Please help fill in the blanks about fuel injection.

[akschu]

Forum,

I'm trying to make a decision about what to run for a fuel system. This decision is completely based on the cost/benefit ratio for my application so having good information is the first step in making a good decision.

The engine I'm working with is a IO-540-C4B5 that mounts the fuel system vertically so I can run a carb or FI, secondly, my fuel system can be gravity fed (I'm building a bearhawk, and live in Alaska, but find this forum to have a wealth of info for any homebuilder) so I don't need pumps if I run a carb.

First I would like to compare the benefit of FI over a carb. This is my current list, can someone who has more experience comment or correct it?

Pros:
Better throttle response
More even EGT, perhaps smoother
More even temps allowing LOP operation
Better fuel economy based on LOP operations
No carb heat

Cons:
Cost is much greater
Requires fuel pump and boost pump
More weight
Local support isn't as good

Throttle response is not a big deal, but weight, cost, and complexity are, so the question is, will a FI system give me enough fuel economy benefit using it LOP to offset the cost, weight, and complexity? Could I honestly expect 20% more economy over a carb? Can I run the carb LOP as well?

Second, if I do go FI what are my options for systems? I know I could go lycoming/bendix, silverhawk, and airflow performance. Am I leaving any out? The Ellison kits don't seem to support 250+hp engines anymore. Any of these I should avoid? I really want a set and forget solution.

Thanks,
schu

[kiwipete]

Schu

Some of the cons you list really aren't completely correct.

FI might actually be less complex. As you won't need a primer system for example and are much better to start in very cold conditions. You won't need a carb heat arrangement.

Yes you need a fuel pump and high pressure boost pump but it maybe wise to have a fuel pump and low pressure one for a carb.

Weight? I don't think there would be any significant difference.


The main thing's that pushed me towards FI were
1) aerobatics - the ability for it to keep running inverted
2) no carb icing worries
3) better economy, it should eventually pay for itself.

Peter

[akschu]

Are you saying that running FI would allow me to to remove the carb heat box and plumbing? That is a little less complex, but I was more talking about the fuel system. Adding fuel pumps is a bit more complex than gravity.

As far as weight goes, I'll have to add it all up, but I'm reasonably sure that two fuel pumps are going to be heavier than the carb box, cable, and scant hose, but perhaps your right.

My questions are more geared toward the fuel savings anyway, I'm trying to justify the cost.

Thanks,
schu

[Tom Hunter]

I doubt you'll be able to save enough money to pay for the added cost of FI unless you run your engine always on economy power settings. And what fun is that?

One thing I don't see on your list is the fact that FI gives you a little more HP. That is the main reason I opted for FI on my plane. That and it is more "modern" than a carb. It also makes your installation simplier.

Adding an electric boost pump is no big deal and the pump weighs very little. The pump is a little pricey however.

Installation is really quite simple. I converted my engine to FI from a Carb with a "kit" I got. Lycon in Visalia, CA can set you up with everything you need and will even take your carb in on trade. I suggest the old standby name in FI systems...it seems to idle better than the others.

Another "bit of fun" of a FI unit is tunning the injectors.
I worked with Lycon also on this.

When converting to FI from a Carb, you need to spend some thoughts on providing an efficient pathway for air to your servo. Also, for efficient servo operation, you want the air to be non turbulent as it enters the servo and passes by the impact tubes.

Also, FI might be a little more intolerant of dirty fuel than a carb. Anyway, you want to plan for providing clean fuel to the injectors. While not specifically designed for this, I have found an Andair Gasalotor (sorry, I don't have the model # in front of me) to be satisfactory for this use in 535 hours of operation.

Tom

[akschu]

Is your kit the bendix/lycoming setup? Which boost pump did you use?

[dtw_rv6]

I went with Fuel Injection when I built my -6. From a complexity standpoint, I have to say that the FI arrangement is pretty straightforward, just make sure you pay attention the manufacuters instructions, as there are several variations on how the fuel supply is run -- nothing difficult, but don't assume your FI plumbing will be just like mine.

As for LOP operations, I'm sure that someone here will tell you they run carburated LOP, but the FI setup really shines when you take the time to balance your injectors.

I'm fairly tight with what I spend my funds on, and I felt that the fuel injection was a worthwhile investment in the project. YMMV.

Don

[N941WR]

Originally Posted by akschu

...Local support isn't as good...

Schu,

Since you are in AK support will be a big deal. Check with some of the other pilots up there, I suspect they will suggest you keep it as simple as you can.

The rest doesn't mean much if you have a problem on some remote river bank.

Just my $.02.

PS. Check your PM's.

[Mike S]

Originally Posted by akschu

Adding fuel pumps is a bit more complex than gravity.


Thanks,
schu

And, not as reliable

[akschu]

If I got with a bendix unit there will be plenty of support. Many maules run IOs. Some pilots are really old school and say to stick with a carb, but others suggest the fuel injection being better since I live in the land of carb ice.

schu

[frankh]

Automotive electric pumps can be had for about $130..Probably another 50 to 80 with non-return valve and pressure regulator.

Depending on where you put the pumps you could probably use a single regulator and non return for both pumps.

Don't forget the filter before each pump.

Frank