LOP question for my 231 (and the debate goes on!)

[M20Kid]

I am new to Mooneys and have never previously considered running any engine LOP; I just didn't have the equipment to do it before.  I now have a 231 with GAMI injectors and a Merlyn Wastegate (no intercooler) and so I installed a JPI 700 specifically to help with LOP operations.  For the first few hours after installing the 700 I ran the engine at the same power settings I had been using previously - about 31" and 2450 with fuel flow around 12.8 gph.

Yesterday for the first time I tried the LOP leaning process on the 700 and found the fuel flow dropped to about 9.5 gph before all the cylinders showed LOP and I had to keep leaning to about 8.8 gph to get all cylinders at least 25 degrees LOP.  I was at 17,000 ft and lost about 15kts cruise speed was still showing 165kts.  It made me nervous to see that low a fuel flow and I didn't stay there long but the engine seemed to run smoothly and all the EGT and CHT were well below normal.  The one data point I don't know during this process is the TIT because my TIT guage appears to read too low; about 100 degrees less than the EGT readings.

I know I need to do a GAMI run test and record the data to get the GAMI spread but there wasn't a huge time lag during leaning before the first and last cylinder peaked and dropped.

My question is this, in my readings on this forum and others I can't see where anyone is getting that low a fuel flow reading at any time running a 231.  It seems far outside of normal and I want to know if anyone has experienced anything like this before.  Also, what are the potential problems as long as all the cylinders are firing and making power?

[rainman]

Rick, I run my 231 LOP in cruise routinely.  I have GAMI injectors that were previously balanced. I do have an intercooler but that is more inportant on the modification of my MP settings.  I flew back to San Antonio from Albuquerque today at 11K and averaged 9.9 gal/hr.  The procedure I was taught is that once I have my RPM and MP settings close (I cruise at 75% power which is 28" MP with the intercooler, and 2500 RPM), I use the TIT and lean slowly 50 degrees lean from peak. I use my JPI 700 for the task and the Shadlin fuel flow is very accurate based on several long trips and fuel fills. After several long trips to Michigan and California, and about 180 hours in the 14 months I've had the plane, the data is pretty consistant for around that altitude.  I'm no expert, but that's what I do and it works great.  My two cents??  Ray

[FAST FLIGHT OPTIONS LLC]

I have an 82 M20K 231.  I fly 28" 2450 RPM. Which equates to 65% power LoP.  FF of 9.5 - 10GPH at all altitudes. I lean to about 50 degrees LoP based on TIT which yields me about 1500 degrees these days. I have stock injectors and no intercooler.

[rainman]

Nick, do you use the gauge that came with the plane for TIT or do you have a JPI or something similar? The gauge (CDT/TIT)that came with my 1979 231 (and I had it overhauled last year) reads about 50-60 degrees low based on the JPI. I'm not sure it matters if you can accurately determine peak. I get about the same fuel consumption you do.  Ray

[kortopates]

Ray, if you're running at 9.9 GPH leaned to 50 LOP, you're no longer running at 75%. MP & RPM are not a valid indication of power when LOP. Power when LOP is calculated using a multiplier of 13.7 based on our 7.5:1 compression ratio for our TSIO-360. Thus at 10 GPH * 13.7 = 137 HP which is 65% power - as Nick reported.. But at 65% power, or any fuel below 10 GPH, you should be at a low enough power setting to be safe enough no matter how LOP you are. The challenge for us Turbo flyers is running at 78% (max cruise per POH is 165 HP in the 252) LOP which equates to 12 GPH. That is if you want to get back to Mooney turbo speeds of the ROP power settting. At high turbo power settings they recommend we run at 80-100 LOP and preferably well below TIT limits. I prefer a max of 1550 TIT and running LOP enough with TIT's low enough can be a challenge. Unfortunately, I haven't yet been able to run smooth and cool enough to pull that off yet. But I've been meaning to collect some new data since making some improvements.

My JPI reads almost a full 100F hotter than my factory TIT, and thus far I've been putting more faith in it than my factory TIT.

[rainman]

Thanks, you're right about the percent power. I intend to increase to 75% but the TIT seems to be closer to 1590? Ray

[aviatoreb]

My JPI reads almost a full 100F hotter than my factory TIT, and thus far I've been putting more faith in it than my factory TIT.

How old is each probe? Isn't it normal for the Tit probe to begin read low is it becomes old? My guess is that the JPI probe you have is newer and it is telling you closer to the true Tit.

[CoachTom]

So guys... Help me understand the procedure for the 231K setup LOP??? Do you climb to altitude (even 20K), set up your long range cruise for the altitude; (2400rpm, 28"mp, 78.6% HP, 120deg ROP), and then reduce mixture to 50deg LOP without exceeding TIT as that appears to be the only limit close to being exceeded?

My LB1 engine with Merlyn and Intercooler will go down smoothly to 9gph, but did not know if this was normal or if I was damaging the engine especially at the top end of the altitude envelope if I went LOP. Understand there is the desire to quickly get through the "red box", but mostly, the usual profile I am at for long range is high and trying to cover as much ground as possible, so didnt know if LOP is the preferred operating parameter.

Any help is greatly appreciated!

[M20Kid]

Thank you to everyone! I apologize for starting this thread and then disappearing but I had a family issue that required some time away from the computer.

It appears that my 9 gph may not have been that far off from the reading some of you are getting. I did notice about 10 kts slower cruise but I could stay up longer and make up the distance by not needing to make that next pesky gas stop.

My next concern is that my TIT guage never reads over about 1500. Having just installed the JPI 700 (but not getting the TIT option installed) I now believe my TIT guage is not telling me the truth. When running LOP my EGT readings are higher than that but the TIT guage stays put or drops. I guess I need to get that guage resolved before I try more LOP operations to make sure the turbo charger is not being compromised.

[231LV]

So guys... Help me understand the procedure for the 231K setup LOP??? Do you climb to altitude (even 20K), set up your long range cruise for the altitude; (2400rpm, 28"mp, 78.6% HP, 120deg ROP), and then reduce mixture to 50deg LOP without exceeding TIT as that appears to be the only limit close to being exceeded?

My LB1 engine with Merlyn and Intercooler will go down smoothly to 9gph, but did not know if this was normal or if I was damaging the engine especially at the top end of the altitude envelope if I went LOP. Understand there is the desire to quickly get through the "red box", but mostly, the usual profile I am at for long range is high and trying to cover as much ground as possible, so didnt know if LOP is the preferred operating parameter.

Any help is greatly appreciated!

you are doing it right....running LOP causes the fuel burn to drop relative to the power...it is more efficient than ROP as more of the fuel is being burned rather than going out the tailpipe. Also, you get the mechanical advantage of the LOP flame front spreading a bit slower in the cylinder which allows your piston to be "pushed" down after it has reached TDC rather than ROP where you get the "hammer of Thor" pounding on the top of the piston as it is nearly TDC. Your engine goes down to 9 gph smoothly because your fuel injectors are nicely balanced. The altitude you are flying has absolutely nothing to do with the physics of running LOP. Finally, and most importantly, heat is the enemy of all engines. LOP operations cause your cht's to drop 40 to 50 degrees and be clearly seen on an engine analyzer. You are right that the single limiting factor in running our turbo'd engines at high power when LOP is the TIT. In my engine, I can't get more than 69% without blowing through 1650 TIT

[Parker_Woodruff]

You are right that the single limiting factor in running our turbo'd engines at high power when LOP is the TIT. In my engine, I can't get more than 69% without blowing through 1650 TIT

Try the Tempest Fine Wires. I'm getting a lower TIT with them.

[M20Kid]

Parker - how much lower TIT are you talking? Obviously enough to notice but I'm just curious.

[Parker_Woodruff]

Parker - how much lower TIT are you talking? Obviously enough to notice but I'm just curious.

Probably 40-80 degrees cooler. I don't remember off the top of my head. Let's just say I can fly 32", 2525 RPM, and TIT sits right about 1580dF at FL210. At any power setting, i never saw a peak above 1625, that's for sure!

[231LV]

Probably 40-80 degrees cooler. I don't remember off the top of my head. Let's just say I can fly 32", 2525 RPM, and TIT sits right about 1580dF at FL210. At any power setting, i never saw a peak above 1625, that's for sure!

Interesting.....the plugs could be accounting for the lower TIT's but it could also be a bunch of other things....I'm running a GB engine so it is already hotter than an LB or MB.....I will do some checking...thanks

[gfhughes]

I fly my 1981 231 with Gami 25deg LOP (richest JPI TIT) at 2350 <1600deg on TIT gauge.

MP chosen so hottest CHT 380deg, coolest above 300deg.

Result is same TAS as POH ROP but at 10.5gph instead of 11.5,

and CHTs 20-40deg lower than ROP.