Knock sensor question

darkstarmedia · Post by **darkstarmedia** » Tue Jan 24, 2006 9:10 pm

I have read a bit about the knock sense circut and the upcoming update. I was wondering how a wet sleeve style block would effect the knock frequency? I was wondering because there would be no real connection between the sleeve and the block. I was thinking the head but the head gasket is there... those whom are in the know, please share....

rufusbooth · Post by **rufusbooth** » Thu Jan 26, 2006 12:33 pm

Hi Richard,
I am no expert by any means and I am sure somebody will jump in and correct me if I am wrong. I do not believe the wet block will affect the frequency of the knock. I believe that is a function of cylinder diameter and shape of the combustion chamber and piston face.

I know that Ford actually places the knock sensor (5.0L V8) on the intake manifold towards the back of the engine. That being the case you should be able to mount the sensor on the intake or the block as it does not appear to be affected by separating gaskets.

I (personal unfounded opinion, Danger!, Danger!) would avoid placing the sensor on the cylinder head as there will be a lot of valve train noise up there. From what I understand that is the hardest thing to filter out of a knock sensors signal.

Hope that helps,

Cheers,

Rufus

darkstarmedia · Post by **darkstarmedia** » Thu Jan 26, 2006 12:37 pm

any formula to figure the frequency??

wes kiser · Post by **wes kiser** » Thu Jan 26, 2006 12:50 pm

Rougly equal to C/(2*b). Where C is equal to the speed of sound at the temperature you are concerned with, and b is the bore. Practically what you should do is to pick a sensor circuit from an engine with a similar bore size. Using the equation I mentioned, you will still only get close (because we don't know the exact temperature, and this is the real world not a textbook). Also the wet part doesn't effect the actual frequency, but will affect the amplitude of the noise. Valve train noise is difficult to deal with because it is frequently close to the knock frequency.

darkstarmedia · Post by **darkstarmedia** » Thu Jan 26, 2006 12:55 pm

how close would the bore have to be?? I have a 93mm bore (3.6614 in).

wes kiser · Post by **wes kiser** » Fri Jan 27, 2006 5:23 am

A chevy 305 has a 3.74 inch bore. I would think that would be close enough. Lots of them (complete with knock sensors and esc modules) are conveniently sitting in junk yards.

IcantDo55 · Post by **IcantDo55** » Mon Mar 27, 2006 11:50 am

rufusbooth wrote:Hi Richard,
I am no expert by any means and I am sure somebody will jump in and correct me if I am wrong. I do not believe the wet block will affect the frequency of the knock. I believe that is a function of cylinder diameter and shape of the combustion chamber and piston face.

I know that Ford actually places the knock sensor (5.0L V8) on the intake manifold towards the back of the engine. That being the case you should be able to mount the sensor on the intake or the block as it does not appear to be affected by separating gaskets.

I (personal unfounded opinion, Danger!, Danger!) would avoid placing the sensor on the cylinder head as there will be a lot of valve train noise up there. From what I understand that is the hardest thing to filter out of a knock sensors signal.

Hope that helps,

Cheers,

Rufus

The 5.0 blocks with knock sensors have them mounted into the BLOCK not the intake. Its behind the intake on the block just about where a Cheby distributor goes. The intake is in front of it.