I see some cam specs listing lift at 448, 512 etc. When the lift is listed at say 295, do you just multiply by the rocker arm ratio of 1.54 to get the total lift of 454.3?

Thanks,

Paul J. - '57 E Code

Pretty much correct unless your rocker ratio is 1:43

Oldmics

Before hydraulic cams came along, you multiplied lobe lift by rocker ratio, then subtracted the running clearance.  Hydraulic cams obviously would not need the clearance subtracted.  I don't know if cam grinders now use 0 clearance on solid cams or not when calculating lift.

John - "The Hoosier Hurricane"

Paul.  You’re right in that when the lobe lift is supplied, simply measure the lobe lift by the rocker ratio for the gross valve lift.  And be cognizant that actual lift at the valve (net lift) will be the gross lift minus the valve lash.  But also be wary of the gross lift figures on a spec card if the rocker ratio is not supplied.  Different cam manufacturers use varying rocker ratios for the Y so just know up front what rocker ratio a particular manufacturer is using if the lobe lift is not supplied.

 

And as Oldmics mentions, make sure you know what rocker ratio you actually are dealing with as the factory rockers are not spot on and especially if the pushrod lengths are being varied.

Lorena, Texas (South of Waco)

Paul,

      It's fairly simple to measure the cam, should you question the Mfr. Measure the across the base of the cam and then the lobe, subtract the difference and you'll have cam lift. You can also set it up on V blocks and measure it directly with a depth gage.  

     

Frank/Rebop

Bristol, In ( by Elkhart) 

Imperfect valve train geometry can cause the lift to be less than advertised as well. .497 is not bad at all for something that should be .505. The relation of the lifter to the push rod to the rocker arm to the valve all have an effect. From what I've seen watching my friend build all sorts of motors, the Y-block is real good as far as the geometry goes. Probably the worst I've seen is Chrysler.


Lawrenceville, GA

Here are links to the articles that were originally published in the Y-Block Magazine regarding both the rocker arm geometry and rocker ratio variability for the Y.  These will help to explain why the lift at the valve can vary even though the lobe lift and rocker ratio is per specification.

Y Block Magazine Rocker Arm Geometry

Y Block Magazine Rocker Ratio Variability

Lorena, Texas (South of Waco)

Can one simply put 1:54 rockers on and gain anything?

Doing Fords for 45 years. '56 Customline Victoria

E.J. in Havana FL

Increasing the rocker ratio will typically give more seat of the pants feel (increase in torque) while also increasing the topend capability of the engine providing the valve springs are not the limiting factor.

Lorena, Texas (South of Waco)

ejstith,

         In a nutshell, yes. But don't expect a hundred HP. Strictly by the numbers, and remember the rockers vary from one to the next, .350 with 1.46's increases to .369 with the 1.54's. You'll also gain one or two degrees of effective duration. That's why Ted told you about the torque gain.   

Frank/Rebop

Bristol, In ( by Elkhart)