Is detonation caused by to much Timing ?? Or not enough timing ?
Does this mean a car is running to lean ? Or rich ?

Thanks !!

:cheers:

Jeff

 

Typically it's caused by a lean condition..And sometimes compounded by too much timing..

Then there is the old carbon deposit type which can be cured by a decarb procedure...

 

welcome to the world of supercharging. i had the same darn problem. jeff how are u? ill be in la tomm, any plans for the weekend. im sure some computer work can fix your problem?

Chan :cheers:

 

taken ls1/ls6 motors some what lean with out detonation during tuning, add too much timing and there it is, usually over 4k rpm. It's more a timing advancement issue with n/a motors......
Hows the beast Jeff?

 

Compression ratio being too high can also cause this problem if your running 93 octane fuel. If the compreesion ratio rises above 11:1 you may start to pre-detinate due to the fact that the heads do not have enough volume thus causing the high ratio. Reducing the timing or removing the heads and maching out volume is one solution. If you just reduce the timing though you will lose power. KJ

 

detonation can be caused for a variety of reasons.
1. not enough fuel
2. not enough timing
3. too much timing
4. not enough octane in the fuel causing the fuel to burn too fast in the chamber.

 

A whole bunch of things.

Heated air intake causes lean mix.
Too lean of a fuel charge.
Too much compression.
Too much timing advance.
Glowing carbon deposits.
Vacuum leak that cuses a lean fuel charge.
Too low of an octane.

Sorry for the long answer but there is a lot of stuff that interacts.





[Modified by Richin Chicago, 11:29 AM 5/24/2003]

 

Don't see how this could cause it...Please explain. I guess it could cause problems with heat in a road racing situation.

 

Hello, I'm new too the forum but I think I have some useful info on detonation. I am a engineering technician/dyno tech for Autolite Spark Plug Company.

Detonation in a internal combustion engine is caused by a spark timing that is to advanced for the octane of the fuel and compression ratio used in that engine.
First off to dispell a common misconception, spark plugs do not cause detonation and changing the heat range of the plug does not influence the occurence of detonation. Preignition and detonation are not the same thing. Preignition is exactly as it sounds, an event that causes the a/f mixture to ignite before the normal spark event.

Detonation occurs after ignition during the power stroke. (after TDC).
The knock that you hear is actually the end gases of the A/F mixture SELF IGNITING (i.E compression ignition) from the pressure of the flame front as it burns ACROSS the combustion chamber/top of the piston.

Think of it this way...the spark plug ignites the compressed A/F mixture on the spark plug side of the chamber. The A/F mixture takes time to BURN (notice I said BURN, not explode. that is a critical but misunderstood distinction) and as it burns a flame front moves across the cylinder consuming the A/f mixture. As the burn is happening pressure and temperature are rising rapidly ahead of the flame front, further heating and compressing the unburned A/F mixture ahead of the flame front. If pressure/temp exceed the ignition point of the fuel it will self ignite. This is where octane rating becomes important, it is the fuels resistance to self ignite. (NOT PREIGNITE)(compression ignition) The reason for the knock is that the A/F mixture does not BURN but EXPLODES, releasing it's energy in an ALMOST instantaneous manner (in relation to a normal combustion event). This in turn creates a flame front that burns back toward the normal flame front and raises cylinder pressure/temp even more.

Detonation is a CHEMICAL reaction and it's components are pressure, temperature and time. (time comes in because if the a/f mixture can be burned quicker, there may not be enough time for the chemical reaction(s) to occur that cause detonation. At least that's the theory (fast burn heads) I have my doubts and questions about this based on what I see at all the dyno tests I do).

Now as too your question of what causes detonation...

Overadvanced ignition timing. To high a compression ratio. Low octane fuel.
Oil/Carbon build up in combustion chamber. (chemical effect with fuel that lowers the octane rating) insulates combustion chamber and slightly raises compression ratio. A combination of all of the above!!!

High intake air and water temps add too the problem. A rich a/f mixture lessens detonation and lean mixtures make it worse. Retarded ignition timing reduces in cylinder pressure and temperature reducing detonation (but exhaust temps go up). advancing timing timing increases both the in-cylinder temperature and pressure making detonation worse. (exhaust temps go down)

sorry for the long post but there is a lot involved with this.

imdrumminman

 

Hey Guys ,
thanks for the education on Detonation !

Great info :yesnod: .


:cheers:

Jeff

 

imdrumminman

Welcome to the forum....

 

imdrumminman,

Thanks, excellent post :smash:

 

Good stuff!!! This is what the Tech section was made for. :cheers: :D :D