Re: Cams, John L.

[Bob Brooks <rbrooks@domain.elided>]

Joel:


jmbrodsky@domain.elided wrote:

>      NOT SO FAST BOB!  No going to lurk mode so quickly!
>
>         About the engines being tuned etc, etc.  That's all preaching
>      to the choir here.  I grew up with my Uncle racing.  Tuning
>      engines with him, and doing it on my own now, that's why I asked.
>      So we're on the level about the ratios and tolerances per
>      blueprinting, etc.  When Dad's '63 Corvette 327 was rebuilt, the
>      if the tolerances were .004, with the correct selection of
>      high/low you can actually get it closer to .0015.  Lots of room
>      for improvement, but it takes time, and GM maximizes
>      return/investment so that's why they do it the way they do.
>
>         So HTH does the cam co. know what the valvetrain specs are?
>

The engine designers, in this case IH, originally designed the motor with
a certain performance level in mind. In the case of IH motors, lots or
torque, not alot of HP.

They developed a cam profile based upon these requirements, and the engine
configuration.   Not real rocket science just alot of number crunching.

The designers in turn hand the design criteria to the somebody else in the
company that writes up a spec for the cams, which call out duration,
profile , lobe centers, acceleration and deceleration ramps.  These in
turn get  turned over to the companies that grind cams.  Initially this
would be the OE suppliers, but if the aftermarket guys want the info, they
can request it as well.  In fact alot of the aftermarket guys are also OE
suppliers.

If you wanted to open up a company called Joel's IH Cams, you could  get
this type of info from either the automotive industry or in a lot of cases
the companies that manufacture cam grinding equipment.

Where it gets interesting is when sombody like Isky or Comp Cams or Chet
Herbert get involved and start making after market cams.  Based upon
experience, and customer feedback for a lot of years they have a pretty
good feel for what changes to the basic cam profile will yeild a customers
desired results.

Wether the customer is looking for more power, Higher Lift,or maybe  more
torque, longer duration, or possibly a combo.

Cams for torque applications tend to have less lift and more duration than
a max HP cam.  They also usually have different lobe centerlines.

Blower cams tend to have less lift, and more duration, but even more
important is the length of time at full lift.   You want to get as much of
a charge in the cylinders as possible, but you don't need the valve real
high to do it, you have pressure.

Duration is measured either at .005 lift, or at 0.050 lift.  Thats why you
may  see 2 different specs on a cam.   The other thing that plays into
this, and that cam rinder change in a perforance cam is how fast the cam
moves the valves.

Stock cams tend to have relativly gentle slopes for opening and closing
the valve.  A performance cam  tends to move the valves faster.  Again you
want to get as much fuel into the cylinder as possible.

The down side is that the steeper the acceleration ramps the more of a
problem you have stopping the valve from moving.  This is the reason
aftermarket cams call out for stronger springs.  Helps get the valves
stopped.

This knowledge of what to change to get more performance out of an engine
tends to be a secret for each company.  So in the case of the aftermarket
guys enough data points to plot the exact cam profiles would be tough to
get.  But not difficult to measure, just a pain in the butt.

I think the problem with getting specific info on the IH factory cams is
that IH does not exist anymore, atleast not the IH that built Scouts and
Travelalls ect.  And the existing company does not have either the
interest and may not even have the drawings used to build these parts.

This long drawn out explanaton is just my opinion, but is backed up with
more years than I care to admit, building both stock and high performance
engines.

Lurk Mode ON

Bob


>      How did they get the numbers?  And why can't Landry get them?
>      Also, one further why don't they spec the cams for lobe height
>      and let the user do the rest, since there are so many cams and
>      valvetrain components on the market.  There must be 100 different
>      types of rockers out there, and many of them are adjustable!
>
>      What gives.
>
>      We're gonna keep you out in the open as long as we can.  You
>      lurkers are gonna pay!
>
>      Regards,
>
>         Joel



--
Bob
rbrooks@domain.elided

Micrel, Inc.
http://www.micrelinc.com