Help With Idle EGT temps-KTM 500

Hi there

We are a Formula Student team based in Greece. We are having some troubles with our tune and we would like to know if you would be able to provide us with guidance.

We are using a KTM 500 exc single cylinder engine from 2012 and our ECU is an ECU Master Classic.

We have a particular problem with our Exhaust Temps at idle (2000-2500rpm for us). We can't get lower than 710 deg C, under normal tuning parameters:

*We are running at an AFR measurement from the O2 sensor of ~ 11.8. Anything richer does not affect the temps and anything leaner increases the temps significantly. Note that the valve overlap on this engine is significant (hense the AFR measured by the sensor might not be the true AFR during the combustion)

*Stock idle timing for this engine is 8deg @1800rpm. However, we are running at 20 deg (@ 2500rpm as mentioned), as any less timing causes the EGT to sky-rocket. Interesting fact, increasing the timing to 35deg makes no difference, but bringing it beyond this point, as high as 55deg, lowers the temps to about 450deg! The exhaust sound at this timing changes to what one hears when under load at the dyno, so for sure this setting can't be right.

On high load, the EGT actually drops to between 600-680deg (running on a very conservative AFR of 11.2)

We have double checked our timing with a timing light during cranking and using a cam reference. However, we have not checked it while the engine is running.

Is there something that you believe could be going wrong, or perhaps the engine is just supposed to run like this?

Any help or suggestions would be much appreciated.

More details can be provided upon request.

Angelos

I think you have correctly identified the problem's cause, insufficient light/part throttle ignition advance. With late timing, more thermal energy is passed out the exhaust than would occur with more advanced timing that allows the hot gases to increase the pressure on the piston.

With your engine choice, it may just have a "2D" ignition map, where it's optimised for best torque while avoiding detonation or pre-ignition. Part throttle efficiency usually has less importance for the engine's usual application.

I don't know enough about the engine, and it's sensors and mapping, but you may be able to use a sensor on the throttle to add a load map to add timing under small openings and reducing load advance as the throttle is opened, with wide open being entirely reliant on the original map's advance.

I would check the cam timing.

Incorrect cam timing was my thought too. The other thing contributing to higher egt would be higher idle rpm. At first glance 700 additional RPM doesn't seem to be a lot but from my experience it can cause up to 180 degrees C difference at idle. But higher idle RPM seems to be a consequence of incorrect timing...