tuning

[turbota633]

hello,
i have been around other turbo buick forums for a year or 2 now reading and trying to learn, although i've soaked up a decent amount of info,as far as hands-on i an a newbie. i've been reading up on the tuning recently, before i try to mess with anything though i want to fully understand what im doin.some terms i want to have a full understanding of -detonation(not sure,to me it sounds like when there is too much knock(?..i know its not good,but i dont exactly know what its is) there is too much pressure in engine,or everything isnt working together all on the same note,and somethin might give and break?) -knock retard and timing retard: i understand that little to 0 knock is best, and that the more knock there is,the less "safe zone" there is before detonation. i cant think of any other questions at the moment. i have a slight understanding of whats good/bad, there is just gaps i need to fill in so i can put it all together and make sure i do things right, i figure asking questions is easier than learning the hard way...blowing a motor. thanks in advance.
-joe

 

[Roc87]

detonation or "knock" is the fuel mixture igniting before the spark plug actually ignites. The reason this is bad is that the piston is on the compression stroke, and the ignition of the mixture tries to force it back down when it's on it's way up . When you get a ton of boost and then you throw in detonation, it's not a good thing. Higher boost, higher timing, poor octane fuel tend to contribute to detonation.

 

[ijames]

Pre-ignition or pinging is when the fuel ignites from a hot spot before the spark plug fires. Sounds like little "tinging" noises and makes extra heat but happens so early in the compression stroke that pressures are low and usually there is no damage - but still don't let it happen.

Knock IS detonation and happens after the spark plug fires, when fuel that the flame front hasn't reached yet decomposes and autoignites. Instead of a nice orderly burning of the fuel from the plug outwards over many milliseconds, a large volume of fuel can ignite essentially spontaneously, giving rise to a very sharp pressure spike up to ten times normal combustion chamber pressures, usually for much less than a millisecond. The pressure spike hammers on the piston top, rings, and chamber walls, and really does sound like you hit the motor with a hammer. This pounds out bearings, breaks pistons and rings, and blows head gaskets.

By the time knock is bad enough for you to hear, the ecm has usually already pulled out 10 or more degrees of timing and you should have lifted long ago. Unless you like building motors tune for zero knock retard and zero esc counts.

 

[microELVIS]

Brings up a question

Not trying to hijack the thread here.

My little knock sensor on my dash, hooked up to the ecm. Is that picking up ping or knock ?

 

[ijames]

Knock.