[Fot] TR4 Rocker Arm Ratio?

[Larry Young]

The answer depends on what you mean by rocker ratio.  If you want the 
ratio of the maximum valve lift to the maximum cam lift, 1.46 to 1.47 is 
a good number.  That is the simple answer and, as you know, I can always 
make things more complicated.

First of all, there is compression of the valve train involved.  I call 
this valve train squish.  The valve train acts like a big spring. The 
amount of squish depends on the spring force and lift. With strong 
springs, this could be as much or more than 0.008 in of valve lift.  A 
few years ago I did a fairly extensive spreadsheet analysis of rocker 
geometry.  I found that the instantaneous rocker ratio varied from 1.47 
to 1.49 depending on the lift, lash adjuster location, radius of 
curvature of the rocker arm tip, height of the pedestals, etc. Suppose 
the average ratio is 1.48 and valve train squish is 0.008, you have a 
cam with 0.375 gross lift and 0.012 valve clearance.  The valve lift 
will be about  1.48*0.375 - 0.012 - 0.008 = 0.535.  If you don't account 
for squish and use 1.46 you would get 0.536.
-Larry

On 11/8/2010 10:18 AM, Rich Rock wrote:
> Amici,
>
>
> I need to know the stock rocker arm ratio.  I have it in my mind that it's
> something like 1.46:1.  How wrong am I?
>
> Rich Rock