3.2 knock sensing?
 

Hi guys,I was wondering if 3.2 ignition is knock sensing. IS there a knock sensor input to the computer? I read on a dsm site that you can connect an LED to the knock sensor somehow, i don't recall how, and the led will light up if the slightest knock is detected. Might be a safe way to avoid any piston melting detonation.

Mike
86 Carrera t

No, the 3.6 is the first production 911 to have the knock sensors in the cylinder banks feeding the ECU.

[This message has been edited by orbmedia (edited 04-18-2001).]

Thanks Orb, i am surprised though, I figured since you can't adjust the timing on the 3.2, that the retard and advance was handled by the computer-completely.

Mike
86 Carrera t

I thought Bruce Anderson said the Knock sensor was first used on the '87 Carrera, hence the higher compression and the knock sensor to retard the ignition timing, then the higher HP #s



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Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in
Sacramento CA

Nope, no knock sensor on 3.2 motronic. Timing curves are "hard coded" in EPROM. This is one of the things the chip tuners play with.

Knock sensors were used on the dual-plug 964 engines. Air cooled engines do not easily lend themselves to "conventional" detonation sensing devices.

RarlyL8 wrote:
"Knock sensors were used on the dual-plug 964 engines. Air cooled engines do not easily lend themselves to "conventional" detonation sensing devices."

Why?

The air cooled engine is too noisy. Water cooled engines have water in the jackets surrounding the heads that muffle the mechanical sounds. Also the valve train of the 911 itself is more noisy than that of most hydraulic lifter autos.
Most of these sensing devices detect the shock wave or "knock" and make timing adjustments accordingly. Unfortunately, this is too late. A more modern approach is to sense the wave front that occurs before the knock and make corrections - before you can actually hear the detonation.

[This message has been edited by RarlyL8 (edited 04-20-2001).]

There is a product called J&S Safeguard that is supposed to work very well. There is someone on the 930 list at Rennlist that has used this on his 930 successfully though I understand that the 964/965 systems are even better because they have one sensor per bank of cylinders.

Although these systems have a tough time on air cooled engines because of their inherent high noise, they can be tuned to work well. The best thing about it is that it gives a visual telltale of knock occurring so you know to back off because too much retard can send EGTs through the roof. I have not tried them myself but hope to one day when I have the spare cash.

[This message has been edited by 930fan (edited 04-20-2001).]

Thanks for the reply, guys!

Mike
86 Carrera t