>
>A-series engines are perhaps a little different that some others, because
the head design limits breathing so much. I'll go with the original poster
that the advantages and disadvantages to an A-series are almost even, in a
given engine build. A-series engines don't respond well to lots of lift,
but they do respond to fast acceleration of the valve, and to lots of
duration at the lift that works (about .350"). Fast acceleration of the
valve results in lots of side thrust with the A-series rocker geometry, so
the guides wear fast. So I think that it would be correct to say that
roller rockers wouldn't give more performance using a fast-ramped cam, and
would give better guide life than normal rockers. BUT by using a cam that
has lower acceleration you can have acceptable guide life with normal
rockers ( and yes, even better life with roller rockers) at the expense of
performance. And that's the whole point of not using newer technology. Not
allowing the roller rockers for the vast majority of racers is moot - they
don't take full advantage of what they can do under the rules for either
performance OR reliability, so who cares? We don't, and shouldn't allow
them simply because they weren't available in the period AND because they do
have increased performance potential for all engines.
>
>Remember that there's always a performance/reliability ratio that decides
what we do to get faster. Colin Chapman used to say that he wanted his cars
to fail on the cool-down lap, then he knew that he'd gotten the equation right.
>
>Cheers, Brian
>
>
>
>At 01:09 PM 1/20/99 -0500, you wrote:
>>
>>In a message dated 1/20/99 12:07:39 AM, PaceCars@aol.com wrote:
>>
>><<Roller rockers are not a performance advantage for A series motors. What
>>roller rockers do is give you longer valve guide life, due to less side thrust
>>on the valves. Roller rockers are noticeably heavier than non-rollers, so if
>>you want to run high revs, non-rollers are probably superior.>>
>>-- that may be true IF there are no other changes to the motor. As I
>>understand it (and I am no expert on BMC motors) the roller rockers allow the
>>use of other parts which can greatly enhance performance.
>>
>> <<Many of the fast guys in SCCA run non-rollers (Comptune sells his own
>>version of non-rollers) due to less valve train mass. >>
>>-- and how often do these "fast guys" rebuild the motor. I've heard they run
>>such radical specifications and high rpm that they install new crank bearings
>>every other session. I suppose if someone in vintage wanted to do that with a
>>non-roller motor and vintage legal parts (whatever that means these days), I
>>could not complain. I also would not envy anyone doing 3 or 4 engine rebuilds
>>every weekend as part of normal maintenance!
>>
>> Sorry, I will not be convinced that roller rockers do not improve
>performance
>>by allowing higher rpm and more aggressive cams and other performance parts.
>>
>> Cheers, Doug Meis
>> (Of course it's easy for me bitch about roller rockers when I've got
>overhead
>>cams AND a roller crankshaft)
>>
>>
>
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