Cams and Cam Gears...

[Rogue]

I know what a cam is (controls the lift/lowering of valves). What I don't know are what the numbers mean corresponding to cams. Could someone explain all the numbers to me? How does changing the number affecter perfromance?

Also what are cam gears? Are they on the end of the cam connected to the timing belt? What are the benefits of adjustable cam gears? How are the adjustable?

Thanx for forgiving my newbness (bike)

 

[Rogue]

anybody?

 

[thewrench]

Dude, you just need to search some, in here and in the NA forum. Look especially for Twilightprotege's threads. We've discussed both a good bit. Twilight started off with some big cams, and made big #s in the top end but never really could optimize them, and now he's reground his intake cam a little smaller, and it's helped his midrange some. It's a lot more involved than someone can really explain in a post, plus, as in everything else, everybody has got an opinion on what's best.

 

[twilightprotege]

^ yeah that.

also, i am in the process of writing a cam discussion paper. already at 3 pages (word doco). wont be ready for a while, but it will be specific to the FS engine

 

[Gen1GT]

Cams are rated two ways. Duration and lift. Duration always stated with which lift, and is in crankshaft degrees. ie 250@.003" lift. That means the cam is pushing on the lifter(which lifts the valve) .003" for 250 of crankshaft rotation. That figure is what they called 'advertised' or 'seat' time. It's not overly useful, since it's not a useable amount of lift. Most cams will be listed at .050" lift. ie 202@.050" lift, which is what my cams are. Here's a reference for how cams are measured.

http://members.aol.com/solomiata/cams.html

Lift is just that, lift. Rated in fractions of an inch, or millimetres. This is the distance the valve lifts off the seat. It's more complicated than that, but we'll leave it at that.

A cam gear can adjust the cam timing or phasing independently of the timing belt. It cam make the valves lift sooner or later than stock. Generally, but not always, retarding cam timing moves the powerband up, and advancing it moves the powerband down. Because horsepower is a factor of RPM, moving the powerband up, increases the AMOUNT of power. ie 100lb-ft at 4500RPM is about 86hp. But that same 100lb-ft at 5000RPM is good for 95hp.

HP=torqueRPM5252

 

[Rogue]

^^thank you, that's what I wanted to know