cam help

[QWKSNKE]

Originally Posted by EHardy1971

This is true,however the increased ratio on 1.7's also causes the valves to open earlier,and close later. Ed Curtis explained it on the corral. I'll see if I can find the thread.

I agree with that statement as well

[86nu]

duration is a number thats machined into the lobe, all a rocker arm is, is a lever on a fulcrum. It just just a tool of leverage. Whether its being pushed open .555 or .585. The pivot point is all that is changed from one ration to another. If you move the pivot point forward or backwards, all you do is change how far it opens, not how soon it opens.

anyways, im not arguing,

[QWKSNKE]

I guess it depends on which duration is being referred to. Adv duration (useless info) or actual duration at .050

[EHardy1971]

Originally Posted by QWKSNKE

I guess it depends on which duration is being referred to. Adv duration (useless info) or actual duration at .050

Exactly. Here is how I found it to be explained,although not the Ed Curtis thread I was looking for...

Going from 1.6 to 1.7 ratio rockers will increase the 0.050" lift opening duration by about 3 degrees but the seat-to-seat opening duration remains unchanged. The area under the lift/opening duration curve is increased and this allows greater filling of the cylinders (more torque).

And...

Think of it this way.
When you are at .047 lift with 1.6 rockers
You would be at .050 lift with 1.7 rockers
The 1.7s will get you to .050 lift sooner (and close below .050 later).
This is how it affects duration at .050

Not trying to start a pissing match,just trying to explain how they would affect duration.

[coupe]

Yes...the increased ratio affects not just the amount, but the speed of the opening too... gross duration is still the same and is determined by the lobe. Duration at any measured valve lift will be more with a higher ratio rocker on a given lobe.