LOP with carb

Steve Brown · #1 03-03-2008, 07:48 AM

Hi All,

Last night on a flight from LLR-PAO I did a little more experimenting with running LOP.

I've got an O-320 with 9:1 pistons and EMag/PMag, Catto 3 blade

While leaning, eventually the motor will start to die, but it doesn't ever run rough.
21" MP
2500 RPM
131 KIAS
10 degrees C
7620' MSL
EGT range 1275-1300
CHT range 350-355
Fuel flow - less than ROP (no flow gauge yet)

When running ROP with the hottest EGT at 1300, the coolest will be 1200 or less. Also, CHTs will often run around 400.

So, the EGTs are more closely grouped and the CHTs are lower running LOP. I'm not sure why the EGTs come together for LOP, but that seems like a good thing.

I don't know my fuel flow yet. Next trip I'll run LOP both directions to get an idea of consumption.

Also, I generally cruise at 135 KIAS - IAS is a good indicator of power. I don't have an "official" power schedule for my engine, but I estimate that to be a bit over 65%.

Next time I'll bump the power up to get 135 KIAS running LOP

Finley Atherton · #2 03-03-2008, 01:54 PM

Hi Steve,
When you say LOP do you mean all cylinders are LOP? At part throttle I can get the back two cylinders to go LOP but not the front two before the engine starts to run rough/dies.
When you get your fuel flow have a look at Curve #13380 (Fig 3-16 in my 0-320 Operators Manual). It may be of use calculating your HP.

Fin
9A, 0-320, C/S, 9:1, LS Plasma III and mag.

Steve Brown · #3 03-04-2008, 07:41 AM

Quote:

Originally Posted by Finley Atherton

Hi Steve,
When you say LOP do you mean all cylinders are LOP? At part throttle I can get the back two cylinders to go LOP but not the front two before the engine starts to run rough/dies.
When you get your fuel flow have a look at Curve #13380 (Fig 3-16 in my 0-320 Operators Manual). It may be of use calculating your HP.

Fin
9A, 0-320, C/S, 9:1, LS Plasma III and mag.

Good question. I have a single EGT gauge with a 4 position switch. Difficult to simultaneously monitor all 4. On the next flight I can also diddle the mixture some while monitoring each cyl to see which way it moves.

It may be flawed, but here is my logic:
If the EGTs and CHTs are well balanced at a reasonable temperature, and the engine is running smooth, it doesn't really matter if all the cylinders are on the same side of peak.

Someone feel free to jump in if I'm thinking wrong.

I use this formula to estimate power:
(RPM/2700) x (MP/29.92) / (OAT/288)

OAT is in Kelvins (C + 273). Basically it proportions current engine conditions with that of a "standard" sea level situation at full throttle, max RPM. It assumes that torque is very flat, and over the narrow 2400-2700 RPM range it is pretty flat.

When MGL rolls out their round gauge infinity series in a few weeks, I'm planning to get some 4 channel temp gauges and maybe a fuel flow gauge. That should shed more light on my actual operating conditions.

Also, when I try this up higher at full throttle I may get a completely different results.

elippse · #4 03-04-2008, 10:13 AM

Quote:

Originally Posted by Steve Brown

I use this formula to estimate power:
(RPM/2700) x (MP/29.92) / (OAT/288)

On the Lycoming Aircraft Engine Performance Data curve 13381, they show about a 1.2" drop in MAP relative to static pressure. That means in your formula you should ratio MAP to 28.7" rather than 29.9"; that will give you about 4.2% more power at 25" MAP than you think. Also, if available, you should ratio induction absolute temperature rather than OAT to 288K, or, if not available, use OAT(C) + 273K, which is what I'm sure you meant. C.F. Taylor says that the maximum temperature drop from gasoline converted to a stoichiometric ratio is 44F, but the more typical drop is 24F. However, you must allow for the stagnation temperature rise above ambient occuring in your manifold, which is 7.2F at 200 mph TAS. This is given by (TAS,mph)^2/5521. So it might be a little more correct to use (OAT(C)-9C+273. That might give you about 3.1% more power than what you thought at 25C. Taken together, that would give you about 7.4% more power at 25C, 25", 200mph TAS than you originally thought. N'est-ce pas?

videobobk · #5 03-04-2008, 03:09 PM

Steve,

My setup is very similar except I have 8.5:1, one E-Mag and a Slick. There are several throttle positions where I can run LOP very well. These aren't so much MAP dependent as just throttle position, how far I pull the black knob. One gives me a very nice cruise at somewhere around 65% power. My rpm is lower than yours, however. My fuel flow is off right now, so I won't quote fuel burn, but it is good. EGT's mid 1300's, CHT's 340ish. I find I can stay LOP better if I pull carb heat, also. I can get my EGT's almost equal. Downside, at full throttle, #1 EGT is quite a bit higher than the others, ROP of course. Compressions are all above 75. And yes, I can pull the mixture and just slow the engine down without it running rough. I think you have a good setup!

Bob Kelly

Finley Atherton · #6 03-04-2008, 03:50 PM

Quote:

Originally Posted by Finley Atherton

When you get your fuel flow have a look at Curve #13380 (Fig 3-16 in my 0-320 Operators Manual). It may be of use calculating your HP.

I forgot you have a F/P prop so thus curve may not be of much use to you. I THINK this curve is based on low rpm such as 2000 rpm below 65% and 2,200 rpm 65% to 75%.

Fin
9A Flying

Finley Atherton · #7 03-04-2008, 03:57 PM

Quote:

Originally Posted by videobobk

Steve,

My setup is very similar except I have 8.5:1, one E-Mag and a Slick. There are several throttle positions where I can run LOP very well. These aren't so much MAP dependent as just throttle position, how far I pull the black knob. One gives me a very nice cruise at somewhere around 65% power. My rpm is lower than yours, however. My fuel flow is off right now, so I won't quote fuel burn, but it is good. EGT's mid 1300's, CHT's 340ish. I find I can stay LOP better if I pull carb heat, also. I can get my EGT's almost equal. Downside, at full throttle, #1 EGT is quite a bit higher than the others, ROP of course. Compressions are all above 75. And yes, I can pull the mixture and just slow the engine down without it running rough. I think you have a good setup!

Bob Kelly

Hi Bob,
Sorry to repeat myself (post#2), but is your LOP with all the cylinders LOP? My understanding is that when the guys with balanced injectors talk LOP they mean all cylinders are LOP. I have seen many carb guys say they can run LOP but I am never sure if they mean all cylinders are LOP.

Fin
9A Flying

petehowell · #8 03-04-2008, 08:25 PM

Hi Fin,

I have a 9A carb -320(8.5) Dual EI. I run LOP - all cyl most of the time. Here she is at high cruise:

WOT/full carb heat - All cyls LOP - I am at 10,500 here and about 145-150KTAS/5-6GPH over Chicago. Same speeds and less GPH up at 12,500 or 14,500

Here I am low and slow. Sorry for the pic quality. 98KTAS/3.3GPH, 1100+ Mi range.

I run carb heat when running LOP most of the time - you lose a bit of MP, but mine runs smoother. YMMV

Finley Atherton · #9 03-04-2008, 09:58 PM

Pete,
Great stuff. A lot of good information to think about. I am particularly impressed that you get all cylinders LOP at part throttle settings ( second photo). As I stated earlier, at part throttle I can only get two cylinders LOP. I will try carb heat at part and WOT and see what happens.
Thanks
Fin

petehowell · #10 03-04-2008, 11:12 PM

Fin,

Here is the the thread where I did my initial analysis with the help of Alex P and George.

http://www.vansairforce.com/communit...&highlight=lop

I went from hopeless to "Hey, this actually works." I run LOP every flight now. Cool and smooth - cheaper, too.

I really think EI with advance plays a big part in it. Sure, well tuned FI is better, but I don't have it - and this works pretty well.