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let's talk about timing

Poil336

Poil336

New member
i've been seeing it timing thrown around in a lot of threads here lately, and i started thinking that i don't know as much about it as i would like to. so i figured i'd ask the forum :th_biggrin2:
basically what i've gathered is that, thinking of the cyclical motion of the piston as a 360* cycle, the degree of timing is a representation of the distance from TDC that the air/fuel begins to enter the combustion chamber - correct?

this leads to a lot of questions. things like:
does 360* represent the entire cycle (intake and compression) or just the intake stroke?
how do you adjust for it?
what's the factory timing?
can you adjust it with factory pcm's, or only aftermarket?
what would a power adder like a nitrous oxide system affect it? NO2 adds volume right?
when you adjust it, are you changing something with the cam to change when the valves open or is it something that controls the injectors?

also, any links to other threads about this would be much appreciated. and if somebody wants to throw in the bore and stroke sizes of a 3800, that would be great. i'm OCD and really like numbers lol
 


i think in this case youre going to have better luck searching the interwebs for your answers, or most of them at least.

stock timing ADVANCE is 16*. usually the more timing you run the more 'raw' the car feels. on the street i think something like 18-20* of timing is enough, but if you want to push the limits then about 24* is where you start reaching the point where its useless to go farther.

ANY power adder means you should be running lower timing in order to avoid 'detonation', which KR is also helping you against. you just have to remember that KR is a reaction to existing conditions so the car already knocked, then it pulled timing.

timing advance has to do with the electrical system, not the actual system. you can 'time' your cam, but not many people have looked into it or seen gains that have been worth doing it. timing the cam has to do with the physical system, but timing advance has to do with when the IGNITION system and when it fires.

that's about all i got right now since im drunk and i really didn't read your post. :)
 
you drunk is probably better than 95% of guys sober lol. best of luck on your drinking quest.

timing ADVANCE, does this mean the the fuel is being injected at the end of the exhaust stroke?
 
Poil336 said:
you drunk is probably better than 95% of guys sober lol. best of luck on your drinking quest.

timing ADVANCE, does this mean the the fuel is being injected at the end of the exhaust stroke?
Click to expand...

the fuel is still injected at the same time. the only thing that changes is when the spark is made to ignite the fuel in the cylinder.

for real though, wikipedia is probably better than me on this subject.
 
that's a first. i'm gonna keep asking though haha.

so the spark comes before TDC, so the flame wall hits it at TDC?
 


dont make me go to wikipedia and copy/paste for you....if no one has given any good answers by tomorrow morning its possible that ill do that...for now, im lazy (drunk).
 
fineeeeee, i'll go look on wikipedia lol. i won't be on till like probably after 9 tomorrow cause of work. do whatever you can to make this thread explode lol

can we get the other nick to give his thought's on the matter? and matt? lol
 


"Timing advance" refers to the number of degrees before top dead center (BTDC) that the spark will ignite the air-fuel mixture in the combustion chamber during the compression stroke. Retarded timing can be defined as; changing the timing so that fuel ignition happens later than the manufacturer's specified time. If the ignition timing, specified by the manufacturer, was to be set at 12 degrees BTDC and it was adjusted to a number lower than 12 degrees BTDC, it would be retarded. In a classic ignition system with breaker points, the basic timing can be set statically using a test light or dynamically using a timing light.
Timing advance is required because it takes time to burn the air-fuel mixture. Igniting the mixture before the piston reaches top dead center (TDC) will allow the mixture to fully burn soon after the piston reaches TDC. If the air-fuel mixture is ignited at the correct time, maximum pressure in the cylinder will occur sometime after the piston reaches TDC allowing the ignited mixture to push the piston down the cylinder with the greatest force. Ideally, the time at which the mixture should be fully burnt is about 20 degrees ATDC. This will utilize the engine's power producing potential. If the ignition spark occurs at a position that is too advanced relative to piston position, the rapidly expanding air-fuel mixture can actually push against the piston still moving up, causing detonation and lost power. If the spark occurs too retarded relative to the piston position, maximum cylinder pressure will occur after the piston is already traveling too far down the cylinder. This results in lost power, high emissions, and unburned fuel.
The ignition timing will need to become increasingly advanced (relative to TDC) as the engine speed increases so that the air-fuel mixture has the correct amount of time to fully burn. As the engine speed increases, the time available to burn the mixture decreases but the burning itself proceeds at the same speed, it needs to be started increasingly earlier to complete in time. Poor volumetric efficiency at lower engine speeds also requires increased advancement of ignition timing. The correct timing advance for a given engine speed will allow for maximum cylinder pressure to be achieved at the correct crankshaft angular position. When setting the timing for an automobile engine, the factory timing setting can usually be found on a sticker in the engine bay.
The ignition timing is also dependent on the load of the engine with more load (larger throttle opening) requiring less advance (the mixture burns faster). Also it is dependent on the temperature of the engine with lower temperature allowing for more advance. The speed with which the mixture burns depends also on the octane rating of the fuel and on the air-fuel ratio.
 


that's a really concept to think about doing 50 times a second lol. you wouldn't happen to know much about load would you? that's another term i'm kinda iffy on
 
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