R

RScott

Well Known Member
I'm building a 9A and some folks with more experience than I have are urging me to go with FI rather than a carb.

I will probably go with an Aerosport engine. FI costs $1,000 more from them. But then there is also the high pressure fuel pump, which I understand runs about $750. And a high pressure filter at some unknown cost. And what else?

How much more is it likely to cost me to go with FI? Will I get it back in resale value? How much fuel will it save? I have heard claims of 1/2 gph and others who should know say a lot less than that. Any other pros, cons other than no carb ice with FI?

Thanks.

Richard Scott
RV-9A Wings almost done, p/u QB fuselage tomorrow!
 
If you buy your engine from AeroSport Power, and if you go with Airflow Performance fuel injection, you will most likely get the AFP pump & filter kit WITH your engine. At least that's what happened to me when I bought my IO-360 from AeroSport. I had already coughed up the bucks for the AFP pump/filter/install kit from Van's, so when I got the dupe pump/filter from AeroSport Power I just sold it to another builder.

Anyway, something to keep in mind...that the cost of FI will probably include the cost of pump+filter...if you go with AFP injection (which I sure would!).
 
I went with a Carb on my -9A

I built an O-320 from an ECi kit and opted for a carb. It is simple, cheap and I can overhaul it myself. I have dual electronic ignition as well and have done a lot of experimenting with LOP/ROP. I have certain points where my mixture distribution is very even (4 EGT Peaks within .1GPH) and I can run LOP. One is a low power setting 16in/2200 @ 3500 ft where I can fly around on 3.8GPH at 125-130 mph in my RV-9A. The other useful one is a high cruise. WOT/2300 rpm at 8000ft. Here by using carb heat and cracking the throttle, I can balance the EGT peaks to within .1-.2GPH. Here the RV-9A will do 170-175 mph TAS on 5.9-6.1 GPH

For the ultimate in saving gas, FI is the way to go. You can control the fuel flows very easily. The system is more complex, but not overly so.

Pros and cons to both systems. If I build again, it would be a toss up. I'd probably go FI to try something different and to go after better fuel economy.

I do think Elect Ign is the key to frugal engine operations. YMMV
 
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Don't worry what everyone else has

In the past it was more of a toss up, but fuel prices have gone down and FI systems have actually got cheaper relative to Carbs which have not dropped in price, keeping up with inflation. My guess is competition of FI systems between Bendix/Precision, AFP and now ECI keeps price competitive.

Carbs are a single source Marvel Schibler (now Precision Airmotive Corp). Also rumor has it (I think there is some truth to it) the long run of Carbs and lawsuit liability with so many Carbs in service, today's price has to cover and absorb the liability. AFP's and ECI's have not been around or sued enough.

The big selling point of the FI is fuel economy, specifically in cruise. With gas prices that is even more valuable. In the past FI would not pay for its self very fast when gas was cheap, but now saving 0.50 gal an hour or what ever adds up. espcially at +$4.00/gal

HOWEVER, you have to be a clever operator and move that red knob very judicially to get max advantage out of FI. If you are lazy and not attentive to power and mixture optimization (minimization of fuel flow) it does not matter what fuel delivery system you have, you will burn more fuel than your hanger neighbor with a carb, who watches mixture and power like a hawk.

However if you can dial-in the FI (even flow out of injectors), using the FI system to its most advantageous AND you cruise a lot, you can save $$$$. However cost, build time will be higher initially, and even maintenance may be higher initially, but with the fuel prices pay back time will be much shorter. Depending on how you fly that might be 5 years or 20 years?

Don't worry about resale, but FI is thought to be a nice selling point or feature. I think HP and constant speed prop are higher up on the want to have list.

Don't worry what everyone else has. A 150HP, Carb, fixed wood prop RV is a rocket and fun fun fun. Fuel Injection does not make the smile much wider. The economy aspect will take many years of flying to pay for itself in gas, but still its a good thing and gets better with worse fuel prices. With that said if buying a new engine today I'd buy FI just because it CAN meter fuel a little more precisely.

Bottom line if buying a NEW engine get FI, because the price is not much greater. If buying a used engine with a Carb, stick with that. Also don't go broke building you plane. There are things you can add later, like going from fixed to C/S prop. However FI is something you want, you should try to go with from the get go. Converting is expensive and selling a used carb is hit and miss.
 
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Talk to Bart

I bought my 0-320D1A from Bart and he talked me OUT of FI. It was a while ago but if I remember the gist of the conversation he seemed to think that if you weren't planning to do a lot of flying around upside down he didn't think it was worth it. I wouldn't hestiate to talk to him about it. In my experience he won't try to push an option on you that you don't need.

Having said all that If I did it again I would seriously consider FI due to the increased economy and the ability to obtain even temperatures between cylinders.

Doug
RV6
 
Carb.

With a clean sheet I was planning FI but then switched to a carb., for a variety of reasons. I found an article by Stein Bruch quite helpful. There is a link to it here.

Scroll down to you come to the Note added 4/10/06. There is a link there.
 
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With an FI you no longer have the 1.2"-1.5" MAP drop across the venturi, so your manifold pressure at full throttle will be almost static + dynamic. That will give about 3% more power and 1% more speed. Carbs are simpler, FIs more complex! An even charge-distribution isn't a guarantee, since all cylinders may not get the same amount of air. That's why there are the GAMI injectors! I recently had two people try out my original two-blade prop on their planes, one an RV-6 and the other an RV-9A. Nothing outstanding has so far shown up, but one thing that did show up is that the TAS calculated from IAS was 9-11 mph greater than the TAS from GPS. One of them used the pop-rivet static port, and the other had the Cessna flat-disc style. Another RV-9 pilot who was there said that his was doing the same, about 10 mph high on TAS. Here's the way to fix this. Start adding layers of Scotch tape right behind the static hole to increase the static pressure to lower IAS, or add layers in front of the hole to reduce static pressure to raise the IAS. Use the two-way GPS runs into and with the forecast winds to obtain avg. GS/TAS. If you are venting static to the cabin, then IAS-TAS are just whimsical numbers with little association to reality, but if they make you feel good, well, what the H**l!
 
elippse said:
With an FI you no longer have the 1.2"-1.5" MAP drop across the venturi, so your manifold pressure at full throttle will be almost static + dynamic. That will give about 3% more power and 1% more speed.
Click to expand...
Where can I find DATA that supports the above statement? (some or all of it)

If there is hard factual data to support this statement, I will convert to FI.

An increase in MAP would mean more horsepower. Informaiton published by Lycoming shows no difference in horsepower output of a fuel injected engine and one that has a carb.

I have 1,988 hobbs hours on flying O-320 RV-6. I have September / October 2007 scheduled for engine work and can put my carb overhaul money toward FI.
 
RV6_flyer said:
Where can I find DATA that supports the above statement? (some or all of it)

If there is hard factual data to support this statement, I will convert to FI.

An increase in MAP would mean more horsepower. Informaiton published by Lycoming shows no difference in horsepower output of a fuel injected engine and one that has a carb.

I have 1,988 hobbs hours on flying O-320 RV-6. I have September / October 2007 scheduled for engine work and can put my carb overhaul money toward FI.
Click to expand...
Lycoming spec. 2213-C, O-320B, curve 11260A, abs. dry manifold pressure, in Hg. at sea level, 2700 rpm, 28.3". Spec 2283-G, O-320D, curve 13381, 28.7". Spec. 2499-G, O235-L, curve 13265-B, 28.4". I know since someone is flying with the prototype EFI I designed and that's what he's experiencing; his MAP is within 0.1"-0.2" of static pressure on run up. Check your MAP at full-throttle run-up against the MAP with the engine off.
 
Numbers....

RV6_flyer said:
Where can I find DATA that supports the above statement? (some or all of it)

If there is hard factual data to support this statement, I will convert to FI.

An increase in MAP would mean more horsepower. Informaiton published by Lycoming shows no difference in horsepower output of a fuel injected engine and one that has a carb.
....
Click to expand...

Gary... Don at Airflow had some measurements in this thread...

http://www.vansairforce.com/community/showthread.php?t=11659

Start at post #10

gil in Tucson
 
az_gila said:
Gary... Don at Airflow had some measurements in this thread...

http://www.vansairforce.com/community/showthread.php?t=11659

Start at post #10

gil in Tucson
Click to expand...
Thanks Gil.

Your's, Don's, and George's numbers in that thread work out. Elippse's numbers in this thread do not make sense.

Lycoming Curve 10156 and Curve 9541-C show no more than 0.5 " - Hg MAP delta at WOT between 2100 and 2700 RPM.

Originally Posted by elippse
"With an FI you no longer have the 1.2"-1.5" MAP drop across the venturi, so your manifold pressure at full throttle will be almost static + dynamic."

The above quote is almost double what Don, George, and you came up with in the other post. I am talking about 320 / 360 Lycomings that are recommended by Van and I assume that Elippse is also.

Posted by elippse
"I know since someone is flying with the prototype EFI I designed and that's what he's experiencing; his MAP is within 0.1"-0.2" of static pressure on run up. Check your MAP at full-throttle run-up against the MAP with the engine off."

Now the 0.1 to 0.2" delta in the follow up post is believable. If there is a 1.2" to 1.5" MAP delta then I need more facts. What engine model number? N number of the aircraft? Test Pilot flying the aircraft? How can I contact the test pilot? How can I get a copy of the RAW data? If it is a one of a kind that is not available to EVERYONE to install in the RV, then the data is pretty much useless. Anyone can sprinkle "pixly dust" on anything and come up with a magic what ever it is they want.
 
I just ran some full-throttle tests on my Lancair 235 with an O-235L2C with a Marvel-Shebler carb. Engine-off MAP - 29.8"; Engine full-throttle 2220 rpm, MAP - 28.5". 1.3" drop!
 
elippse said:
I just ran some full-throttle tests on my Lancair 235 with an O-235L2C with a Marvel-Shebler carb. Engine-off MAP - 29.8"; Engine full-throttle 2220 rpm, MAP - 28.5". 1.3" drop!
Click to expand...


Exactly as expected.
 
Thanks, Walter! 'Don't know where those lower drop figures came from, but anyone selecting a new high-performance carb for a car knows you have to select the carb drop; they come in several available drops and it affects the air-flow calcs.
 
Another Data Point

I gathered quite a bit of data on the mp drop issue in carbed RVs about a year ago with the help of folks on this site and the Matronics site. I would suspect some is still in the archives. I did this to compare my James induction system with Vans FAB (filtered air box) due to some concerns over induction turbulance.

To do some comparisons I collected data on seven RV 6/7/9s that had fp props, stock carbed 0320/0360s, and stock Vans Filtered air boxes (FAB). All were tested by checking the mp gauge (all but two had digital mp guages) before engine start and at full throttle right at lift off -- which happened to be close to 2200 rpms in all but one case.

Average mp drop with the stock carb and the FAB from Van was .8"mp. I had been told that anything below 1" was pretty good . Additionally, at speed the Vans FAB provides some ram.

BTW, my problem was the stock James carb box which Will James has since redesigned. Since the redesign was going to delay my flying I made my own from fg. Mine is barely larger in inside diameter than the carb throat and has no sharp corners as well as gentle ramps to move the air from horizontal to vertical into the carb. My mp drop is .6" consistently and with the James cowl I am also getting a nice ram effect at altitude.

Cheers,

db
 
If you have the $$, go FI. I've got a carbureted 160-hp O-320. About the only good thing about the carb arrgt is the ease of starting. Shoot a little prime and it'll light and start running at starter rpm on the 3-4 blade every time. My FI friends always end up snorting and sputtering at startup. And that's when cold.

But all the items mentioned above about efficiency, ability lean more aggresively, run smoother, etc. all make FI more desirable to me.

there's 2 cents worth...
 
It is all in having a system...

Low Pass said:
If you have the $$, go FI. I've got a carbureted 160-hp O-320. About the only good thing about the carb arrgt is the ease of starting. Shoot a little prime and it'll light and start running at starter rpm on the 3-4 blade every time. My FI friends always end up snorting and sputtering at startup. And that's when cold.

But all the items mentioned above about efficiency, ability lean more aggresively, run smoother, etc. all make FI more desirable to me.

there's 2 cents worth...
Click to expand...

When mine is cold, it will start in 2-3 blades (the first guy never has a chance :p ). When hot I have cranked it up to 20-30 blades. I have not got a good procedure for hot starts yet.

Here is what I do cold:
Mixture and Throttle in. Fuel pump On. Master switch On. Wait 5 seconds.
Fuel pump Off. Mixture Off (out). Throttle cracked (almost off). Engage starter and when the engine catches, move Mixture in for smooth operation. On my Mixture this is usually about half in.

YMMV

For hot starts this is the procedure that I use, but need to improve:
Mixture out Throttle cracked. Master switch On. Engage starter and when the engine catches, move the Mixture in.

I think that my problem with the hot starts is the fuel line has vapor in it.
If I turn on the fuel pump to clear the vapor won't I end up with the engine being flooded?
If I ever get this figured out I will share my findings.

Kent
 
It's beauty

If you are into hot rod's and auto racing, carbs are still popular, even with EFI. It's beauty is simplicity.
 
Simplicity...

My carbed 320 generally starts like a car. I don't have a primer. I have a mark on the throttle quadrant for 1k rpm. I hit the key, give it a shot of throttle and pull the throttle back to the mark. It lights right off and warms up at 1k. No muss, no fuss.

I agree though that if money is no object, go for the fancy stuff. But, you might be surprised at how happy you can be with a simple arrangement....

John
 
Hot start -->

Mixture ICO, throttle 1/2.

Upon firing, advance mixture to 2/3 and retard throttle to idle. With a little practice you can make this happen so well you'll impress your friends with a carb who are normally idling and waiting for you engine to start.
 
FI it is

My requirements are inverted, overall simplicity and auto fuel. I originally planned for an Ellison TBI which I thought would fit these requirements perfectly. However, it turns out that the ETBI does not like auto fuel, it will desintegrate the rubber. I asked ellison if they could change the rubber to another material anytime in the future, but thy answered that it would not be cost effective for them (somehow I find that a strange answer for a small company like Ellison regarding things like simple rubber gaskets, but??).

This leaves me with FI, and also narrow down my engine options to Superior or Mattituck (that I know of), due to issues about warranties with auto fuel.

So much for my requirements for simplicity :) On the positive side, carb ice is one problem I don't have to think about anymore. Overall, a bit more complex mechanically, but a bit less complex operationally + greatly added safety margin.

Regarding fuel economy of carb vs FI I don't see that as an issue at all. The use of auto fuel will roughfly cut my fuel cost to 50-60% anyway with today's prices, and if and when that changes, I can allways use the cheapest alternative.
 
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