Fuel Injection Systems

I have started this thread for two reasons
To drag the information exchange about FI away from the discussion on the merits of the 0-340.

To find out as much as I can about different types of FI V Carb.

What I would like information on is real world differences in fuel consumption with Precision/Airflow and Fadec units V carburation. Costs of maintenance for the different systems. What are the starting difficulties and how are they overcome.

I am running an 0-320 in my RV 4 with the standard Marvel carb and at 2400 an using about 9USG/hour which equates to almost $100 for fuel at that RPM. Yes, 1 USG is about $10.50 in the UK. This will help me make a decision about converting to FI

Steve,
I use to own a Twin Comanche with injected IO-320s. We programmed for 8 gallons a side at 160 kts. which was WOT at about 2400 rpm and 7000 feet. this method was used for several thousand hours on this plane.
My RV-10 has the Airflow throttle body injection with the purge valve set-up. That makes it very easy to hot start.
If you really want to get as fuel efficient as possible ($10 per gallon will do that!) I would use the EFII ignition and fuel injection system. I'm installing the ignition system next month and will eventually install the fuel injection.

Hi Steve,
My -4 with IO-360 AIA, Bendix FI, and Slick mags, down low burns 8GPH ROP at 160knots and above 5000 feet I run it LOP at 6.5 to 7GPH at the same speed or more depending on altitude, 10k? would be more like 176 knots LOP at about 7.2GPH.

Hot starting, Throttle open ?? mixture closed, crank, when engine starts open mixture about half or more, works every time.

Cold starting, Throttle cracked, mixture open, pump hand wobble pump 6 times, put shoulder belts and head set on, close canopy, start engine, works every time.

Maintenance costs so far none, My engine was built in 1989, I overhauled it in 2006 with 900 hours on it, it was running good so we did nothing with the FI, just put it back on, the O/H now has 1200 hours on it. 2100 hours over the past 24 years with no problems. The engine O/H was only done because we found the crank case was broken between #2 and #4 cylinders.

Sounds like you could save a lot of $$ in fuel!

Steve,
If fuel consumption is your main goal then the only way FI will help is if you are going to run LOP. Having said that I will give you a real comparison from a flight today.
ROP 72% power, 59f, 150 kts, 4100 DA = 9.2 GPH
LOP 72% power, 59f, 150 kts, 4100 DA = 7.8 GPH

Same direction of flight. I just happened to be reading my data from a flight when I saw your post.
1.4 GPH difference.

Steve - 9GPH on a 320! Wow! I hope thats a typical average with lots of touch and goes and full rich acro.

I get 8.5 to 7.5 in the 200HP -8 depending on how high I want to go. This is based on many hours of cross country time. Preliminary flights in the Rocket seem to indicate I can get it under 11GPH... Pretty good considering it's 260HP.

Hot or cold starts with even the standard Bendix (no purge valve) are no problem once you understand what's going on. I've only flown standard Bendix for the last many years and can count on one hand the number of times I couldn't get it started on the first try.

Toobuilder said:

Steve - 9GPH on a 320! Wow! I hope thats a typical average with lots of touch and goes and full rich acro.

I get 8.5 to 7.5 in the 200HP -8 depending on how high I want to go. This is based on many hours of cross country time. Preliminary flights in the Rocket seem to indicate I can get it under 11GPH... Pretty good considering it's 260HP.
...

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Hardly. O-320 will see 13-14 or more gph at WOT near sea level. On the other end, LOP, ~50-55% power, I've seen 5.1 gph (IO-320, 152 kts, 15k ft). 9 gph at 75% power is where they run.

Steve, I understand you wanting to make a wise decision and asking the multiple layer question you have. Problem is you will get scattered answers with all sorts of data but mostly inconclusive for diagnosis as it will only ever be an 8/10 answer. Unless you know how to fill in some blanks in some they will be meaningless.

Of course if you knew how to fill in the voids, you would not be asking the question in the first place. This is not meant to be a rude statement, even though it could be taken that way.

Quite simply if you want any chance at running your engine with a BSFC of below 0.40 then the best way to do that is with a IO engine. The difference between a Precision Airmotive and a Airflow Performance is the post code it was made in. Don at Airflow provides great help here on VAF if that helps.

Sure if you get a carb engine with good distribution it may run almost as well, but it will never be quite as good. The laws of physics do not allow it.

Low Pass said:

Hardly. O-320 will see 13-14 or more gph at WOT near sea level. On the other end, LOP, ~50-55% power, I've seen 5.1 gph (IO-320, 152 kts, 15k ft). 9 gph at 75% power is where they run.

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Understood, and thats the meaning of my post. I do a lot of cross country work so I'm LOP. If Steve does a lot of the same kind of flying, then 9 GPH is way out of line. OTOH, if he's blasting around at low altitude and short hops, then 9 GPH is understandable.

And David's point is well taken. Just because I spend hours on end at 10,000 feet LOP does not make my fuel burn at all valid for someone who flies differently. Unless you plan on going high and LOP, then injection is not going to give you much economy over a carb.

Good information.

Hi Guys

Thanks for all the input so far.... this is exactly what I am looking for, especially the last post by Michael. In England ( a small country), most of our flying is short hops often below 3000 feet.

In my 4 from the midlands where I live I can be over the coast to the south in less than an hour. Over the Welsh coast in an hour and the same out to the east coast. Only venturing down to Cornwall or up to Scotland would put more than 3 hours on the clock. However, I do intend to fly to the south of France at some time.

I guess when I have broken the engine in and can run at lower RPM the burn will drop significantly?

Hi Steve,

I would second the opinion that says there is no practical difference in Airflow & Precision injection systems, that to achieve lower fuel consumption requires aggressive use of the red knob (and a good engine analyser), and that starting problems are myths once you learn an appropriate technique.

The cost to convert will be at least ?3K - and you may have to fit an O-360 air scoop to the cowl as the injector body is longer than the carb. I'm currently running a carb and regularly run at 25 lit/hr for around 135kt (RV-6, leaning as much as I can at all altitudes), a good electronic ignition helps a lot.

Because of the better fuel distribution from FI you should be able to see a drop of 2 or 3 lit/hr with FI (again leaned right off). Means there will be at least a 500hr payback time. I would go EI first and see how your engine responds.

Pete

Unless you plan on going high and LOP, then injection is not going to give you much economy over a carb.

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Steve and Michael, there is some crazy misbelief that you have to be high and low power to run LOP. This is simply not true.

Steve for low level work, I will climb to say 1000-2000' WOT, pull the RPM back and do a Big Mixture Pull, and it is really easy when you know a fuel flow to aim for, but a BMP parks you safely LOP at 80+% HP, so why not.

Yes you can run carb engines LOP, and the O-320 is a fine example, but generally speaking the IO version is better on both the Rich side and Lean side of peak.

I have posted this before, so many here will be sick of seeing it, but you might gain something from it.



As for starting problems or anything else??the IO system is better. I noticed Smokey Ray had some comments about swing starting in the outback?.not sure about that, I do not swing start in the city either

My colleagues at APS know a thing or two about engines, one here in Australia is the countries leading engine builder and engineer. 25+ years in the industry, and I can assure you my comments are in harmony with theirs. I am not a fan of consensus of opinion, sometimes it is applicable but here the facts are what they are. It is up to you armed with the info supplied.

Concensus is 99 people all holding the same opinion, until one person comes along with data that blows the hypothesis. Now you have a 1% majority rule .

RV10inOz said:

Steve and Michael, there is some crazy misbelief that you have to be high and low power to run LOP. This is simply not true...

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My point about being high was not as a "condition" for running LOP. I run LOP down low all the time. My point was that I do serious cross country work and I'm up high to gain the TAS benefit and cover some ground. And long cross country flying is where you are going to gain the most benefit (economy) from a fuel injected engine. "High and LOP" was a characterization of the mission and meant to contrast with Sunday morning breakfast runs or pattern work, that's all.

fuel savings

I am running an o-320 with 9:1 pistons. I run 10-12 LOP consistently with about a 6-8 degree CHT spread without carb heat. Any leaner and its gets rough. If I were to convert to FI and able to run 20 LOP with CHT's within a few degrees of each other, how much less fuel burn could I expect. For example if peak to 10 LOP is .5gph, would 10 LOP to 20 LOP also be .5gph or does the curve drop off significantly above 10 LOP.

You are proof like some I fly here, that the O320 is a nice LOP performer. It is a great little engine.

Notwithstanding and I have also a bit of experience with an IO320??it is better overall, because it is easier to operate that way and smoother, because the spread was far better than the 0.5GPH.

There is no gain in running excessively LOP, you actually become less efficient eventually. Refer to the 1/BSFC curve below, courtesy of Adv Pilot Seminars

Hi Steve..

Echoing the above, Alister and I have an O-360 and IO-360 between us, and have moved from Mags to single P-Mags to Dual P-Mags. As you say, UK flying tends to be lower level, say 2000'. Summary:

1. LOP is (far) easier with the IO. However, Alister manages it with a Carb, but harder work / more limiting on settings.
2. It is, IMHO, essential to have 4x EGT and pref 4x CHT
3. The biggest leap in ease of LOP is Electronic Ignition. I do not think you need a "good" EI, I would suggest they are all good and essentially do the same.
4. 2x P-Mag is a little better than 1x P-Mag
5. Maybe due practice, I find LOP easier at the lower levels.
6. 150KTAS on 25L/hr [6.6USG] is standard (RV-8). I would hope an RV-4 would be better?

David's graph sums it up - you only want to be just LOP. With Mags it is quite hard to go far LOP, I found it got rough. With EI it will run fine very LOP - it just goes slowly

LOP

Hi ALL

Again thanks for the replies. I actually run a Lightspeed ignition and one mag. I have EGT/CHT on all 4 cylinders.

Having read all these replies and considered my current flying in the 4 I doubt I really have a problem. As I am breaking in the engine and have to keep the power up and temperatures down I have been reluctant to lean aggressively.
When I have leaned it it has been rich of peak again to keep temps down.

Now, all my T's and P's have been well in the green, my home built plenum is working fine. So, I will try some L of P operations and note the temps and see what fuel burn I get then.

If you are breaking in, it is better to do it LOP.

1500' WOT, 2500-2700 RPM and 80dF LOP.

This gives you MUCH BETTER breakneck by better BMEP, with lower overall ICP and CHT.

Exactly opposite to popular myth.

Hi Steve,
I ditto what Andy said. I have an O-320 w/dual P-mags and a Dynon D-180 for engine monitoring. For years I heard all sorts of horror stories about running LOP and was reluctant to even try it.

I believe I've read everything possible about LOP operations. I saw and read David "Shot Duck" Brown's chart and decided to try the BMP and see what happens. Well, I was favorably rewarded. For a carburetor, my spread is pretty good. Generally, running somewhere from 5* to a max 20* LOP I can get 130 +/- knots at 5.2 to 5.5 gph. (Any more than 20* its rough.) I was/am shocked at the numbers and didn't believe them at first. But I do this on a regular basis now. If I'm up just smashing bugs or not in a hurry, well I now use fuel flow for my power management plan. It saves me a good $10.00 to $14.00/hr.

A good buddy of mine has a Flight Design CLT w/Rotax 912 and does about the same, maybe burning a little more. That's a wonderful comparison I'm thinking.

I'd love to have Fuel Injection; but running LOP regardless has been a pleasant surprise to me. So thanks to David and others for getting me to give it a try. Count me in the LOP camp now.

Cheers,

Saving fuel

Hi Steve
I have an ECI IO 375 with Precision FI, dual Slick mags, and a coarse, fixed pitch prop on my 7A with 120 hours TTSN. This is my first injected engine, and until I learned how to start it (my procedure and results are similar to Russ's description), I considered swapping it for a carburetor. I get the same consumption and performance numbers as Russ (although I have to confess my speeds are in MPH, not knots). My flying is a mixture of 3-4 hour cross country legs around 10,000', and short hops to neighboring strips.

Even though I (now) like my FI engine, and will get another if the opportunity arises, I would not change a carb to FI on a flying aircraft as the cost and time to change two fuel pumps, fuel line plumbing, intake manifold, cowl, and possibly throttle, mixture, and exhaust will suck up time and money better spent on flying.

I am also very conscious of fuel costs, and recommend the following to maximize the efficiency of these excellent planes:
-Slow Down. Most RV'ers cruise well above the best range power setting. I typically set power at 50% for long distance and local flights following climb or takeoff. According to my EFIS, my economy tops out at 30 mpg at about 40% LOP, however the plane feels better at a 50% power setting which yields 28 mpg. (avoid continuous low power settings until your engine is completely broke in) My hanger neighbor has a Rocket, and jokingly complained it is hard to build time on the machine because it gets everywhere so darn quick!

-Lean aggressively by ear at low power settings. Your engine does not care about altitude, only manifold pressure. For short hops I take off with full power ROP, reduce throttle to 60% power at 1000', lean until the onset of roughness, then enrich until roughness goes away. This results in happy engine monitor readings, and about 50% power at 7.0 gph. I can fine tune the power down to about 6 gph if I care to fly as slow as a Cessna 182.

-Try running premium automotive fuel if possible in your circumstances. I am a believer in mogas, and would run some even if it were the same price as avgas. With my compression ratio I run straight avgas in one tank for take off, and also to manage the risk of vapor locking I experience on mogas in warm weather with just the engine driven fuel pump running. In my area, mogas runs about 2/3 the cost of 100LL, and it is better for spark plugs, valve train, and the environment.

-Consider one of the electronic ignitions which save fuel by advancing ignition timing at low power settings, and also by providing a better spark which allows your engine to run leaner before the onset of roughness. I researched 5 good systems and spoke to owners to determine the system I like best, and have this as my next planned upgrade