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Fuel Injection - What are Your Thoughts ?

Fuel Injection

Fuel injection on a four cylinder Lycoming can result in as much as 1 gallon/hour less fuel consumption than a carburetor. Exactly how much depends on the intake system and carb.
Fuel distribution is much better on injected engine allowing better leaning and loan of peak operation. Many carbs do not permit lean of peak, some do.
 
No carb ice.

When I built my engine (2007) at a Superior build school, the price differential was only a few hundred dollars, so well worth the cost at that time. Assuming I'm saving 1/2 gallon/hour by running LOP, so far I've saved 350 gallons x $3.00/gallon (very conservative fuel cost estimate) or north of $1000. YMMV.

Greg
 
I have flown several carb'ed RVs and the #1 issue I always see is un-even fuel distribution as displayed by a 4 point CHT / EGT indication system, especially at partial throttle. Usually at W/O throttle the CHT/ EGT split is fairly even, anything less than that may cause a "front / rear" split. The 1/2 cylinders can run as much 300 deg cooler EGT than the 3/4 cylinders, which run hot anyway, at certain throttle plate positions. One has to wonder how healthy that is for the engine and how much power is being made in such a condition. The issue of O-360 sumps on O-320 engines and the corresponding lip just above the carb may also contribute to the un-even fuel distribution. With a carb, the fuel is introduced at one central point, the carb. Irregularities in the induction system can result in un-even flow. With F/I, the fuel is injected directly at the cylinder, resulting in very consistent CHT/EGT and the ability to run LOP. I have been very happy with the AFP FM series of F/I units. Once you understand the purge valve, hot starts are simple and reliable. No carb ice issues and the ability to pull sustained negative G are also in favor of the F/I system. Initial build cost and simplicity of installation seem to favor the Carb, but the long term fuel efficiency and safety (carb ice) seem to favor the F/I system.
 
I opted for Don Rivera's Airflow Performance FM-150, my first ever fuel injected Lycoming. I'm not having any starting problems commonly attributed to mechanical fuel injected aircraft, and the way it operates when running is better in every regard.
I did operate a Mazda Rotary engine in my RV-8 for a while, the automotive style electronic injection has a lot going for it. Simple Digital Systems, and EFII are 2 examples.
My son Peter installed a Rotec TBI in his RV-4 so he could fly upside down. It's often called an injector, but I call it a Diaphram Demand carb. It runs very well, and in our case has very even fuel distribution.
I don't reject any of these fuel systems, even the Marvel carb has benefits.
But I am happy with the FM-150 and will stick with it.
 
WA85 said:
I have flown several carb'ed RVs and the #1 issue I always see is un-even fuel distribution as displayed by a 4 point CHT / EGT indication system, especially at partial throttle. Usually at W/O throttle the CHT/ EGT split is fairly even, anything less than that may cause a "front / rear" split. The 1/2 cylinders can run as much 300 deg cooler EGT than the 3/4 cylinders, which run hot anyway, at certain throttle plate positions. One has to wonder how healthy that is for the engine and how much power is being made in such a condition. The issue of O-360 sumps on O-320 engines and the corresponding lip just above the carb may also contribute to the un-even fuel distribution. With a carb, the fuel is introduced at one central point, the carb. Irregularities in the induction system can result in un-even flow. With F/I, the fuel is injected directly at the cylinder, resulting in very consistent CHT/EGT and the ability to run LOP. I have been very happy with the AFP FM series of F/I units. Once you understand the purge valve, hot starts are simple and reliable. No carb ice issues and the ability to pull sustained negative G are also in favor of the F/I system. Initial build cost and simplicity of installation seem to favor the Carb, but the long term fuel efficiency and safety (carb ice) seem to favor the F/I system.
Click to expand...

This issue above can be addressed relatively simply, as I did with a tapered insert fabricated after the fact by manufacturer and installed by me later, as others have done. Why the engine builders don't do this out of the gates, or fix this issue entirely, is beyond me...

Back to the question; the carb is simple. Which is what I like most about it. Sure, I would like to have FI, but thinking through that installation, plumbing, electrical etc. was time/money I chose to avoid. Still like the simplicity of the carb. Fires up every time, no primer installed either.
 
Aerobatics?

FI runs in any orientation. A carbureted engine will quit under zero or negative G operation. This makes the choice simple for me. YMMV.
 
I elected for Fuel Injection from the get-go when ordering my engine. It was one of the best decisions I made (... right along with the LSEI ignition on the R. side.) I would not change that decision under any circumstance. There's nothing complicated about the Bendix-style injection, and as others said, it will let you run LOP and save significant fuel over the life of the aircraft. In my case, the difference between running 50 degrees LOP and 75 degrees ROP is 20% fuel savings. Nothing to sneeze at. :) The FI pays for itself pretty quickly.
 
Dbro172 said:
... Sure, I would like to have FI, but thinking through that installation, plumbing, electrical etc. was time/money I chose to avoid. Still like the simplicity of the carb. Fires up every time, no primer installed either.
Click to expand...

There's nothing wrong with a carb if it fits the mission of the aircraft, but I'm trying to figure out your comment about the FI system being more complex? Same fuel valve, same number of fuel lines to the engine, same filter, same number of electric boost pumps (1). To what are you attributing the extra time?
 
If using an AFP FM series F/I unit

If using the AFP FM series F/I with purge valve, Note - During my RV-8 build, the only items I found to be a little more complicated to install for my AFP FM-100 were the purge valve control cable and return plumbing, alternate air control cable and the mixture and throttle controls required custom built cable brackets. Much of this was complicated by the RV-8s gear towers and me attempting to run all my cables through the LH side of the firewall. I wanted my baggage area free of cables. Three control cables and two fuel lines running through the LH side of the firewall. Prop control would be a another. The wide body RVs probably don't have these issues. A carb installation still requires the same basic set of controls (throttle, mixture, carb heat control), so the AFP purge valve system is the only item that adds to the complexity of the build. Vans does a great job in the FWF kit of supporting a carb installation with drawings and the cable attach bracket. I made the decision to go with an AFP FM-100 fairly late in the build process and I had to add some new firewall penetrations that I hadn't planned on, but it worked out OK. The purge valve return line plumbing into the fuel valve took a bit of thinking and cussing, but there are plenty of VAF discussions how its been done. I used a banjo fitting to feed return fuel to the RH tank. If choosing between an AFP FM series F/I system or a carb, my advice would be to decide early so that when build the fuselage, it will be easier to install the purge return line and plumbing, especially on the RV-8. I could not be happier with the AFP FM-100 and the support Don Riveria has provided.
 
+1 for fuel injection. Saves money and pays for itself in no time if you fly it right.

Besides, when was the last time you saw a new car with a carb? 'nuf said!
 
fuel injection

+1 for fuel injection and electronic ignition.

The carbureted O540 on my 182rg would stumble and spit any time I would get close to a lean mixture.
My O360 in the RV7A with PMAG on the right is smooth while I lean until the power just fades away. At altitude I control rpm with the mixture. The throttle is almost always full in.

I don't mind the mixture knob. Most of the time the power is at a given level and I like having control. If we had a good electronic injection that had backup like the PMAG, I might consider it on a new engine.
 
NDrv8r said:
I don't mind the mixture knob. Most of the time the power is at a given level and I like having control. If we had a good electronic injection that had backup like the PMAG, I might consider it on a new engine.
Click to expand...

Why not look at the current EFII system? Just because the backup generator would be a separate item instead of physically built into the unit is no reason to disregard it. Plus, in adding that separate backup generator/battery, you gain redundant power for any EFIS you might install as well. You're going to need it for the fuel pumps anyway...

My thought on the mixture knob (which probably won't be popular round these parts) is that it's a distraction from flying the airplane. The "benefits" of manually-controlled mixture over a decent automatic system are vastly overstated, and do not outweigh the large potential for the mixture knob actuator to improperly actuate the knob (with consequences ranging from burning too much fuel, to early TBO or a failure from cumulative damage, to an engine failure in the very near term).
 
rmartingt said:
Why not look at the current EFII system? Just because the backup generator would be a separate item instead of physically built into the unit is no reason to disregard it. Plus, in adding that separate backup generator/battery, you gain redundant power for any EFIS you might install as well. You're going to need it for the fuel pumps anyway...

My thought on the mixture knob (which probably won't be popular round these parts) is that it's a distraction from flying the airplane. The "benefits" of manually-controlled mixture over a decent automatic system are vastly overstated, and do not outweigh the large potential for the mixture knob actuator to improperly actuate the knob (with consequences ranging from burning too much fuel, to early TBO or a failure from cumulative damage, to an engine failure in the very near term).
Click to expand...

The mixture control has been part of flying since aviation was invented just like a tail wheel, rudder, elevator or aileron.
Are you suggesting the typical pilot is dumbing down, like mentally incapable of managing a mixture knob?
I've flown with EFII with the Sub H6, it was boring. :)
 
David-aviator said:
The mixture control has been part of flying since aviation was invented just like a tail wheel, rudder, elevator or aileron.
Click to expand...
The mixture knob was "part of flying" for so long not because it's the ideal way to do things or because it's impossible to fly without one, but rather because it was the best way of achieving good engine operation and fuel economy at the time it was implemented. We now have better ways of doing things. Manually babysitting the engine doesn't make one a pilot; it makes one a flight engineer.

Are you suggesting the typical pilot is dumbing down, like mentally incapable of managing a mixture knob?
Click to expand...
No, I'm suggesting that every second the pilot is heads-down fiddling with the mixture knob is one second not spent scanning for traffic, maintaining situational awareness, navigating, etc.; and every mental clock cycle devoted to babysitting the engine is one less devoted to more important tasks. Once properly set up, an automatic system like EFII won't forget to adjust the mixture, won't forget carb heat, and won't improperly set the engine due to inattention or miseducation. How many engines get ruined, how many airplanes crash, because the pilot forgot the carb heat or mis-leaned the engine?

I've flown with EFII with the Sub H6, it was boring. :)
Click to expand...
I want boring; that's why I've decided to go with EFII. No magic black art to starting, just turn things on and crank. No fiddling with a mixture knob every time I change the power; it does that itself. No carb heat to worry about or forget to apply. More time to look out the canopy and enjoy the view :) I'll spend the extra time and complexity and fiddle-time once, up front, rather than keeping it "simple" and making the operation more complex on every flight.
 
FI decision factors?

In the moderately distant future, I'm going to start comparing FI systems to determine which one I'll select for my IFR-capable, cross-country focused RV-10. Since I'm brand new to this engine-thing, what factors should I consider?

The PMAG route certainly looks attractive but the 6cyl version is a brand-new beast. It probably won't be by the time I have to purchase but I want to consider all my options carefully.

Your input on decision factors would be appreciated. I've searched but couldn't find anything with my limited search skills...

Thanks!
 
I've been flying my IO-360 FI RV6 since 2001 and thoroughly enjoy flying with FI. Flying LOP at 5 gph is a leisurely way to enjoy the local scenery. Recently I replace a magneto and Lightspeed with two P-Mags. On my first flight I leaned to 4.4 gph. I dub the setting Rotax mode.
 
For me FI is the only way to go. Over the years it seems to me that vibration is hard on carbs. In old carbs the shafts and moving parts always become ill fitting.
You do not have to worry about carb ice and the fuel distribution is much better.
A carb is ok on my lawn mower but I do not want one on my plane.
 
hoyden said:
I've been flying my IO-360 FI RV6 since 2001 and thoroughly enjoy flying with FI. Flying LOP at 5 gph is a leisurely way to enjoy the local scenery. Recently I replace a magneto and Lightspeed with two P-Mags. On my first flight I leaned to 4.4 gph. I dub the setting Rotax mode.
Click to expand...
I have a carb on my O-360 with dual P-mags and can easily fly LoP.

My typical flight is at 8500 to 11500 feet, 150 to 155 TAS and less than 7 GPH LoP.

Here is a picture of an extreme non-stop flight from Houston, TX to Greenville, SC.
20140502_154724.jpg


I have one photo showing me running 141 KTAS while burning 3.1 GPH LOP.

It is the dual P-mags that make this happen.

With 650 hours on my FP carbureted -9, I would put the money into fuel injection before I bought a CS prop.
 
(Dumb Question Alert)

Do the fuel injection engines NOT have the lower cowl scoop? I like the scoop and WANT the scoop!

I see -8's and -7's without the air intake scoop on the bottom cowl, and I always thought those were the fuel injected ones. Am I correct? :eek:
 
Both

Fuel injection servos can be mounted vertically (with the lower cowl scoop) or horizontally (with the duct or snorkel inside the cowling with the filter in the pilot's side cooling air inlet) depending on which sump you specify.
 
terrye said:
Fuel injection servos can be mounted vertically (with the lower cowl scoop) or horizontally (with the duct or snorkel inside the cowling with the filter in the pilot's side cooling air inlet) depending on which sump you specify.
Click to expand...

I have the horizontal servo and will be using the scoop for combustion air.

I like the scoop too.
 
When I ordered my finish kit (same time as fuse kit) I bought the cowl with the scoop as I planned on using the carb because I wanted simple and inexpensive. Now that I've read through this thread, I'm seriously thinking of going FI.

At least I can still use the same cowl! ;)
 
s10sakota said:
When I ordered my finish kit (same time as fuse kit) I bought the cowl with the scoop as I planned on using the carb because I wanted simple and inexpensive. Now that I've read through this thread, I'm seriously thinking of going FI.
At least I can still use the same cowl! ;)
Click to expand...

Don't let these guys "scare" you into changing your life. While FI is great, a good carb system works great also. RVs and Lycomings have been flying for many, many years with carburetors. Mine has been flying since 1993 and my CHT run very evenly. I can run LOP. Lycomings and particularly RVs with Lycomings are not commonly prone to carb ice.
If you want to change over to FI, that's fine. But do a little more research before you make that big investment.
As you say, carbs are simple and inexpensive and run with very low fuel pressure.
 
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FI

One more reason to consider FI
FI is your friend if you plan on running mogas.
You can certainly run mogas with a carbed engine but having your fuel system pressurized to 25 psi (typ for FI) lowers the likely hood of developing vapor lock in your fuel system.
AFPs FI is approved for all types of gasoline including pure ethanol.
 
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