LOP MP at high altitude

[231LV]

Quick question for the group running turbo’s; last week I was on a trip that had me at 17k ft. My MP was maxed out at 24 inches with throttle pushed all the way in. I was running LOP at about 11 gph, 2500 rpm. I have an intercooler. Does this MP sound abnormally low? I haven’t been this high in quite awhile so I couldn’t recall what I typically saw in the past but it seems that I was able to see a higher MP previously. I ask because I was experiencing a similar “ lower than normal” power output even though everything on the JPI said all was well inside the cylinders. I thought I was having a turbo related issue and had my mechanic check it but all was well. It wasn’t until annual that my mechanic ran a compression test and found one cylinder dead even though it looked fine on the JPI. I’m wondering if I may have another dead cylinder. The JPI says all is well.....the engine is run out...old GB with about 1900 hrs.

[StevenL757]

What does your AFM say about MP settings at that combination of altitude, RPM, and FF settings?

[231LV]

I’m running LOP so the manuals are not really relevant as they are settings for ROP

[kortopates]

I would have expected you would have more MAP available. The only way to really be certain though is to do a critical altitude test. Climb at full 40" MAP, and 2700 rpm and rich until you are no longer to maintain 40" (100% power). Per your POH you should be able to get to about 14000' Density altitude before power starts dropping off with MAP (assuming without a Merlyn). 

Edited May 3, 2018 by kortopates

[231LV]

That is a good plan. Of course, the max MP my engine can tolerate is 37 inches due to the intercooler

[jlunseth]

Well, you weren't LOP if you had 24" of MP and 11 GPH.  But you probably weren't hurting anything either.  If you had been LOP, you would probably have had a fuel flow in the vicinity of 8 point something to 9 GPH.  Power setting is too low to do any harm though, in the range of 60-65%.  I can't say if 24" is normal or not for your engine at that altitude.  I do know that HP falls off pretty quickly for me, after I exceed critical altitude, which is about 22k in my aircraft depending on the day (I have the intercooler and the Merlyn).  You might try dialing the fuel flow back a little at that altitude, you may have been losing power because you were too rich, see if that does anything.

When you do your test, you might get a little higher than 14,5 because of the intercooler.  The fixed wastegate will put out a certain max output from the turbo, and because of the intercooler, whatever that is will produce 100% HP somewhat higher just because the intake air is cooler, that would be the theory anyway.  So you might get to 16-16,5 before you are maxed out.

[231LV]

A ff of 8 to 9 gph would cause my engine to quit....I typically run 10 to 11 gph  when LOP but I will dial back my ff until it stumbles as you may be correct that I was still not running lean enough

[Warren]

I frequently fly cross country at 16-18k.  I have a 231 with intercooler and upper deck pressure controller.  At these lower levels I run approx. 33”+ MP, 2500 rpm with lots more throttle available.  LOP at 75% is 11.5 gph and I am usually limited by TIT so run somewhere between 11 and 11.5 gph.

At these settings I see CHT 330-360, EGT 1500-1550 and TIT above 1600.

If your plane is setup like mine, there is something going on as you should be able to easily maintain much higher than 24” MP.

My manual (1985 M20k, with the LB engine) states that at 16k, 2500 rpm best economy is 11.2 gph and 30.3” MP.  This is in the stock configuration without intercooler and upper deck pressure controller.

[jlunseth]

LOP is a fuel air ratio.  Your are LOP at 11 GPH if your MP is up around 32” or more.  I use 34”.  Once you are LOP, adding more MP does not increase power because power is a function of fuel flow when LOP (mostly).  So 32” and 34” MP at 11 GPH are basically the same power setting, but the 34” setting is leaner.  But if you reduce the MP to 24” and use the same 11 GPH you are not LOP anymore, the fuel/air ratio is rich.  I use 24.5 for an approach speed power setting.  I start at a LOP cruise mixture, which for me would be 34” and 11-11.3 GPH.  That would be 71-72% HP.  To make the approach setting I just pull the throttle back to 24.5 or so, and in the TSIO360 the mixture is interlinked and tries to maintain whatever fuel/air ratio you set.  It comes back with the MP.  So I wind up in the high 8’s or around 9 GPH for a fuel setting when I do that.  I don’t know exactly how LOP that is, but I don’t care either because it is under 65% HP and it is pretty hard to hurt the engine at that power setting no matter what fuel flow you use. You can certainly use 11 GPH at 24”, you just are not LOP, your are ROP somewhere.

Edited May 6, 2018 by jlunseth

[gsxrpilot]

In my 252 with the MB engine, 11 gph would be right at peak. LOP for me is usually 9.0 or 9.5.

[jlunseth]

There again, at what MP?  If you are at 36” and 11 GPH, I’m pretty sure you would be LOP. I am not saying that would be healthy for the turbo, it would be working pretty hard, but you would be LOP. If you are at 32” and 11 GPH, not so much, maybe a little LOP. 9.5 and LOP is about a 62% power setting, that’s using 210 max HP, if yours is 220 then its a little less than 62%.

[gsxrpilot]

The TSIO360 Mike Bravo is the 210 hp engine.

I've never gone over to LOP at anything over 65% power. I've got some pics of the gauges showing MP 25.3, RPM 2500, GPH 9.5, and 62% hp on the EDM-900. 

From memory when I'm moving the mixture slowly from ROP to LOP, the EGT's are peaking around 11 to 10 gph.

[jlunseth]

I don’t doubt it.  At 25”MP that would be the place the mixture would peak, I have never paid much attention to peak in that range but I think it would be around 10.5.  At normal cruise MPs, say in the 28-32” range (intercooled engine), peak seems to happen in the 12’s and maybe the high 11’s. I have been using 34” and 11.0-.3 with pretty good success for a few hundred hours.  If anything, the engine has gotten better.  I was out a couple of days ago, CHTs were in the 320 range and TIT around 1585.  Probably will seew the temps come up some as the weather gets warmer.  Good magnetoes, plugs and wires seem to make a big difference.  

[231LV]

15 hours ago, Warren said:

I frequently fly cross country at 16-18k.  I have a 231 with intercooler and upper deck pressure controller.  At these lower levels I run approx. 33”+ MP, 2500 rpm with lots more throttle available.  LOP at 75% is 11.5 gph and I am usually limited by TIT so run somewhere between 11 and 11.5 gph.

At these settings I see CHT 330-360, EGT 1500-1550 and TIT above 1600.

If your plane is setup like mine, there is something going on as you should be able to easily maintain much higher than 24” MP.

My manual (1985 M20k, with the LB engine) states that at 16k, 2500 rpm best economy is 11.2 gph and 30.3” MP.  This is in the stock configuration without intercooler and upper deck pressure controller.

That sounds like the numbers I am used to seeing...thanks very much

[N201MKTurbo]

If you have a Merlyn pressure controller than something may be wrong with it. If you have the stock fixed wastegate then it may need adjusting. I would also look at the popoff valve. The turbo could also be bad, you should borescope the turbine wheel. If you overheat it the ends of the turbine wheel melt off and it looses performance.

[231LV]

A follow up to the original post...yesterday, I took off for our trip back home. We were at sea level departing CA (KLVK) and on climb out, I noted only 28 inches of MP at 100% hp....something was way wrong with this picture. As I was sorting it out and turning cross to downwind at about 3k ft, the engine "burped" and power dropped off pretty severely. I elected to return to the airport and had a non-event landing. The plane is sitting on the ramp awaiting a mechanic to tear into the engine and determine what went wrong. In the meantime, my wife and I drove the 12 hours home.

[Warren]

Bummer. Glad you were able to land safely and hopefully it is easy to find the root cause quickly.  Painful drive but better to be safely on the ground. Good luck with your fix. 

[gsxrpilot]

23 minutes ago, 231LV said:

A follow up to the original post...yesterday, I took off for our trip back home. We were at sea level departing CA (KLVK) and on climb out, I noted only 28 inches of MP at 100% hp....something was way wrong with this picture. As I was sorting it out and turning cross to downwind at about 3k ft, the engine "burped" and power dropped off pretty severely. I elected to return to the airport and had a non-event landing. The plane is sitting on the ramp awaiting a mechanic to tear into the engine and determine what went wrong. In the meantime, my wife and I drove the 12 hours home.

Do you have an engine monitor with data logging? If so, you should upload the data to Savvy Analysis and post the link. Someone on here will likely pinpoint the issue often saving hours of expensive A&P time to troubleshoot the issue.

[231LV]

1 hour ago, gsxrpilot said:

Do you have an engine monitor with data logging? If so, you should upload the data to Savvy Analysis and post the link. Someone on here will likely pinpoint the issue often saving hours of expensive A&P time to troubleshoot the issue.

yes...JPI 800...Unfortunately, the JPI (with the data) is in CA and I'm in AZ...

[N201MKTurbo]

2 hours ago, 231LV said:

A follow up to the original post...yesterday, I took off for our trip back home. We were at sea level departing CA (KLVK) and on climb out, I noted only 28 inches of MP at 100% hp....something was way wrong with this picture. As I was sorting it out and turning cross to downwind at about 3k ft, the engine "burped" and power dropped off pretty severely. I elected to return to the airport and had a non-event landing. The plane is sitting on the ramp awaiting a mechanic to tear into the engine and determine what went wrong. In the meantime, my wife and I drove the 12 hours home.

Was it making 40 inches on takeoff? 

[gsxrpilot]

1 hour ago, 231LV said:

yes...JPI 800...Unfortunately, the JPI (with the data) is in CA and I'm in AZ...

I've taken to keeping the USB key for the JPI in my flight bag. So if there's ever a problem, I can quick download the data log and take it with me. I can always upload it later when I'm home, in the office, or other convenient time online. 

Also as a matter of habit, I download the logs every few weeks and upload them regardless. I find the Savvy site to be a nice repository where I can look back at all previous lights anytime I like.

[231LV]

3 hours ago, N201MKTurbo said:

Was it making 40 inches on takeoff? 

Nope...28...typically, I have to pull back the throttle to 37 inches for the intercooler and avoid overboosting....that was my first warning that something was way wrong.....as I rotated, the power remained steady at 28 so I started figuring maybe a turbo problem which is when the engine suffered a severe power reduction which I corrected with what little throttle I had left. Everything on the JPI looked normal...just dropped across the board as if I suddenly pulled the power back. Things happen pretty quickly and I was fortunate that I was on downwind at about 3k ft....easy decision to return

[N201MKTurbo]

1 hour ago, 231LV said:

Nope...28...typically, I have to pull back the throttle to 37 inches for the intercooler and avoid overboosting....that was my first warning that something was way wrong.....as I rotated, the power remained steady at 28 so I started figuring maybe a turbo problem which is when the engine suffered a severe power reduction which I corrected with what little throttle I had left. Everything on the JPI looked normal...just dropped across the board as if I suddenly pulled the power back. Things happen pretty quickly and I was fortunate that I was on downwind at about 3k ft....easy decision to return

I hate to nag, but you shouldn't have taken off if it wasn't working right. 

[carusoam]

Hmmm....

231LV,

Quick Question for you....

Have you seen Erik’s thread from last week?

Some of what you are describing seems to be a repeat of some ideas that may have been covered here...

 

So if you are feeling like somebody said, don’t fly that thing without knowing what is and isn’t working right... there has been some discussion you might be interested in....

It’s been going on for a few days already...

PP thoughts only. Not a mechanic...

Best regards,

-a-

 

[231LV]

Hadn't seen the thread but glad it all worked out well for Eric....my situation was not nearly as dramatic and basically a single turn in the pattern....I will post what happened after hearing from the mechanic.