I currently run a Holley 2 bbl carb on my experiemental aircraft (Chevy 4.3L engine, Edlebrock Manifold). I am wondering if there are any carbs that automatically adjust mixture by means of an O2 analyzer, or other wise. That would compensate for the various altitudes I fly at. Your help is appreciated.

 

Perhaps you should swap over to a TBI setup...'cause that's pretty much what TBI is, a carburetor that's controlled by things like O2 sensors and manifold pressure and such.

 

Welcome aboard. That's an interesting choice of powerplant. Been airborne yet?

Buick used a CC 4-bbl on their 4.1, and a CC 2-bbl on their 3.8. LG4 and L69 305's had a CC q-jet.

The TBI recommendation is a good one, though.

 

Thanks for the replies. I have flown the aircraft for 130 hours and it performs well. I would certainly like to go to TBI, but know nothing about it except that it must have a line returning to the fuel tank for recirculation. That would be a major problem. I have a Chevy 4.3L with Brodix heads, Edlebrock manifold and Holley 2 bbl carb. The 2 bbl has the jets out as well as the powervalve and I had a piece made that fits behind the bowl that I can adjust in flight by means of a cable. It simply opens two ball valves allowing fuel to flow where the jets would normally be. Presto, leaning or richining at various altitudes. Works pretty good. Now I plan on installing an O2 analyzer in the header and adjusting by that in flight. I thought there might exist a carb that would do that automatically. Another problem with this installation is that everything is shoehorned under a close fitting cowl. Changing anything is difficult as I do not have normal hood clearances where small adjustments are easy. That makes things a little difficult.

Thanks for your replies. If you have additional information, advice, model numbers, or where I can get books to read on the subjects, I certainly would appreciate the information.

 

Well thats a new one.

Unfortunatly I don't believe there is an auto carb that'l do that..at least not that I've ever heard of. Why can't you adapt some older aviation style carb to work? Maybe a pair off an old cessna or something. I havn't the slightest clue how they work..but it would seem to be a better place to start.

How do you deal with fuel control at various angles? Holleys have problems with that when used on 4x4's...let alone an airplane I would imagine...

 

Actually, no problem with fuel control at various angles. I assume as a 4X4 goes through its paces, fuel in the bowl is constantly changing angles, sloshing, etc. In an airplane, I am normally doing positive g manuevers. That keeps the fuel where it belongs and operates as if it is straight and level. Even doing aerobatic manuevers such as aileron rolls and loops, positive g's keeps everything turning (especially the propeller) as expected. But, don't try any zero or negative g manuevers!!!! Once that float moves up, well, I don't have to explain to you guys the next step follwed by cleaning the seats after landing. But that is the same for Holley or an aircraft carb, they both work the same. The only way to perform in the negative g area is fuel injection.

 

hmmm. They do make Adjust-a-jet metering blocks that let you change jet size by turning a screw. Maybe you could hook up a small servo motor to one of those. It would essentially work the same as your cable operated ball valves, but it would be more controllable and precise. You might even be able to work out a system that controlled that motor by a **** with graduations for every few thousand feet. Might even be possible to program something that would do that on it's own....but thats beyond my expertise.

I never thought I'd say this, but TBI just might be your ticket. Generally I think TBI is about the worst system ever designed, but this is one area where it might fit the bill, and allow you to not have to be so careful about maintaining a limited G range. Physically speaking anyway.

Only problem is I seriously doubt a stock TBI ECM will do the job from a programming standpoint. You'll never get it to run right in those conditions, and I'd REALLY hate to have it stall or get picky mid air.. Might have some luck with an aftermarket DFI, but then you may as well go to a full-on aftermarket port injection system designed for it. Obviously, thats not your first choice or you would have done that in the first place.

What is the operatign range of the motor RPM wise? What is the elevation range it sees?

 

The operation range of the motor is between 3100 and 3700 RPM. I keep it slow as there is no need to turn it faster. I can get about 190 MPH TAS at 3700 RPM but at 3500 RPM I'm flying along at 170 MPH TAS and only buring 8.3 GPH of Amoco. Typically, I fly in the range of 1,000 to 12,000 feet.

 

I would say to get tbi also. why is the return line a big problem?

 

The reason I like the idea of the tbi is it is fuel injected and you could then do the negative g stunts and it would adjust itself to the altitude you were working in.