If an aluminum block and heads are used, standard small block chevy, the knock sensor from the original iron block will not operate correctly. Am I correct?

 

No.

The KS is nothing more, or less, than a little microphone, mechanically and acoustically (not electronically) tuned to the resonant frequency of the cylinder bore.

Therefore if you have a 4" bore, you need a knock sensor for a 4" bore. Doesn't matter if your CID is 302, 327, 350, or 383; 4" bore is all you need to know. In any of those cases, a stock one for a 350, would be appropriate.

The tuning isn't all that sharp though; if you used a 305 one (3.736" bore) in a 350, it would just be somewhat insensitive compared to stock specs.

Aluminum and iron have nothing to do with it. Neither does anything whatsoever to do with the heads.

But since there's no such thing as a "standard small block Chevy" with an aluminum block, it's kind of a moot point.

 

I could be wrong, but I would assume "standard small block chevy" is meant to distinguish it from LS-family engines.

 

Sorry I should have said gen 1. I think that is the correct term for an 89 SBC. I was wondering that since the knock sensor is designed to pick up a certain frequency on an iron block an aluminum block would have a different knock tone/frequency and the sensor may create problems. Has anyone had any experience with this on aluminum blocks? Didn't have much luck with a search on this. Thanks GWW

 

No an aluminum 89 SBC block, even if such a thing existed, would not have a different "tone", because that is determined by THE BORE, not the casting material.

I happen to occasionally buy, refurb, and sell professional grade woodwind musical instruments, when I have nothing better to think about... same thing goes on in that business, except instead of aluminum vs iron, it's plastic vs wood vs metal tubing. Well guess what... out of all the instruments that can be made out of any of those 3 materials (say, oboe or clarinet or flute) THE ONLY thing that determines the tuning is the DIMENSIONS. The material is totally irrelevant.

 

You know sofa I never really thought of that but youre right. There are very specific equations to give you resonant frequencies and harmonics with open pipes, closed-end pipes, etc, and none of them have a variable for the material, which I presume would be the density. That comes into play for other formulas, but not the ones involving frequency.

 

Material affects the transmissiblity of the sound, but not the frequency of the sound transmitted. Iron absorbs more sound than aluminum, but that's amplitude, not frequency.