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Rocker arm ratio

R

ruedikuhn

Donation Time
Hi all,

I am looking for the rocker arm ratio. none of my manuals spec them. i am rebuilding the head and would like to figure the pressure over the nose. i am using isky 626 springs and getting to high a seat pressure. about 120lb. i can,t find any retainers that would give me more length. any other suggestions will be appreciated.

Thanks Ruedi
 
R

RootesRacer

Donation Time
First of all, totally wrong section for this post.

Correct section would be stock alpine, or modified.


Stock ratio is between 1.38 and 1.42 depending on how sloppy the machinists were on that day.

These are actual ratios I have measured on several engines worth of rockers.
 
RootesRooter

RootesRooter

Donation Time
ruedikuhn said:
Hi all,

I am looking for the rocker arm ratio. none of my manuals spec them. i am rebuilding the head and would like to figure the pressure over the nose. i am using isky 626 springs and getting to high a seat pressure. about 120lb. i can,t find any retainers that would give me more length. any other suggestions will be appreciated.

Thanks Ruedi
Click to expand...

Did remove the washers under the springs?
 
R

ruedikuhn

Donation Time
roots racer thanks for the respond. we removed the shimms but left the seat in place. did not think it would be good to have the spring sit on the alu.
 
mightyohm

mightyohm

Donation Time
I attempted to measure RAR to check these numbers. My unscientific method involved taking a photo of the rocker lined up as best I could and measuring the image on screen. It would be much more accurate to use a dial indicator but I don't have a head on the motor to check. Anyway, I thought this image might be interesting food for thought. It looks like the ratio is very close to 1.4.
 

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R

RootesRacer

Donation Time
mightyohm said:
I attempted to measure RAR to check these numbers. My unscientific method involved taking a photo of the rocker lined up as best I could and measuring the image on screen. It would be much more accurate to use a dial indicator but I don't have a head on the motor to check. Anyway, I thought this image might be interesting food for thought. It looks like the ratio is very close to 1.4.
Click to expand...

The totally correct way requires a dial indicator to measure valve lift and a prior measurement of the same cam lobes nose to base dimension.
This measures average lift ratio.

The lift ratio becomes nonlinear as a function of rocker position to the valve stem.
 
mightyohm

mightyohm

Donation Time
The homogolation form for the Series 5 includes valve lift 0.406" and lobe lift calculates to 0.298. That gives a rocker ratio of 1.36. Edit: see my post below, I didn't include lash in this number, so it should actually be 1.4.

The homogolation form is an interesting document. I was not aware of it before today:

Series V: https://historicdb.fia.com/sites/de...6401/homologation_form_number_555_group_3.pdf

There's also one for the series 2: https://historicdb.fia.com/sites/de...6401/homologation_form_number_30_group_gt.pdf
 
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