QUOTE(SirAndy @ Dec 12 2003, 08:29 PM)
"Import Cam: PORSCHE 914, VOLKS 411, Type 4, 1700-2000cc Grind No. (VP-228) Type (Combination) Intake (27-63) Exhaust (63-27) Lift (.433) Valve Lash Cold (.008) Duration (270°) .050 Duration (228°)"
This means (in order of appearance) that the intake opens at 27 degrees before top dead center (BTDC) and closes 63 degrees after bottom dead center (ABDC) and the exhaust opens 63 degrees before bottom dead center (BBDC) and closes 27 degrees after top dead center (ATDC). This is called the cams
phasing. From these numbers you can work out how many crank degrees the valves are open at the same time, or thier
overlap. This cam has 54 crank degrees of overlap (Inlet opens at 27 BTDC + exhaust closes at 27 ATDC = 54).
Lift is pretty familiar to us all. This cam lifts the valves 0.433 inches.
Duration is the amount of time that the valve is off it's seat measured by the time that the valve is actually touching the seat. 0.050" Duration would be measured by the time the valve is 0.050" from the seat because when the valve is this close to the seat, flow drops to near zero. In effect the valves aren't really flowing much at all for 52° of the duration, 26° of the opening ramp and 26° of the closing ramp. It's a decent camshaft, but fairly conservative. You can add some lift and some exhaust duration (split duration, where the intake and exhaust are open for different amounts of time) and get a much more exciting cam.