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Knock at rev limiter

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So I listened to the pod cast with Ioannis of Plex and Andre and there was a segment where Iaonnis touched on knock caused by the rev limiter strategy. They did not delve much further into it, but I'd be interested in learning more on this.

Is it a real concern? Inducing knock due to the rev limiting strategy? If so, how on earth do drift cars get away with living on the limiter?

Drifters who know what they are doing are not on the limiter. To properly hold a drift you need to be able to modulate the wheel speed up and down. so riding the limiter removes a lot of control from the vehicle. Same as with rally, the noise that is often heard and is taken as being on the limiter is actually antilag.

Thank you for the response Stephen.

Any tutors care to share thoughts on the knock at limiter scenario Iaonnis mentioned in the podcast?

Not having seen/listened to the actual podcast, just from experience. You can have a knock like noise, or actual knock (defined as an uncontrolled ignition event) when on the limiter as the use of ignition cut can leave unburnt fuel in the combustion chamber. When the next firing event occurs in that combustion chamber, the rich pockets of fuel are able to self ignite, generating knock.

I imagine ignition cut without fuel cut and a burn in/onl the exhaust valve/manifold on overlap could ignite the start of the intake or be hot enough to pre-ignite the compression stroke. Running continuously with significant retard will likely heat the valves and head more further next cycle too.

If it's not a 2 stroke or rotary using pre-mix oil and any turbo if fitted isn't novelty oversize requiring antilag effect even near the event limit, I don't know why you wouldn't use fuel cut for a hard limit, assuming you have appropriate valvetrain control.

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