Not quite LOP, is this a problem?

kentb · #1 05-20-2007, 05:53 PM

I finally got around to trying to run LOP. My setup is a lightspeed EI on top and a mag on the bottom. IO-320, CS prop, RV9A with 55 tach hours on a rebuild engine.

Two flight legs of about 1.4 hours each.

The first leg at 7500 ft 2350 rpm 23.4 map. I slowly leaned and here are the number for each cylinder as they peaked:

ch 2 peak at 1452 at 8.3 gph
ch 1 peak at 1415 at 8.1 gph
ch 3 peak at 1430 at 8.1 gph
ch 4 peak at 1431 at 7.9 gph

By the time 4 peaked the engine was starting to run rough and #2 (the first to peak) was 1430 on the EGT. I increased the mixture to smooth operation and the EGT went back up to 1440.

At this setting I was burning 8.2 gph at 149 kts TAS.

On the second leg of the trip I flew at 9500 ft. Again rpm was set at 2350 map was 20.9 and fuel flow was down to 7.7 gph, TAS 147 kts. The EGTs were:

ch1 1380
ch2 1410
ch3 1390
ch4 1389

Do I need to get balance injectors to be able to lean better?
Is there something else I should be looking at?

Kent

Rivethead · #2 05-20-2007, 06:40 PM

Why aren't you watching your CHT's? Just a question I'm not trying to be critical.

mannanj · #3 05-20-2007, 06:41 PM

Contact Don Rivera at Airflow Performance at Spartenberg SC. He has a web site and will work with you over the net to get peak performance by balancing the fuel flow through each injector nozzle. Check out Dan Checkoway's web site for his thoughts on this. Sorry I'm not computer literate enough to attatch these web sites to this message. Google works wonders!

Much has been written on this subject, but these are your best bets to get up and running fast.

petehowell · #4 05-20-2007, 08:20 PM

When leaning, EGTs react more quickly than CHTs, so as long and the CHTs are not excessively hot, they are not as important. I think the numbers you posted were certainly EGTs, not CHTs.

Kent, as a comparison, I have an carbed ECI O-320 with an E-mag/Pmag combo. At 7500 ft, WOT, 2300 rpm, I can run at TAS of 150kts and lean to 5.9-6.1 GPH. My #3 goes lean first and #2 usually goes lean last about 0.2 GPH later. I need to use full carb heat to balance the mixture (theory is better fuel vaporization), and use the throttle plate to steer the mixture to the lean cyls. For example, if my 1&2 cyls are running rich, I nudge the throttle in a touch and it will lean them out a bit. If they are too lean, I pull the throttle out, and it will richen them up. I end up 20-50degF lean of peak, and the CHTs really drop off.

I hope my mentor in this area - Alex Peterson will jump in. He knows all about FI and leaning techniques and taught me all I know.

Good luck - lots of $4 avgas to be saved with intelligent, aggressive leaning.

AlexPeterson · #5 05-20-2007, 09:07 PM

Quote:

Originally Posted by kentb

ch 2 peak at 1452 at 8.3 gph
ch 1 peak at 1415 at 8.1 gph
ch 3 peak at 1430 at 8.1 gph
ch 4 peak at 1431 at 7.9 gph

By the time 4 peaked the engine was starting to run rough and #2 (the first to peak) was 1430 on the EGT. I increased the mixture to smooth operation and the EGT went back up to 1440.

Kent

That spread isn't too bad - it could be better though. It is much better than most carbs will deliver. The data you need to keep is all the egt's vs fuel flows, so that we can chart what is going on. I am a bit surprised that with that relatively narrow spread, you can only get about .4 gph LOP on #2 before roughness. I don't know how limited LOP is with only one advanced/EI ignition though... Keep in mind that the actual egt numbers are not important, and do not try to compare one cylinder's egt to another's.

Next time I fly I will turn off one EI and see how well I can lean it on only one ignition (which is essentially the situation you have - a lot of the burning is underway before the mag fires, so the flame fronts are not meeting in the center of the cylinder).

grantcarruthers · #6 05-21-2007, 12:53 PM

By my understanding you are in the middle of the worst temps where you were running. Definitely not LOP and in the heart of the danger zone. With that said if you are at 65% or below you should be okay if CHT's happy. The way I read your data you were slightly LOP on one cyl and slightly ROP on the other 3. With the low MP and high alt you were prob less than 65% which means anywhere LOP/ROP is safe from detonation??

kentb · #7 05-21-2007, 01:30 PM

My chts were 350-370 the temp that I posted before were EGTs. This power setting at 7500 was 70% and at 9500 was 67% according to the engine monitor.

Kent

osxuser · #8 05-24-2007, 07:46 AM

You can try swapping injector around port to port to see if you can get them closer. IE swap the first and the last to peak to see if they will average out in the other position. I know a guy with an IO-320 in a Glasair who did that to a decent degree of sucess.