flyinghi

My problem is complex. Based on info from the carb tech group, I would like to understand if I can use a TBI in my particular application. I use a Chevy 4.3L V6 in my experiemental aircraft. It is basically stock with a set of Brodix aluminum heads and an Edlebrock 4 bbl intake manifold. I have a Holley 2 bbl on top of that supplying gas. The carb has been modified with a leaning block in place of the jets. I can use a cable to adjust mixture in the cockpit by opening or closing small ball valves in place of the jets. I use an O2 analyzer in the cockpit to reference for adjustment.

My problem is that I would like to have an automatic adjustment of mixture at various flight levels and also keep fuel flowing to the engine at various attitudes (I assume with an O2 analyzer). If I go negative g's for even a second, I put the engine at risk of shutting down.

I understand from others who have replied to my previous posts that I should consider TBI. So off to the Jegs/Summit catalogs to try and learn something. I did find a Holley kit (2D digital system) that seems to include quite a bit of equipment but I am interested in what thoughts others would have or advice you might be able to provide me. I'm unsure, having never dealt with any type of fuel injection, what is needed (now you see why I selected a carb originally - KISS Theory- keep it simple, stupid).

Can I use the Edlebrock manifold I currently have (2111 4 bbl).
What will need hooking up? I assume some sort of connention to my O2 sensor??? Is there anything else? Remember, I do not have a speedometer so is some sort of speed signal required? I will have to use two fuel pumps, one as a spare. I understand from others that I will need a fuel pressure regulator. I assume this means a return line from the regulator back to the tank (or possibly, I could simply return back to the suction side of the pumps for a small loop?).

I know this is a lot of questions but I am interested in some thoughts on what I am planning. I realize I need a good manual to read and learn more prior to starting, but real life answers are better. Can anyone recommend a book I can purchase?

Your help would be appreciated.

JPrevost

This sounds like an engineering project , my cup of tea.
All EFI is basically the same, it's definatly better than a carb setup and especially so in aircraft applications.
TBI is the entry level EFI and it's more KISS than a carb. A carb has more moving parts and less accuracy making it complex in unreliable. If you plan on using TBI it's going to require you to program your own eproms but this is true for all EFI but more specifically speed density (no MAF sensor to read in air flow). www.diy-efi.org has LOTS of information and www.tunercat.com has software to program your own eproms. You can do eprom tuning with visual graphics and all the cool jazz for less than $300 but more like $350 if you want the TunerCat software (I recommend it).
The fuel pressure for TBI is very low, it's around 9psi stock and typical carb fuel lines can usually handle that kind of pressure on the supply line. I don't know what the advantages and disadvantages of using a mechanical pump would be but it seems that electric fuel pumps are the standard even for TBI applications.
You'll need all the sensors from a chevy truck that came with either a 4.3, 5.0 or 5.7. I'd also recommend you use either the 8746 or 7747 ecm. There is little difference but the 7747 was used with the 4.3 so I'd recommend using it and not worring about the 8746 and it's extra goodies. The only difference is an added intake air temp (not to be confused with engine coolant temp) and highway mode for lean cruising and better gas milage.
To get a TBI EFI system to run as well as a carb you only need a MAP (manifold/atmosphere pressure) sensor and a TPS (throttle position sensor). I also recommend using all the other sensors just because it would make for a much more flexible system and easier to tune. If I had this project I would grab a wiring harness out of a 4.3L truck with a 7747ecm and install the CTS and knock sensor into the block, the CTS can be installed anywhere in the coolant jackets, it's usually in the intake manifold for easy access. The advantage of using a GM ecm is that it's already been hacked to death which means it's never been so easy to tune your make your own custom chips/eproms AND it's cheap AND it's already got all the additional features like closed loop (o2 sensor) and lots of room for improvement if you ever dip into the assembly programming (soon to be just as easy as burning an eprom).
The 7747 ecm even has tables where you can specify the o2 values you want the ecm to stay around. For example, if you want to run slightly rich in closed loop, you can make adjustments in the ecm try and stay around .600 volts instead of the default .450
Converting to EFI isn't as hard as people make it out to be. Those guys doing sequential EFI with $$$ injectors and $$$ timing/spark voltage is definatly a hassle, TBI is a piece of cake.
The only trouble with TBI is that it doesn't have enough sensors. This can be good for the KISS system approach but it can also be a PITA when trying to have the system take into account misc. stuff like fuel pressure variations, octane ratings, exhaust gas temps, that kind of stuff.
If you've got any questions about buring eproms the diy_eprom board is just a few clicks away. The experienced members Grumpy, Trax, and Glenn are always a LOT of help with technical questions. I know for a fact that I would have a carb on my car if it weren't for Pablo and Grumpy!

steve8586iroc

If you do decide to go to an aftermarket system make sure you get a digital ecm like Holley' 950 Commander that has provisions for the O2 sensor. This ecm also comes with all the nessasry software to program it with a laptop. This system also comes with almost everything you will need to run in closed loop with the possible exception of the O2 sensor or knock sensor. This alone will save you a couple hundred bucks or more. Whatever you choose to do, and there are advantages to both, I'm sure you will have a fine flying mochine.

Steve

flyinghi

I'm already starting to understand this better. I still have a question concerning the Holley Commander, though. As I reviewed the data for this unit (and it seems like it has everything I need), I see it has a 700 CFM 4 Barrell. First of all, is a 4 barrell what I need or do I need a 2 barrell? I do need fuel economy in flight and currently have a 2 bbl carb. Possibly, the 4 bbl TBI and 2 bbl carb are nowhere close to the same thing. I just don't want to suck up excess gas so an opinion would be appreciated.

In addition, will this unit fit my standard 4 bbl Edlebrock manifold or will I need a TBI manifold just for this application? I guess I can get this information from Holley on Monday, but I'm just thinking during the weekend.

Hey, thanks for the good advice from you guys.

Now, if I can just wish Bobby Labonte to victory tomorrow (if I don't freeze at the race).

JokerRS

I'm sure that all you would need is a two barrel tbi. Many people here are using two barrel TBIs on four barrel manifolds.They either buy an adaptor or make thier own out of aluminum.

flyinghi

Thanks for the additional information. Since my last note, I see Holley is now selling a model 950-19S 2 bbl Commander 950 system. In the text, it specified a 2 bbl flange adapter for the 4 bbl manifold. Additionally, I found an installation manual for this system so I will go through it and see how difficult it will be to install and program. Who out there volunteers to sit beside me to program this thing while I fly it around???

Now my final problem is the fuel pump and regulator. Does this system require a return line back to the tank or can a regulator keep pressure even without a return line?

steve8586iroc

The Holley tbi's have a built in regulator and you will need a return line. Wether you get a 2barrel or 4barrel tbi unit it is still tunable for your setup. With the heads and intake you have you are probably making some good power so a 4 barrel will give you the extra potenial you might need for spirited flying while still being able to provide the economy you want. Of course I could be wrong. Theres not a lot of differance between the 700cfm 4b and the 670cfm 2b tb's. There is also the 400cfm tb that you might want to look into also.
One other thing you don't have to be concerned about is the idle problems us car freeks do.

Steve