Especially in two cylinders. I've not yet pulled any plugs but I expect them to now have a nice tan complexion. I expect to be saving some gas especially in the cruise and loiter ranges. Since this comes with a mixture control it is possible to lean it out in flight if needed - though do so only if you know what you are doing.

I'm not sure exactly which pumps these are as they came with the kit. They have internal check valves and were packaged in a really nice manifold setup. I installed them on the firewall where as before they were under the passenger seat. I now have low pressure only fuel aft of the firewall and hp forward.

Here is a picture of the kit where you can see the pumps.

Re: EFI Rotax 9XX conversion

PostPosted: Wed Dec 10, 2014 2:44 am
by john2
What is approximate cost of the kit? Is there any weight gain/loss?

Re: EFI Rotax 9XX conversion

PostPosted: Wed Dec 10, 2014 1:05 pm
by BRS
john2 wrote:What is approximate cost of the kit? Is there any weight gain/loss?

Questions like prices should be taken up with the vender ( About 6K$.
I think the installed weight is two or three #'s less. The intake and throttle body (I'm told) weighs the same as one carb and one intake. I think it might be more. That would only be about 6 lbs (see pic). Then the pumps are heavier and there is the computer and programmer, a few wires and circuit breakers etc.

Re: EFI Rotax 9XX conversion

PostPosted: Sat Jan 03, 2015 11:23 pm
by BRS
I've learned that the EFI setup is power hungry. Really it's no surprise as it's electrically controlled. What I found was that my measly little 6Ah battery which worked just fine before was no large enough. The problem is that the alternator does not put out enough current at low rpms to keep up with the current needs of the EFI so the battery gets drawn down. So if I do a long low-power (rpm) descent then taxi and shut down, the battery may not have the juice to get me started again. Happened once, I was lucky to be where I could connect a charger for a few minutes.

So I installed a 12Ah battery from EarthX. The 12Ah battery was only about 1/2" larger on two sides and 1.5lbs heavier than the old battery. Flight today looks like this will work out just fine. I think the ultimate solution would be to install a different stator with more current availability at low rpms. I know of one in the works which should produce 30 amps instead of the stock 18amps. Watching to see what happens.