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Problems during dyno testing

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We are facing problem in our engine tuning session.

The problem is when we give throttle rpm peaks to 8000 within 10-20% throttle any idea what the cause is ?

We have checked all our sensors, injector , wiring, we are going little rich in fuel map for now and little advanced in ignition.Situatuon is same in both loaded and unloaded states.

I hope you may help us in any way with this.

Darshan pal

Team Defianz Racing

If I'm understanding correctly then you're saying that you're seeing an rpm that you feel is too high with a small throttle input? This can be related to the size of the throttle butterfly being used, or alternatively the relationship between the pedal position and the throttle butterfly. Basically the engine is receiving too much air and fuel which results in the high engine rpm. This is a fine line and you need to have sufficient progression in the airflow vs throttle position otherwise it can be difficult to control the torque delivery of the engine.

We are using the KTM-500EXC-F engine, according to the FSAE competition we have to put a restrictor of 20mm in our intake system, for that we have made a venturi with an added plenum(airbox) and TB of 28mm. We are using DTA s80 pro ECU.

I am attaching the ignition and fuel map ss below have a look at it and help us in knowing, is ignition and fuel map seems a reason for this or not? We know that we are running rich in fuel map, but as we are reducing the fuel pulse width there is not much change is lambda value I am still wondering what the reason can be?

And the problem is still the same engine revs to 7000-8000 within 10% throttle in neutral and 20-25% throttle in 3 and 4th gear.

PS:- 1.) Throttle calibration is checked.

2.) Injector test is done too.

Attached Files

I'm sorry, but I don't get what your problem is?

As Andre suggested, an engine will free rev' easily in neutral and run out to quite high rpm in the intermediate gears if allowed to reach equilibrium (engine power equals total drag) even on what seems to be a small throttle opening - and remember, that first part is actually opening quite a large percentage of 'full' throttle. The more efficient the engine and driveline the less the throttle opening required.

If I were you, as it seems it is the progression that is the problem, I would change the pedal-TB ratio so the initial throttle pedal movement has less opening of the TB but towards the end of the pedal travel there is much more TB opening - it's progressive rather than linear - and should make it much smoother to use. Another advantage is by moving the TB sites closer together as the initial opening occurs, you can get the mixture and ignition better optimised as that's when the airflow changes the most.

You're using an electrically operated throttle, so something I have come across before shouldn't apply - a carbie loosened off and applying enough throttle force through the linkage was lifting it and causing an air leak. Have a good check over the intake side and see if you can find anything obvious, perhaps having it idle while applying moderate pressure to the components and/or use some brake-clean or engine start around the gasket and throttle areas to see if it gets drawn in and alters the idle speed?

Any chance your manifold (downstream of the throttle / restrictor) has developed a leak, or is so large that the throttle alone can't control the speed. Will the engine still run if you put your hand over the throttle intake?

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