Knock Sensor

DaveEFI · Post by **DaveEFI** » Wed Mar 17, 2010 7:55 am

I've got a knock sensor kit for use with my RV8 and MegaSquirt, and wonder where to fit the sensor. Iit's a through bolt type. I know where they go on later engines fitted with them - but wonder what the easy way is on a block not made for one?

daxtojeiro · Post by **daxtojeiro** » Wed Mar 17, 2010 10:25 am

Apparently they need fitting in the middle of each cylinder head, you really need the original sensors to make it work, as they are tuned for the knock frequency of the specific engine.
Youll also find the valve train can upset them at high rpm, so try to mount it where the original ones were if you can. To be honest, they do give a lot of false readings and are only really worth adding on highly strung turbo motors. Just dont go any higher than 28deg advance at WOT on a NA RV8 and youll be fine, if you have knock then you have other issues,
Phil

topcatcustom · Post by **topcatcustom** » Wed Mar 17, 2010 12:13 pm

I know little of this trickery- but if they are best off going on the cylinder heads why did rover mount them on the block walls?

DaveEFI · Post by **DaveEFI** » Wed Mar 17, 2010 1:38 pm

topcatproduction wrote:I know little of this trickery- but if they are best off going on the cylinder heads why did rover mount them on the block walls?

To get away from valve train noise is my guess. I did wonder about just drilling into the water jacket, fitting a stud with the tread well sealed, and bulding up a flat surface for the sensor with JBWeld or whatever.

DaveEFI · Post by **DaveEFI** » Wed Mar 17, 2010 1:43 pm

daxtojeiro wrote:Apparently they need fitting in the middle of each cylinder head, you really need the original sensors to make it work, as they are tuned for the knock frequency of the specific engine.
Youll also find the valve train can upset them at high rpm, so try to mount it where the original ones were if you can. To be honest, they do give a lot of false readings and are only really worth adding on highly strung turbo motors. Just dont go any higher than 28deg advance at WOT on a NA RV8 and youll be fine, if you have knock then you have other issues,
Phil

I can vary the frequency and Q of my knock sensor electronics - it's home made.
I'm trying to get as economical a cruise as I can so may be using more advance than just for power. And I'd guess there's a reason for most modern engines having them.

daxtojeiro · Post by **daxtojeiro** » Wed Mar 17, 2010 3:52 pm

DaveEFI wrote:
daxtojeiro wrote:Apparently they need fitting in the middle of each cylinder head, you really need the original sensors to make it work, as they are tuned for the knock frequency of the specific engine.
Youll also find the valve train can upset them at high rpm, so try to mount it where the original ones were if you can. To be honest, they do give a lot of false readings and are only really worth adding on highly strung turbo motors. Just dont go any higher than 28deg advance at WOT on a NA RV8 and youll be fine, if you have knock then you have other issues,
Phil
I can vary the frequency and Q of my knock sensor electronics - it's home made.
I'm trying to get as economical a cruise as I can so may be using more advance than just for power. And I'd guess there's a reason for most modern engines having them.

I've designed and built many circuits for these and I've looked into this in great detail when I wrote the code for the knock retard section of MS and its the sensor thats the tuned part of the circuit, you can add what ever filter you want to the amp circuit.
OEMs spend a lot of time on R+D, they dont get any sensor and pop it onto the block. Take for example the Chevy sensor, that has a tuned frequency of 5.2Khz and work between 4900 and 5600rpm.
If your advancing soo much at cruise that you have knock then you have a serious issue, youll get missfires first.
Sorry, sounds negative, please don't let me put you off, but also, don't rely on it as it simply wont do what you hope it will,
Phil

DaveEFI · Post by **DaveEFI** » Wed Mar 17, 2010 4:38 pm

daxtojeiro wrote:
DaveEFI wrote:
daxtojeiro wrote:Apparently they need fitting in the middle of each cylinder head, you really need the original sensors to make it work, as they are tuned for the knock frequency of the specific engine.
Youll also find the valve train can upset them at high rpm, so try to mount it where the original ones were if you can. To be honest, they do give a lot of false readings and are only really worth adding on highly strung turbo motors. Just dont go any higher than 28deg advance at WOT on a NA RV8 and youll be fine, if you have knock then you have other issues,
Phil
I can vary the frequency and Q of my knock sensor electronics - it's home made.
I'm trying to get as economical a cruise as I can so may be using more advance than just for power. And I'd guess there's a reason for most modern engines having them.
I've designed and built many circuits for these and I've looked into this in great detail when I wrote the code for the knock retard section of MS and its the sensor thats the tuned part of the circuit, you can add what ever filter you want to the amp circuit.
OEMs spend a lot of time on R+D, they dont get any sensor and pop it onto the block. Take for example the Chevy sensor, that has a tuned frequency of 5.2Khz and work between 4900 and 5600rpm.
If your advancing soo much at cruise that you have knock then you have a serious issue, youll get missfires first.
Sorry, sounds negative, please don't let me put you off, but also, don't rely on it as it simply wont do what you hope it will,
Phil

Thanks, Phil. Are you actually saying not to bother with one? I'd be happy not to.

daxtojeiro · Post by **daxtojeiro** » Thu Mar 18, 2010 12:55 pm

Hi Dave,
all Im saying (not very well I have to say) is you must use the correct sensor and position it where they fitted it, if not then you wont detect knock when you need to.
Knock is really an issue at WOT or there abouts, not cruising. Stick to 28deg at WOT and it shouldnt knock, if it does then you have issues you need to cure. Have a read of this file if you want to:
http://www.extraefi.co.uk/software/knock.pdf
Phil

kiwicar · Post by **kiwicar** » Thu Mar 18, 2010 1:38 pm

Hi for my 2p worth, if you are really going for as lean a burn as you can, rather than fuss with knock sensors, which as Phill says really shouldn't be relied on at cruse you could stick in alot of timing advance at cruise and use water injection to control the initiation of the mixture burn (ie avoid detonation). The water will enable you to get a very lean mixture fully burnt without the very high peak cylinder pressures at TDC that cause detonation. In theory the state change from liquid to gas of the water will extract more energy of combustion that can then be converted to mechanical energy by the engine. However If it were me I wouldn't be bothered with doing any of this on a rover that has such a rubbish cylinder head to start with.
Best regards
Mike

stevieturbo · Post by **stevieturbo** » Thu Mar 18, 2010 9:05 pm

The noise does travel through the entire block/head and can be heard almost anywhere.

Obviously some locations are better than others though.

But for a n/a build, its probably rather pointless having one.