I recently bought a 440 that has a Crane roller cam installed along with Mopar style adjustable rocker arms. Crane recomends .020 intake and .022 exhaust valve lash settings.
I have heard a old racers trick to increase or decrease duration is to loosen up the settings. Is this true?

Thnxs
Zoomer59

 

Yeah, but the range is limited. Too little lash and the valves dont seat and the engine runs rough. Too much lash is worse. You risk bending pushrods or having them pop out. This can be catastrophic especially when the lifters are popped out of their bores and the engine loses oil pressure. Other problems? The loose lash can cause early cam and lifter failure.
I am the adventurous type and like to try different things, but I'd be inclined to stay pretty close to the factory suggested lash settings.

 

Your not going to feel any seat of the pants improvements, if thats what your looking for. But yes on some motors it can make a difference.