retarding timing ?
retarding timing ?
So just wondering what retarding the timing does pertinent to a high boost application? Does retarding the timing essentially lower compression since the spark will come later, which in turn means the cylinder will be past tdc?
Re: retarding timing ? (Darchangl)
On high boost ka-t's on pump gas, you retard the timing to prevent detonation, which is an abnormal/destructive combustion event caused by excessive heat and pressure after combustion is initiated by spark.
It's a series of cause-effects for why boost makes detonation:More boost and fuel increases the mixture's burn rate, making peak pressure/temps closer to tdc, making less combustion volume, making overall higher pressure and temperature(think of the ideal gas law: PV=nRT. Reducing volume increases the pressure.), increasing propensity for knock.
Retarding the timing shifts peak pressure to a later crank angle, increasing the combustion volume, reducing propensity for knock.(again, think of the ideal gas law - increasing the volume reduces the pressure).
On non-knock limited engines(using race gas, low CR pistons, etc..), you could retard the timing to shift the pressure peak to a more advantageous crank angle, improving torque via more leverage against the crank rather than by maximizing peak pressure. To find the best timing, you have to balance between peak pressure and crank leverage to get the most net torque. Hope that helps.
It's a series of cause-effects for why boost makes detonation:More boost and fuel increases the mixture's burn rate, making peak pressure/temps closer to tdc, making less combustion volume, making overall higher pressure and temperature(think of the ideal gas law: PV=nRT. Reducing volume increases the pressure.), increasing propensity for knock.
Retarding the timing shifts peak pressure to a later crank angle, increasing the combustion volume, reducing propensity for knock.(again, think of the ideal gas law - increasing the volume reduces the pressure).
On non-knock limited engines(using race gas, low CR pistons, etc..), you could retard the timing to shift the pressure peak to a more advantageous crank angle, improving torque via more leverage against the crank rather than by maximizing peak pressure. To find the best timing, you have to balance between peak pressure and crank leverage to get the most net torque. Hope that helps.
Re: retarding timing ? (Darchangl)
amazing explanation. exactly what i wanted to know. thanks