Quote:
Originally Posted by steve25
While Thumbing through a DV book on BBC motors once again I came across info I had failed to recall.
DV gave very detailed info that I will try and condense.
If the Cam is of a solid type and has been designed to work with 1.5 rockers and is working well as part of the overall combo then if a change to higher ratio rockers is implemented these changes are needed .
To get the full benefit of that rocker change because the change itself may not provide any benefit, and indeed could reduce both torque and Hp.
When I higher ratio rocker is used the motor thinks that the Cam has been advanced.
The faster opening rate changed the intake part of the overlap triangle, it has increased in area.
This needs to be compensated for by retarding the Cam 1 to 1.5 degrees especially if a ratio increase has gone from 1.5 to 1.7 or more.
The lash needs to change also with the higher ratio to keep the ramp on the lobe working as intended.
In going from a 1.5 rocker to a 1.65 the lash ( minus expansion) needs to be increased by some .004”.
If this is not done DV then states that the advantage of a faster opening rate can be lost.
I found this very enlightening and this all assumes that in each case the geometry was adjusted very well.
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Thanks for the explanation I was looking for.