What’s engine knock?

Chances are that, if you’re learning or you’ve already mastered tuning, you came across some devices that can help you spot engine Knock.

These devices, are basically a combo of microphone/amplifier/headphones which will help you listen to what’s going on inside the engine.

Engine knock sounds different because the combustion isn’t happening at the same speed rate and not at the same timing compared to normal engine operation, but it’s not easily audible by ears if not using something directly in contact with the engine e.g. a Det can. For these who wonders what’s engine knock I suggest you to check at least this page:
https://en.wikipedia.org/wiki/Engine_knocking

When you have realized that avoiding engine knock is mandatory for good engine reliability, you’ll understand the importance to have a device that helps you to detect it: Det can or also called Knock sensing device.

These devices are pretty expensive to buy. Ofc the products on the market have better features but, if you’re on a budget and enjoy building your own stuff, you can build one by yourself.

Building the device

To build this device you will need:

  • An amplifier (DC 12V+) with an IN, for the knock sensor, OUT for headphones and a trimmer to control volume. I’ve used: TPA3116D2 Board DC 12-26V 100W TPA3116DA Mono bought it from here.
  • A suitable Knock Sensor, someone suggested using: 22060-30P00 (which is a knock sensor for Nissan) and this works flawlessly. I bought it from here.
  • 5 meters of audio shielded 18awg cable. I bought it from here.
  • A suitable box to keep the amplifier protected.
  • A set of headphones to sacrify, there are filtered headphones (for industrial use) which I’m being told they work the best, but they cost a fortune, so IMHO you should stick to common medium quality head-covering headphones.
  • 5 meters of electrical cable for your 12V supply, I’ve used 11awg cable for home power, which is more than enough for the low current flowing through.
  • a pair of electrical faston to connect the wire to the knock sensor.
  • Heat shrink tubing.
  • Scissors or cable splicer,
  • Optional: soldering iron to solder faston to cable to get the best connection possible.
Building process of the knock det-can

Once you bought all that stuff, the connections are very simple:

Splice the electrical cable (11awg) on both the extremities, then connect it to the VCC port of the amplifier

GND = and 12V = +

This will be your in-car power supply cable, just connect it to a car switched power supply or battery voltage.

Splice your shielded audio wire, then connect one extremity to the IN input in the amplifier board and the other extremity to the knock sensor using fastons and heat shrink tubing (solder the faston to the wire if possible). Polarity here doesn’t seem to matter, try it by yourself switching wires and see what works the best for you, to me it doesn’t matter.

Splice your headphone cable, yes i know it will be sacrificed, and connect it to the Audio Out of the amplifier. Alternatively you can buy a female headphone jack plug (usually 3,5mm) so you do not need to sacrify your headphones.

Now, find get a box that can contain the board, drill holes for wires, drill an hole to reach the trimmer from the outside and close the box. No need to seal it permanently as the hole for the trimmer will still be open but, hey, it will look much better inside a box 😀 and using a box will avoid electrical shorts that could be cause moving or touching the naked board around.

Homemade Knock detcan
Homemade Knock detcan final product

The final product is shown in the above picture. This looks pretty professional to me.

Using the knock detection can

Using the det-can is pretty simple. Wire the VCC power electrical wire to any switched or “hot” battery voltage supply wire and ground and find a place to install the knock sensor to.

The best place to install it is on the block close to the cylinders or, even betterm close to the combustion chamber. Since the hole is 8mm diameter you can install it in any M8 or M6 bolt (using a washer) . Every engine is different so you should find the place which works the best for you.

Getting used to effectively spot knock on an engine is pretty easy, you can use a small, but a little risky, trick: induce low knock on low rpm partial throttle (be careful to not induce it when on boost as it can be very destructive). To induce it, just give it 2 degree timing on that area until you hear the engine sound change. When the engine sound turns noisy, like steel marbles moving around in a can, that’s engine knock. The best would be to experiment on an engine we don’t care about and take some experience to tune your worthy engine.

Enjoy your tool and show it off, you’ll look very professional when you tune with your headphones on!

Thanks for reading.