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Rich Knock and Low Timing Question

Practical Standalone Tuning

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Hi Andre I often hear from people saying running to rich can cause rich knock but i've seen stock tunes running low 10s never heard them suffer rich knock issue. Can you give me a example what afr Rich knock start to occur?

I also heard from people running timing to low can break the engine melting exhaust valves , how low of a timing do we need to reach engine failure? If MBT is 20 degrees would runnig 7 or 6 degrees consider way to low and break or melt something ?

I have never experienced a situation in my career so far where a rich AFR will result in knock. In all cases on pump fuel that I've experienced you will end up with the engine rich misfiring if you keep adding fuel.

Alcohol fuels however while resistant to knock are more susceptible to pre ignition and this is made worse with a rich AFR. There are a lot of aspects that add up to an alcohol fuel promoting pre ignition though and a rich AFR is only one of them.

As far as melting exhaust valves, yes this is possible if your timing is too retarded as the EGT increases. It will however also depend on the way the engine will be used. For example on a road car it's very difficult to use enough full throttle to cause damage. On a race track though it's a different story.

It's hard to give you a solid line in the sand as so much will depend on boost pressure, fuel, engine design and usage. If I had to give a guide line I'd probably not want to see the timing drop into single digits at high rpm. It isn't uncommon though to see timing drop much lower than this around peak torque.

You can use EGT measurement just after cylinderhead and just before turbine, check the stock one from original calibration in long WOT condition, and respect this limit or decide a new one.

This is a valid idea Leo however just the same as the OE tuning strategy for AFR, their expected EGT isn't always a maximum limit. OE's are notoriously conservative in most cases and hence their EGT threshold will likely be a lot lower than what you could get away with in practice.

Car manufacturer engine base tuning is done on engine bench in steady state condition (most severe conditions) and usually a margin is taken from the OEM limits to cover engine scattering. (Injector, MAP or AFM sensor...)

So yes it is impossible to reproduce these conditions on the road that's why you can decide a new limit from your player level ;)

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