Adding a knock sensor

[berlow94]

Anyone here have experience with adding a knock sensor (or two) to an M20?
Going to a standlone ECU and would like to have it Knock limited (closed loop knock control) for safeness.

I'm assuming you would have to figure out an appropriate mounting boss and then have everything acoustically tuned for the bore size and spacing.

[nomansland92]

I run active knock control on my m20 with haltech

Here's how I mounted it to the side of the block





To set it up just did the math for the knock frequency for now and set the dB rating above natural engine noice, next time on the dyno if I have time I'm going to run into light knock on purpose and verify the settings and adjust if needed.
But so far it works great and Is a great safety feature.
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[mr2peak]

Anyone add a knock sensor with megasquirt?

[berlow94]

Anyone add a knock sensor with megasquirt?

I don't think MS actually has well functioning knock control or the ability to knock limit a motor.


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[mr2peak]

This kit here: http://www.viatrack.ca

It is recommended in the MegaManual, but the MegaManual also says it's for "Experimental purposes". Everything else I've read says that it works quite well.

Relevant MegaManual link http://www.megamanual.com/ms2/knock.htm

[downforce22]

I want to add a knock sensor also, curiously following this thread

[TobyB]

knock sensors are more for tow vehicles than race cars

says David Redszus on a different forum... cracked me right up.

t

[berlow94]

says David Redszus on a different forum... cracked me right up.

t

Ya that sounds like somebody stuck using 30+ year old engine managment. Does he know what "knock-limited" means?


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[downforce22]

Anybody get their installed yet?

[ForcedFirebird]

I have found an n/a m20 stops making power well before it knocks (using the angular squish pistons/head anyways), but the coolant drain hole on the passenger side of the block would be a great place for one. The flat pistons and 200/731 head may be a different story, though.

[Coyote_ar]

what i've read, is that the M20 makes so many noises from its valvetrain, that the knock sensor tends to pick them as knocking when its not really happening. and if you lower the sensitivity of the sensor to avoid false positives, then you wont detect knocking when you can tell its happening (on the dyno).

again, this is not first hand experience.

[digger]

I have found an n/a m20 stops making power well before it knocks (using the angular squish pistons/head anyways), but the coolant drain hole on the passenger side of the block would be a great place for one. The flat pistons and 200/731 head may be a different story, though.

by all reports Rama has had great results with flat tops and the 200/731 heads, it would have the same knock suppression capabilities as the 885 with the OEM style slugs. of course this is assuming you set the engine up correctly with suitable static CR , cam timing, piston to head clearances and a proper tune etc

on the other hand ive got couple mates with generic slugs with 885 and they are knock limited quite a bit it seems

[ForcedFirebird]

by all reports Rama has had great results with flat tops and the 200/731 heads, it would have the same knock suppression capabilities as the 885 with the OEM style slugs. of course this is assuming you set the engine up correctly with suitable static CR , cam timing, piston to head clearances and a proper tune etc

on the other hand ive got couple mates with generic slugs with 885 and they are knock limited quite a bit it seems

That's odd about the slugs. We tuned an eta with an 885 head for Time Trials in 2 different configurations so that a simple ECU swap and ballast, it could compete in two classes the same weekend - it got a track record in both classes and the two drivers won a full set of Hoosier's as a result. Anyways, the car made the most power with 27°, and the de-tune was in the low 20's (23° IIRC)

In contrast ITB 2.8 we built was left at 30.6° max, it was losing power with anything over 32.

Either way timing in the 30's *shouldn't* cause knock on an m20 so long as fueling is good. For fun we ran one up to 45 just to see if there was anything audible, but there was none, nor any evidence on the plugs it was just a dog with that much timing. Many times we dyno a stock m20 with stock electronics and they are in the 14 AFR's at WOT (but find mid-13's to be the "sweet spot), they are fairly robust over all, and pretty "detonation resistant" as they were designed.

[nando]

An NA M20 isnt likely to be knock limited before MBT anyway. I honestly think you are overcomplicating things..

Edit: ForcedFirebird beat me to it and he has even more M20 experience than me. Knock control is a waste of time on an NA M20. My personal engine reached MBT long before the knock threshold.

[tschultz]

This kit here: http://www.viatrack.ca

I have read about this one in a few places and a few people use it. Seems like a smart addition if you are trying to develop a good safe tune...

An NA M20 isnt likely to be knock limited before MBT anyway. I honestly think you are overcomplicating things..

Edit: ForcedFirebird beat me to it and he has even more M20 experience than me. Knock control is a waste of time on an NA M20. My personal engine reached MBT long before the knock threshold.

So then how does one fine tune timing if one has no idea if knock is occurring? By the time you hear it, isn't it already too late?