Anyone explain what the degree numbers on a cam mean?

[PeteE30Tourer]

Just because i like to understand these things, can anyone explain what is meant by the numbers quoted for uprated cams, e.g. 272/284. I gather one is for the inlet and one for the outlet valves, but what does it really mean? How does this affect engine performance as the numbers change, i.e. what's the difference between a 272/284 and a 284/284?

[Borderbmw]

Basically the numbers mean the duration of the inlet/exhaust lobes when the cam rotates a full 360 deg,so it stays open for say 270 deg of a 360deg rotation etc,hope this helps mate?

[Jos]

The longer the duration is the more fuel/air mix can enter the engine, the more fuel/air there is the more power is produced. Same for the exhaust side, the longer it is open the more waste gas is expelled from the cylinder.

Reasonable explaination here:

http://www.streetracersonline.com/articles/camshafts/

[PeteE30Tourer]

Excellent - thanks again Jos - very interesting reading.