DavidNJ

I really don't know much about hydraulic lifters. My race car has solid lifters. OHC engines I have worked with are direct action--solid lifters.

When figuring valve opening you just subtract the lash (and an allowance for flex) to get the lift. Some cam manufacturers list the advertised duration at approximately the lash divided by the rocker ratio. Some don't.

However, what happens with hydraulic lifters? Do they collapse, reducing total lift? Do they pump up increasing lift? Do they compress just a little? I noticed comp lists the advertised duration at .006 in for hydraulic rollers.

What does this all mean?

Thanks,

David