What is Detonation ??

[BoostinGSR]

Hey, I was just wondering what is detonation and how do I know if my car is detonating? Thanks for any help [img]smile.gif[/img]

<font color="#a62a2a" size="1">[ September 26, 2002 04:26 AM: Message edited by: BoostinGSR ]</font>

[waveoff]

Detonation happens when the air/fuel mixture explodes instead of burning evenly. This explosiong is usually heard as a rattling sound coming from the engine while under load (e.g. going up a hill, bogging the engine, etc.). It can lead to hot spots on the piston or cylinder walls which in turn will cause more detonation or preignition. Read http://www.aera.org/Members/EngineTech/engine.htm Or you can search a number of different search engines for an instant answer to your question.

[96IntegraRS]

Also, I think the best analogy of the sound that detonation makes is the sound of marbles in a coffee can.

You will find in your searches that not all detonation is audible; keep this in mind. But the stuff you can hear is definitely damaging to your motor.

Chuck

[blownLS]

A really quick way to rebuild your engine....... he he he I speak from experience [img]frown.gif[/img]

Severe detonation is when your air/fuel mixture ignites under compression before your spark plug even goes off. Like a diesel engine. But most of the time we here light detonation (marbles in coffee can). This is when the mixture completely ignites before the crank angle reaches 12 degrees AFTER top dead center. It forces the piston to push straight down on the con-rod (instead of rotating around the crank) which in turn pushes straight down on your rod and main bearings. Think of it as standing on your bike pedals instead of pushing it around the crank (if you do not have the top pedal at true TDC of your bike crank your weight would force the pedal to ground). The same is true in a car engine. All of the energy is transfered vertically in the block instead of rotationally around the crank.

So since it "usually" takes ~30 degrees to ignite all of your fuel, your 16 degree advance ignition timing should completely burn your mixture by 14 degrees after top dead center. But there are a lot variables that effect the timing of your air/fuel burn rates like octane, compression ratio, engine speed etc.... But we wont go into that right now.

[Marc]

This should help: http://zhome.com/ZCMnL/PICS/detonation/detonation.html

http://www.strappe.com/plugs.html

[waveoff]

Also keep in mind that TOO MUCH fuel can also cause detonation. The excessive fuel in the cylinders takes up space and will "raise" the compression ratio. Same goes for water injection. Too much water will have the same effect but could also hydrolock your motor. When I installed my 8 psi pulley I left my cartech set where it was at 6 psi (no restrictor, static FP of 60 psi). When at 6 psi my FP would max out at 86 psi or so with no detonation. At 8 psi, my FP was off the scale (gauge read 99 psi) and I was getting some very audible detonation. I ended up having to install the restrictor in my cartech and turning the bleeder out one turn (static FP stayed at 60 psi). At 8 psi my FP maxes out at 90-95 psi and I'm detonation free.

[BoostinGSR]

<BLOCKQUOTE><font size=2 face="Verdana, Helvetica, sans-serif">quote:</font><table border="0" width="90%" bgcolor="#333333" cellspacing="1" cellpadding="0"><tr><td width="100%"><table border="0" width="100%" cellspacing="0" cellpadding="2" bgcolor="#FF9900"><tr><td width="100%" bgcolor="#DDDDDD"><font size=2 face="Verdana, Helvetica, sans-serif">Originally posted by blownLS:


Severe detonation is when your air/fuel mixture ignites under compression before your spark plug even goes off. Like a diesel engine. </font></td></tr></table></td></tr></table></BLOCKQUOTE>

Isn't that Pre-ignition? Theres a difference between Pre-Ignition and Detonation isn't there?

[blownLS]

<BLOCKQUOTE><font size=2 face="Verdana, Helvetica, sans-serif">quote:</font><table border="0" width="90%" bgcolor="#333333" cellspacing="1" cellpadding="0"><tr><td width="100%"><table border="0" width="100%" cellspacing="0" cellpadding="2" bgcolor="#FF9900"><tr><td width="100%" bgcolor="#DDDDDD"><font size=2 face="Verdana, Helvetica, sans-serif"><font size=2 face="Verdana, Helvetica, sans-serif">Originally posted by waveoff:
The excessive fuel in the cylinders takes up space and will "raise" the compression ratio. Same goes for water injection. Too much water will have the same effect but could also hydrolock your motor. </font></font></td></tr></table></td></tr></table></BLOCKQUOTE>

How can water and fuel injection raise compression ratios? I may be wrong, and if I am would like to be corrected. The way I understand fuel and water injection, both atomize almost immediately and then vaporize on the compression stroke changing state from a liquid to a gas. Gases do take up space, but the little amounts we inject into our engines would not raise compression to that much of a noticable difference (no different than comparing compression ratios on a dry dessert-like day to a foggy morning). The water creates a high humidity enviroment in your compression stroke, helping to dissapate heat (evaporative cooling process), no different than sucking in air on a foggy morning or when it is raining.

If I am wrong, then will someone please educate me correctly.

The hydrolocking process I understand. It would take a large amount of "standing water" not water vapor to do this. Water is not compressable so once you have injested "liquid" water that equals the volume of your combustion chamber the piston cannot move any further up on the stroke unless it pushes the head off of the block.

<font color="#a62a2a" size="1">[ September 27, 2002 08:43 PM: Message edited by: blownLS ]</font>

[waveoff]

Most of what you say is correct, but I'm talking about excess liquids that atomize into droplets too big to evaporate on the compression stroke and remain in a liquid state. The presence of any liquid on the compression stroke will generate extremely high cylinder pressures. I once had an airplane engine quit on me after detonation snapped a rod and cracked the crankshaft. We later found out that the cause of the detonation was a fuel pump which was flowing 1 1/2 times more fuel than it should have been. After a certain point, an overly rich mixture will cause cylinder temps to rise as well. Different people will tell you different things. I'm just relaying my experiences.

[blownLS]

I hope you had more than one engine..... [img]eek.gif[/img]