Valve lifts higher than heads flow.

[Loves302Chevy]

I was watching the latest Engine Power where they were building an LS engine. They chose heads that maxed out at .600 valve lift, but chose a cam with .625 lift. I'm wondering the reason for this. I realize that with this greater valve lift, that the valves would cross the max flow .600 lift point twice, instead of only once. Is there any reason for doing this, or would this just lead to unnecessary valvetrain wear and tear?

 

[Grumpy]

yes theres a damn good reason, and thats the fact that peak lift is not where you gain the vast majority of the ports airflow potential
think about the math a bit , at 6000 rpm, the valve is going from seat to full lift and back to its seat,3000 times a minute, thats 50 time's a second
but that 50 times a second includes the full 360 degree rotation, peak lift rarely lasts more than 40 degrees of that rotation, or about 1/10th of that time.so how much air flow can occur in that exceedingly short time of 1 /500th of a second the valves are near peak lift, but to reach that peak lift the valve must stay open 3-4 times longer if you were to measure from the mid lift point 'in its rotation.
this is why the mid lift flow is critical, its where the majority of port flow
occurs



http://garage.grumpysperformance.co...alves-and-polishing-combustion-chambers.2630/

http://garage.grumpysperformance.com/index.php?threads/valve-seat-angles-and-air-flow.8460/

 

[Strictly Attitude]

if you go watch the video that was posted about ls engines by nelson race engines he explains this to a T the cam spends more twice as much time at mid lift then max lift.

 

[Loves302Chevy]

Thanks. That's what I thought, but it is good to have it confirmed from knowledgeable sources.