advancing timing

[Racincc85]

i have heard people say that advancing your ignition timing a few degress will add a small amount of power. Why is this? I'm confused as to how all the aspects of ignition timimg work ( ie retarding timing prevents knock). I read some of the other posts and was still somewhat confused. If someone could explain all this to me i would appreciate it.

[crxlvr]

advancing the timing will allow for more air and fuel to be mixed in before the spark ignites resulting in more flame, in turn producing more power, to far advanced and you get detonation and pre-ignition.

[MagicRat]

Originally Posted by crxlvr

advancing the timing will allow for more air and fuel to be mixed in before the spark ignites resulting in more flame.

This is not correct.

Advancing the timing SOMETIMES gives the burning fuel/air mixture more time to burn before the piston reaches the bottom of the stroke. This makes the combustion more complete and extracts more energy from the burning and expamding gases produced by combustion.

However, if the ignition is too advanced, the mixture starts to expand and burn before the piston is at top dead center. This does two things:

1. The fuel air mixture begins to burn around the spark plug, and as they expand, they rapidly build cylinder pressure in the combustion chamber, causing the unburned portion of the fuel to combust from heat and pressure. This is called detonation (not preignition; that's something different). This detonation causes engine damage and is a less efficient method for burning gasoline, so combustion is incomplete and you lose power.

2. The gases start to expand before the piston is at the top, so the engine starts to work against itself.

[TechX]

Well with timing it is usually an rpm thing. If you retard timing the engine starts better and you run smooth without knocks. The trick is to advance enough to where the car still starts good and does not knock or pre-ignite. The advanced timing usually gives you more power at a higher rpm range. Magic Rat is right and sorry crxlvr you are not correct this time.

[bjdm151]

TechX and MagicRat are correct. Over advancing can cause knock, but whan advanceing and retarding timing, you can actually watch the power band move to lower rpm when retarding and up rpm when advancing. When advancing you can make more horsepower with this because of the hp formula---HP = (torque x rpm) / 5252. If your making 100 lb/ft of torque at 4500 rpm it would be (100 x 4500) / 5252 = 85.8 hp. If you advance timing enough to move that 100 lb/ft at 6000 it would be (100 x 6000) / 5252 = 114.2 hp. So if you can effectivly raise that rpm you will make more power. Think about formula one they are using three liter engines spinning and making an estimated 800 hp but they are spinning the engine at about 18k rpm.