A couple years ago I had a stock cam and 5 high performance TR4 cams run
on a Cam Doctor. This is a very accurate machine to measure the cam
lift curve. Of course, you can measure the curve with a degree wheel
and dial indicator and you can get pretty good numbers for the lift and
velocity (first derivative), but you won't have enough accuracy to get
acceleration. Here are a few results I observed:
1. the maximum flank acceleration on a stock cam is twice as high as 4
of the 5 performance cams.
2. the maximum velocity on all but one cam was low enough to allow use
of small block chevy lifters.
3. the recommended valve lash on 3 of the performance cams was so large
that first contacted occurred on the flank at high velocity.
Needless to say, this data completely changed my opinions about cams and
cam grinders/designers.
Someone mentioned using greater acceleration rates with high rocker
ratios. You should keep in mind that the valve spring rates and valve
weight scale with the square of the rocker ratio, i.e 21% greater for
1.65 vs 1.5. If everything else is equal, you'd have to tone down the
acceleration rates on the cam to maintain similar forces on the cam and
tappet.
Larry Young
roadandtrack@bigpond.com wrote:
> I would be deligthed to ehar form anyone who has such cam data .....
> Terry O'Beirne
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