Measure it with dial indicators: mount the rocker on the head, or clamp the
rockershaft in a vice, or some such, move the pushrod size say .200", and
then see what the valve end does. This will get you real close. Better is
to do it on the engine, measuring actual valve motion compared to pushrod
motion, which eliminates some of the geometry issues.
I'd suggest that you call Elgin Cams, they have a lot of this stuff figured
out and should be able to advise you on a cam, particularly if you have the
flow data and know the rest of your engine build.
Cheers, brian
At 09:44 PM 1/27/99 -0500, you wrote:
>Hi all,
>
>I've been lurking for a while, and this is my first post. I'm in the middle
>of building a motor for my first season of Vintage racing, and have a number
>of questions. I'm new to all this stuff so please bear with me! :)
>
>I'm currently working on a 'theoretical' camshaft. We will have the head
>flow benched, after modification, to settle on a valve lift - then choose
>our cam lift. One of the variables is the physical rocker arm ratio - I'm
>using the std MGB rocker arms - not roller rockers. This ratio was quoted by
>the factory at 1.426 however advice from people who have checked these
>figures on many many motors, say that they are actually a lot lower and vary
>greatly from motor to motor. I'm aware of the 'effective rocker arm ratio'
>as mentioned at mgbmga.com, but I need to work out where my arms are at
>before they even start to move - so I can at least calculate the indicated
>ratio and work from there. Can someone advise me of a method to measure
>these things up? :)
>
>Cheers,
>Neil.
>--
>Neil Cotty, Sydney Australia
>1970 MG B GT / 1959 MG A 1600 MK1 / 1956 AH 100/4 BN2
>
>
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