Turbo guys...question

[jlunseth]

Well, I am not going to play with the high temps high up for awhile.  In the teens and in my engine, EGT's, CHT's and CDT  can all be lowered if need be by making the mixture richer.  For whatever reason, up at FL230, making the mixture richer would lower EGT's and CHT's, but send CDT spiking.  I have been to FL200 without a problem, but above FL210 or 220 my engine just starts to get unhappy.

At one point we had been flying along for quite awhile at FL230, probably close to an hour, with everything stable but the CDT just one degree below redline.  I decided to try adjust the mixture to lower the CDT and the minute I did the engine backfired and wanted to quit, so we told ATC we wanted to go to 17 and did so immediately.  We had no further problems at 17.

 

[roundout]

The ambient air is way thin up in the twenties. That's probably why your CDT gets high. Cooling systems are much less efficient there and the turbo turns in to a heat pump. Even though the airplanes can go there, I typically don't go above FL190 unless there's a very compelling reason. I won't go above there without a pulse-ox meter, for certain. There are plenty of good reasons to stay lower and few to go way high. 

 

FWIW, the turbo systems on the Bravo and Acclaim are superior to the TSIO360's but they still suffer above FL200. 

[jlunseth]

I have the oximeter and a mask with a mike.  That's the other thing, the mask with the mike seemed like a cool idea, but the mike sure is terrible.  I am sending it back to PF to see if they can get a better mike in it, but ATC could not hear me.  The mikes on all my headsets work just fine.

My engine is pretty well set up right now.  I could keep everything cool up high except for the CDT, that was just plain hard to control, and as I mentioned earlier somewhere around FL200 the control mechanism went into reverse.  When I enriched the mixture, CHT and EGT would go down, but the CDT would go up really quickly and dramatically.  Don't know why.  Probably more unburned fuel entering the exhaust system and burning there.  Also I suppose the wastegate is fully closing at that point, and the wastegate is an opportunity for the turbo to offload some temperature also. 

Given this experience, it is a little hard to believe that the 252 got rated for FL280.  I know it has a different turbo and intercooler setup, but still,  the change in the engine was pretty dramatic.

[Mcstealth]

Given this experience, it is a little hard to believe that the 252 got rated for FL280.  I know it has a different turbo and intercooler setup, but still,  the change in the engine was pretty dramatic.

I was thinking this exact conflict before you wrote it.  Given the differences your engine has, I would still not think they would affect the performance up high. Is your intercooler set up drasitcally different?

 

[Mcstealth]

Oops. Re-read the whole thread. Yours is a 231. Stil you shouldn't have such a dramatic spike. Somethning to ponder......