Knock Sensor

Last updated: September 25, 1998

Date: Thu, 24 Sep 1998 22:28:45 -0500
From: Shiv Pathak

I've known John Pizzuto from J&S Electronics for a couple years now. I used his Safeguard knock sensor on my turbo Miata with good results. Better knock sensor logic than the system that came on my TEC-II. Brian Richard also has good experiences with his Safeguard for the FD. Abel and Adam S. use them on their drag cars too. SCC's Project RX-7 will be using their system in the near future. J&S's new design (functionally the same, just a lot prettier now) will also be availabe in a few weeks. Cheap insurance for your rotary, it would seem. I've heard that Adam has said it has saved his engine many times... I've had no first-hand experience on rotaries yet...

J&S can be reached at 714-534-6975.


Date: Thu, 26 Mar 1998 21:56:07 -0800
From: "David H. Lane"

I have a J&S unit on my car, which is an '85 GSL-SE with an after market turbo. I also have the read-out for the amount of retard being dialed in. The object is to set it up so that you get no reading under max boost. This is as opposed to setting it up to rely on it routinely to retard the spark under boost. You shouldn't see it activate unless you are messing with things, and have probably gone too far. You will know it is right if you have established a baseline where you know boost is about the max you can safely run. Set the J&S unit to activate at any point above that.

Of course, if you hear detonation, you need to make it a little more sensitive. My unit is set so that the screw slot is on a line between 11 and 5 on a clock face, about a quarter turn clockwise from the least sensitive position. I have also discovered that if the unit is too sensitive, it will retard the leading plugs past where the trailing plugs fire. For some reason, this seems to cause pinging.

I have not hooked up the yellow wire because I have not had a problem, however, I do occasionally see a flicker on the indicator when the car is off throttle--especially if I have just completed a high boost run. It isn't worth worrying about.

If you don't already have it, you should get the read-out to tell you what is going on with the knock sensor. As an alternative you can use a volt meter hooked up to a mini jack and plugged into the front of the control box. J&S makes a version of the read-out with a parallel line of LED's that is an A/F meter. The combination meter takes up very little room. I wish I had gone that route. Twenty-twenty hindsight, eh?


Date: Wed, 04 Nov 1998 13:46:17 -0500
From: Shiv Pathak

J&S Electronics has visually redesigned their knock sensor for the 3rd gen RX-7. It now looks like a pretty anodized box now and far more presentable than the previous plastic units. For those who don't know, Adam and Abel both use this unit (although they don't like to tell anyone.) It has saved more than one motor, from what I've been told.

For a engine that can be destroyed by one knock, it looks like a good precautionary measure since the stock knock sensor doesn't seem to have the necessary authority range to prevent knock on a modified engine. John Pizzuto as J&S told me that Mostly Mazda (925-686-9055) is the exclusive dealer on the West Coast.

The kit includes a electronic control unit (with sensativity adjustments) and a microphone. Installation is simple and requires very little wiring. Costs $425. An optional plug-in a/f ratiometer and ignition retard monitor is a $150 option.

Blatant plug, I know, but I've heard and seen good things about this product. The guys at MM consider it a highly recommended upgrade for those with a free flowing and higher boosting rx7. A good idea for the track too. I used one on my 330hp turbo Miata will good results-- stock bottom end for 50k miles before the car was totalled.

FWIW, the product will be covered in Part III of SCC's Project RX-7 (Feb. issue)


From: Shiv S. Pathak []
Sent: Tuesday, December 01, 1998 9:20 PM

Just got back from some Project RX-7 dyno testing at Superior Dyno Service in Hayward, CA.

(non J&S stuff snipped)

We also tested with varying degrees of J&S sensitivity, from no retard (insensitive) to 4-5 degrees retard at certain rpm (pretty darn sensitive). Surprisingly, no measurable hp change either way.

It seems the only place that the J&S wants pulls out timing is at 3000rpm when the secondary injectors turn on and when the 2nd turbo hits (sudden change in load). Worked as designed... very nice. However, even when the J&S was disconnected, car was never close to knocking, but it nice to know that the J&S is listening carefully-- ready to pull out timing in case something goes wrong. When we up the hp more and get closer to the fuel limits of the car, it should be very helpful. Anyway, it's a nice safety feature to have on the track when the car is under heavy loads for long periods of time.

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