Reply to "Dropped a valve..."

> The point to ME is that you are going to gain torque in the engine by
> opening the valves at a faster rate then the lifter on a solid cam lobe
> can follow, i.e., it is a more radical cam profile.

There is acceleration and there is velocity. The two are separate concepts.
A flat tappet cam can accelerate faster off the seat but a roller can achieve
higher velocity. If you set up a cam on blocks or centers and use a lifter
jig or plot it out on paper, it quickly becomes apparent that the range of
actual lobe profiles is limited. For flat tappet cams, the diameter of the
lifter or the length and curvature of the finger follower defines the limits
of possible profiles. Once your pressure line gets to the edge of the
follower, there's no more to be had. For rollers, the diameter of the roller
is your limiting factor. Eventually the pressure line reaches the height of
the axle, and spits the roller off to the side. In practice, there is a
duration point below which a flat tappet will make more power and above which
a roller will make more power. Also, large port engines (like 351C-4V and
429/460 BBF) do not respond well to high acceleration rates.

> If you are telling me that you are installing a roller cam for the purpose
> of dealing with less ZDDT in the oil, then that is mighty green of you and
> in my opinion kind of ridiculous too considering that you only have a valve
> train that will rev to 6500 rpm or so?

That's why many engine builders go to rollers. Too many flat tappet cam
failures. Added power can also be a bonus. For a flat tappet cam to
make the power of a similar roller, it is going to wear at a rate that
may be unacceptable. For a flat tappet, wear is pretty much a function
of load at the pressure line. The more aggressive the flat tappet lobe,
the higher the spring pressure and the faster it wears. That's why the
OEM cams have such a low ramp rate. They had to last 100,000 miles back
when oil had a lot of ZDDP. For hydraulic rollers, oil viscosity and
pressure are your main limits, where leakdown starts to change the valve
motion significantly from the lobe motion. For a performance flat tappet
cam, longevity is sacrificed first. You can load the cam more heavily,
and shorten the ramps to make power but the candle that burns twice as
brightly burns half as long. A hydraulic roller cam can make very good
power and last much longer. Solid rollers have their own set of problems
(oiling at idle, valve lash pounding the tiny needle bearings). Power is
cheap. Longevity is not.

> In addition you are increasing the possibility of catastrophic failure in
> the valve train exponentially because of additional components.

You keep confusing hydraulic and solid rollers. Hydraulic rollers have
been used for decades in OEM applications and have proven very reliable.

> Hum? Excuse me. Must be me?

Apparently so.

> Well that head has to come off to fix the valve. If your local machinist
> is correct and the valves have been floated, there should be some pretty
> obvious marks on the pistons.

Floated valves don't necessarily hit the pistons. He also mentioned bounce
which is not float.

> Like I said, after market roller camshafts and valve train are going to
> require much more maintenance and should be treated as a "race" prepped
> engine.

Then why is it I have more than 220,000 miles on a roller cam (stiff springs
and 1.7:1 rocker ratio) that shows no wear?

Dan Jones