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Luis · Post by **Luis** » Wed Jun 01, 2005 7:46 am

I´m searching for some info on the 2.0 v6 turbo engine, it´s 12v and i think it has a Knock sensor.

I want to put a knock sensor on my car, why? i´m going to try edis6 + megasquirt on my car, but i want a knock sensor for safety (and tuning) reasons.

Mats · Post by **Mats** » Wed Jun 01, 2005 8:28 am

I just had a lecture on knock sensors and I'm telling you, it's hopeless for amateurs like us.

We are talking about frequency, amplitude, crankshaft degrees, how much to lower the ignition, how much and how fast to raise it again and on and on...

i.e. If you can get a signal of a knock that you can't hear (don't underestimate the human ear) with your own two ears I salute you, but it would probably be too late already...

Put a brakepipe on a banjobolt on the intake and route it into the car, thats your knock sensor.

Jim K · Post by **Jim K** » Thu Jun 02, 2005 1:32 am

A few months ago, I designed and built a knock sensor indicator for a friend in the mapping business who didn't want to spend the high market price for a commercially available item (you can't beat $20+the knock sensor itself!). Detecting knock and using the signal for further ignition parameter processing are two entirely different things. I can visualize a possible circuit able to do that but its going far beyond the DIY limits. I just wonder why hasn't any ignition firm (Mallory, MSD, Jacobs etc) come out with a programmable ignition incorporating incremental knock correction? Strange, isn't it?

Jim K.

kai · Post by **kai** » Thu Jun 02, 2005 2:00 am

@Jim: would you share that circuit with us ?

MD · Post by MD » Thu Jun 02, 2005 2:05 am

I got a knocker sensor and it works real well on brunettes with a 38dd cup with a range of up to 200 metres and best of all it cost me nix.

Jim K · Post by **Jim K** » Thu Jun 02, 2005 3:18 am

MD, I got one too, coupled to a crowbar but it gets embarassing sometimes on the beach...face down in the warm sand...aahhh!

Jim K.

Kai (you must be the new tennant here), I repeat this is only a knock indicator cct with 10 LED's, not an intelligent ignition!

kai · Post by **kai** » Thu Jun 02, 2005 3:42 am

@Jim: Yes new on this Forum.
I know it is only an indicator, but I was just curious how you implemented the filtering and amplifying (if there is any). I think your LED driver must be an LM3914/5 or similar?

Luis · Post by **Luis** » Thu Jun 02, 2005 5:54 am

Well, i´m planing to use a 75 1.8 turbo knock sensor, the "Megasquirt ´n´ extra" has an input for the knock sensor, so i think i can give it a try.

Maybe that DIY knock sensor is an electret microphone and a vumeter?

Jim K · Post by **Jim K** » Thu Jun 02, 2005 7:08 am

First (Luis) a knock indicator is not that simple. The sensor is a special piezoelectric element in an equally special package, requiring specific mounting arrangements in order to transmit the proper signal. The most involved part of the cct is the highly selective filter (bandpass) which lets the proper frequencies through to the amplifier. The LED indicator part is a regular VU meter available in any electronics store (this also covers Kai). Setting of sensitivity is best done on a dyno but different engines respond indifferent ways. Unforunately, best power is usually observed at the onset of detonation!
Jim K.

Mats · Post by **Mats** » Thu Jun 02, 2005 11:45 am

IMO it would be way easier to measure ionisation in the combustion chamber through the spark plug.

Post by **Zamani** » Thu Jun 02, 2005 2:40 pm

You mean those special pressure sensing spark plugs? I read that on the Autronic forum. Those vendors are not interested to sell anything to individual buyers.

Or are you talking about something else?

junglejustice · Post by **junglejustice** » Thu Jun 02, 2005 4:24 pm

Bouncing off of what Mats has already stated here;

Since we have purchased about 7 or 8 Innovate Motorsports LM1 data-logger and air/fuel-ratio meters now, I decided to have a conversation with them about built-in knock-sensing for their units, if nothing else - for tuning purposes...

They had some surprisingly negative things to say about them in general. The feeling among their engineers appears to be that there is too much inefficiency - especially in aftermarket units because there are so many different harmonic frequencies in there and two, their opinion was that a good tuner with the correct equipment should be able to eliminate any and all pre-ignition...

Don't shoot the messenger....

SydneyJules · Post by **SydneyJules** » Thu Jun 02, 2005 6:46 pm

My BMW mates are using the factory ECU with an intercept on their turbo M Coupe, just for the knock sensor. They're running 30psi of boost into a REAL expensive engine that tries to jump off dynos when it hits boost, so they're having trouble tuning the top end of the rev range.

Apparently it cuts ignition straight away, and adds fuel. Fair enough, but the owner is loaded, and doesnt care how much it costs.

Many tuners out here use ear muffs. Turns out the "rattling of keys" noise gets through better when all the low pitched noise around you is gone.

Just tune it right and you wont hurt anything!

kai · Post by **kai** » Thu Jun 02, 2005 11:20 pm

What frequencies are we looking at ?

You can also "sense ions" with normal sparkplugs. Measure directly after the spark. This can ofcourse only be used when you have one coil per sparkplug/cylinder.

Best Knock detector would be a DSP with its Fourier transformation functions. I think a lot of engineers are a bit scared of these because you need a deeper understanding of the maths involved. After a Fourier "transformation" you can look at any frequency seperately so you wont have to use extensive filtering which is the hardest part to get right in any measuring circuit.

Mats · Post by **Mats** » Fri Jun 03, 2005 1:22 am

JJ: Exactly, every engine has it's own frequency and stuff to dampen out so it's difficult to see the tendency to knock before it's knocking.
This is what we are really interested in, one high rev knock can blow an engine and is very difficult to detect/hear. low rev knocking is annoying and harmful in another way but high rev knocking is the destroyer.

I was talking about measuring with the regular plug after the ignition, this is done per cylinder every cycle. Saab's Trionic system has had this feature many years and thus has individual ignition tuning per cylinder and adjusted all the time when driving. Pretty nice... You can even re-learn the ECU to use a better fuel or alter the maps depending on other stuff by removing the battery leads a while and then do a high load pull on high gear (the longer/heavier load the better) and by that get a new base map. How cool is that?

Best place to put a knock sensor?