Knock Levels - Rb20

[want_33]

apolagies as im sure there are hundreds of posts on this topic, but search function is not helping me out today. if someone can just point me in the direction this thread can be closed.

safe knock levels on rb20det

cheers

[lookingforboost]

I think anything under 60 is ok ?

[t_revz]

check paulr33`s FAQ and it might be in there. i think he has said b4 around 100 is where powerfc brings on the warning light unless its been changed by the tuner. ideally below 30. mine doesnt go above 20 unless i cant get 98

[paulr33]

60 turns on the engine check light flash

max knock level is 255

20/30 is ok

[want_33]

mine never really got over 40 from what ive noticed on the hand controller, but this batch of fuel iv noticed it hit 50, 80 a couple of times and once was 92. i still have well over half a tank of fuel left tho so i cant really just change it straight up. got a 4 hour trip to do in it this weekend and and most of that fuel will still be in it...

i always fill from the same bowser at the same servo, shell v-power

[JonnoHR31]

either keep it off boost til you use up the fuel or fill the tank now and hopefully get a good batch

[jiffo]

mine never really got over 40 from what ive noticed on the hand controller

You've got a hand commander, pull a few degrees timing out of it.

Go Settings, IGN/INJ, reduce the timing by say 5 degrees.

Next time you turn off and re-start it's back to where it was as these are only test settings.

[JonnoHR31]

2 degrees would be more than enough for a slightly shit batch of fuel

unless you filled the tank with heptane?

[tridentt150v]

or try a proper octane booster, one that works. You can substitute methanol/toluene if you know what your doing. I know methanol works, a litre in half a tank would probably fix it. Or top the tank up with E85 and have a 50/50 mix.

[JonnoHR31]

50/50 e85 without tuning will make it run lean

octance booster is a good idea for a temporary fix but dont use it all the time as it kills plugs and o2 sensors etc real fast

[toffy]

my tuner told me if my rb20 gets to 40 or above on the pfc h/c to take -2deg timing out as above mentioned

[Rolls]

At what levels are you actually getting real pre ignition and not just noise?

[want_33]

rolls im not sure what you mean so ill answer to the best of my ability

in low rpms in most gears the knock is very sparatic and climbs easilly over 40, iv i labor it it goes up to 90ish, but if i drop back a gear and rev it out it stays quite low.... not sure here what to do. im about to head out so ill drop 2 degrees out of it and see how it goes, realy hoping its just bad fuel

[Rolls]

I mean at what level (number) does it translate to the motor actually knocking or having preignition, obviously it isn't knocking all the time so there must be some threshold +-25% or something where it is actual preignition.

[DVS JEZ]

he means can you hear your motor rattling from inside the car? pinging

[JonnoHR31]

I mean at what level (number) does it translate to the motor actually knocking or having preignition, obviously it isn't knocking all the time so there must be some threshold +-25% or something where it is actual preignition.

i think your a little confused. pre ignition and detonation are two different things with different causes. also theres no set number that defines knock, you can have a tiny part of the mixture knocking which generally wont do much damage or make much noise (resulting in a low knock number if everythings working properly) or you can have most of the mixture pinging which is obviously bad and would generally produce much higher knock readings. everyones opinion is different but for power fc's most people considering anything under 30-60 safe.

OP, 40 isnt very high at all, like i said either pull a couple of degrees of timing or fill the tank. 90 isnt even all that bad if its at lowish rpms.

[Rolls]

Yes I realise they are different things but Im fairly sure a knock sensor will pick up pre ignition as well as detonation, perhaps it does only pick up the later Im not sure. Either way I thought that detonation was pretty much an all or nothing thing, either most of the mixture detonates or it doesn't, is it possible for just a tiny bit to do so?

I guess my real question is how does the scale translate to actual detonation, is there a certain amount of noise (eg 40) where there is zero detonation, and a certain amount where the entire mixture is detonating (255) obviously these would be inexact figures with large spread but I was wondering if there was any documentation by Nissan on what levels generally translate to.

[paulr33]

apexi set the engine check light to flash at a level 60 which they believe is enough to warn you

anything over 60 i would be getting it checked by a tuner. the usual culprits when you exceed 60 knock are

too much boost

penis fuel

too much timing

intake temp too high (poor pod, poor intercooler, no intercooler, poor intake, too much boost)

fix one of those to resolve the issue and/or back out timing at the same timing

taking out timing using temp ignition adjust always removes the knocking

[want_33]

i pulled 8 degrees out of it and seen almost no change.... is it possible that my power fc has reset and lost its tune?

its not boost a its only low rpm driving, reving it out its fine, nothing in the intake has changed so im leaning towards fuel

[JonnoHR31]

if you've pulled 8 degrees with no change to knock levels then its likely its not actually knocking, possible but unlikely. could be a dud sensor or something rattling in the engine bay near the sensors

are you absolutely sure you pulled 8 degrees? set 1 of your monitor values to ign timing and see what it reads before and after changing the temp adjust

Yes I realise they are different things but Im fairly sure a knock sensor will pick up pre ignition as well as detonation, perhaps it does only pick up the later Im not sure. Either way I thought that detonation was pretty much an all or nothing thing, either most of the mixture detonates or it doesn't, is it possible for just a tiny bit to do so?

I guess my real question is how does the scale translate to actual detonation, is there a certain amount of noise (eg 40) where there is zero detonation, and a certain amount where the entire mixture is detonating (255) obviously these would be inexact figures with large spread but I was wondering if there was any documentation by Nissan on what levels generally translate to.

Knock sensors usually cant pickup pre igniton afaik as its not a metallic knock as such, more an extremely fast, high pressure burn while the pistons coming up, can melt holes in shit. suppose they might pickup a knock at the end of it as the piston reaches the top if its still burning and pings as a result of the pressure, but its fairly different to your normal pinging from too much timing.

its very possible for only a tiny bit of the mixture to ping for all sorts of reasons. poor atomisation, poor chamber design, uneven pressures, hot spots etc can all cause it.

as i said theres no set number for whats knock and what isnt. even if you know exactly whats happening in the chamber at what pressure and burn rate etc do you call it knock instead of just a clean burn? all combustion makes noise, hence why you always have some sort of knock reading when driving, i've never seen a power fc display a max of 1 after a drive. it all comes down to whats safe and what isnt, and again theres no set number and even if there was it'd be different for every engine, ecu, knock sensor etc. you can only go off other peoples and your own experience and opinions, which as i said usually equates to somewhere between 30 and 60 being the safe limit with a power fc. personally i dont even look twice at anything under 60 on my car, but i dont need it as a reliable daily and the motor is just a slapper so i'm not as careful as others might be.

each to their own

Edited October 26, 2010 by JonnoHR31