The EGT gage only works for loaded wide open throttle operation. It is useless otherwise.  Huh??

 

Perhaps you could further clarify this point.

 

Al G  

The EGT gage responds very quickly to changes in temperature. So, at 140 MPH on a long straightaway you might hit a bump and the carb goes over rich just a small part of a second, and you will see that on the EGT gages. The needle moves too fast to keep track of, So, I installed a movie camera and a second gage dash board to record the actual readings rather than trust the driver to deliver such data with adrenaline still running out of his ears.

 

We use the EGT to be sure that we have not gone over 1650 degrees on either rotor, and that most of each lap was right on 1600 degrees. This is difficult because the carb runs leaner in right turns than in lefts, and under hard braking the front rotor gets way over rich and the rear rotor gets way over lean. None of this matters because you use the 1650 as your maximum and if it runs richer in one situation, no damage.

 

The engine is happy at 1550 or 1575. It will be down a few HP but still no problem.

 

No such fussing around is seen in injected engines and a more solid outcome should be available.

 

Suppose we have this pig dialed in and are hammering along at 180 Knots, sitting right on 1600 degrees.

The RV whatever you took off with is no longer a factor but the oil temps are at 200 and climbing. You pull off just a hint of throttle, and as if by magic the oil temp comes down to 190. Say the speed drops to 170 now.

 

Note that the EGT is far down as well. Fuel flow is down slightly. The EGT is showing BTUs per second.

A very slight reduction in throttle setting reduces air flow a considerable amount. The controller reduces fuel  flow to account for mass airflow. So mixture stays the same.

 

Now suppose the B controller is dialed in for best "lean of peak operation" so, we accelerate to cruise speed well rich of peak EGT. Then switch to "B". Still wide open throttle No pumping losses from a throttle reduction. You get better fuel burn because of the excess oxygen available. Less fuel is still burning as it crosses the EGT probes, so EGT comes down, so less stress on the pieces and lower oil temps which adds a bit to power.

 

A piston airplane engine that can run lean of peak in every cruise situation can make TBO. Many die young from cracked heads and dropped exhaust valve heads. Some engines do not have enough compression to run well lean of peak EGT. Like most IO-470s. IO-550s love lean of peak operation.  My friends Bonanza flys faster on less fuel with a 550 than it did with the 470. Exceeds airframe red line while on steep climb out still over airport property. Very low cylinder head temps.

 

At partial throttle the EGT gages will be far down the scale and of little value. So, mixture data is not available. For a good mixture profile you need a heated O2 sensor. One in each header would be nice 

 

Lynn E. Hanover