Fresh rebuilt engine running out of throttle at 12500

[FlyWalt]

Hello all,

I typically run our 231 at 31 inches and 2500 rpm and lean to 50 ROP.

 

Our motor was recently overhauled and has been running relatively smoothly. I have all of 15 hours on it. While doing a recent trip I noticed that after level off 12500 I had to slowly add throttle over several minutes to maintain 31 inches. Then, once I reached full throttle, the power continued to creep down slowly to about 29 inches.

 

I desended to 10500 for turbulence and found that she maintained 31 inches without a problem. However I would love to get some insights as to what is going on here. She puts out beautiful take off power at sea level without a problem.

 

Thanks,
W

 

 

[KSMooniac]

Sounds like a wastegate problem to me.  Better talk with the shop that installed it.

 

Also, 50 ROP at 31" and 2500 RPM is a terrible power setting if you want your cylinders to last.  I won't tell you why as there are lots of discussion here about power settings and there is no need to do it again.

[John Pleisse]

Upper deck controller or stuck waste gate?

[Skywarrior]

At high altitude and high power setting, I would strongly recommend running 200 ROP.

 

Yes... seriously.

[FBCK]

With good injectors, you can run a 231 or 252 lop, burning less fuel and cooler cht, I do it that way. Sounds like a waste gate issue to me, but it might be the turbo is not working well either, I would check both.

[Awful_Charlie]

If the MP is changing itself whilst all else remains constant, I would be very suspicious. My initial feeling is you have either an exhaust leak, or the turbo bearings are collapsing. Other possibilities might be a leak in some of the control hoses somewhere, but these should be easy to find, particularly if they are the oil ones. I would however get it checked ASAP - if the wastegate is fully closing at 11,000' and it can't make full boost something is definitely wrong, and it might just be something that could embarrass you if it fails further. If the wastegate is not fully closing, then you have a control system problem, usually oil is my understanding, but there are a myriad of possibilities

[Alan Fox]

As the system has just been replaced go with the basics first....Retorque all the induction hose clamps , and check for exhaust leaks...

[N201MKTurbo]

It sounds like the fixed waste gate is adjusted too far open.

 

Did they disassemble the waste gate when they did the overhaul?

 

Do you have a Merlyn waste gate?

 

If not do the following:

 

I believe it should be set for a critical altitude of 19000 feet.

 

Screw the waste gate in a couple of turns. Noting the number of turns. Test fly the plane to find the new critical altitude. Find the ratio of the number of turns to critical altitude change. Readjust to 19000 and test fly again.

 

Repeat until it is correct.

[ryoder]

Sorry to hear this. Good luck.

[FlyWalt]

We are scheduled to visit the engine shop next week. I will post what they find.

[jlunseth]

My thought on this is completely different.  It is certainly possible you have a turbo control problem, but more commonly a problem with the turbo control results in cycling, not a consistent drop.  My question is what conditions were you flying in?  The early 231's had an issue with induction icing.  Any particulates in the atmosphere will cause it, but the most common at altitude is ice crystals.  When you are in it, the ice crystal clouds look to be a either a sort of generalized haze at altitude, or you may see and hear glistening crystals, you hear them as they strike the aircraft.  The ice collects on the air filter, building up and blocking the intake air.  The solution is simply to close the Alt Air door (actually, I am not sure close is the correct word, it is more a matter of switching).  Intake air then comes from inside the engine compartment, which is warmer, less dense air, so there is a loss of horsepower but it is not major, maybe an inch of MP.  The symptoms you would see before closing the door are exactly as you describe, slow loss of MP, the pilot attempts to compensate by opening the throttle further and the MP continues to decline.  If you get out of the conditions the ice will eventually melt off and power is restored.  I have experienced this several times.  An automatic door was installed and was retrofitted to most 231's so the door switches air sources on its own.  The Alt Air light on the annunciator will come on.  You may wish to check and see if yours has the automatic door or if the door has failed.  The ability to switch to a warmer air source is quite important for turbo aircraft because of the altitudes we fly at.  12,500 is a little low for this to be happening, but it is winter so the cold temps needed to produce the condition will occur lower down.

 

I agree that 50 ROP is a bad place to run the engine.  I would go at least 100 ROP.  The GAMI/APS people advocate even a higher setting, 150 or 160 ROP, but I think that fits the big bore Bonanza turbos better than our engines.  I have run my engine for hundreds of hours at 2450 RPM, MP to make 75% power, and 13.3 GPH, which gets you between 100 and 125 ROP.  50LOP would be fine but not 50 ROP.