Intending to do fuel only TBI on 4 cyl aircraft engine

[lgrant]

I don't recall if I ever posted an intro message but my account was not deleted so maybe so. Maybe I joined before the intro message requirement?

Can someone point me to a comprehensive thread on adapting a GM system to a non GM carb situation. I think I have a pretty good idea of what needs to be done but would be good to see it in writing. The areas I am least knowledgeable about are the bin files and tuning and also the initial setup.

Will likely use an Iron Duke system but those may be marginally small - I think my cfm requirement will be around 200 and I'd rather error on the large side. Does anyone know the cfm rating on the vanilla Iron Duke TBI? Would be nice to land a 1 bbl from the 1984 Fiero pace car or, more likely, the Holley knockoff. Engine is 235 c.i. and will never (hopefully) spin up to more than 3,000 rpm. Red line is 2,800 (prop tips should not be allowed to go supersonic) and most of its work will be done 2,000 to 2,200. In terms of engine competency (it's stock, freshly overhauled and in compliance all the manufacturer bulletins), I would compare it to a mild build.

Regarding ECM setup, I'll need to shut off the spark advance feature, the VSS input and, no doubt, other parts of the system. The exhaust is simply 2 cyl on each side feeding into their respect open exhaust pipe (no muffler). So I will need to noodle the O2 thing a little and figure out what works best. Perhaps installing on one side and assuming the other side is going to look pretty much the same will work.

Thanks in advance to all.
Larry

[dave w]

I don't have any experience with an aircraft engine. I'm a touch nervous even posting in the tread asking information for an aircraft engine.

I don't have a link to share for a TBI installation. The DeBiase EFI link (http://www.slantsix.org/articles/dib...conversion.htm) is an awesome overview of a GM EFI Conversion. Most of the information on the DeBiase link will apply to a TBI conversion. I would suggest using the under hood 1227727 (aka '7727) ECM for a TBI 4 cylinder application. I don't remember which years GM used the '7727 with TBI 4 cylinder vehicles, 1989 ~ 1992 most likely. The 1227730 is an under dash ECM that electrically identical to the 1227727.

To operate fuel only, I'm thinking only the MAP Sensor, TPS, and a Distributor Reference Pulse DRP are all that would be required. An MSD 6A box can supply the ECM with the needed DRP.

dave w

[1project2many]

Are you sure TBI is appropriate? Wouldn't a system with port fuel, with better altitude correction for fuel pressure, be a good choice? Why not control spark as well? Wouldn't you want to keep the engine out of detonation?

Anyway, there were several threads years ago on diy-efi and gmecm by an individual (Steve Parkman?) who was putting a gmecm on Subaru engines for aircraft use and selling them. He went by "swagaero" for Swag Aeromotive. He also did a fair amount of work with other engines in aircraft and was published in Contact! magazine several times.

http://lists.diy-efi.org/pipermail/d...98-January.txt
http://www.retro.co.za/efi/DIY_EFI/1997/efi2-293.txt
https://groups.google.com/forum/#!to...lt/ggkMhwrCduI
http://www.contactmagazine.com/backissu.html

NTSB Identification: LAX99FA052 . General Aviation
Accident occurred Friday, December 18, 1998 in TUCSON, AZ
Aircraft: Parkman VARI-EZE, registration: N81EZ
Injuries: 1 Fatal.

This was the maiden flight in the aircraft, and during construction,
the pilot made numerous design modifications to the airplane which had
changed the flight and performance characteristics. Instead of the
airplane's engines recommended by the designer, the pilot had
installed a GM Geo Metro automobile engine, which the
pilot altered by the addition of a Mitsubishi turbocharger. The pilot
also altered the fuel computer chip to adjust the fuel flow,
attempting to achieve a 2-gallon-per-hour consumption rate. The pilot
told associates that the engine produced 78 hp at 4,800 rpm. Engine
technical data showed the actual power output of the unmodified engine
to be 79 hp at 6,000 rpm. Severe detonation was found in the engine
during postaccident examination and it is believed that it most likely
would produce only 55 percent of rated power. Following takeoff,
witnesses saw the aircraft in a nose high attitude and it never
achieved more than 100 feet agl. Some witnesses said the nose attitude
was as high as 15 to 20 degrees just before the crash. The pilot
radioed that he was having a problem and said he had to put
the aircraft down. The airplane collided with a tree during the
attempted forced landing and a postcrash fire consumed the wreckage.

The National Transportation Safety Board determines the probable
cause(s) of this accident as follows:

The pilot's failure to attain and maintain an adequate flying airspeed
during the aircraft's maiden flight, which resulted in a stall/mush
condition. Also causal was the pilot/builder's decision to modify the
engine and the fuel system control microchip, which resulted in
detonation and a severe reduction in power output, and led
directly to the pilot's inability to attain and maintain airspeed.

[lgrant]

Scary report 2MANY.

Unlike the unfortunate pilot-builder, my plan would be to evolutionary as opposed to revolutionary. Don't know all the details of the build, but the addition of a turbocharger, which would likely call for a lower compression ratio than what existed, would have been a major error. Further, there are "club" propellers that can be constructed that will act as a crude dyno (small power envelope based on rpms at, or near, redline) and, had it been used in this case, it would have 1) told the builder that the engine didn't have the requisite power; or 2) cremated the engine in a stationary safe spot on the ground.

I do know of a Continental O-200 (real aircraft engine) that has been converted to MPFI and DIS - it's a SDS system. Seems to run fine - I wish I had that installed on my (very similar) engine. But that's much more work than converting to a simple TBI system - moding the intake runner tubes to take the injectors; adding a signal wheel for ignition; etc.

Do we believe that a properly installed and tweaked TBI system would be superior to a carb system? Probably, but no guarantees. My problem is that my recently purchased aircraft has a carb that (Marvel Schleber MA-3), inexplicably, does not have mixture control (for altitude variations). So I'll have to change it out at likely a cost of $800 - $1,000. If we think that TBI is superior to carb and can do the proper altitude adjustments, then why no do that? Not only does it solve the mixture control problem (and carb heat problem and fuel primer problem, neither of which we have discussed), but there might be a 4% or 5% improvement in power (torque) and maybe even an improvement in fuel consumption.

Serendipity: removed the carb today and the throttle bore is 1.6875" which is very close, if you believe info on the WWW, to the size of the vanilla Iron Duke single bbl TBI. Again less work.

So, for now, I'll continue with the game plan. But I love the input. All ideas and cautions are very, very welcome.
Larry

[Six_Shooter]

This is one request I wouldn't even make a DIY type suggestion on, knowing what requirements there are for aircraft. I work at an upholstery shop and when we re-build an interior, we have to buy certified for aircraft use leather and other materials.

Even though I love DIY and re-purposing parts that were never meant to be together, I strongly suggest finding certified conversion electronics for your project.

[lgrant]

Six_Shooter, I appreciate your thoughts on "certified" aircraft parts. It's an environment that I live with every day. That said, I pretty much agree with the guys over at DIY Auto Tune (MegaSquirt) who generally take the approach that an engine is somewhat like a rose - an engine is an engine is an engine. Through annual inspections over the years, I've almost come the the thought that certified aircraft components/parts are less durable than ordinary automotive parts. Lots of stuff gets DQed and has to be changed out. Are the specs too tight or is it just crap? Probably equal quantities of both.

Okay, looking at the fuel only TBI installation, we have an ECM, one or two injectors, TPS, O2 sensor, fuel pump, and one or two other sensors. One of the autos that I drive is a 96 Jeep Cherokee that has 225K on it (still runs great) and MPFI instead of TBI. The only part that has failed in 225K miles is the O2 sensor and that was intermittent until changed out. If believe the average speed of a ground vehicle is in the 45 mph range, that's 5,000 hours. I think that's a terrific record, certified parts or no!

The most dangerous part/possibility of/in flying is losing power on takeoff. That's why pilots, in preparation for flight, do WOT run ups checking power (static rpm - prop acts as a dyno) and as many systems as possible. Losing power on takeoff is really bad news - losing power in just about any other situation is manageable.

I thank you for your concern but, based on my personal experiences, the "certified" label is somewhat down the priority list. But keep your thoughts coming- everyone's input is extremely valuable.
Larry