gvx wrote:Its terminology could have been worded different saying the majority but read the whole statement and look for the words street build. and .705 may not be the average street build that a street rodder wants power from 2500-6500 RPM's so I would rather have 510 average ft lbs torque and 515 average Hp than 25-50 lbs lower average #'s sacraficed for a high peak#. In a drag only application you are correct where you are running a 5500 stall shifting at 7200 the peak trumps average as this guy's components and cam says that he is doing a street toy engine.randy331 wrote:Have you actually measured/mapped out the time a valve spends where?gvx wrote: the valve spends a fraction on time at peak lift the range.
On one I mapped that had a net (actual measured) peak lift of .705" the valve spent 26 crank deg above .700"lift.
It had a duration at .050" of 258*.
So the valve spent 10% of it's .050" duration time in the top 1% of the lift.
I don't consider 10% of the valve open time, a fraction of time, (or at least it's an important fraction of time) and that 10% is when the piston is at a high speed.
I want my ports good during that 10%.
gvx wrote: On the heads these mods will help mid lift that no body thinks about the valve spends a fraction on time at peak lift the range in-between is where the majority of the time flowing into the cylinders. Help the mid lift and help the curve across the band. Higher over all average is faster than a higher peak for a street build.
The trend is the same on street cams.
On a Comp cam magnum HYD roller lobe that has 236* @ .050" lift, it has 160* @ .200" tappet lift. With a 1.5 rocker it'd be .570" peak lift. It'd have .300" valve lift at .200" tappet lift. So it would spend 68% of it's time in the top 50% of the lift curve. The trend is the same over the nose on this lobe too, but I don't remember the numbers without looking them up.
Most all cams spend a good deal of time just off the seat, and close to peak lift going over the nose.
Guess it depends on which place you believe is the one to optimize.
Me,.. I'll work on the top half and let the bottom fall where it falls.
And as far as making good average HP,... try doing that without good peak HP.