Advice on positioning second knock sensor for tuning

[Danbob]

Hi all,. I'm using a knock link system which utilises a broadband Bosch knock sensor as a secondary aid for tuning.
Unfortunately on my engine there is no appropriate m8 threaded hole around the combustion chamber area on the block or head. Best I can get is on the top of the head in the middle, near where the rocker cover bolts up.

Question is, for purposes of tuning, can I trust a sensor placed there? The system appears to be working, I get lights detecting knock at high Rpms as I'd expect due to valve train noise, but it's currently telling me I have no knock around the danger area 3-5000 rpm.

As this is my first time tuning, can somebody let me know if you'd expect for it to pick up genuine knock mounted up on the top surface of the head?

Thanks
Dan

[Yves]

The head is usually too noisy from the operation of the valvetrain. Not sure what your engine is, but on my SBC the general advice was to use the hole in the side of the block just above the pan rails. Even there it's virtually unuseable due to the noise from the valvetrain. I do run a mechanical roller cam, which of course is not good noise wise. When people inquire about knock sensor, I usually joke it's better suited at detecting valvetrain issues than knock. Subsequently I don't really use it and just observe my spark plugs closely and listen to the engine.

[Danbob]

I'm running a Toyota 3SGTE four pot. DOHC with solid lifters, no rockers.

I know the location is not ideal and if I decide to run both systems in the car permanently I'll find a way of mounting it near the OEM sensor,. But just need to know if as a temporary solution having it on the head should give me any confidence at all?

For example do any Dyno tuners quickly stick a knock sensor on the head to monitor? Rather than trying to get something in under the car onto the block?

[rukavina]

Not sure what sensor you have but can you stack them both one atop the other in the same oem hole. As long as there tight and have continuous metal to metal contact , not counting the Bolt it should work

[Danbob]

Unfortunately not an option for me as the OEM sensor is a m10x1.5 thread which scews directly into the block whereas the knock link uses a Bosch donut type sensor which needs an m8 bolt to secure it.

[Danbob]

For future people reading this thread I spoke to a well respected tuner at a Yesterday who told me they regularly attach a knock sensor on the top side of the head while tuning and are able to detect knock from there.

[benckj]

Running a 3sgte myself I will be curious to what comparative results you find between new sensor and the stock Toyota one with MS signal conditioning. I'm still trying to get my MSPNP dialled in to effectively read real knock but have no way to check if correct.

A couple of years ago I had my car on dyno while I was running the stock ECU and the Tuner placed a knock sensor and headphone input to a bolt on the valve cover. Believe he got more input from the headphones than any sensible knock sensor readings. Didn't really mean anything at the time because I couldn't adjust any settings.

[Danbob]

Back to back results will take a while as I'm still running stock ECU at this point, I just wanted to use the knock link as a way of checking I wasn't getting knock as I moved the boost up over the weekend as I was competing in a sprint.
It all worked out in the end.
I've built a megasquirt 3x with the integrated knock module and if all goes to plan I'll get that installed and running over winter ready for next year. I plan to have megasquirt reading the stock Toyota knock sensor and get an adapter to fit a Bosch sensor to the M10 boss that sits just to the side of the stock sensor and run a knock link from that to give an overcheck until I fully trust that the ms3x is working right with the OEM sensor