Carb vs. f.i. cost -- Place to post excel worksheet files?
 

Is there any place we can post excel worksheet files so that we can link them on posts as we do with pictures? I'm working through the relative, long-term cost of fuel injection vs. carb and want to see if my assumptions are accurate. I'm trying to figure out the true cost of the higher initial price of fuel injection (including opportunity cost--cost of lost interest) relative to the interest that can be earned on the fuel savings from fuel injection.

I can't answer your spreadsheet question, but...

Realistic numbers are that people who fly LOP with FI burn between 1 and 2 gallons per hour less that carb'd planes flying right next to them. Some carbs can run this way also, but not most. If is it 1 gallon per hour, and one flies 100 cruise hours per year, that is $400 per year at today's fuel prices. At an "interest" rate of 10%, that covers $4000 initial investment. It really depends on how much you fly and what the differential cost is. Gas prices will continue to go up. Range is another variable to consider.

Sorry Alex-
I found a flaw in my logic that I'm working through... I'll try to post the spreadsheet when I've got it figured out. I reposted the gist of my original question above.
Steve

FI makes more sense
 

Hi Steve,

Given that the price differential for carbs and FI on a new engine is small now, the argument for a carb is really reduced. I have an O-320 in my -9A and am lucky enough to run it LOP. When I bought my engine the price differential was over $1000 - it seems to be less now.

The only argument remaining is that is easier to overhaul. If I were buying today - I'd put FI on for sure and dual EI to really take advantage of running lean.

As far as posting spreadsheets - might need to set up a free xdrive account and post it there with a link. Also you could paste the spreadsheet into MS Paint and save as a .jpg then post as a picture. Good luck!

Thanks Pete.

I definitely agree with you on a new engine. It doesn't seem to make sense to buy a carbed engine these days if you are buying new. However, I'm buying overhauled from Aerosport, and there the price differential is still about $2500 for the engine + another $600 for the fuel pump.

Assuming I flew 100 hours per year, saved 1.5 gph, earned 10% per year on my fuel savings, and lost 10% per year in opportunity costs (due to the initial outlay for f.i.), my spreadsheet suggests that it would take me about 7 years to recoup the money spent on fuel injection. Obviously a lot of variables, however, especially with fuel prices and future maintenance. That's what I'm trying to figure out with the spreadsheet.

Thanks again.

Dual EI
 

Steve,

Not to muddy the water, but I think many carb engines can be run LOP if they have dual EI with advance. It requires some futzing, but that becomes second nature after you do it for a bit. It might be the best of both worlds for you. It works well on my engine and well in a -9A where screaming top speed is not a top priority. Drop me a line if you want to have a phone call to discuss more.

Another member here and I are working on a movie (HD no less - get the popcorn!) to show how I run my O-320 LOP with a carb. If it looks to be useful, I'll post it. Nothing as exciting as what Groucho does(love his stuff), but it might save a few folks some $$.

According to my fuel flow instrumentation, fueling records, EGT's, and the Lycoming fuel flow tables, I regularly run about 0.5 - 0.8 gph LOP. I can't tell you how - I just lean it back until I don't like how it sounds, put it in a touch - and there she is....

Oh yeah, old fashioned carb and magnetos. Just my experience, and I'm not going to disagree with anyone that says they'd rather have Injection....

Paul

FI vs Carb
 

Paul,

Curious what your EGT temps are running in your LOP procedure? I do the same per Lycoming at OSH 07 and see 3 of 6 cylinders go LOP in DYNON EMS Lean Mode then it starts to run a little rough. Nice to have the new % of Power reading also to help with detonation issues. I can get down to 10-11 GPH which is within 1-2 GPH of IO-540 in LOP. Running 0-540 in RV10........calculated 7-12 years to pay for FI. Bigger reason to stay Carb for me was Ease of Start (hot or cold). Seems like you never know what engine start procedure will be from each FI engine. Starting procedures vary a lot ......some start well and others crank forever............flood.......sputter.......etc. This MAY be a pilot issue more than an engine issue also.......but a Carb engine is very consistent IF timing is set properly. My prop turns once and she fires.........watching FI planes on the field start makes my starter and battery hurt all the time.

JMHO
Dean 805HL

I really don't pay any attention to the "absolute value" of the EGT's, since that is more dependent on the distance that they are placed from the exhaust flange, and that's generally different for everybody. For the Val, it usually peaks in the 1390-1410 range. I just use the graph lines on my GRT EFIS/EIS display and watch the four temps come together and just knee over the peak.

My reasoning for the carb is similar to yours, but I have an open mind for the future - with more and more people going injected, and new systems coming on the market, there is always room for re-evaluation. For now, I like the maintenance and starting simplicity of the carb.

Paul

Thanks for all the replies. This is one of those big decisions that I had thought I had made once and for all a long time ago. I had kind of forgotten what having to make big decisions was like!:eek:

I should probably stick with my original carbed plan given the 6-7 years it would (conservatively) require for me to offset the f.i. cost. And if Pete is correct that running LOP is a reasonable possibility with carbs and a good engine monitor, that may be the best of both worlds for me. I will take you up on your offer to chat sometime, Pete. Thanks for the offer.