Recommended TIT CHT Temps for Cruise

[Pat Schmitz]

I recently purchased a 73' T337G Pressurized Skymaster. I have found some information in the original POH, but very limited.

This plane is equipped w/ the GEM guage, and Riley Intercoolers. For those out there operating turbocharged 337's - what TIT, EGT, and CHT do you try to operate at when flying normal cruise at around 75% power? I am just now beginning my transition training, and this is my first experience w/ Turbocharged aircraft. I want to take advantage of your experience and insight to get the most time from these engines possible.

Thanks in advance for your help!!

Pat

[Paul Sharp]

I'll add what I use for my Turbo '67 model (not presurrized). It only has EGT in it (factory style although I've replaced them since buying the plane, but with the same gage).

The "best power" settings, I believe, are 50 degrees rich of peak. But I run them about 100 rich of peak, under the theory that a little extra can't hurt in case a cylinder or two are leaner/hotter than the one where the probe is. It only adds about a gallon/hour (both engines, total) to do that, so I think it's worth it in terms of longer engine life.

You can run them at peak, but not for higher power settings (not 75%, for example). I still don't think I would care to do that although I doubt it's a horrible sin at say, 65% or less. I think the peak setting would equate to "best economy."

The EGT gages are just a releative thing. You carefully lean to find the peak (takes only a minute or two if that); then if you have the older factory style gages like mine you can set the red indicator at the peak, then enrich them slowly until you have as many marks as you want cooler - 25 degrees for each mark on the gage. So I lean to peak and then push it back up until the needle drops four marks. I don't loose any sleep over whether I happen to miss it by one mark either way, although I generally keep them pretty well "tuned" at the 4 marks rich point.

If you change altitudes and/or RPM/MAP settings, you have to re-lean again. But I have found for my normal flights things seldom change much; I generally fly a lot around the 8K mark and almost always at 70 to 75% power.

Your gages may be different, and you mentioned TIT which I don't have, but I don't know that it makes a lot of difference so long as you know you're not burning things up and being relatively conservative. The old EGT gages can be fairly quirky, and I simply bought new replacement models for mine from the OEM. You have to replace the EGT probes and wires (all a set that is carefully constructed as to length, etc.) once in a while, too, if you expect to get good readings, even if EGT is a "relative" thing.

[Paul Sharp]

Will add to my own comments: You said you had the GEM gages. I'm assuming that means you have the types of measurements you mentioned, which would add TIT to what I have. And you may have readings for individual cylinders or at least a better measurement system. But so long as you know the TIT doesn't peak over what it should, and the cylinder head temps don't get over the limits, I would suspect that leaning may still be a basic and fairly good way to figure your settings. I would have thought that the GEM installation would include some settings info, but??

BTW, when I am in a "climb" configuration I generally follow the POH settings: 2600 RPM / 28" MAP, 14.5 GPH. I have found that one GPH meter reads a little different than the other, so I make sure the EGT meters read reasonbly similar, using the lowest one as a "yardstick" of sorts.

[Jerry De Santis]

I have a 1975 P337G Riley with A/C, intercoolers etc. I general cruise at 70 percent power and front and back engine cylinders are normal between 310 F to 385 F and CHT's in front engine between 1350 F and 1425 and in the rear engine between 1380 to 1525 F. I generally have 1.5 to 2 gph fuel flow more for rear engine than the front. Oil temp in front engine from 180 to 190 and in the rear engine 160 to 180. That's right, my oil temp. is lower in rear engine. I have good compression on all cylinders and about 600 hours over TBO. I cange oil every 25 to 50 hours depending on my schedule. I like running engines cool.

Jerry
N34EC

[Pat Schmitz]

Jerry and Paul -

Thanks for your reply's!

That is exactly the type of information I am looking for.. Just want to take advantage of any good information I can find to avoid any major problems.

Jerry - in your reply you stated - "CHT's in front engine between 1350 F and 1425 and in the rear engine between 1380 to 1525 F." I am assuming that was a typo, and you meant Turbo Inlet Temps (TIT)? I have been running mine around 1450, but had heard or some people running them in the 1600's - I was concerned that 1600 was too close to the mfg's never exceed of 1650..

My rear engine baffles all seem to be in great shape, and the rear engine cooling is good. It does seem like I have to run the rear throttle a little higher to keep the same MP/Fuel flow on the Shadin.... I assumed this might be due to higher hours on that engine.. I have about 400 on Front/1000 rear.

Pat

[Jerry De Santis]

Pat, your right! I meant to type EGT.

Jerry