Hearing Knock

Hi all,

Just watched the road tuning course. A lot more comprehensive than I imagined so thanks for that - and the worked example at the end is great.

My question is around knock. I've been listening to my and a couple of other engines and I'm always struggling to distinguish knock from just noise. In the video Andre says that you can hear the knock clearly - I've listened a few times but it isn't obvious to me and I'm never sure I'm identifying the correct noise. I've done research on the subject so recognise it in "sales" recordings and the like, but as a result of lack of confidence in this area, I'm nervous to advance my (or certainly anyone else's) car until I have this nailed!

I use The Knock Box with the helicopter pilot style headphones (http://theknockbox.com.au/).

Does anyone have any tips, or sample recordings with and without knock?

Cheers!

Go to the middle of this page:

http://www.plex-tuning.com/products/plex-knock-monitor-v2-0-new

You should be able to distinguish the knock sound (little "click") like around 12s on the 10khz

Hi Ludo, thanks for that.

You're right, on that demo you can hear it quite clearly... just on my car it seems more difficult! You never know, maybe I've not actually produced knock on it yet! I have been quite careful with it to date.

I think what bugs me is I can't hear it clearly on Andre's tuning video. The visual aid is brilliant, but my old ECU doesn't support that.

Accurately distinguishing knock is definitely one of the more tricky parts of our job. A quality knock detection system like the Plex is very helpful with achieving this but it can still be hard on a noisy engine. Provided the engine is mechanically pretty stout, the best option is to purposely induce some light knock so that you can hear the difference and distinguish between this and background engine noise.

Thanks for the tip Andre. I'll give that a try next time I'm out.

hi guys, is it possible to advance the timing at light cruise speeds to hear knock? say 2000 rpm

is this so you can hear what it sounds like? It is possible but not advisable

In many instances you won't be able to induce knock at light load and low rpm. You will simply move past MBT and the result will be a decrease in torque. Unless you have a very high compression ratio or a very low octane fuel, you will usually need a little more load to make the engine prone to knock.

Andre (or anyone else who has experience with this),

Your previous post says that you can't really induce know at low RPM / light load.

On the course you do the steady state tuning by hitting each cell and advancing until you get more torque or hear knock, however if you can't hear knock, and if you're road tuning (therefore can't feel the torque as we're doing steady state), how do you gauge the limit at the lower RPMs, or for that matter even up to about 4500 before you start the "pulls".

I assume there's some experience here, but do you also have some maximum advance that you know there's no point surpassing at particular rpms?

Thanks!

You're right, in many instances while road tuning you won't have any real feedback due to not being able to make the engine knock and hence a conservative approach is really your only option. Some of this does come down to experience and for example most engines will want to see somewhere around 30-35 degrees of advance at light load cruise. It's not uncommon to see as much as 40-45 degrees in a factory calibration at some points however the increase in torque at this sort of advance angle is also typically minor.

Hello again. I've been back on my 3SGTE (stock configuration, but forged) - getting somewhere with this knock now.

Winding the car up to 3000/3500 with a little load - say around 90-100KPA - I can advance until I start to hear the uneven "crackle" of knock, which pleases me as I can actually hear it with quite a low volume set and still pick it out.

My questions though:

- on this car, I was able to wind it up to about 40 - 45 degs at 3000ish as above before hearing this! Does this sound too much - do you think I'm missing something further down and actually hearing more advanced knock? I've dialed it back down in the mean while.

- with the car dialed down and with a conservative advance profile (feeling quite low on power) between 2000 - 4500 and 0 - 180KPA I can hear no knock on steady state tuning - no crackles, no ticks. However, when I then start driving around to test it I hear the odd random tick from time to time but hard to repeat. There are no spikes in my advance curve and as I say, it's quite conservative. Thoughts?

- finally, low down in the revs, at less than 2500, I don't appear to be able to get any knock even with it dialed up to the 30s in vacuum. This is road tuning so it's difficult to feel any power difference, so I've left it somewhere which feels nice for drivability - does it sound right that I wouldn't be "knock limited" at this level, even running on low grade (95 octane) pump fuel?

Thanks for any help!

That's good that your hearing it now, What ECU are you using? does it have knock control?

Chances are at roughly 90-100kpa you will not be knock limited so managing to reach 40-45 degrees of advance before hitting knock is quite possible. You will be way beyond MTBT so dialling it back is not only sensible, it will gain you extra torque.

hearing the odd crack isn't a worry, especially if it isn't repeatable, there are lots of variables which can attribute to this, especially if it's from a sudden acceleration, take a look at your accel enrichment and AFR's in case you are getting a leaner spot, some ECU's even offer an ignition trim for sudden acceleration conditions.

Less that 2500 in vacuum areas really shouldn't be knock limited, the 3S-GTE is designed to be boosted so it would be a major design flaw if it was knock limited, what you'll find is that you are going way past MTBT so dial it back so that you are running the minimum timing for what feels nice to drive to avoid undue strain on the engine.

Thanks for the response Chris.

I'm on a classic! A Motec M4. The ECU is great, but finding a laptop to operate it is getting harder and harder!

I'm encouraged by your response. Out of interest, assuming no knock heard at higher RPMs and loads, what would you consider a maximum sensible advance where gains could still be had. I've always considered a low load threshold of about 35 sufficient - difficult on the road to tell if I'm getting any gains. Higher in the load I am definitely knock limited, so seeing figures below 30 in positive boost.

I don't believe my ECU has an ignition trip for sudden acceleration - but I will check the settings again. The odd cracks I heard were not on hard acceleration though, just randomly as I smoothly moved around the map. Interestingly sometimes they happened after lift off - again not suddenly which is odd as the car has fuel cut turned on.

Question: when I do find the "crackle" sound on steady state, how many degrees would you recommend to back out. I've noticed that I get a light crackle initially - just the odd, but repeating tick tick tick, then add a couple of degrees I get a constant crackle. I've typically backed out 5 degrees from there, then moved about the load about that area a bit to confirm there're no ticks at all. For safe measure at the moment (while still working on the map) I've backed a couple more out - which is why I was surprised about those odd cracks.

Cheers!

I had to use a DOS emulator to use it, worked fine on a Windows 10 laptop. I doubt I would tackle another after the first and last that I done as it had so many idiosyncrasies in the software.

In the mid range I would play it safe if road tuning, anywhere you feel like you're not getting gains then back it out. Seeing figures below 30 at the top end is not uncommon, I'm tuning an MR2 tomorrow so I'll post up peak timing figures once I'm done.

When your hearing the crackle in a knock limited area I'd pull out at least 2 degrees from the point you start to hear it start to tick, if your in the crackle then you are in a real knock situation and back off at least 4 degrees and try it again.

As you're moving around the map you are in a transient state, you will occasionally hear the odd tick, especially if your in a fuel cut area, there will still be fuel getting into the chamber from the wall wetting that takes place in fuel delivery. The transient areas will take some work,especially if your ECU doesn't have acceleration enrichment etc, it's been a long time since I've looked at the software, you may need to sacrifice some timing or run a touch richer to compensate.

Peak figures at 1.6 bar on a gtx28 turbo went into single figures at full load 6000+ rpm, we had to pull everything back due to a throttle body leaking.