[email protected] (Dave Williams)
Ford  03 Jun 1997

-> ..the engine doesn't care whether is has a hydraulic roller lifters,
-> "alf" mechanical peanut lifters, "Godzilla vs MegaGodzilla" roller
-> lifters.. what it cares about (in terms of horsepower production) is
-> where, when, how long, how high, and how quickly the valves are
-> opened.

The engine doesn't care, but the cam does.  Once you start pushing the
limits the cam profile determines what type of lifter you'll have to
use.


-> I prefer the mechanical flat-tappet in a street/strip driven car over
-> a *hydraulic* roller is you can have a more agressive ramp, due to

True.  However, down in the "street" range, modern hydraulic flat
tappet profiles work quite well.  Looking at my stack of cam catalogs, I
find off-the-shelf "street" hydraulics typically have shorter durations
and higher lift than their solid counterparts.


-> The reason I prefer the mechanical flat-tappet over the *solid
-> roller* is that IMHO any solid roller that will make power OVER a
-> mechanical flat-tappet will have a non-streetable valve ramp. The
-> advantage of the roller is that is can be very agressive.. but the
-> "street rollers" aren't any more agressive than the flat-tappets, a
-> wash.

True.  The reason for this is, while the roller can impart more
velocity to the profile than a flat tappet, the flat tappet can impart
more acceleration.  The flat tappet is limited by the contact line of
the lobe against the base of the lifter.  The contact line moves to the
edge of the lifter on opening, which is why the diameter of the lifter
is a concern.  Rollers, on the other hand, don't have that problem.
They have a different problem - the angle of contact between the roller
and the lobe moves from vertical to nearly horizontal as acceleration
goes up.  Once you get past a certain point the lobe simply wipes the
roller off the bottom of the lifter.

The result is, for (speaking in general terms) durations of less than,
say, 250 degrees can be most optimally ground for a flat tappet, while
larger lobes will work better with a roller.


-> enough that it doesn't beat the rollers out of the lifters @ idle
-> where the lifters/cam have little/no splash lubrication. Solid Roller

Hydraulic rollers don't have that problem.  Nor to any of the solids
I've used - they've fed the rollers oil through via the lifter oil
supply.

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[email protected] (Dave Williams)
Ford  07 Dec 1998

-> I have a question here...Why is it that roller cams are harder? I
-> figured the roller cam would be in a easier to live environment than
-> having a flat tappet sliding across it.  I understand there is oil on
-> the surface, but there is oil on the roller cam as well.  Anyone care
-> to explain this?

A flat tappet cam operates with simple sliding contact.  The roller
tappet cams, er, roll.  The convex roller comes closer to a true line
contact than the flat tappet does, which puts higher surface load on the
cam.  Eventually the lobes will show an odd wear pattern called
brinnelling.

There are cases where you can run a roller follower on a cam not
designed for it.  A prime example is the 2-liter Pinto motor.  But the
Pinto isn't really a flat tappet design; the followers are curved.  So
are the 2300.  Loads are about as high as with rollers, which is one
reason the engines had cam problems in the early years.  You can put
roller followers on the stock cam and they'll work just fine.


-> What is the advantage of a billet?  Forgings are stronger due to the
-> way the grain structure gets deformed in the forging process. Or is
-> this a volume thing where it doesnt pay to forge some of the more
-> wild, low volume grinds?

It's a volume thing.  Cams, even race cams, come premade - they are
cast with the lobes in pretty much the right places, the bearing
journals are finished, cam bolt holes drilled and tapped, and gears
finished.  They come on big pallets.  All the cam company does is finish
the lobes to exact size and profile.  If you want an exotic profile,
different lobe centers, or a different lobe arrangement - for example,
running "Buick" heads on an SBC, there's not enough metal to do the
grinding without going through the case hardening into the soft core, or
there might not be enough metal there period.  So the cam grinder uses a
special blank with round lobes, or whittles the whole thing out of a bar
of 8620 steel.