cam lift specs


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By Fordy Guy - 15 Years Ago
This post is for John Mummert if you're out there watching

  I notice when you are advertising your cams you give the lift of each grind. What ratio are you using, 1.43 or 1.54.  Just curious

By John Mummert - 15 Years Ago
Bud, I use the 1.54:1. Specs vary a lot because some cam grinders use 1.50:1 for Y-Blocks. Most give spec without the valve lash taken out. This is gross lift. Also, most cams come up .002-.004" short of the grinders listed lift. So if they're claiming .300 lobe lift the cam will often measure .295-.297" actual lobe lift. Then wether you calculate rocker ratio at 1.43, 1.54 or 1.5 plus with or without lash and claimed lobe lift or actual lift you can see the numbers can be all over the place.

An example would a cam with claimed .300" lobe lift X 1.54:1 = .462" valve lift. But the cam measures .296" lobe lift and has .019" lash. Actual lift at valve would be .437".

By Fordy Guy - 15 Years Ago
Thanks for the explanation John, appreciate your time and your great knowledge.
By Y block Billy - 15 Years Ago
John,

The grinders could be figuring in the oil film on the cam, which could be up to .003" bringing the lift back up to their spec?

Just a thought.