[email protected]
Ford  25 Jun 1980
I'm curious if anyone here has had any experience with controlled valve
toss in small block Fords.(no I don't mean valve float)


[email protected] (Dave Williams)
Ford  26 Oct 1996
-> I'm curious if anyone here has had any experience with controlled
-> valve toss in small block Fords.(no I don't mean valve float)

Ballistic cam profiles?  Fiat played with that back in the '70s, but it
was very dependent on valve spring quality.  They gave up and went to
playing with VVT stuff.


[email protected]
Ford  26 Jun 1980
>  Ballistic cam profiles?  Fiat played with that back in the '70s, but it
> was very dependent on valve spring quality.  They gave up and went to
> playing with VVT stuff.

Close but this is new as far as being out in the open anyway,I'm sure it
has been used in secret for ever though.

Valve float is when the lifter comes out of contact with the base circle
of the cam,,,bad.

Valve toss is when the lifter comes out of contact with the nose of the
cam(hopefully controlled) thereby giving more lift.
Idea is to have a spring with a higher seated rate to prevent float and
yet have less open rate so the lifter will be tossed up and away from
nose and get more lift(and power increase).It is the coming thing in
classes of racing where the rated lift of the cam is restricted but the
spring rate isn't.I've heard it is hard to control.The spring gets all
sorts of occilations that are hard to control.The latest is a different
pushrod to absorb the occilations but still work as normal and not bend
too much as to cancel out the benefits.

I was just wondering if anyone has had any experiences with it in class
racing.

[email protected] (Dave Williams)
Ford  28 Oct 1996
-> Valve float is when the lifter comes out of contact with the base
-> circle of the cam,,,bad.
-> Valve toss is when the lifter comes out of contact with the nose of
-> the cam(hopefully controlled) thereby giving more lift.

Yep, that's what used to be called a ballistic profile.  Fiat was
playing with it, not so much to get extra lift, which they didn't really
need, but to get more area under the lift curve without increasing the
duration.  The faster you open (and close) the valve, the more area you
get.  The problem is, you can open the valve fast enough to overpower
the valve spring and have the follow just keep on truckin', which
usually causes problems.  Like destroying the cam and followers.  The
idea was to go ahead and chuck the follower on past the lobe and design
a closing ramp that would accomodate it coming back down.  The problem
was, to cover much of an RPM range the ramp became so long all the
advantage of the faster opening was lost.

The True Way, of course, is desmodromic actuation, which goes all the
way back to 1898.  The cam opens the valve, the cam closes the valve.
We don' need no steenkeeng springs!  The oh-so-glorious Formula One cars
and their pneumatic springs are still... springs.  Renault, Mercedes,
Ducati got it right, though the new owners have committed the crime of
neutering the desmo motors with springs in the interest of saving a few
petty lira...

Desmodromic valves are coming back, wait and see.  Next time the CAFE
screw gets turned again and the OEMs are looking for some fangleage to
nurse a few more MPG or RPM out of their engines, these century old
mechanisms will suddenly become very new, very high tech.  The valve
springs are the only big energy suck left in the modern Otto cycle
engine; begone!  And on top of dispensing with much valvetrain friction
and all the parasitic loss of the springs themselves, the cam designers
will be able to get truly brutal valve accelerations without worrying
about the springs crapping out short of the EPA's minimum emissions
lifecycle, or breaking and causing warranty claims.  It'll all be in the
name of clean air and fuel economy of course, but that's easily fixed...

The "valve toss" concept will only work over a narrow RPM range, is
heavily dependent on the springs, rockers, lifters, and pushrods (and
even valveguide fit, and believe it or not intake and exhaust pulses are
not insignificant - just figure up a 20psi reversion pulse hitting a
1.6" exhaust valve sometime.  If you had lots of money you could get
away with it, but it's a disaster waiting to happen.  For a qualifying
motor it might be a good idea, but to try to run it in competition would
require changing springs at strict intervals, if not more.

There's lots of ultrasupertrick stuff out there.  Much of it even
works.  But the tale of the tortoise and the hare applies to auto racing
as well - you can't win if you can't finish.  Lots of points champions
take home a big check without ever having finished in the top three -
but they're there every race, and they finish every race.

The other old saying is "Speed costs money, how fast do you want to
go?"  Which is true, but speed money is cheap.  It's *reliability* that
turns your wallet inside out.  How long can you afford to run?