Camshaft Lift And Duration How Does It Work

[sikisdr69]

Hi GUYS

I done a lil searching around but couldnt find the answers to what i need, if there is a thread on it sorry for creating a new one but i couldnt find so if you guys can forward me onto it if there is one it will be much appriciated.

I want to know the meaning of Duration in degrees on a camshaft how does it work, is less lift more duration better than more lift less duration,

The cams im thinking of putting in my LS/Vtec conversion are between the Buddy club spec 3+ and the toda spec B cams. The specs of each are as follows

TODA SPEC B
Int-295 dur. / 12.0mm lift
Exh-285 dur. / 12.0mm lift

BuddyClub SPec3+
Int-296 dur. / 11.4mm lift
Exh-290 dur. / 11.8mm lift

As you can see toda spec b has bigger lift but the buddyclub has more duration, now my understanding of duration is that it will leave the valves open for a longer period of time but what i dont understand is the degrees given as a spec along with the cam, can 1 degree make a big difference, also performance wise would any of you know roughly how much different these 2 cams are.

My understanding of cams are bigger lift bigger power, but i have a good feeling that im not totally correct so can someone correct me on that or lead me in a direction where i can correct myself.

thanks alot guys

[EG5[KRT]]

basically the lift is how much the valves are open for.. i.e height it opens..

duration is how long the valve is open for

360 deg is full circle .. so eg. 296 degresses open..

then u work out when the exhaust valve opens

and work out how long the over lap is

by working out how long the intake valve is open while the exhaust valve is open so that it shows how much scavenging/cleaning of the combustion chamber there is. could b mayb 6 deg over lap etc..

[sikisdr69]

i got the fact of the lift the bigger the mm the more it opens, but is it similar to have lower lift and longer duration to higher lift and shorter duration, coz by concept of life it would work in a sense that a shorter lift but bigger duration should keep the valve open long enough to actually let out the same as a bigger lift and shorter duration and also i how would i work out when the exhaust valve opens and when the overlap occurs, by looking at it the toda spec B cams look like its going to produce more power but i could be wrong has anyone done a comparison like me or tested in real life

[EG5[KRT]]

well i guess u gotta calculate the valve opening area and then compare to the time i guess to understand which has more air intake for that duration period..

also you have to think bigger lift tho will b better i belive coz it takes more time for the air to go in at high rpm..

so mayb bigger lift is better for top end and shorter lift but longer duration is beter for lower rpm torque..

i guess its the way you tune the computer to get more power out of the cams as well.. not just installing the cams

i believe when you get buy the cam they should show you the cam specs.. i heard tehre is a card or something..

but yeah if you have more specific questions mayb you should call Toda for specs and mayb ring someone who knows about the buddyclub specs..

[ZeForce]

If Im not mistaken, piston speed and acceleration need to be taken into consideration when choosing the appropriate duration and lift...

[bennjamin]

in the time you typed this thread, you could of typed it in google and found this

http://www.rbracing-rsr.com/camshaft.html

Interesting read.

[turtleEK1]

in the time you typed this thread, you could of typed it in google and found this

http://www.rbracing-rsr.com/camshaft.html

Interesting read.

nice... is a good read!

[SINISTR]

www.howstuffworks.com - its got a fairly good explanation and animations on how it all goes together. won't tell you specific ways a certain profile works but the general idea is there.

[dsp26]

GENERALLY speaking if your not going to the link posted above this...
Lift = Power
Duration = Power Band


If Im not mistaken, piston speed and acceleration need to be taken into consideration when choosing the appropriate duration and lift...
not really... it will always be relative as they all run off the crank/sprockets....