Safe knock threshold for RB25

[cdorhout]

For those that have had their RB25s professionally tuned, or have tuned their motors themselves, what is the max level of knock that I should be experiencing for a good safe tune?

I'm tuning my car myself on the street, and basically so far I've pulled fuel back in the rich cells until I start to see a little knock on my PFC. The number on the PFC I think is arbitrary (0-100)?? But it's the only number that I can reference.

My car is already much faster while keeping the knock very low. So, is it safe, for example, to tune your RB25 to a constant knock level of 40 (at WOT) all the way to redline? I see on the forums that different levels of knock are "safe" for different motors. The SR it seems is more tolerant of knock???

I'd like to get the opinion of someone who is an experience tuner or has learned from a professional.

Thanks!

[themadscientist]

"how much knock can I have" sounds quite similar to "how much radiation can I survive". You shouldn't have any knock if the car was tuned correctly. If you have it you should determine what is causing it and fix it, be it higher octane fuel, dropping the boost or trimming the timing.

[gawdzilla]

if the question you're asking is "what number should i look for on my PFC to tell me what is a safe knock", you won't really know. I have found that the PFC reading varies from car to car, engine to engine. you need to find what your safe knock number is and aim to stay around that.

mine saw up to mid 40s and it was still fine from what i could tell. (no matter how much timing i pulled or added the number would be solid around there, so i attributed it to some other noise).

another car i've tuned wont see more than 10-15 knock count.

in order to get a feel of the threshold between real and false knock, i would suggest fiddling with the tune a bit (in slow incrememnts of course).

first free rev the motor while in neutral and see where your knock goes... use that as a judgement of whats safe.

then go get some octane for the car... and see if your knock counts improve. if they don't, then you probably are not knocking.

[cdorhout]

Yes, 0 knock is great for a grocery getter. But when you want to extract the most power, you tune to the limit of safe knock.

Out of the box, the PFC doesn't warn you of knock until 40. So I guess I'll stay safe and tune for around 30ish.

Tuning is so hard to learn I'm finding. I suppose to get really good at it you'd have to go to EFI Univerisity classes. Tuning one car doesn't really justify spending that kind of money for me though.

gawdzilla, I notice that my car has less knock in cold weather. So that leads me to believe i'm already at the "real" knock level. But yes, I should spring for some high octane gas and do some logging. thanks!

[gawdzilla]

Yes, 0 knock is great for a grocery getter. But when you want to extract the most power, you tune to the limit of safe knock.

Out of the box, the PFC doesn't warn you of knock until 40. So I guess I'll stay safe and tune for around 30ish.

Thats not really how you want to look at it. Don't assume that 30ish is safe for your motor. that could be real knock.the knock sensor is just a microphone which picks up noise at a certain frequency. unless your knock sensors are broken, i doubt even a grocery getter will pick up 0 at all times.

try to experiment with the threshold starting from states where you know theres "no chance" of knock. Really low load with good octane, then work up from there. change the octane around and see if there is any difference. Cold temperatures i would imagine knock being worse if it was real knock

[sil_eightyRPS13]

most ppl dont like to see anymore than 30knock on the powerFC. anything over 60 and theirs some serious issues..

[jrb92se]

i just got my pfc ive had a regular knock reading of between 4 - 15 with 93 octane fuel. a couple of times after cold start i got a knock reading high as 22 but it hasnt gone higher then that. when im driving under normal conditions its got a knock readout of 1.