Knock Sensor on a Nord?

[brook308]

Hi All,

Who out there is running a knock sensor on a Nord?

I'm thinking about running one on my turbo race engine but from what I've read it's not easy to get a valid signal on a Nord let alone a turbo race version.

I was hoping to have the sensor feed back to my 123 ignition to back off timing and set off a light in the cab so I know when it's kicking in.

I run blow through dellortos so I can't control fuel only timing.

Cheers

George

[AikenDrum105]

Hi George,  I've mounted mine off the lower intake manifold mounting near cyl3.  There's still a good amount of scattered noise particularly at higher rpm - but up to 3500/4000 or so it's pretty clean.

That's on a normally aspirated TS  with MeqaSquirt injection  -   if you can use a knock sensor that has the ability narrow down the sensing window to certain parts of the engine cycle that makes a big difference - as does the use of a wideband sensor to allow you to tune it to the unique ping frequency of your engine.   


http://www.alfabb.com/bb/forums/engine-management/203129-nord-knock-sensor-mounting.html

Hope that helps a little !

[brook308]

Thanks Scott,

Do you happen to have a part number for the bosch sensor you used?

I'll have to do some research on these suckers as I have no idea what their output is and how to deal with it.

I don't have an ecu on this motor so was looking for some sort of on/out output from the sensor to drive a relay but it sounds like the output is something that then needs to be tuned/interpreted by an ecu.

The car's running on AVgas at the moment but I want to go back to pump 98 and put some timing back when on boost. Very close to deciding on a water-meth kit, probably a stage 2 AEM to install but I thought at the same time I'll look at knock detection, as I want to run 15 psi which is about the limit of the carbs and the 123 dizzy.

[AikenDrum105]

As it happens, I do.  This one was recommended to me by Festy as a generic wideband knock sensor - have a search on ebay for "infiniti knock sensor"  the original bosch ones are expensive, but there are plenty of aftermarket ones that are cheap and cheerful (and offer a range of connectors to suit - I usually go with the bosch 'junior timer' style to match the rest of my loom) 

He's actually developed a very nice knock sensing kit himself  - I'd drop him a PM and see if any are still available and if they'd be able to help in your application.

http://www.alfabb.com/bb/forums/engine-management/190352-what-stock-75-ts-motronic-can-cannot-do-53.html#post1291849

[brook308]

Cheers Scott, i've sent festy a PM

[MD]

brook 308,

I have a festy install kit on my TS supercharged engine. It is a Bosch style sensor. It is located on the back of the head where the (I think) the factory sensor was placed.
Is it successful? Well partially. Still trying to "tune" it onto the detonation noise as opposed to engine mechanical noise. Presently it is a work in progress.
I use a high power LED behind a a simple red light lens to signal detonation. This part works well.
My next attempt is to fine tune the detonation noise by recording the analogue audio output from the sender and festy is going to analyze that for the noise frequencies (I think). Once we know that, we can then use some better filtering to narrow down the actual detonation noise.

[Craig_m67]

Wow
I'd love to see this car, does it get out much ?

[brook308]

brook 308,

I have a festy install kit on my TS supercharged engine. It is a Bosch style sensor. It is located on the back of the head where the (I think) the factory sensor was placed.
Is it successful? Well partially. Still trying to "tune" it onto the detonation noise as opposed to engine mechanical noise. Presently it is a work in progress.
I use a high power LED behind a a simple red light lens to signal detonation. This part works well.
My next attempt is to fine tune the detonation noise by recording the analogue audio output from the sender and festy is going to analyze that for the noise frequencies (I think). Once we know that, we can then use some better filtering to narrow down the actual detonation noise.

Cheers Mike,

So am I correct in assuming the actual knock sensor itself is just an acoustic coupler and the smarts lie in the ecu that then interprets the output from the sensor?

[MD]

So am I correct in assuming the actual knock sensor itself is just an acoustic coupler

That part is correct. The follow on from this is a separate processor module made by festy to analyze the sensor info and produce an LED output. The output could be fed into an ECU that had the facility to alter timing or fuel but that would depend on the type of ECU. eg. the Haltech doesn't have it. Don't know about others.

The key problem is differentiating between electric noise generated by mechanical noise that is interpreted as detonation and ACTUAL detonation signal that needs attention. This requires very careful filtering if it can be done at all using this technique.

[MD]

Wow
I'd love to see this car, does it get out much

If you mean mine...

While I am developing mine, I tend to go out testing at the GEAR meetings. See the calendar here:http://gear.org.au/#/calendar/4577134852

Other outings are sporadic but we only frequent Lakeside and QR under AAASA license requirements.

[festy]

mmm... knock sensing - a topic I could ramble on about for hours 
There are a few different types of knock sensors, some are tuned to a specific frequency range (commonly called "broadband" sensors which is rather misleading) and others that are not tuned (called "flat response"). Then there's others like harmonic broadband sensors etc, but for aftermarket fitment your best bet is a flat response sensor.
They are in effect just a microphone - if you record the signal they produce, you get something like this.
If you listen to that, the knock isn't the loud noise a few seconds in, it's the quiet metallic twanging that follows.

I've had great success with those ebay generic knock sensors that Scott linked to earlier. Avoid GM sensors, because they're not flat response type.

I installed one on my nord by making a replacement block drain plug:




The ideal location is as close to the compustion chamber as possible, while being as far away from other noise sources as practical. Cam chains are noisy, so the back of the engine is preferable for us.
The TS's sensor location in MD's photo looks pretty good.
I've tested one on the inlet manifold of my EFI-converted nord, even being right next to an injector it gave very decent results.

But acquiring the signal is the easy part - detecting knock in amongst the background noise is not so simple.
To give you an idea, here's a representation of a signal from a knock sensor - there's a knock at about 6000Hz:


Here's another example:


The rough knock frequency for an engine can be calculated from the cylinder bore, that will get you into the right ballpark to start with.

A few years ago I wanted to add a knock sensor to my Alfetta but there wasn't really anything decent available so I designed my own.
When I'm setting up a knock system on a car the first step is to calculate the knock frequency, then with the engine idling I increase timing for a second to induce knock and start dialing in the knock filter settings.
Once I can reliably detect knock at idle, I go for a drive around the block (with a laptop, as passenger) and tweak the settings to get the best detection.
A while ago I set one up on an EFI'd Fiat twincam. It took about 5 minutes in my driveway to do the initial configuration, then 10 minutes driving around the streets to fine tune before it was giving reliable results.
Here's a log from during the fine tuning - there's a few bits of knock as revs start to build after gear changes but as soon as the timing gets stepped back by the knock retard function, it goes away:


On a track car it's not quite that easy, as knock is harder to detect at higher RPM because all the background noise is so much louder.
But with a bit of time and effort you should still be able to get decent results. My modules have been fitted to some pretty crazy cars before...

And brook308 if you ever want to have a chat about converting to EFI, I can help
My conversion cost me about $300 total, and is a million times better than carbs.   




 

[MD]

Somebody buy festy a beer. I mean what a guy ! Intelligence to burn but happy to share.

Is he an asset (and then some) to the Forum or what !!

[brook308]

Somebody buy festy a beer. I mean what a guy ! Intelligence to burn but happy to share.

Is he an asset (and then some) to the Forum or what !!

Yep fair lump of R&D there. Will get in touch with festy to work out a way forward.