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MG MGA - Knock Sensor

In an earlier post Dominic said:

"I use the pertronix linked to a J&S safeguard. The Safeguard is a VERY nifty bit of kit that advances and retards the timing in real time on each cylinder, using info received from a knock sensor mounted at the front of the engine block."

Has anybody else tried one on an MGA?
I did have one on a Triumph sports car, but it proved unsatisfactory. In racing conditions, or on the Dyno, it was triggered by other vibrations.

For Dominic,
You say that it retarded ignition timing on individual detonating cylinders. My Motec unit retarded the overall timing when detonation took place on any cylinder. I find it difficult to see how it would identify the actual cylinder by sensing engine block vibration.
Vehicle manufacturers use a special spark plug incorporating a knock sensor, but these cost several thousand dollars per spark plug, and are only used for engine development.

Mick
M F Anderson

In a part answer to my own question, I suppose that an engine management computer would know which cylinder would be firing at the time the detonation occurred. However, I would not be too keen on an engine running at full load and full RPM with individual cylinders firing on different timings.

Mick
M F Anderson

Mick

I am also prone to questioning snake-oil solutions. I can only say that it took a little fiddling to get the sensitivity correctly set on the J&S. Too much and the car is sluggish, too little, there is a risk of detonation, but when set right, just great. On a knackered engine with lots of internal rattles, you are probably right, it won't work. On a correctly set up and well balanced engine with correctly set valves, it works a treat. It also has a facility to limit RPM. The unit can be set to either retard individual cylinders or all of them, using a switch on the panel. The amount of retard can also be set the same way. The knock sensor was a new unit that I picked up on ebay for about 20US.

Try reading the manufacturer's web site, and do a google, there is a lot of positive comment out there. It's normally used for high performance race cars, so high load and RPM do not appear to be a problem.

I also suggested the unit to a local Jaguar specialist who had spent weeks trying to solve detonation problems in a higly tuned e-type. He took the plunge, and it cured all the issues in one go. He was extremely positive too.

I have found that if the oiler for the Judsn is sending too little oil and the vanes are rattling a bit, that this causes false positives, so I have to wind the oil supply up a bit, but apart from that I can only report good things.

The next step is to fit a threaded bos to the exhaust for an Air/Fuel sensor, as the display for the J&S (hidden in the ashtray on my car!) also has an AF section to indicate lean or rich running. I have the sensor already (ebay again) but that will be a winter job.


dominic clancy

Just one last thing - a modern engine management system does make an engine run with each cylinder being fired at the optimal point for power and emmissions, rather than the timing being fixed and constant. Anyone running a knackered distributor in their A is also doing the same thing, albeit with a random timing variable as the shaft flops around, and absolutely no measurement and control loop in the system to optimise anything!

For those among the brethren suffereing from this affliction, I heartily recommend Jeff Schlemmer!


dominic clancy

This thread was discussed on 20/08/2008

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