how do you figure lift on a camshaft with 1.5 or 1.6 rockers?

Question

The cam says it has .465/.488 at 1.5 ratio, so to find out how much it would be with 1.6 rockers i took .488 / 1.5 then multiplied by 1.6. this = 5.2053333

The heads i am using say they can handle up to .520 lift.
Am i going to have a problem with the .0053333333 lift that is above the maximum .520?

Answer 1

I'd check the clearance between valve retainers and valve guides/seals and see how much space you have at full lift

All the published specs are "guidelines only" and only for standard engines.

There's several aspects which are variables among rebuilt motors,hot rod/modded engines,blueprinted engines etc
they cannot account for.

Rocker angle for example.
A Decked Block with Milled Heads and a Reground Cam having other-than a standard base circle,,different lifters .....
and standard length pushrods can yield a rocker angles which produces a few extra thousandth's of Net Valve Lift.
All beyond Mfg's Calculated results.

If Head Shop Says .520,,,,

You could blind build it with a .490~.500 cam and be reasonably certain you'd at least not have Retainer/Guide bind.

But anytime you are working that close to edge of suggested limits,,it's always wise to Double Check.

Im sure You'd probably be OK.
But it's not MY time & money I'm gambling to say that.
Ya know??

It's extra work if your heads are already assembled,,
but it's Cheap Insurance to double check.

Good Luck with your project,,sounds like You're brewin' some strong stuff.

Answer 2

At high RPM's, your valves can extend past the regular lift height because of valve float, weak springs---best to call a good machine shop in your area for advice on whether the valves might contact the pistons if the clearance is that close or over the limit. Could go with a thicker head gasket or have the piston domes cut out or relieved a little.

Answer 3

Take the advertised lift, divide it by 1.5, then multiply that number by 1.6. Your 465 becomes 496 etc.