why is a sports-camshaft bad for idle ?
Posted: Fri Mar 11, 2011 1:36 am
Hi,
I start "thinking" as a driver of a big 4x4, which needs torque at low revs and needn´t be able to be chased on laps.
If I changed the camshaft for one which promises more power and torque then I will get one, whith a longer duration. So the cam lobe will be longer - and the valve been opened earlier and closed later. That in turn gives the cylinder more time to shift the gases (mixture/exhaust) - which is a benefit at high revs, when the time for each cylce is relatively less.
But why does this cam affect the idle badly. Why will the idle be lumpy, the idle MAP higher and why the fuel consumption increased (*) ??
(*) is that just because of a greater overlap of inlet/exhaust valves, "erratically" shifting more fresh mixture into the exhaust ? And/or is it due to more power being developed at those higehr revs which certainly imply more fuel being used ?
I start "thinking" as a driver of a big 4x4, which needs torque at low revs and needn´t be able to be chased on laps.
If I changed the camshaft for one which promises more power and torque then I will get one, whith a longer duration. So the cam lobe will be longer - and the valve been opened earlier and closed later. That in turn gives the cylinder more time to shift the gases (mixture/exhaust) - which is a benefit at high revs, when the time for each cylce is relatively less.
But why does this cam affect the idle badly. Why will the idle be lumpy, the idle MAP higher and why the fuel consumption increased (*) ??
(*) is that just because of a greater overlap of inlet/exhaust valves, "erratically" shifting more fresh mixture into the exhaust ? And/or is it due to more power being developed at those higehr revs which certainly imply more fuel being used ?