questions about timing
01-05-2005, 04:11 AM
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Depending on rod angularity you want the timing [advance] to have burned 66-70% of fuel by 16-17.5 degrees after top dead center. The Flame speed of fuel.
Due to non homogenity of fuel from filing to filling [each rev repeat cycle] there is never any perfect advance........just a range of 2 degrees where the Average of thousnds of firings work best at one temperature.
Some times the answer is how many horsepower do I gain per degree of retard! depends on fuel compostion [ratio of 32 components] and air temperature.
To allow usual junk US fuels most times the factory uses a 3-4-5 degree underadvanced ignition curve as a safety factor.
Don't confuse initial static advance as measured with timing light] with a real world calculated [by 16 variables] running advance..........WOT can be 22-29 degrees -----cruise 36-44 degrees depending on rpms and load.
decelerating may be less than TDC power cuts before after shifts can be zero.
Roughly each degree above standard requires 1.0-2.0 points more motor test octane ratio........the higher the octane the lower the fuel BTU value [as MTBE or ethanol have much lower BTU per gallon.
No real way to answer your question depends on too many variables.
Keep in mind that to stop knock requires 5 times [at least 5 degrees of retard] so better to always be underadvanced than to ever have a knock where knock sensor signal causes a 5-10 degree retard by ecu.
Dynos do not properly load engine for a quarter mile run so setting advance on a dyno is almost always WRONG for the strip or street [especially the street].
Due to non homogenity of fuel from filing to filling [each rev repeat cycle] there is never any perfect advance........just a range of 2 degrees where the Average of thousnds of firings work best at one temperature.
Some times the answer is how many horsepower do I gain per degree of retard! depends on fuel compostion [ratio of 32 components] and air temperature.
To allow usual junk US fuels most times the factory uses a 3-4-5 degree underadvanced ignition curve as a safety factor.
Don't confuse initial static advance as measured with timing light] with a real world calculated [by 16 variables] running advance..........WOT can be 22-29 degrees -----cruise 36-44 degrees depending on rpms and load.
decelerating may be less than TDC power cuts before after shifts can be zero.
Roughly each degree above standard requires 1.0-2.0 points more motor test octane ratio........the higher the octane the lower the fuel BTU value [as MTBE or ethanol have much lower BTU per gallon.
No real way to answer your question depends on too many variables.
Keep in mind that to stop knock requires 5 times [at least 5 degrees of retard] so better to always be underadvanced than to ever have a knock where knock sensor signal causes a 5-10 degree retard by ecu.
Dynos do not properly load engine for a quarter mile run so setting advance on a dyno is almost always WRONG for the strip or street [especially the street].
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