Knock protection
Turbo Mini Forums

Hi
Thought I would post some info on this subject.
I am currently building up a bigger capacity engine with higher compression ratio and a different cam in order to improve response and low end torque. It will most likely be more susceptible to knock so I thought it would be a good idea to try and get knock protection working on my current engine.
Purchased an ExtraEfi box below and a Bosch sensor screwed to a convenient place on the block





I know it may not be the optimum position but it was convenient.

To calibrate it the sensor, the sensitivity was turned down such that the dash mounted knock output LED (which shows when it thinks knock occurs) was just not flashing at max speed and max boost
The idea being any level higher than this will be true knock.

I know I have some slight audible knock when I advance the ignition around 4000rpm so used this as a guide to see if the light went on and indeed it did. So the protection was enabled in the ECU and looking at the logging showed that it did retard the ignition.
So this should help with the new engine at lest to ensure I can retard the base map if needed with some confidence.

what ecu are you using this with ? i tak it the knock box wires into your ecu

Done now needs redoing lol

Interesting!

from what Ive read you might run into an issue with it there picking up mechanical noise from the tappets, when I was looking into doing similar I was going to put the sensor on the top alternator bracket hole.

I have tryed the fuel pump bolts, alt bracket, dizzy bracket and top steady bracket drivers side the last one was the cleanest noise wise but im unsure if it could even hear how good it could have been listening to cyl 1/2/3 although i reasoned that 4 would be the most likily to knock first

Yes i moved to the darkside

Instagram @jdm_brett

thats a logical sounding reasoning.

Very interesting indeed, I've got a knock sensor off a 1.6 Maestro, mounted at the front of the head.
Again probably not the ideal location, maybe not even the right type of sensor and weather it still works or not is anyones guess!

At some point I'll put the scope on it and have a look.

How much was the Knock-Tek box?

I think because I'm not revving too high, the difference between real knock and mechanical noise is sufficiently large. Of course I can't be sure but it does seem to pick up real knock at the point where I have heard it before with the ignition advance I used to generate that knock.
Also I have read that the Bosch sensor is well tuned to pick up knocking frequencies, I believe around 4-10kHz.
If knock is generated at a low enough speed then the level maybe lower than the high speed mechanical noise but the ECU (MS1 V3) has a parameter where you can ignore knock above a given engine speed ( I use 5500rpm)
Here is a link to the box

http://www.extraefi.co.uk/Misc_products.htm

Edited by matnrach on 6th Jul, 2013.

Very interesting indeed, I'Sorry, double post, damn phone

Edited by Woodsman on 6th Jul, 2013.

Any such system needs the sensor tuned to the expected knock frequency for you bore size.
And to stand any chance of filtering out the crap, not only do you the user need to adjust all the filtering settings manually whilst checking yourself for detonation, in reality it also needs to only listen for a short window when knock might occur.

Usually around 10BTDC and 40ATDC or thereabouts. Hence it also needs tied in with crank angle and ideally needs to know which cylinder is on firing stroke so it can identify which cylinder may have knock detected.

Without all of the above, automated knock detection can become very unreliable. All systems really are only as good as what the user/tuner puts into them in order to make them work for any specific engine.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

your right brett, number 4 is the one to knock its tits off first,

so i would opt for a suitable position somewhere there ?

Edited by matnrach on 6th Jul, 2013.

I have my knock lite on the steady as well , it works well. apart from when I ignore in a fit of

''bloody good launch im not backing off for no stinkin light /no no no back the hell off you idiot!!!!'' internal dialog conflict ..

followed by oh dear ,we appear to be running on two.humph.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I had semi decent results with it there tbh checked with manual det cans before pulling the mini off the road and concentrating on the skyline, on that I ran fully sequential fuel/spark and dual 'wideband' knock sensors with tuned frequence and all the tweeks I could throw at it after reading up a lot I descovered using the 2nd and 3rd octives where theknock signal is half as strong but the noise is a lot less
Once I have built my new engine I 'should' be running fully sequential with the above system (actually robbing the skylines ecu for the time being)

Yes i moved to the darkside

Instagram @jdm_brett

http://item.mobileweb.ebay.co.uk/viewitem?...nid=65012949215

This is what I have been using ignoor the wiring if you strip that back there is the 2 wires and plug

Yes i moved to the darkside

Instagram @jdm_brett

I expect that the Subaru sensor is quite similar to a Bosch one ( I used one off a Vauxhall 16v and ran it to the box with shielded wires)
Reasonable knock does produce quite a high level of excitation from what I have seen before. So we maybe lucky with the setup.
At least it is better than nothing for my next engine with higher ratio.

All sensors are similar, certainly in appearance. Some are narrowband and designed for specific vehicles and frequencies, others are wideband and the frequency can be fine tuned in the software.

Unfortunately no easy easy to tell which is which

An in-cylinder pressure transducer would be the best option. But listening for knock in a crank referenced window certainly doesnt need that. Knock monitoring as I describe is fairly common now with modern ecu's and is much better as it helps remove a lot of noise.

I think the J&S Safeguard retrofit stuff does something similar.
If it doesnt do the window thing, it does identify each cylinder as it has reference to which cylinder is firing either via an injector trigger or coil trigger. So again each cylinder can be trimmed if need be.

But what it also does, is help see which is real knock and which might just be a noisy piston. It is surprising sometimes how much noisier a single piston can be in an engine when using a knock sensor to listen for noise.

No matter what setup you use, I'd still recommend you fit a basic type stethoscope ( google det cans ) and listen yourself so you can confirm the accuracy of any electronic knock detection.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Phormula KS-4

Been doing some digging the above system and its older versions seem to be decent tuneable and reliable systems

Edited by Brett on 7th Jul, 2013.

Yes i moved to the darkside

Instagram @jdm_brett

Ks-4 is the system I used while setting up mine along with an inovate wideband lambda system for fuel monitoring

Vems have removed the functionality of knock detection from the firmwares for quite some time. The developers are working on something for the last 2 years and are getting close to introducing it. I am led to believe it may be more closely related to how modern engines use 'active' ignition advance. The difficuty for them I presume is making it easily tunable to the vast array of engines without destroying them. The base ignition map needs to be right for the engine before and above anything else. This system does use the knock window and band pass filters to filter out unwanted noise.

Previous firmwares with knock included could easily tell you which cylinder was knocking if you ran a cam sync sensor.

I have the sensor already installed and can log the raw data from it