Timing..someone just explaine it to me..

[toki]

Ok yeah, I know, it determines when the fuel is ignited in relation to the piston being in it's cycle, but I am wondering how retarding/advancing manages to yield off knock, and I am just under the impression it can yield power gains also? I just need to understand exactly in what way it helps these things...I know it's a pretty newb thing, but I just never learned it.

[f8sjester]

http://auto.howstuffworks.com/ignition-system1.htm

try this out. . .

[[Zero-S]]

Yes it can yield power gains. I advanced mine (through the distributor) and noticed a slight gain:).

[toki]

Thanks for the link you f'in moron, all it told me was what I said before, I know it CAN do those magical things, i just want to know WHY, and to exactly what degree.

At what point does advancing the timing become detrimental rather than helpful? I know you have to burn higher octane gas so it doesn't ping, I am assuming that's because that the combustion is stronger at hotter, due to the more compact area it's burning in? If I were to advance my KA to 10 BTDC, would I would be able to feel it? Would I need to run race gas for that?

I just want some real numbers.

[KSee777]

sorry to post a question on top of your question toki, but to advance the timing, do I rotate the distributor clockwise or counter clockwise?

[corn322]

I think how it works is it's all about how long the combustion charge is pushing down on the piston.

retarding the timing makes the explosion happen later in the rotation, giving it less time to reach maximum pressure in the combustion chamber.

advancing the timing causes the explosion to happen sooner, and the charge can exert the maximum pressure on the cylinder, forcing it to move faster and harder, thereby making more torque.

if you advance or retard the timing too much though, the car won't run very well. or at all. retard the timing a lot and the car wouldn't be able to stay on, 'cause it's making nearly zero torque. advance the timing too much, and the the fuel/air mix will explode while the piston is still coming up. now take that piston comming up, and the explosion pressing down, somthing has to give. having it that early probably means valves are still open too, and the combustion charge will escape though those.

[C-Kwik]

Timing more or less just changes peak cylinder pressure. Since timing is usually always run in advance from TDC, combustion begins before TDC. While the air/fuel mixture burns, the gases will want to expand. The earlier it starts, the more it will want to expand. Since the piston is still moving up, the volume is dcreasing, so pressure increases rapidly. The earlier the combustion starts, the more pressure will be seen in the cylinder as it approaches TDC. The higher the pressure, the more likely it is to detonate. But higher peak cylinder pressures helps put more energy into the crank. More energy into the crank means more HP.

[C-Kwik]

having it that early probably means valves are still open too, and the combustion charge will escape though those.

You'ld have to be about 90 degrees or more advanced before that happens.

[bendychicken]

corn332, there is no explosion in the combustion chamber under normal circumstances. The only time an explosion occurs is when there is to high a tempiter in the chamber and the mixture all ignites simultaneously. This creates a sudden surge of pressure and makes a pinging noise. What's happening normally is actually a controlled burn of A/F mixture. There is an actual flame that starts from the spark plug and moves it's way across the chamber. As the mix is burning it creates more and more gases like carbon dioxide and carbon monoxide and a whole slew of nitro carbones. These gases create the pressure in that pushes the piston down. The only problem is, if the gases started builing pressure at top dead center the piston would be past it's best leverage point on the crank shaft when the gases reach peek prussure. So in order to get good pressure in the chamber and good leverage on the crank at the same time the gases have to start being produced BEFOR T.D.C. this is the reason for timing advance. If the timing is advanced to far though, the gases will build up too much pressure as they are being compressed by the piston moving up. This causes the unburnt A/F mixture in the chamber to rise in tempeture as it's compressed. When the tempiture of the A/F mix exeeds a certain point(determined by octaine rating) it ignites all at once(Explosion, Detonation etc).

Hope that helps. Very good and important question toki

[toki]

Ok, most of this is helping, but just to clarify for me to better understand, TDC is the point where the piston is done with the compression stroke, I.E. the piston is as high up as it's going to go, so BEHIND TDC is the piston on the process of approaching TDC, meaning it's not fully compressed? Correct?

So advancing it would mean that it fires closer or farther away from being at TDC?

[toki]

Timing more or less just changes peak cylinder pressure. Since timing is usually always run in advance from TDC, combustion begins before TDC.

Ok there is the answer to that, I guess what I was meaning to ask then was, would retarding it any amount show gains? I am guessing no since someone said the proper leverage was more advanced then retarded?

So if I advanced it to say 30 BTDC would the leverage be too low and and off, and not produce the right amount of torque?

[DAEDALUS]

Just to be clear, BTDC means Before top dead center, not Behind. The flame travels some finite speed, so the goal is to ignite the mixture at some point such that you get the most combustion complete at the point in which it can do the most work, but without causing predetonation. Remember though that this optimization only occurs at a given RPM under given conditions. The higher the RPMs at optimization, generally the higher the peak power. But the faster the engine runs, the more stress you put on the components until something fails.

So there are 2 obstacles to avoid: Destroying the engine and causing pinging. Because of design optimization, these 2 usually happen around the same time.

30 degrees at idle is way too much advance. With the engine running that slow, a lot of the work of the burning gasses would actually be fighting the piston in its upward movement toward TDC. Look at the animation in the howstuffworks link. Imagine a flame burning through the chamber when its moving slow like that, and the piston is on its way up. The engine would stop dead, maybe go backwards for a moment.

[toki]

those damn B words all starting with the B....

Ok, so if 30 would stop it, why doesn't 20? Like the KA is stock.

[DAEDALUS]

Again, the combustion takes a certain amount of time to complete. A piston 30* BTDC will take 50% longer to reach TDC than a piston at 20* BTDC. So if you have spark beginning at 30* BTDC, the burning gasses will have more time to combust and act against the piston, which is on its way up. In any case, only after the piston hits TDC and begins to move back down does the combustion add power to the stroke. 30* might be OK at some very high RPM, probably more than 5,000, but at idle it might kill the engine, or at the very least, make it run like crap.

[4felix20]

So what is a good number for toki to advance his timing to? If he should even adjust it..

[DAEDALUS]

I don't think anyone can say for sure without loads and loads of testing. All engines are different. How efficient is the cooling system? What is the hottest temperature the car will be run in, and at what altitude? How much carbon build-up is there on the pistons? How much toluene is in the tank? Too many variables, and even if you knew all the numbers, the answer would still be an educated guess at best. The "optimum" timing depends on your definition of optimum. If you want to remove all safety factors, that's one thing, but if you want to run your engine hard with an 80% chance of it lasting more than 10,000 miles, that's quite another. In general, it's a good idea to start by advancing the timing by not more than 2-3 degrees, since this probably won't destroy the engine. Beyond that, you increase the chances of it knocking under certain conditions. You might not feel it, but your knock sensor will, and it'll act to save the engine by decreasing performance. Go 2 degrees for a week and see how it feels. Then another degree, and see if it feels better or worse. You can keep advancing 1 degree at a time, but soon you'll be doing all harm and no good, and whether you'll realize it before you damage something is uncertain.

[toki]

Thank you Daedalus, I must say you are one of the few people that I actually see answer questions (Atleast mine) completly and accuratly on this board.

*video game music plays* KNOWLEDGE LEVEL ON TIMING: 2STAGE 2: BEGIN!!!!!!

So now, does my ECU be a cool kid ECU and automatically advance my timing when at high RPMs where it would help to optimize performance, or doesn Nissan not put cool kid ECUs in it's 1989 entry level "performance" cars? If not, would a piggyback from GREDDDDDDDDDY or some other place with a name not pronouncable in English be able to do a cool kid thing like auto advance my timing or better yet, let me program it?

[toki]

*whistles and sways back and forth looking non chalante*