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LOP with carb

 
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kbob(at)cox.net
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PostPosted: Tue Jun 13, 2006 4:20 am    Post subject: LOP with carb Reply with quote
I have to throw in my 2 cents on this one. My initial thought was to run a
FI system, but the simplicity & budget of the carb won out.

The bonus was the economy is better than expected. The engine is an O-320 w/
9.2:1 CR and a single Emag. The EGT's are only equal during WOT operation,
otherwise they are 100 degrees off (some rich & some lean). I can get to
about 30 LOP before the engine runs rougher and is unhappy. Fuel burns are
7.0-7.2 depending on altitude. This is at 155 kts in a 6A dragging steps,
fixed pitch Sensenich and a nose gear around. So the answer to the question
below is that carbs can run economically.

How does this compare to others - I don't know - but I'm happy with the
results. You make choices and move forward. I'll spend the thousands I saved
on fuel and go places. Have fun everyone!

Kelly Patterson
PHX, AZ
RV-6A 64 hours
----------______________________

Well, clearly there will be disagreements on this thread. I have no clue
about the actual percentage of users which have trouble with carbs vs FI,
but I do know that I burn less fuel with my Airflow Performance FI than most
carb equipped planes do. A noticeable amount less. I have flown many, many
hours side by side with other RV's, on long cross country flights, and at
cruises in the 155 - 160 knot TAS range, where I burn between 1 and 2
gallons per hour less (this is at MAP's of about 22", 2300 rpm, relatively
low percent power, maybe 58 to 60%). How many of you cruise with fuel flows
of 7.1 to 7.3 gph, at 155 to 160 ktas? Most carbs cannot be run, even with
electronic ignition (a big factor), in the LOP region. I do not have much
experience with my plane in the 75% power regime, but the differences would
be expected to be even greater there, since keeping the engine out of the
"red zone" (higher cht's, among other nasty combustion effects) is more
important there, and tends to spread the LOP/ROP fuel flows even more.

Even at 1 gph savings, it equates to something like $3000 worth of fuel at
today's prices that I've saved up to now in 759 hours of flying my RV.

I would welcome flying side by side with anyone wanting hard data,
particularly where so many variables are involved.

For those building and trying to decide, I simply have offered another
viewpoint.

Alex Peterson
RV6-A N66AP 759 hours
Maple Grove, MN

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alexpeterson(at)earthlink
Guest
PostPosted: Tue Jun 13, 2006 4:45 am    Post subject: LOP with carb Reply with quote
Quote:


I have to throw in my 2 cents on this one. My initial thought
was to run a FI system, but the simplicity & budget of the
carb won out.

The bonus was the economy is better than expected. The engine
is an O-320 w/
9.2:1 CR and a single Emag. The EGT's are only equal during
WOT operation, otherwise they are 100 degrees off (some rich
& some lean). I can get to about 30 LOP before the engine
runs rougher and is unhappy. Fuel burns are
7.0-7.2 depending on altitude. This is at 155 kts in a 6A
dragging steps, fixed pitch Sensenich and a nose gear around.
So the answer to the question below is that carbs can run
economically.

How does this compare to others - I don't know - but I'm
happy with the results. You make choices and move forward.
I'll spend the thousands I saved on fuel and go places. Have
fun everyone!

Kelly Patterson
PHX, AZ
RV-6A 64 hours

Kelly,

You have a nice setup, which seems to be well balanced. We have a 7A here
which has a carb and is also well balanced (with respect to fuel/air charge
to each cylinder). However, it seems to be more the exception than the
rule, and seems to be luck of the draw.

Again, side by side flight, equalizing ground speeds, is the only real way
to know one's true fuel efficiency compared to others.

Alex Peterson
RV6-A N66AP 759 hours
Maple Grove, MN

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bicyclop(at)pacbell.net
Guest
PostPosted: Tue Jun 13, 2006 9:26 pm    Post subject: LOP with carb Reply with quote
Kelly,

We've got a 160 horse O-320 with Sensenich, carb and single Lightspeed
ignition in our 6a and have just the opposite results. Our EGTs run way
off when WOT. Pull a tenth of an inch MAP or maybe 2 tenths and they
fall right in line and then can be leaned to run LOP. We then get about
7-8 gph and around 150 - 155kt depending on altitude. Another trick I
use sometimes is to give it a little carb heat and then re-lean. It
seems to help bring the EGTs closer together. A bonus is that, when LOP,
the CHTs also run pretty equal and low.

All the same, I'll have fuel injection in my next plane. That and a
constant speed prop.

Pax,

Ed Holyoke

--

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dan(at)rvproject.com
Guest
PostPosted: Tue Jun 13, 2006 10:15 pm    Post subject: LOP with carb Reply with quote
EGTs being "closer together" doesn't matter. It's the "GAMI spread" that
matters...the delta in fuel flow across all cylinders' EGT peaks. If you
have zero GAMI spread you're in good shape.

At WOT cruise, my EGTs run as much as 100F difference from hottest to
coldest but honestly I could care less. The GAMI spread is 0.1 gph or
better.

)_( Dan
RV-7 N714D
http://www.rvproject.com

---

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