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...

Hi everyone

Concerning the cam timing, it has been checked and in general it is very difficult to mess it up for this engine. It is a 1cylinder engine & there is only 1 overhead camshaft. However, the cam timing, as it is from stock, is quite aggressive (see attached picture). The exhaust valve opens quite soon and the intake-exhaust overlap is significant. Also the stock compression ration on this engine is 11.8:1 (currently measured at 11.4:1)

Those factors can contribute to increased egt at idle, but does really the stock engine run that hot as well? I assume not, and that is why I am trying to find what is going wrong.

Regarding the load map question, we are running alpha-n, so our load map is indeed the tps.

Finally, if we indeed need more timing at idle (remember the stock idle timing is 8deg), then:

*if the timing we are applying is correctly setup, then the egt drops at 40-50 deg idle timing, which does not seem right...

*if the timing we are applying is incorrect, could you elaborate on what we can check to fix it? Because we checked our timing during cranking with a timing light and it was correct. So what could be going wrong?

Also as mentioned, when increasing the timing to the absurd 40-50 deg @ idle, the exhaust sound changes to what one hears when under load at the dyno, which can't be right because we are at idle, so no load...

Since this is a Formula Student car, you probably have a huge intake manifold below the throttle -- and that's why you can't idle at 1800 RPM? I would bet that with the large overlap, you are probably still getting exhaust gasses into the intake, so there is not as much oxygen to be measured by the O2 sensor. So perhaps you are running effectively a lean mixture (not much air/fuel mass). When there is not much cylinder mass, the flame front burns very slowly, and sometimes large ignition timings are required. Or it's still burning as the exhaust valve opens.

Experiments you might want to perform to learn more:

- what is the air temperature near the cylinder head in the intake manifold?

- what is the oxygen content of the intake manifold (mount another wideband O2 sensor in the intake manifold, and calibrate it for % oxygen -- do you get 20% like free air, or less?

- What is the exhaust pressure -- is there a way to decrease this through exhaust design - if it does have pulses, is here a way to make sure the lowest pressure is when the exhaust valve is closing? Perhaps the reason you hear the exhaust note change is because of complete combustion before the exhaust opens, and therefor different exhaust mass flow.

- What happens if you decrease the volume of the intake manifold (perhaps put something inside your existing manifold to take up the volume) - does this help? If it does, could you make a variable volume manifold that only increased the volume just before the restrictor becomes choked?

- Could you make a new cam with different timing (maybe even cut and re-weld a cam as a test?)