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Carbureted vs. Fuel Injected…?

D

Duncannon

Active Member
I realize that a fuel injected engines can get better fuel burn than carbureted ones, and are a bit more expensive in both purchase-price and overhauling/rebuilding. I also heard that FI engines (particularly o-320/360 engines) tend to hit overhaul sooner, though a great variety of factors determine how long an engine lasts.

I like to think a pilot who will spend their average flight time at lower altitudes (maybe 5k feet) would be better off with a carbureted engine, vs. those who stay up at hypoxia altitudes? About how much fuel does FI save over carbureted, assuming the two engines (say a Lyc o360) are flown at the same altitude with identical power settings and leaned the same? And is there any truth about FI’s hitting overhaul sooner?
 
My carb works fine.

I have considered changing my O-540 to injection but have not for a couple of reasons.
1) it would take a very long time at 1 gph to pay for the change.
2) my motor starts like a sewing machine hot or cold.

As to performance, I see very good high altitude performance. I have been to 22,800’ DA and routinely cruise in the upper teens.

YMMV
 
Injection

The only flaw in your question is that you wouldn’t have to lean them the same. Even at low altitudes the injection will let you lean much more than a carburetor will. Running low power settings lean of peak will burn less fuel. Let’s say you burn one gallon an hour less over the course of 2000 hours. At $7.00 an hour that’s $14000 dollars. The difference in cost between the two most likely doesn’t approach that.

The advantage carburetors have is that they are simple and easy to start. If you’ve got a fixed pitch prop which is also simple to operate, the carb setup is great because you just get in and go without much thought to engine management. Adding a constant speed prop and fuel injection makes engine management much more “difficult” but also precise which can save fuel and also give better performance.
 
Flew carbureted since day one. Then after a few years flying my RV-10 with FI, I would never go back to carbureted. Once you master hot starts for your particular plane, that becomes a non issue.
 
While people can debate the fuel savings with Fuel Injection, I suggest that the ability to skip a fuel stop on long cross country trips is the big advantage.

I do ~173kts TAS at ~8 gph in the RV-8 (IO-360-M1B). You can get someplace with a standard 42 gallon fuel load.

Hot starts are never a problem (dual pMags).

Carl
 
It's my understanding that the distribution of fuel to each cylinder is better in
a fuel injected engine than in a carburated.
This means that it's possible to lean the fuel injected engine more aggressively and will result in a slightly lower fuel consumption than in a carburated. The fuel injected engine is not sensitive to induction icing.
When fuel is added to the air stream in a carburetor the temperature drops when the fuel evaporate. Carburetor icing is a known risk when the air is moist and the temperature is between 23 - 68 F. Engine may stop if the carb- heat valve is not open.
Comparing fuel injected / carburated engine, there is no difference in the TBO (time between overhaul) or expected life time of the engine.
The difference in the cost of fuel is very small comparing fuel injected to carburated. 0.5 -1 USg p hr.
The fuel consumption is directly related to hp. When you lean an engine you are reducing it's fuel consumption and the power output.
Every 10 years the carburetor/ fuel servo needs an overhaul.
Buying a new carburetor is less expensive than a fuel injected system.
If you have the money, I guess most people would go fuel injected.

Good luck
 
Duncannon said:
I realize that a fuel injected engines can get better fuel burn than carbureted ones, and are a bit more expensive in both purchase-price and overhauling/rebuilding. I also heard that FI engines (particularly o-320/360 engines) tend to hit overhaul sooner, though a great variety of factors determine how long an engine lasts.

I like to think a pilot who will spend their average flight time at lower altitudes (maybe 5k feet) would be better off with a carbureted engine, vs. those who stay up at hypoxia altitudes? About how much fuel does FI save over carbureted, assuming the two engines (say a Lyc o360) are flown at the same altitude with identical power settings and leaned the same? And is there any truth about FI’s hitting overhaul sooner?
Click to expand...

So whats is your question or concern, or are you just looking to chat ?
 
Carb

Just for giggles you might look at cars, trucks, motorcycles, four wheelers, snowmobiles, boats, and even lawn mowers...

Pretty much all FI in one form or another with electronic ignition.

It's ok though, because carbs and mags are better, and that's how it's always been done...:rolleyes:
 
Flying different ships experience :)
The -8 was injected with standard mags = almost impossible LOP ops…
My -6.9i carbed with dual LSE and iridium plugs = way better leaning ability, thanks to the EI.

Ordered a new engine for my steed, and that will be carbed again.
- carb factors, a minute + consumption difference, engine quits after about 2” inverted flight.
- Injection factors, hi pressure fuel around, eventual need for fuel return lines, capricious engine starts when hot, several reports of single injector clogging.
 
My RV-6 first flew in 1997. 30-years ago, it was two to three thousand USD more for fuel injection and fuel was just over $1 per gallon. At that time, I wanted fuel injection but was not willing to pay the price to get it so ended up with a carb. Right now, I am too cheap to convert to FI but any new airplane I build will have fuel injection. The cost in 2023 between carb and fuel injection Lycoming or clone engine for an RV is not very much. The fuel injection engine cannot get carb ice and has much better fuel distribution to each cylinder.
 
Another advantage....

I like FI for the simple fact that carb ice is not a thing. Not that managing carb heat is difficult or anything, but a surprising number of aircraft have stopped flying due to carb ice. For me the added safety is worth something.
 
Duncannon said:
Primarily whether or not the TBO time would be any different (I read where someone else had asked that), and exactly how much fuel is saved between the two.
Click to expand...

Lycoming published recommended TBO time as being the same.

Fuel burn difference is all controlled by the operator / pilot and how much they lean the mixture. I have flown a lot of cross-country formation with other RVs. Amount of fuel used per leg depends more on the pilot use of the mixture when we are all traveling at the same speed and altitude than carb or FI.
 
Dan 57 said:
Flying different ships experience :)
The -8 was injected with standard mags = almost impossible LOP ops…
My -6.9i carbed with dual LSE and iridium plugs = way better leaning ability, thanks to the EI.

Ordered a new engine for my steed, and that will be carbed again.
- carb factors, a minute + consumption difference, engine quits after about 2” inverted flight.
- Injection factors, hi pressure fuel around, eventual need for fuel return lines, capricious engine starts when hot, several reports of single injector clogging.
Click to expand...

Sorry but I doubt the iridium plugs have anything to do with the ability of leaning an engine. Also mags don’t have anything to do with leaning an engine. It’s the evenly distributed fuel flow to the cylinders that allow the engine to be leaned. The reason why most carb engines can’t be leaned very well is because of the fuel distribution to each cylinder. In carb engines all the cylinders don’t peak close to each other. Usually before the last cylinder peaks, first cylinder to peak is already running too lean and the engine begins to stumble. The cylinders of a FI engine peak within 0.1-0.3 gph and all the cylinders are able to run LOP before the engine stumbles. As long as you have around a 40 micron in-line filter clogged injectors are common. CORRECTION: As long as you have around a 40 micron in-line filter, clogged injectors are UNCOMMON. Also the fuel servo itself has a finger filter

Regarding fuel savings, figure 1-1.5 gph however you need to be at an altitude and/or power setting where you are not in the Red zone. If you usually fly below 4-5K feet and rarely go on xcountry flights then FI doesn’t really benefit you. And like someone mentioned, you certainly don’t need to worry about icing.
 
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When I changed from standard to iridium plugs, I immediately noticed the ability to lean to a point where the engine noticeably looses power, with barely any roughness if at all, on the deep side of LOP. This was not possible previously.

Regarding icing, I now have flown > 1.2Kh in the last 4 years with my ship, standard Vans FAB, in rain, in icing conditions, in low and high humidity, all kind of temperatures, and never had any sign of carb icing :)
 
Safety/failure pts

Dan 57 said:
Flying different ships experience :)
- Injection factors, hi pressure fuel around, eventual need for fuel return lines, capricious engine starts when hot, several reports of single injector clogging.
Click to expand...

This plus no rats nest of fuel tubing and mutiple connections next to your left leg and engine compartment.
 
Because I was inverted...

I have come to realize that very few RV pilots choose to turn their airplanes upside down. But if you are inclined to do so, an RV equipped with fuel injection is definitely a plus.
 
RV equipped with fuel injection is definitely a plus
Click to expand...

absolutely, and even more so when matched with an inverted oil system.

My steed usually experiences some inverted moments on each flight, but all in more or less positive acceleration.

Carb or injection? For my use, the carb is a better choice. Nowadays most people will choose an injection, but the benefits are not as big as many think, the more so if one flies the average 50 hours a year.

And then there is FI or EFI. Also here one can argument with all the pros & cons. In the end it is each individual's decision, and being informed should help in making the right one :)
 
EFI

EFI offers the best of both worlds….the preciseness of FI, no chance of “carb ice”, along with ease of starting that carburetors have. On top of that, auto fuel can be ran without fear of vapor lock. Combining both EI and EFI offers even more advantages. Theres lots of information here on systems from SDS and EFII that my be worth a read, especially if you’re on the fence as far as which way to go.
 
Duncannon said:
I realize that a fuel injected engines can get better fuel burn than carbureted ones, and are a bit more expensive in both purchase-price and overhauling/rebuilding. I also heard that FI engines (particularly o-320/360 engines) tend to hit overhaul sooner, though a great variety of factors determine how long an engine lasts.

I like to think a pilot who will spend their average flight time at lower altitudes (maybe 5k feet) would be better off with a carbureted engine, vs. those who stay up at hypoxia altitudes? About how much fuel does FI save over carbureted, assuming the two engines (say a Lyc o360) are flown at the same altitude with identical power settings and leaned the same? And is there any truth about FI’s hitting overhaul sooner?
Click to expand...


Assuming we are comparing the carbed vs. injected version of the paralel valve engines only (angle valve engines are a whole different breed), one only has to look at the induction system (sump) design to see the issues. The updraft sump is a truly horrible piece of engineering from a performance standpoint. It features a very small plennum area relative to displacement, and the runner transitions are crude by even 1930's tractor standards. This torturous path from the inlet to the head is bad enough if there is only air to pass (as with fuel injection), but when you ask that same slug of air to navigate the twists and turns while trying to carry relatively heavy droplets of fuel (from the carb), its a miracle some cylinders get any fuel at all.

Yes, carbs "work". The engine will run and fly the airplane. Is each cylinder getting the same mixture? Not a chance in ****. With FI, the fuel is added at the cylinder and the amount is determined by the actual airflow this particular cylinder sees on this particular engine. This often crazy airflow mismatch from cylinder to cylinder will require sizing the injector nozzle to accomodate. Few FI systems with equal sized injectors work perfectly right from the get go, but even still, they do have the built in advantage of avoiding the pitfalls of a "wet flow" induction system and the pooling of fuel in stagnation areas and dropping out of suspension due to boundary layer influence.

All that said, FI provides a theoretical performance advantage, but the question remains if you are the type of operator that will exploit that advantage? If you are a Sunday morning pancake flyer who operates full rich below 5000 feet, then it probably does not make any difference.
 
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Toobuilder said:
Assuming we are comparing the carbed vs. injected version of the paralel valve engines only (angle valve engines are a whole different breed), one only has to look at the induction system (sump) design to see the issues. The updraft sump is a truly horrible piece of engineering from a performance standpoint. It features a very small plennum area relative to displacement, and the runner transitions are crude by even 1930's tractor standards. This torturous path from the inlet to the head is bad enough if there is only air to pass (as with fuel injection), but when you ask that same slug of air to navigate the twists and turns while trying to carry relatively heavy droplets of fuel (from the carb), its a miracle some cylinders get any fuel at all.

Yes, carbs "work". The engine will run and fly the airplane. Is each cylinder getting the same mixture? Not a chance in ****. With FI, the fuel is added at the cylinder and the amount is determined by the actual airflow this particular cylinder sees on this particular engine. This often crazy airflow mismatch from cylinder to cylinder will require sizing the injector nozzle to accommodate. Few FI systems with equal sized injectors work perfectly right from the get go, but even still, they do have the built in advantage of avoiding the pitfalls of a "wet flow" induction system and the pooling of fuel in stagnation areas and dropping out of suspension due to boundary layer influence.

All that said, FI provides a theoretical performance advantage, but the question remains if you are the type of operator that will exploit that advantage? If you are a Sunday morning pancake flyer who operates full rich below 5000 feet, then it probably does not make any difference.
Click to expand...

Mike, I agree with all you said above. The vertical induction sump/intake runners are pre WW II tractor technology. The tuned [equal length intake runners] sump/runner system used on the angle valve IO-360-Axx series engines and the parallel valve IO-360-M1B engine are worth a few extra horsepower as well. A little light reading on the benefits of tuned induction.

https://www.kitplanes.com/building-a-tunable-carbon-fiber-induction-plenum/

Tuned intake systems became the norm in auto engines 37 years ago!

Charlie
 
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FI is like driving a standard transmission. The experience requires more interaction with the engine rather than just push and go.

I've been flying my FI IO-360 RV-6 since 2001 without issue. Most missions are low and slow and my average fuel burn per fill-up is under 5 gal/hr.
 
I regularly fly between 14 and 18Kft to avoid the cumulus granitus, and have been flying mine up to 20.5Kft without any issue… but for the reduced power at these altitudes ;)
Yes, a carb is an antiquated method of delivering the mixture to each cylinder, but it is easy to operate, easy to install, and very reliable.
The pros and cons of each system are known, and I’ll most probably stay with the carb comes my replacement engine.
 
Carb technology introduced in the 1890ies.
FI technology introduced in the 1940ies.

Fuel injected is around 50 years better.:D
 
flowed heads

my carbed 0-360 has flowed heads from lyc thunderbolt with mags. can be leaned as far as I want with no roughness. my sweet spot is 155 kts at 5 gal/ hr.
 
Fuel Injected for sure

As mentioned before, once you master the hot start in your plane there's no problem.
 
Never-ending debate!

To the OP’s original question - I’ve never heard of a difference in overhaul times because of induction system choice, at least with our Lycoming horizontally-opposed direct drive engines.

In terms of everything else - I don’t make induction system choice a real driver, unless I am looking at aerobatics. We have four Lycoming-powered ships in our hangar - two with carbs, two with Injection. All can (and do) run LOP - the injected motors going leaner, but the power drops off so rapidly, how much leaner do you need to get? (The trick with the carb is to bring the throttle off the wide-open stop to get better mixing - you can get LOP, but just not as deep before it starts getting rough)

I like the smoothness of injection when I get lean. I like the fact that I can fix a carburetor in a cornfield if I have to. I like the fact that the fuel pumps are cheaper with the carb. I like that the Injection doesn’t care which way is up. I like that if it gets REALLY warm at a fuel stop in the middle of nowhere, I have less worry about hot starts with the carb - sure, I know how to hot-start fuel injected engines, and am pretty good at it … but I worry less with the carb.

Bottom line - pick what is appropriate for your application, not what everyone else says is best for theirs.

Paul
 
Maybe a little clarity from Paul regarding the LOP ops with a carb - its not how far you can go LOP, its how tight the GAMI spread is that has a major impact on power. Leaning to XX degrees and "still smooth" is all well and good, but is not really a data point. Its right up there with all the EI people that say it "...starts like a car, cold or hot..." or "...idles better...".

I can go very lean and still go smooth with EFI, but with the ability to instantly zero out the GAMI spread I can pick back up quite a bit of power compared to a very wide spread. In other words, theres a difference in speed between 8.5 GPH with zero GAMI and 8.5 when one cylinder is barely firing and another is slobbering rich.

If you angle the throttle "just so" or crack a bit of carb heat or are just plain lucky, you might have a tight GAMI. And sometimes you wont, no matter what you do. With FI you can almost always get a tight GAMI no matter how bad your induction is.

For many, this difference is inconsequential - for others it's a compelling capability differentiator. But the difference does exist.
 
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