C'mon kiddies, play nice.

Loren, do you not remember being banned for this nasty behavior that seems to be escalating. The post above and several other in this thread, is a direct attack for something else that you seem to know very little about. Seems to me that you criticize those who do this and then you turn around and do exactly what you jump other people for doing. Thinking is something that you should do prior to posting. Address the questions and share what information you have or don't post. http://www.pelicanparts.com/support/smileys/wat5.gif

" in all cases, detonation will not occur without a dramatic rise in CHT "

Randy, Grady - great thread. And Bill V. probably has the most comprehensive answer yet. I'm not a water-cooled fan yet...but give it a few years in CA., where the octanes might continue to fall, and I'm certain air-cooled Porsche owners may resort to either buying water-cooled P cars, or paying $6-$7 bucks per gallon for race gas.

In any case, I'd like some basic answers to what I believe are basic questions about detonation:

1) Are some forms of detonation not as bad as others? In short, can the detonation that is not heard be less costly to the engine than the marble in the cans one does hear?

2) What other signs can there be of detonation, particularly the kind not heard? Is loss of engine power one sign?

3) Can't an a/f ratio test through the RPM show to an extent, detonation via lean readings? If the engine is lean, there's more of a chance of detonation - just a given.

4) I don't at all get "the mic" discussion. When I think of "mic" I think of something like a stethoscope hooked to the engine with a speaker that goes straight to the driver to "listen" to the motor. BTW: that's no joke. It's the first image that came to me when I read "mic."

5) The fan issue rpiper brings up: if a thread exists, can one post a link, please.

6) Doesn't driving style matter? In hot weather, where it is assumed the heads are also hot, my 3.0 pinged like crazy. It didn't do this (as much), when I went easy on the accelerator instead of stomping it. So, can driving style help eliminate the pinging, at least in hot weather, vis-a-vis feathering the throttle and avoiding WOT?

I'm sorry about the questions, guys. A lot came to me when reading everyone's posts.

Thanks.



SmileWavy

"Doesn't driving style matter? In hot weather, where it is assumed the heads are also hot, my 3.0 pinged like crazy. It didn't do this (as much), when I went easy on the accelerator instead of stomping it. So, can driving style help eliminate the pinging, at least in hot weather, vis-a-vis feathering the throttle and avoiding WOT?" - dd74 -

Yes, to driving style to a LIMIT. The engine load is the key factor for detonation/pinging.
The effect of engine load on whether detonation/pinging occurs results from; cylinder
head temp, ignition timing, fuel octane, & combustion chamber design. Very light engine
loads rarely exhibit detonation/pinging.

"In short, can the detonation that is not heard be less costly to the engine than the marble in the cans one does hear?" - dd74 -

Not really. Check out the damaged engines via the links on this thread.
The owner was unaware until the engine was "opened". There're NO set
rules as to when damage will or will not occur and the extent of it, and
that's why knock sensors are used.

"Can't an a/f ratio test through the RPM show to an extent, detonation via lean readings?" - dd74 -

No, because you still have the cylinder temperature & ignition timing variables
which are unknown. The AFR determination helps to possibly set a margin of
safety, but the extent of the margin is unknown.

"When I think of "mic" I think of something like a stethoscope hooked to the engine with a speaker that goes straight to the driver to "listen" to the motor." - dd74 -

Not a bad analogy. It's the engine control module (ECM) that's doing the listening,
and retarding the problematic cylinder. The ECM can "remember" what cylinder caused
the pinging, but without a cam position input, it doesn't know the cylinder I.D.
to possibly change its AFR.

What real control does the car operator/owner have over the prevention of detonation/pinging
on engines without knock sensors?

1. avoiding ignition advances beyond the engine's specs
2. using the appropriate octane fuels
3. avoiding excess engine loads, e.g. wrong gear for a lengthy heavy grade
especially on very hot days

1) a stick of dynamite, to an M-80, to a 'ladyfinger' . . . all go bang . . .its a matter of degree.

You are not going to remove a tree stump with pop-rocks, and you are not going to blow your engine with sub-audible detonation. (though some imply that any detonation is evil)

If you have a loud exhaust heavier detonation will be masked.


Yep, it is an accoustic event.

Loren - thanks for the answer. Here's one more question: if one were to take two identical high compression engines - one equipped with CIS the other with Webers, would the engine with Webers be less susceptible to detonation because it is moving more fuel through the motor (depending, of course, on jetting and float positioning etc)?

Or, in the case of rpiper's 3.0, would he have less detonation if he had Webers?

"if one were to take two identical high compression engines - one equipped with CIS the other with Webers, would the engine with Webers be less susceptible to detonation because it is moving more fuel through the motor (depending, of course, on jetting and float positioning etc)?" - dd74 -

Possibly yes, given that the carbs probably would result in richer AFR.
Obviously, you can't say for sure because you don't know how close you are
to the detonation/pinging point, i.e. based on the timing, cylinder temps,
and octane.

All three explosive events can cause damage - whether blown-off fingers to blown-off faces. So...

...as to the analogy with sub-audible detonation, and the claim it won't blow an engine - possibly it won't "blow" the motor, but it might indeed damage the engine. Otherwise, why was this thread started if SAD (sub-audible detonation) is not harmful?

I guess the question is, given your thoughts is: What is harmful? What is regular wear and tear? Does every engine at some point detonate?

All in all, have you any experience with engines suffering SAD?

I have a loud exhaust. It does not mask detonation, particularly heavier detonation.

Grady listed gauge mfg

http://forums.pelicanparts.com/showthread.php?s=&threadid=186805&perpage=20&highl ight=head&pagenumber=1

Ron - you read my mind, man. ;)

1 - yes, I'm pretty sure it would be less damaging ... except that since you don't hear it, you don't quit driving...

2 - there will be changes in the exhaust gas mix -- think Ron or someone noted that above

3, 5 - ??

4 - yes, that a diaphragm microphone - the kind we are all used to. But a mic is any device that turns acoustic waves (in any medium - in this case, alloy) into an electrical signal.

6 - sure it will matter; detonation is strongly influenced by the load on the engine too

"guess the question is, given your thoughts is: What is harmful? What is regular wear and tear? Does every engine at some point detonate?" - dd74 -

There are no set rules and that's EXACTLY why knock sensors are used!.
Yes, every engine will detonate/ping given the right set of variables.
Obviously, one could have a mechanical engine design which would
not ever detonate/ping under any condition, but it's utility becomes
impractical.

As to normal wear & tear detonation/pinging, I personally think it's to be avoided, but "To each his own".

Read again here http://www.avweb.com/news/columns/182132-1.html
under "How Damaging is Detonation?", as it basically infers "avoidance".

as has been wirtten (here ?) mixing conditions can create pockets of micro detonation . . . ah, find John Cramers link. (earlier in this thread -- not that it's the final word on the subject, but it's pretty damn good)

Alright, looks like I have some reading to do.

Thanks, Glenn.

Thanks everyone else. Great stuff, guys.

SmileWavy

It isn't directly related to the detonation issue here, but I was rather amazed to read about some issues the development engineers at John Deere faced at the end of the line of the two-cylinder recumbent engines ... the spark plugs were completely at one side of the cylinder bore, and the biggest of the engines had a 6.125" bore x 7.00" stroke. There was a limit as to how long a flame front could take to travel to the other side and complete the combustion cycle ... even though these particular engine's power peak was around 1200 rpm! The 413 cubic inch Model 70 engine cited was introduced in 1954, and featured a new cylinder head design featuring a new "Cyclonic" high-swirl combustion chamber! I just happened to have had some interesting experiences with a John Deere Model 70 engine and electrical system on my uncle's farm in the summer of 1970, while <b><i>Le Mans</b></i> was in production ...

dd74,

Regarding the 'mic' and listening for detonation ... according to Bosch, the characteristic 'signature' of detonation is a signal in the 5 - 10 kiloHertz range, and includes higher harmonics. The signature isn't present when an engine is running normally, so it is really a matter of high-pass filtering the 'mic' signal and determining if a signal above a certain background noise level is present or not. Not that difficult, really, for Bosch or Porsche ... in spite of many protestations to the contrary on this board!

Short intakes tend to have better atomized gas than do long runners. Smaller particles means better conversion of combustion into power.

Warren - in short 5-10 kHz is audible to the human ear, correct? (I don't know), and the "certain background noise level" I assume is the engine itself. Given this, is it audible "detonation" or at least that which Bosch and Porsche describes, is what we really should be listening for and concerned about instead of sub-audible detonation?

dd74,

Yes, the 5 - 10 kHz part is audible to human ears, but the harmonics may not be! The problem with the human ears and brain processing is ... discrimination in the presence of the 'background noise' ...

It would probably be fairly easy to use an active filter circuit and electronic detector ... wired to a piezo sensor ... triggering a big blue dash warning lamp to signal when detonation is happening. I did a bit of detonation 'detection' experimentation back in '74 on a VW engine when the 100-octane gas started disappearing ... in my recollection, the throttle angle, hence loading of the engine was key to the detonation, but there was a range of throttle positions that produced audible detonation, even over loud exhaust! I am quite certain that a modern piezo sensor and detection circuit could alert us to detonation before we could hear it ... and probably preclude engine damage, if the human in control of the throttle used the information on a timely basis!

Piezo sensor with a blue light - that's sort of what I was wondering about - a way to detect the detonation and a manner in which its detection can be delivered.

Also about human hearing - it is highly discriminating and can be the basis of paranoia that the engine is doing something it indeed is not doing. For example, noisy valves, harmonics due to loose parts or solid motor mounts, might be confused for detonation...

Very interesting, Warren. Can a device like what you did for the VW in '74, be hooked up to a 911 engine, with the light located somewhere in the car's interior?