Spark knock question

Ita Racer
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Posts: 36
Joined: Sat Aug 10, 2013 8:03 am
Location: Tampa Florida

Spark knock question

Postby Ita Racer » Tue Apr 27, 2021 10:24 am

I have 7A motor. I care know if I am having spark knock while racing. Any Ideas to add to get this info
85 AE86 Race Car
91 Supra non turbo
96 Celica convertible
2006 4 Runner

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Posts: 2759
Joined: Fri Jan 11, 2013 10:21 pm
Location: Wellington, New Zealand

Re: Spark knock question

Postby jondee86 » Tue Apr 27, 2021 3:36 pm

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...


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.


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
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