What makes the power?

[brc80]

I was just reading the cam guide and was curious to see some cams with less lift but more duration make about the same power as a cam with more lift and less duration. So does one need the other? Or is it safe to say more of either will make more power?

 

[civicious]

my guess would be one needs the other.


more lift results in the valves opening further. more duration results in the valves staying open longer.

theoretically, if the valve opens really high, but doesnt stay open for very long, you'd get the same amount of air/fuel as if it opened not as high, but stayed open longer.

 

[posol]

yup- pretty much.

the only difference is that higher durations make power higher in the rpm band before topping out/falling on their face.

 

[StyleTEG]

More lift tends to increase the peak WHP, where duration tends to shift the powerband upwards. (and as you move peak torque higher in the RPM band, it creates more HP due to the age old equation HP = Torque * RPM / 5252).

The reason some cam manufactures choose to have less duration, is because for the most part the average Honda owner is cheap when it comes to their engine build. They have no problem spending the money to do the easy work on the head, but they rarely want to touch the bottom end.

It should be pretty apparent that more duration and lift is the way to make the most power. However the drawback to more duration is the intake valve stays open longer, during the compression stroke. The result is some compression is lost when it is pushed out of the still open intake valve. (dynamic compression)

The way to correct this, is simply run more compression. This leads back to people not wanting to replace pistons. So they are left with nothing but milling and running flat top valves to increase compression which can only do so much.

So these stage 1 / stage 2 cams are often designed with that in mind.

 

[CRX-YEM]

A really good explination of camshaft specifications

Duration effects engine idle, a high duration cam will have a very rough idle and low vacuum. Have you ever heard an old muscle car that sounds as if you can hear every cylinder fire that's due to a very larger duration cam.

changing the lift and duration change the area under the curve.

A high lift short duration has a narow band
typical for trying to produce more hp

were a lower lift long duration has a wide band
typically produces more torque

 

[StyleTEG]

I would like to note that on VTEC heads, in most cases the idle is hardly effected due to the ability to run low duration nonvtec lobes and high duration vtec lobes.

Less duration in the lower end technically makes more power anyways.

 

[Speedracer228]

Originally posted by CRX-YEM@Nov 2 2004, 09:02 AM
A really good explination of camshaft specifications

Duration effects engine idle, a high duration cam will have a very rough idle and low vacuum. Have you ever heard an old muscle car that sounds as if you can hear every cylinder fire that's due to a very larger duration cam.

changing the lift and duration change the area under the curve.

A high lift short duration has a narow band
typical for trying to produce more hp

were a lower lift long duration has a wide band
typically produces more torque

[post=410532]Quoted post[/post]​

thats a good writeup, it explains everything pretty clearly
good find