- Knock is one of the biggest killers of performance engines
and in this lesson, you're going to find out
what knock sounds like and how an ECU can detect it.
Now we're going to have a brief demonstration
of knock audio on our dyno here using our Nissan 350z
to demonstrate what's going on.
Now we're using the plex knock monitor version two
to bring you the knock audio.
And at the same time so that you can visually see
exactly what's going on,
we're also going to be looking at the data logging
from the Link G4 Plus ECU.
Now I'm just going to briefly explain what's being shown
on the data logging.
The first parameter in our data log
here is our engine speed.
And moving down from here you'll be able to also see
the throttle position and the ignition timing.
Next we've got a group here that is demonstrating
the amount of noise being generated on each
of the six cylinders on our engine.
And we also have a knock threshold,
which you can see this is the white line being shown
on our data log.
Now the knock threshold essentially,
this is the point where if any of the cylinder noise levels
exceed this threshold,
the ECU will deem that the engine is knocking,
and take preventative measures.
At the bottom we also have another group,
which shows the knock count.
So any time an individual cylinder knocks,
this counter will increment.
Alright let's get our engine running now,
we're going to perform this test at 2000 RPM in fourth gear.
OK so we've got our car running now in fourth gear,
and we can see that at the moment we're sitting
just below 2000 RPM.
You can see that I'm not using very much throttle right now,
we're only using about 14% or 15% throttle,
so I'm barely touching the throttle,
and there's not much load being placed on the engine.
At the same time you can see that at the moment
we have 26 degrees of ignition advance.
Now the important point to note now is if we look
at all of our individual cylinder knock levels,
these are all below that threshold which currently
is sitting at 40.
And at the same time if we listen to the audio signal
that's coming through, all we're currently hearing
is just the normal background engine noise
that we can expect to hear in any engine.
Now that we've seen what the knock signals
are looking like with no knock and you've heard
what the engine sounds like with no knock occurring,
what I'm going to do is I'm going to open the throttle fully
and this is going to result in some knock occurring.
You'll hear the audio note change,
and at the same time you'll be able to see the individual
cylinder knock levels exceed the threshold.
So let's do that now.
So we can see that when I've gone to full throttle
at this point, the ignition timing now has advanced
out to 45 degrees and this is what has resulted
in our detonation that you would've been able
to audibly hear.
At the same time we can see that there's several instances
where our cylinder knock levels have exceeded
our knock threshold.
And while that's happening we can see that our knock
counter has incremented on a number of the cylinders.
Let's perform one more test and we'll just go through
that again so you get another opportunity to hear this.
So this test should give you some insight
into what knock sounds like when we're listening
to it through an audio knock detection system.
Now admittedly some engines are a little bit more
difficult to distinguish between that normal background
noise level and the actual sounds of knock.
And at the same time other engines,
the distinction is actually even clearer
than what we have here on our 350z.
That was just one lesson from our EFI tuning
fundamentals course.
This course is the perfect place to start
if you want to learn how to tune EFI,
or for those who are just interested in finding out
how EFI tuning works.
For more information and to purchase the course,
click the link now.