[Terry Lutz]

I don't have the opportunity to fly my RV-8 that often, so each time I have some time at home I try to improve the airplane. The engine is an O-360 A1D, with 9:1 pistons, Ph 3 cam, mag on the left and a Lightspeed II on the right, with a Hartzell blended airfoil C/S propeller. When I enter the traffic pattern and bring the power back (mixture rich), the EGT starts increasing (on all 4 cylinders), and going through about 1500 rpm it will rise up above 1500 degrees. Once at idle, it's normal. But if I need to fly level with flaps down, the EGT heads back up with throttle application. I have checked ignition timing, and had the carb overhauled, with the largest metering jet recommended. Other than than an to decrease predictably with throttle reduction.

 

[Ironflight]

Wow, I've been flying the Val for close to 1,000 hours, and have yet to notice what the EGT's do in the pattern!

First thing to check, of course, is if you're idle mixture is good - do the old Mixture pull to cut-off and see if you get the expected rise. if that behaves, then I'd not worry about the mixture.

The other thing to think about is that absolute values of EGT don't mean much in these piston engines - the value you get is highly dependent on the distance of the probe from the exhaust valve. If you have the probes close, the temps will read higher, which doesn't mean that you are above "normal" - just that you mounted them closer than others have (You'll just burn out probes more often...). If all four cylinders are doing the same thing, I expect you don't have a real problem.

Now, of course, I have to look at my EGT's in the pattern when I fly tomorrow!

Paul

 

[Jetj01]

I have the same engine/prop...

Hi,

I have the same engine and prop combo as you, except with the LASER ignition. Here is what happens to me: When I have been cruising, like yesterday at 7,500 feet, and have been at my prefered power setting of 22-23 MP and 2400 RPM, I usually set an EGT of 1340 degrees (for what ever reason???) using mixture control. Upon beginning descent I pull the throttle back and the EGT will substantially rise if I keep mixture the same. This is a normal reaction to a decrease in fuel flow but either a remain-the-same or increase of airflow into the carb inlet, exact EGT numbers are reliant on our EGT probe placement, but CHT should decrease during the same application, as mine does. Excessive CHT is what cooks engines. In my case, as I begin my descent, I also increase the mixture proportionately to not get the stated excessive (for me anything over 1400 EGT...random pick) EGT heat spike and that works for me. But this is the physics behind the EGT increase as you pull power during descent in a carburated engine. Not unusual.

Well, for my application anyway, your milage may vary!