MoTeC Global Forum

All,
I know this is a kind of "sensitive" topic to discuss and before we go and take any advises on this post as the bible, we need to understand that this can be a case by case thing.

After all, I'd like to still have a discussion here about setting up the knock threshold in M1. I have watched all 3-4 of the knock related webinar posted by Motec using M1 and I understand most of the parameter and the tactic to set it up.

My biggest question is that how would a tuner go about creating up a "safe" knock in a turbo charged engine?
- advance the timing @ Lower RPM (2000-3000) + high load?
- Low Octane Fuel?
- Log engine noise @ all rpm ranges @ different frequency to identify the best frequency for all RPM range
- Other suggestions?

This is such an interesting topics and I'd like to hear some suggestions

Hello,
Just a few thoughts on the subject. Knock is never a great thing but all engine will stand a small amount of knock, just listen to cars taking off at the traffic lights on a hot day, you will hear lots of them have one or two knocks. The biggest problem with knock is allowing it to build uncontrollably and for sustained amounts of time. As for inducing knock on the dyno for the purposes of setting the knock system it is probably not the job for someone not experienced with listening for knock, if you don't know what it sounds like then you should probably get someone who has plenty of experience to help.

On the dyno during set up it would always be recommended to have a set of knock headphones as a separate system to monitor yourself (my suggestion). This way, regardless of what the ECU is saying during the set up you can hear and make your own decisions. Also running low octane fuel is good because it will simply allow knock to be created easier. We normally use 91 octane fuel here in place of the 98 we would use for the final tune.

The engine load needs to be enough to induce knock so light load probably will not do it but giving you a "one number answer" to suit all engines would be a little irresponsibly of me. For an example on a factory turbo engine you are probably making plenty of boost and torque by 3000rpm so you could start there.

We would normally find a point we are happy with and increase just two sites of the ignition map so we can hold the engine at the rpm with the dyno, start with the load/throttle just below this and move up through our increased sites in a quick fashion, hopefully with a couple of good knocks on the way through. This point probably does rely on the engine not being too far away from a well tuned ignition timing point anyway. If putting in an extra degree or two picks the HP/Torque up a lot you should proably give it a good tune to start with so you know you are not 6 or 8 degrees away from where you need to be in the first place.

You would normally set your knock A, B C and D frequencies at something like 8K, 10K, 12K and 14K, the knock should show up in ones of them. This is where the secondary set of knock headphones will really come in handy, if you heard knock but did not see it you will need to change your knock frequencies. If you see the knock in the 12K, for example, you could then use that as your main frequency and set the other three a bit closer like 11.5K, 12.5K and 13K. Within a hand full of runs you should be able to narrow in on a frequency that is more than usable.

Just remember, all engines are different so it may take a little bit of work. No matter how much information we supply to tuners I regularly get calls saying that the engine they have on the dyno now is doing something a little different.......which is exactly why I am unable to give a list of numbers to start with that are definitely correct.

Happy to see what others say.

Setting up knock control on the M1 is something I've done a few times lately. I'm not a particularly experienced tuner, so it has been a fairly scary process, but I haven't yet destroyed any engines doing it. I would be interested to hear feedback on my thoughts below from those with more experience

Generally I've started with the process similar to what Mark has suggested, which is the same as the few webinars from Motec and High Performance Academy that I've watched. The key things I've found that I think are worth knowing are:
1 - Start with a pretty good tune
as Mark says, you really need to start with an engine that has the ignition timing tuned pretty close to optimum already. The reason is that if you advance the timing 5 degrees and it doesn't knock, but you pick up a 20% increase in torque, the noise level does increase fairly significantly just due to the increased cylinder pressure (I presume). This has lead me astray in the past when I've started with very conservative timing to get a baseline noise level, set knock thresholds, then started tuning the timing only to find the thresholds being exceeded with no knock, simply due to the increased torque from the increased timing. This is also true if you start with low boost and then increase it significantly.

2 - best frequency often changes with engine speed
A couple of times I've found a good frequency to listen on at low RPM (usually the first harmonic - around 5-8kHz), but found that once I get into the "useful" RPM range the background noise is too high on this frequency, but there is a better signal on the second harmonic (double the first). This may not be an issue on a typical road car engine that only revs to 7k, but much higher than that and it gets pretty tricky.

3 - back to back with some C16 to double check
When you're setting up knock thresholds, it can be really useful to throw some C16 (racing fuel) into the tank and do a run to get a noise level that (probably) represents no knock. If you've tuned your timing to the limit of knock on pump gas and you then do a run on C16, the noise level should be pretty similar. If the noise level drops, it probably means you had some knock.

One of the trickier things I've found is that while big knock events are relatively easy to see/hear, it seems that with the M1 you can pick up minor knock events that you can't really detect with headphones, and it's difficult to know whether these are acceptable or not. This is probably where experience becomes useful.

Great advise guys.. let me try to sum up a few points here.

Step 1) spend time to tune the fuel and ignition map for MBT. I believe the best practice (simplify version)is to keep increasing the timing until you see the torque/Hp curve started to drop then dial back a few degree.

Step 2) log the knock frequency at various frequency(8k, 10k, 12k, 14k) during a few full ramp run (monitor with knock headphone to ensure no knock during the event) and get an idea of a normal operation noise level at all rpm range.

Step 3) potentially pick a rpm (start @ 3000) + semi-high load and advance the timing for a few degree to see if the knock sensor register higher noise then the range captured during the clean run.

Step 4) Pick the best frequency that has the best signal to noise ratio during the knock event and setup the remaining knock control parameter.

Is this a good rough guideline for tuning the knock?

My next question would be, once the engine is properly tuned, is it possible to tune the knock control without a dyno?

Hello,
I have reached out to my tuner and had some discussion about tuning for knock. His approach will be first to fully tune the engine (fuel and ignition) on regular pump gas. Then replace the fuel with race gas with the same tune and run the full range to learn the know baseline.

Then set the threshold slightly higher than the base noise and there should be it. Any comments?

mr2andy wrote:Hello,
I have reached out to my tuner and had some discussion about tuning for knock. His approach will be first to fully tune the engine (fuel and ignition) on regular pump gas. Then replace the fuel with race gas with the same tune and run the full range to learn the know baseline.

Then set the threshold slightly higher than the base noise and there should be it. Any comments?

No offence, but that's dynoing rather than setting up the knock control. You need to follow the procedure as detailed in the webinars, there's no shortcut.

First point, without actually following the procedure, how do you know the correct frequency to set? The following picture is a real world example, done with a SKM rather than M1 but the concept is the same. SBC on engine dyno, with light knock induced (cyan areas). In this case, if you chose at random, say 8 or 10kHz, you would not detect anything much at all, whereas 9kHz gives a fair ratio of signal to noise , and 6 kHz is just noisy. This is where the headphones come in so you can hear the knock if it doesn't appear on any of the frequencies you are looking at.



If you don't want to put steps in the ignition map you can wire a dial potentiometer to an AV input and use that as a timing trim dial to add timing once the engine is stabilised on site. Listening to the knock here is also crucial. One good tip I did get was to not use noise cancelling headphones. In my case cheap tinny earbuds with good ear protectors over worked well.

Mark and Malcolm cover some pretty good points. Mark knows the Motec knock system inside out, so his points are doubly valid.