If by profile one means duration and lift then there is a power
advantage with a roller cam over a flat tappet cam given equal profiles.
The roller cam (as mentioned by Larry) allows higher lift rates and the
valve will therefore spend more time at (nearly) full open with the
roller cam.
It is interesting to note that the flow through a valve is maxed out at
something like .25 X effective valve head diameter. For instance, with
a 2" intake valve it really doesn't help much to have a lift higher than
.5" in the first approximation. In fact there is some power increase
with higher lifts because the cam with .55" lift will allow the valve to
spend more time at or near the theoretical maximum flow (.5" in this
case) than a cam with .51" (for instance). But, with a flat tappet cam,
in order to keep the ramps reasonable the duration will have to increase
in order to achieve the higher lift. Plus the higher lift increases
stress on the valve train. With a roller cam you have higher lift rates
and therefore can achieve equal flow to the flat tappet profile with
less duration and lift. This is easier on the valve train and better
for economy and low end power (given equal engine outputs).
Frank
> > street. Many knowledgeable people that I have spoken with
> said that they
> > die quick deaths if they spend much time idling. If you are
> going to use
> > the same profile as the original 289 hp you won't gain any
> HP by using
> > roller lifters.
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