Can someone explain to me what detonation is and how it happens.

Thanks!

 

copied and pasted off some dsm site and haven't even read it so can't vouch for the information below but maybe this will help a little. try google dot com!
http://mw.dsm.org/tipdetail.asp?TipID=4

Detonation when the air/fuel mixture in the cylinder explodes, instead of burning rapidly.
(To be really technical, detonation is when the flame front moving through the cylinder exceeds
the speed of sound.)

This is bad for two main reasons:

1) The sudden shock load can break parts - the repeated shock loads of constant
detonation is like running a jackhammer in your engine.
2) The temperature inside a detonating cylinder is much hotter than normal, and can get
hot enough to melt aluminum.

Symptoms of detonation:

1) A loud pinging or rattle/knocking noise. It sounds like a bunch of marbles inside a
tin can. (This is why detonation is commonly called "knock")
2) Higher than normal exhaust gas temperatures
3) Little "flyspecks" of aluminum on spark plug center electrodes and the center
insulator. This is the dead giveaway indicator for detonation. Examine your plugs with a
magnifying glass. Little ***** of aluminum clinging to the plugs means that you are detonating.
(It's aluminum from the pistons being vaporized and condensing on the plugs)
4) Engine damage (holes in pistons, melted spark plug ground electrodes, etc.

Causes of detonation:

1) Low octane fuel
2) High static compression ratio
3) High boost levels
4) Excessive spark advance
5) Lean fuel mixture (may be insufficient fuel pump capacity/pressure, insufficient
injector flow, air flow sensor out of range)
6) High inlet air temperature / low air density

For a given fuel octane rating, an engine can only stand so much boost, spark advance,
compression ratio, and mixture leanness before it begins to detonate. Therefore, as increasing
boost, spark advance, compression, and leaning the mixture tend to increase power, _the onset
of detonation is normally the limiting factor on the amount of power a given engine
configuration can produce_ Collorary: _to produce maximum power, an engine should be running
right on the limit of detonation

In a non-computer-controlled car, this is a very difficult thing to do. (Do a pass, pull the
plugs, check for the flyspecks, change something, go faster, pull the plugs, check for the
flyspecks etc. ad nauseum) However, the DSM CPU has a knock sensor that "listens" to the engine
to detect knock. If the sensor detects knock, the ECU first cuts back the ignition advance, and
if it still knocks, cuts the boost levels. Result: a drastic loss of power, and a safe engine.
If you have somehow limited the ECU's ability to retard the spark (unlikely) or cut the boost
(easy) then it is still possible to get into a destructive detonation scenario. It is still a
good idea to pull the plugs every couple of runs and inspect them for signs of detonation. Keep
an eye on the boost and EGT gauges!

Fixing a detention problem

1) Use higher octane fuel
2) Reduce the level of whatever it is you have increased (boost, advance, etc.
3) Reduce inlet air temp with a bigger intercooler
4) Confirm proper ECU/knock sensor operation.

OK, if I can easily adjust boost, spark advance, and mixture ratios, (and to a certain extent
inlet air temp) what should I have more of to make the best power?

Excellent question. I don't know. I suspect that boost is worth more than spark advance, with
mixture ratio somewhere in the middle. If I had a PMS, a datalogger, and a dyno, I think I'd
set spark advance to about 2/3 of the possible range the computer provides, set the mixture a
little on the lean side, and then run the boost up to the detonation point, and back off a
little. Then I'd play with the mixture to see if I can get more power, or get the motor to
stand more boost. Once I've got a good WOT boost level and mixture ratio, then we see how much
more advance it can take. Maybe.

Note that we haven't taken inlet air temp or density into account here, nor have we allowed for
real-world factors like: how fast can the wastegate react to boost spikes? This is just an
educated guess. Bottom line? Lots of testing. Lots. And you can't get the inlet air temp too
cold.

 

there is detonation and pre-ignition, pre-ignition is what most people talk about when their timing is advanced to far, the ignition occurs too soon, and the timing has to be backed out.

detonation is when there is a piece of carbon, or something inside the combustion chamber that heats up to the point where when the heat created from compression combined with it it is enough to ignite the air fuel mix, before the spark plug fires.

both of these are bad in that the shockwave created by the expanding gas slams into the piston as it is still traveling up towards TDC. this is bad because it fatigues engine parts really quickly and it is a sure way to put holes in your pistons, windows in your block, or a number of other very fun to fix issues.

also, if your car is in good running order if the fuel air mix is burning to quickly the shockwave from the advancing combustion reaches the piston too quickly it will cause pinging, which in essence is the same thing.

the lower octane rating of the fuel the faster it will burn in your combustion chamber, and the higher compression you have the higher octane rating you need to keep the flame from advancing too quickly and hitting the piston before the optimal time.

hope that helped, and I hope others will correct me if I am wrong on any of my points!

 

I just got my crower 62403's (B18A) installed a couple of weeks ago. I am on 91 octane and reduced the timing back to 16 from 18 when it was pinging big time. However, my car is still pinging, I can really hear it going up hill.

Is there anything I can do to stop this?

I am at the point of taking out the cams, and going back to stock ones. Current mods include: CAI, DC 4-2-1 header, and MSD ignition.