Rev happy.

[Unbridled5.0]

I have no idea but I’m not sure if cutting off fuel while under boost is going to be a good idea. I know air/fuel ratio is extremely important for cars running boost so I’m not sure how that would work.

Not really, it may be manageable N/A but with compressed air coming in at it's peak at redline, the last thing you want to do is go lean, that's a recipe for carnage. In fact, the WOT lambda/fuel mixture is intentionally set lower to provide an additional measure of knock resistance (among other things), cutting fuel would spike it.

This is a late response, but how would an engine reach a lean condition with no fuel going into it?

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[Angrey]

This is a late response, but how would an engine reach a lean condition with no fuel going into it?

It's the very definition of lean, but you can't go instantly lean. In theory, the injector can remain closed, but this assumes that any residual hydrocarbons that weren't combusted got evacuated in the last exhaust stroke. I guess the good news is you'd have gobs of air and perhaps a tiny bit of combustible material, so even if it did pre-detonate it wouldn't have considerable force. But just keep in mind it doesn't take much if pushing against the pistons at the wrong timing.

No one is a fan of ignition/fuel cuts. In the case of bouncing off the rev limit, it's the lesser of evils and necessary to protect the motor. It's long been held that the harsh herky jerky nature of sudden ignition disruptions at the very least contributes to bad engine harmonics and at worst, shock loading to oil geroter gears and such.

It's one thing to do it on over rev protection (which should be a blue moon event) it's quite another to do it as some sorta ergonimic driving aid for each shift (something that would mean the motor would experience it tens of thousands of times over a service life.)

 

[Unbridled5.0]

It's the very definition of lean, but you can't go instantly lean. In theory, the injector can remain closed, but this assumes that any residual hydrocarbons that weren't combusted got evacuated in the last exhaust stroke. I guess the good news is you'd have gobs of air and perhaps a tiny bit of combustible material, so even if it did pre-detonate it wouldn't have considerable force. But just keep in mind it doesn't take much if pushing against the pistons at the wrong timing.

No one is a fan of ignition/fuel cuts. In the case of bouncing off the rev limit, it's the lesser of evils and necessary to protect the motor. It's long been held that the harsh herky jerky nature of sudden ignition disruptions at the very least contributes to bad engine harmonics and at worst, shock loading to oil geroter gears and such.

The way I've always understood it is the term "lean" is only used when there is an actual A/F ratio present in the cylinder, with not enough fuel. The situation we're talking about- when the injector is turned off- the fueling is absent and no more A/F ratio exists, rich, lean or otherwise. It's just air getting pumped at that point, with a spark that does nothing because the vast majority of spent gases have left, and nothing of measurable value is left to combust in the cylinder. (Assuming a healthy, well-tuned engine.)

That said, it seems perfectly safe to me to cut fuel when rev-limiting. Boosted or NA. No fuel = no chance for combustion. And besides that, fuel costs $, and when not burned in the cylinder, can load up in the exhaust and backfire and damage oxygen sensors and catalytic converters. I'm 99% sure the manufacturers use fuel-cutoffs instead of spark.

Agree, hitting the limiter doesn't do the engine, in particular the timing components, any favors. Take the tachometer readout with a grain of salt, realize they aren't exactly accurate, and that neither are our reaction times for shifting, and make the shift a few hundred RPM before reaching the limiter.

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