Contour Enthusiasts Group Archives Forums General General Engine question

I was thinking about this the other day. What are the advantages and disadvantages to having dual overhead cams, as opposed to single overhead cams or other ways of lifting the valves? More hp, more torque, better fuel economy? Just wondering.

DOHC (Dual OverHead Cam)s are normally associated with 4 valve-per-cylinder head designs where you have a cam off to one side for the bank of intake valves on that side of the head and a second cam for the other bank of exhaust valves on the otherside of the combustion chamber. SOHC (single) is usually associated with 2 valve per cylinder designs, since there doesn't have to be near as many different cam lobes (i.e. fewer valves). 4 Valve per cylinder engines were invented because of their wider powerbands, since the primary intake valves and intake runner diameter and length can be tuned for low RPM power, while the secondary intake valves and intake port runner diameter and lengths are tuned to come on (with aux. computer controlled throttle butterflies) only at higher RPMs, thus making the motor more powerful and efficient throughout a wider operating range. The advantage to having the 2 exhaust valves in each cylinder is because goemetrically speaking, 2 smaller diameter exhaust valves fit better in a round cylinder, and can flow more air than one big valve, because the big valve can only be so big before it would physically interfere with the intake valve's position in the combustion chamber. Did I make sense?

Yeah, thanks.