Adding a Knock Sensor

[frankc]

I am planning on using the Electromotive XDi2 for the electronic ignition project on my 2.7, and given that this unit contains an input for a knock sensor, I wondered if anyone has tried adding a knock sensor to a pre-Motronic 911 motor. Would I gain much by advancing the timing a bit more and having a knock sensor back things off when necessary? My setup is Webers, SSIs and Mahle 2.7 RS P&C (meaning I am only at 8.5:1 CR). If yes, where and how should the sensor be mounted? Where is it mounted on the 3.2 motor?

I did some searching here but did not come up with anything.

thanks for any insight or advice,
Frank

[efhughes3]

I think it's a tough addition since air-cooled 911 motors are pretty noisy and it's tough for the sensors to discern what a knock is. I'm no expert, however. I'd call Clewett Eng and ask them, they know these systems and 911's.

[frankc]

My bad - I thought the 3.2 Motronic motors had a knock sensor, but after a little more research I discovered that the sensors weren't introduced until the 3.6/964. But since these motors were still air cooled, their must be a way make this work.

I will be purchasing many of my direct fire parts from Clewett, so I will ask them about it.

Frank

[jpnovak]

Frank,

You can add a knock sensor. Yes a 911 motor is pretty noisy but the frequency range of detonation is different than that of the valve train. The base of the CIS throttle linkage plate stud seems to be an acceptable location. This is at the cylinder/case intersection for #3.

There are a few options but if you are going to a Clewett system use theirs for ease of installation.

[frankc]

Jamie,

Thanks for info. I was thinking that the sensor would have to be mounted closer to the head for some reason. If it can be mounted in the location you mention, that would be great. I may have removed that stud when I put the Webers on, but a bolt will certainly do.

I figured a high compression setup would benefit most from a knock sensor, but I'll see what Clewett has to say.

Frank

[jpnovak]

The base of the cylinder and/or case is a good area to mount the sensor. the shockwave from detonation is transmitted down through the piston, rod and into the crank where it can be detected on the case web.

[dfink]

Have just installed TEC3r and it was suggested by Richard Clewett not to use a knock sensor. This is on a 3.2 rebore to 3.4 with 10.5:1 JEs
Said the engines are very noisy. The TEC3r also has an input for knock. It might be something I give a try sometime but hate to push the engine that close to the limit.

[frankc]

Originally Posted by dfink

...it was suggested by Richard Clewett not to use a knock sensor.

Hmmm, not what I wanted to hear. I'll have to ask Clewett what is different about the 3.6 setup to allow the knock sensors to work on that motor.