Gareth,

I'm affraid you've got a little muddled up.

Let me give you the figures to try for yourself.

At 6000 rpm it takes 10ms for one rotation of the crankshaft to occur. For a cam of 260 duration the inlet valve open time per cycle is 10ms X 260/360. It really is that simple. (Rememeber the total cycle time is 20ms at 6000rpm but the inlet valve open time is ONLY 7.2ms)

You're forgetting that 4 stroke engines are 720 degree per cycle and that cam duration is quoted as crankshaft rotation per cycle.


rich,

It depends what we are trying to achieve. In an ideal world we would only inject fuel that is fully atomised into a fast flowing air stream. (i.e. inlet valve open)

In practice we actually end up using ALL the time available per cycle (720 degrees) and continue to inject even after the inlet valve is shut so that when it opens again we've had the maximum time possible to flow as much fuel through the injector as possible.

I.E we are more concerned with flowing the MAXIMUM amount of fuel than at the theoretically correct time.

Please bare in mind the above info is only with regard to injector flow on high power turbo engines at WOT and is not an issue that we would normally consider for an N/A engine that have a much lower specific bhp figure, or a turbo engine at light throttle.

Its perhaps also worth me mentioning here that this issue is actually quite acute to the fact we only have 4 cylinders on the YB. This means the specific bhp per cylinder ends up extremely high and why we end up using virtually ALL of the 720 degree time span!!

For example my engine running 1000cc injectors actually has to run them open for 650 degrees when running 650bhp.