osin68

I have been logging tunes for sometime now, and was wondering why after you lift off the gas after a WOT run dose the timing goes up?
Thank You

dc_justin

iTrader: (13)

After you let off the gas, cylinder air mass drops rapidly, timing necessarily increases as you hit that area of your spark table.

osin68

But why? Is it to burn off excess fuel in the cylinders?

dc_justin

iTrader: (13)

No, timing is higher because the charge density is much lower. At WOT, density is very high, so it doesn't take long for that mixture to burn entirely, hence the lower timing value. When the mixture is less dense, more time is needed to burn, thus the higher timing.

osin68

So basically the same-thing I said. Less density of air rich fuel mixture.

dc_justin

iTrader: (13)

The fuel mixture doesn't have anything to do with it, it could be AFR of 11:1 or 15:1 and the timing will need to be high with both. The mixture will be at a point where the molecules are spread out much more than they are at WOT, causing the burn to occur much more slowly, requiring the ignition event to occur much earlier in order to have complete combustion.