Originally Posted by enkeivette (Post 3587)

Learned something, thought I'd share.

Camshaft duration is a measurement of how long the valve stays open in crankshaft degrees. And the measurement is taken from one specific lift point to that same closing point on the closing end of the ramp.



But, since duration is measured at the cam itself from the manufacturer you would think that rocker ratio is totally independent of this. Well yes, and no, and yes again.

What really matters is the lift at the valve (obviously) and if we measure the lift at the valve at a specific point (say .05 again) with a higher ratio rocker, the valve will reach that point slightly sooner and slightly later, creating a slightly longer degree arc.

Although, if we were to measure valve lift at .00000000000000000000001 (you get the point) there would be no difference in duration, as the cam begins to lift the valve when it begins to lift the valve, period. Rocker ratio cannot change this. However, we do not end the measurement at the very closing point of the ramp. Why not? Probably because there is a negligible amount of air flow at .00000000000000000000001 lift. :huh:

Is your head spinning? Mine is. :sm_up_there:

So in conclusion, yes rocker ratio can affect dynamic duration. The rule of thumb seems to be 2 degrees for every .1 ratio on the rocker arm.

In otherwords, if you had 220 degrees of duration with a 1.6 rocker on an LS1, you'd have 222 degrees with a 1.7 rocker. My cam is a 236 in, 242 ex. split duration with a 1.5 rocker and with my new 1.65 rockers, my duration will jump to 239 in. and 245 ex. :D

Originally Posted by enkeivette (Post 116821)

Guy... YOU JUST PROVED MY POINT! Come on man, admit you were wrong. You went on the comp website searching for similar cams and you still couldnt even find one!

What you posted is a 232/234 duration .595/ .6 lift LS1 cam, and a 230/236 duration .570/ .576 lift SBC cam. The LS cam has more lift, for a roughly equivalent duration. Admittedly, a closer gap than what I usually see, but still congruent with what I said. LS cams, less duration, more lift than SBCs.

Find a SBC cam with a .6 lift cam, and the duration will be ridic. Now stop trying to prove me wrong and start discussing why there is a difference.

I'm thinking, with more valve surface area you need less lift to flow the same amount of air? Maybe thats why this 420A 4 valve motor has way less lift.

Originally Posted by enkeivette (Post 116823)

Ya, I understand the fuck out of cams bitches. Coming soon: Apollo Cams. Wheres 5.0 blow to make fun of my ego again?

Originally Posted by enkeivette (Post 116826)

Advertised lift is all that matters!! Thats how much the valve is moving! Who gives a shit what the base lift is!

Originally Posted by 94cobra69ss396 (Post 116834)

There's a lot of arguing over nothing really. Adam, your buddy can adjust the LSA to whatever he wants. So have him put it on a dyno and run it with a 114 LSA and a 110 LSA and see what difference it makes.