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LOP Turbo Arrow.

I have a Turbo Arrow which, until last year, was factory stock in the engine and instrumentation department. I did a top overhaul last year as my almost 1000-hour cylinders were using too much oil. I historically ran at 33 to 34 inches MAP and 2400 RPM and did not have any overheating issues except for long climb outs in summer, when the electric pump on low helps cool the engine.

As part of the top overhaul project last year, I installed the Merlyn wastegate as well as the LoPresti cowl. I began experimenting with other power settings. I found that I can now run 65 percent power, maintain my previous airspeed, burn less fuel and the engine runs cooler. I have since tried lean of peak. Using the "big pull" process, I found that at 65 percent power, TIT peaks at 1600 degrees at 11 GPH then drops back to 1550 at 10 GPH. Oil temperature is about 160 degrees F and CHTs are about 350 degrees F.

I have read and reread your lean-of-peak article in the January 2009 issue and also reread your January 2003 article on your Mooney 231 with GAMIjectors. I have concerns whether I can safely operate this way with the standard Piper instrumentation or is it absolutely essential to install an engine analyzer somewhere in my limited panel space? My biggest concern is that even though 65 percent power at 10 GPH LOP seems to work ok, are there one or more cylinders which might still be running ROP and overheating?

Robert Moulic


To operate lean of peak with confidence, you should have a multi-probe digital engine monitor. Without the data it provides, you'll have no way of knowing which cylinders are peaking when and what your individual CHTs are. You may or may not need GAMIjectors. But get the monitor first, then do the lean test and take it from there.

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Title Annotation:LETTERS
Author:Moulic, Robert
Publication:The Aviation Consumer
Article Type:Letter to the editor
Date:May 1, 2009
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