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Spark knock question

Posted: Tue Apr 27, 2021 10:24 am
by Ita Racer
I have 7A motor. I care know if I am having spark knock while racing. Any Ideas to add to get this info

Re: Spark knock question

Posted: Tue Apr 27, 2021 3:36 pm
by jondee86
Take a look at your sparkplugs... do a plug "chop". Straight after the finish line or as soon
as you can safely do it, switch off the engine and pull the plugs. Get hold of a jeweler's
loupe or a 5 to 10 times magnifier and examine the porcelain part of each plug looking for
signs of detonation.

You will be looking for tiny black flecks of carbon fused to the porcelain or tiny silver balls
of aluminum stuck to the surface. The carbon has been shaken loose from the piston top
of rings by the detonation shock waves and the aluminum is picked out on the overheated
piston top. The top of the piston will show tiny pits especially near the piston wall.

This picture is from the internet and shows black flecks...

Image

This picture is one of mine and shows a whole bunch of melted stuff stuck to the porcelain.
Turned out to be mostly the ceramic coating melted off the top of a GZE piston :D Notice
that to the naked eye these plugs would look to be near enough OK which it why you have
to have a decent magnifier to see the first signs of det in time to tweak your tune.

Image

Other methods depend on what ECU you are using. Aftermarket ECU's will usually have
knock sensor inputs and you can log the number of knock counts you are getting. Or you
can buy separate knock detector system like PLEX etc.

Cheers... jondee86

Re: Spark knock question

Posted: Wed May 26, 2021 4:08 am
by Davegt27
never heard of spark knock

do you have any idea what your C/R is ?

how about type and octane of the fuel your using ?
do you have an AF ratio meter ?


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