Detonation, Knocking & etc.
 

OK, here is a newly started thread at Grady's request....


We should probably define terms and describe the effects and signs (how they 'present' in medical terminology - symptomology) but I ain't gonna since others can do a far better job.

But I do have 1 comment to offer re: "knowledgeable dyno operator can spot the signs of detonation" from a prev. thread.
- tho true, he will only find 'big' knocking -- some recent engine research (1980's??) has found that there is micro-detonation that cannot be detected by humans. I think some of the more advanced engine mgmt. systems (Saab comes to mind for some reason) with knock detectors can detect these tiny knocks ...

We feel we've flogged this dead horse until it's unrecognizable.

I believe you mean "dead dog".

http://forums.pelicanparts.com/uploa...1131564473.gif

Is that what it is . . . kind of unrecognizable. ::cool:

Randy;

See, you just can't start an intelligent thread/discussion on certain topics.
Some just don't want to hear it! It's sad isn't it, the response you get on
this (technical?) forum. Just review the 3.2 threads on performance chips
and "pushing" the ignition advance maps.

"...... that "detonation" refers to abnormal explosion(s) AFTER the normal ignition. If spontaneous ignition occurs before the spark plug fires, that's a different and far more dangerous condition: "preignition." Either condition can lead to the other, and once they start working together, catastrophic engine failure is only seconds away."

Ha, Loren . . you, the guy who holds info so close to your vest ...

Many of us have gone on and on, with this topic already.

Advantage of twinplugging

Why do lean cars run hotter?

. . . are a couple of five star threads, of the dozen that I've chimed in on.

good idea for another 'ultimate' thread. Im massively concerned about detonation in my high hp 3.3t because i can't really afford for it to happen. the engine alone is going to cost me more than ive ever spent on a complete car so this is probably my biggest concern at the moment. how do I ACURATLY measure detonation? I understand why it happens in turbo engines (too much boost-lean a/f) but how do i gauge when its close to happening?

While this is a modest 2.0T piston it illustrates why this is important.

http://forums.pelicanparts.com/uploa...1131572134.jpg

http://forums.pelicanparts.com/uploa...1131572170.jpg

http://forums.pelicanparts.com/uploa...1131572197.jpg

http://forums.pelicanparts.com/uploa...1131572227.jpg

No, I didn't do this on the dyno. It was towed in after "loosing
power."

Had this been a 90 mm, 95 or larger, it would probably have
collapsed the piston around the top ring first.

I understand that Porsche’s knock sensor is a piezoelectric
contact microphone who’s frequency characteristics only pick
up the high frequencies characteristic of detonation and not
all the other engine noise. Who knows something about this?

Best,
Grady

Before we rehash it, though ( which I wouldn't mind doing) let's everybody start from the same baseline- by reading the below.

http://www.avweb.com/news/columns/182132-1.html

Grady - that sounds vaguely familiar re the mic...

really, would be a vibration sensor more than what we usually think of as a mic tho.

to my understanding

severe detonation quickly leads to pre-ignition. Pre-ignition is easy to measure as the EGTs skyrocket.

Hey Grady - just noticed that hp item next to the piston. What is it? Something interesting?

Randy,

It is probably semantics more than anything. I think of an
accelerometer as a “vibration sensor.” A sensitive one works
just fine as a microphone. Then there are several different
kinds of “microphones;” acoustic- what we speak into with
a gas medium, hydrophones- for listening under water using
a liquid medium and contact microphones where the medium
is solid. Just word play.

The real issue is knowing the characteristic of the knock. I’m sure
there are many professional papers on the subject. I suspect
that if you recorded engine noise without knock and did a
spectral (Fourier) analysis it would differ from the same recording
and analysis with knock. I will speculate that almost all the
difference is high frequency audio to ultrasonic above our
hearing.

I think the knock sensing “contact microphone” frequency
response characteristics are very non-linear and detect only
the knock frequencies.

I think the Flugmotor had both a thermocouple (green arrow)
and a knock sensor here (red arrow):
http://forums.pelicanparts.com/uploa...1131590292.jpg
http://forums.pelicanparts.com/uploa...1131590342.jpg

Apparently these heads were used in a 914-6 and seem to only
use the thermocouple for head temp. This certainly looks like a
good location for a knock sensor if it can stand the heat.

Porsche now uses a single knock sensor for each bank located at
the base of cylinders #2 and #5. It has a cast piece that goes
to near the junction of the cylinder and head (Can’t find a picture
just now.) to conduct the knock “sound” to the sensor.


I went and re-read the links and articles. I’ll work on a summary.

Best,
Grady


PS: That is my ever useful hp28C (my favorite) in addition to my
old 25, 35, 45!, 48SX, two 28Ss and a spare 28C.

Long live RPN!

G.

"The real issue is knowing the characteristic of the knock. I’m sure
there are many professional papers on the subject. I suspect
that if you recorded engine noise without knock and did a
spectral (Fourier) analysis it would differ from the same recording
and analysis with knock." - Grady Clay -

The early engines like the 964/993/928 with knock sensors used a frequency
domain type of detection, e.g. a tuned detector (mic), or a highly tuned analog
circuit. The later engines (996) with a more powerful microcontroller probably
now use a time domain analysis, i.e. a signal processor implemented in software
like you might find on a lowend PC with a non-hardware modem. This approach
provides much greater discrimination in determining the knocking signal.

The 3.2 guys need to read & understand this thread when they consider
using a performance chip on engines without knock sensors.

Credit Randy with a gold star for starting this thread!

It was Grady's idea!

Ah ha. .that would explain the plague of 3.2's ending up with holes in the pistons?



wait .. what plague?

Randy,

Started to read your initial post and felt immediately - hey, now this is a thread that should contribute with a lot of great insights. A thread that I would read regardless of length.

Thanks (I know, Grady too) !

Of course, I can´t contribute with nothing (as usual)..

The same plague that produced all the 3.2s with broken rod bolts....

Loren, Loren, Loren...sigh. This is your intelligent contribution to this technical discussion?

You make vague statements implying that there's a problem with using performance chips in 3.2s. You try to implicate one particular chip supplier but you don't have the balls to come out and say who it is. Of course the implication is it's Steve Wong. But you offer no evidence of any 3.2 engine having ever been damaged by a Steve Wong chip or any other chip for that matter.

You have been asked, even challenged to provide proof of your allegations many times. You have never met the challenge. When asked, you redirect readers to other threads that have little to do with the question, like this one. There is no proof to be found here.

You seem to be an intelligent fellow otherwise; you provide good advice to people who are having problems with their engine management or charging systems. Yet on this one topic you seem to have a permanently damaged brain management system.

One has to ask, "Why do you continue to do this?" This has been going on for at least two years. When your behavior deteriorates to name-calling and stalking, you get yourself banned from this BB for a while. Yet you persist in making vague claims that you cannot support. You get your butt spanked every time - it has happened at least a dozen times. One has to think that you enjoy the spanking.

My apologies to Randy, Grady et al, but Loren posted a link to this thread. Maybe everyone else is willing to let this slide again, but I'm really sick of it and I will call Loren on it every time he posts this BS.