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Hi. being a noob and a hobbyist rather than a professional, knock scares me.
How dangerous is it? Will it destroy my NA engine in the blink of an eye or does it require more effort ;)
I have been doing some minor testing leading up to some actual dyno time, and my logging shows some knocking, reduced after switching from 95 to 98 octane which makes me think it is genuine knock and not false knock. Obviously I will talk to the professional when I get to the actual dyno time and have him listen to it, but my lack of experience has me worried.
I know enough to know that I don't know enough :)
The less than useful answer is 'it depends'. Let me try and explain a little further. The chance of knock doing damage is dependent on the specific power level of the engine. This is why we've probably all heard some old timer rocking up a hill in their 1980's Toyota Corolla audibly knocking because they're in the wrong gear, yet the engine will probably keep going for another 100,000 miles with no damage. On the other hand with one of our 4G63 drag engines that put out 1200-1300 hp, knock would likely damage the engine almost instantly.
With an N/A engine you definitely can do damage due to allowing the engine to knock, however they are much more resilient than a turbo or supercharged engine for the reasons just discussed. A good example is our 350Z which has been put through the ringer in the name of training over the last 4 years, purposely being made to knock, yet it's still going strong. There are a couple of caveats to this: When I purposely induce knock I will do this at low rpm and low load where the cylinder pressure isn't massive. This makes it unlikely to do damage. Likewise I don't allow the engine to suffer sustained knock under high load - ie if I'm doing some ramp runs and the engine knocks at 5500 rpm I'll back off and abort the run rather than staying in the throttle.
Long story short, while you don't want to allow sustained knock, brief periods of knock in a low to moderately powered N/A engine are unlikely to result in damage to your pistons. It's all about being a little smart with your tuning.
Cheers, thanks for the in depth info :)
Pleased to hear the Nissan is still going strong since I am knocking about in a Nissan :)