Re: Cam Timing (once again!)
Posted: Mon Jul 03, 2017 11:47 am
Hi Vince
I have lost track of what cams your fitting. If SE or Sprint cams then there is not much reason to move from the standard Lotus settings as Torque improvement is marginal. They are fairly conservative cam duration's to begin with and playing with MOPs for torque versus power really only gets relevant with longer duration cams.
I guess the convention of referring to timing around TDC came because the relationship to TDC is what is important when considering inlet and exhaust timing events so that are the key numbers to remember, especially in a single cam engine when the relative timing is machined into the cam profile.
If your analysing an engines thermodynamic efficiency performance by doing 4 stroke cycle pressure diagrams you do it over 0 to 360 degrees and then from 360 back to zero so the pressure loop connects over the full 720 crank degrees of the 4 stroke cycle . You tend to do what makes the analysis easy to comprehend.
If looking at cam timing on a crank rotation basis thats fine just be careful of your starting point. If you start at TDC of compression and ignition cycle then exhaust MOP occurs at around 250 after TDC and then inlet MOP occurs at around 470 degrees after TDC. ( think I have that right doing it in my head)
cheers
Rohan
I have lost track of what cams your fitting. If SE or Sprint cams then there is not much reason to move from the standard Lotus settings as Torque improvement is marginal. They are fairly conservative cam duration's to begin with and playing with MOPs for torque versus power really only gets relevant with longer duration cams.
I guess the convention of referring to timing around TDC came because the relationship to TDC is what is important when considering inlet and exhaust timing events so that are the key numbers to remember, especially in a single cam engine when the relative timing is machined into the cam profile.
If your analysing an engines thermodynamic efficiency performance by doing 4 stroke cycle pressure diagrams you do it over 0 to 360 degrees and then from 360 back to zero so the pressure loop connects over the full 720 crank degrees of the 4 stroke cycle . You tend to do what makes the analysis easy to comprehend.
If looking at cam timing on a crank rotation basis thats fine just be careful of your starting point. If you start at TDC of compression and ignition cycle then exhaust MOP occurs at around 250 after TDC and then inlet MOP occurs at around 470 degrees after TDC. ( think I have that right doing it in my head)
cheers
Rohan