stroked small blocks in the race cars?

[eschaider]

Originally Posted by CompClassics

Blykins,

What is your thought on running a hydraulic cam profile using mechanical roller lifters? Longevity?

Camshafts are ground with a lobe rising off a camshaft base circle. The amount or rise the lobe exhibits above the base circle multiplied by the rocker ratio is the lift observed at the valve less any mechanical distortions in the mechanism while operating.

As the cam grinder transitions from base circe to the opening ramp on the cam he builds in something called a clearance ramp. For solid lifter cams this is a gradual take up of the valve lash designed to minimize the hammering effect each time the lifter experiences moving from the cam base circle to the actual opening ramp of the cam.

Cam designers sometimes will speak of 0.006" lift durations and also 0.050" lift dutrations. The 0.006" lift duration is essentially the beginning of the actual opening ramp after the clearance ramp and represents the beginning of actual valve movement. This number is helpful in backing into some things like ramp acceleration rates. The intake port will not begin to flow significant air volume until the 0.050" lift point. This is the Harvey Crane originated duration measurement point for guys like us to compare cams.

This is a pic of a cam lobe from CompCams identifying the nomenclature associated with the various points on the cam lobe. Notice the clearance ramp notation on the lower right of the picture.



When you cut a cam for solid lifters (roller or flat) you need to provide clearance ramps to take up the valve lash gently without hammering the operating components to death. The Hydraulic lifter cam (roller or flat face) has no valve lash to take up because of the hydraulic lifter's 100% in contact with the lobe design.

As a result the clearance ramp used on a solid lifter cam to soften the impact on valvetrain components at each valve opening event is not present on a hydraulic lifter version cam. If you put a solid lifter tappet (roller or flat face) onto a hydraulic grind camshaft it would have a much foreshortened service life because of the hammering effect the valvetrain would experience without the clearance ramps.

Because a hydraulic lifter (roller or flat face) always operates at zero lash, hydraulic lifters can be safely placed on solid lifter grind cams but that begs the question why would you do this, other than to get away from lashing the valves — there is no performance advantage.

If the cam was ground as a solid lifter cam use solid lifters (lashed correctly), If it was ground as a hydraulic lifter cam use hydraulic;ic lifters. Don't mess with the primal forces of nature.


Ed