Re: Stock CAM specs

[jlandry@domain.elided (John A. Landry)]

As the little green aliens inserted a searing hot probe into the sternum of
Doug Rasmussen <DougRasmussen@domain.elided>, a blood curdling scream was
heard...

>  So what's the deal, are all stock IH cams the same grind?

The cam used in the 304, 345 and 392 is exactly the same between all three
engines with no changes for gasoline, year or emissions!

This may seem strange in today's rage of camshaft specialization, but take a
look at the IH engine performance charts and the numbers speak for themselves.
The stock cam produces lots of torque down low in the rpm band... right where
it should for a stock IH engine!

But yes Doug, you're smart to "shop" for a cam before you throw an engine
together.  I just went through the process myself as I'm about halfway through
a 392 rebuild destined for my Traveler.  Like just about anything in life, any
cam you buy involves making a choice between positives in performance and
negatives.  I came to the conclusion that in the 392, the stock IH cam is
nearly perfect if you want lots of torque in a broad rpm band starting low.
To be sure you can maybe get more torque and definitely more horsepower, but
this will come at the cost of moving everything up in the rpm band.  As you go
for more horsepower, other undesirable engine characteristics begin to become
a bigger factor.  Things like emissions, fuel economy and drivability become
serious considerations.

In my case, I talked to lots of people, read a lot of books and did a lot of
comparing.  I came away convinced that for me the stock IH cam cannot be beat.
It's perfect... right from the factory.  IH knew what they were doing.  I've
been told by one machine shop that so called "newer" cam grinding terminology
has resulted in more sophisticated cam designs being available now... designs
that were never dreamed of in the 60's and 70's.  But for the IH engine used
in it's original intended application, I'm not so sure how high tech they
really need to be.  I think there's a lot of mystery and hype involved with
cam selection and just like with carbs, everyone things bigger must be
better... or aftermarket must be better.  Not always.  Just as it's very hard
to resist buying a carb too big and over carbureting an engine, it's equally
as hard to simply settle for a stock IH cam.  I feel comfortable with my
decision.

But that's not to say some engine builders really need a different cam.  If
you are going to need more rpm from an engine and are making other
modification to achieve that, then by all means a cam is needed that can take
advantage of those changes.  I don't know much about rock-crawling, but I
presume an engine in that sort of rig will be asked to pretty much idle over
boulders all day long.  So an engine in a rock-crawler will need an engine
that produces very high torque at very low rpms, have a smooth reliable idle
and good low rpm operation.  This sounds like the perfect application for the
factory cam.  Depending on the final gear ratio, a highway cruiser engine will
be operated at a different rpm than a rock-crawler, so you'd want a cam that
would give the engine it's best fuel economy and torque at the intended cruise
speed.  When you have a combination of operating conditions, then things get
more complicated.  You have to sort of balance out the negatives and come up
with a happy medium.

I thought about going to Delta Camshaft in Tacoma, WA to have a cam custom
ground, but I was worried about ultimately getting a cam that was inferior
(for my needs) over the stock cam in that it might push up the torque curve in
the rpm band.  Even if I were to be able to convince them to make a cam
exactly like I wanted, I probably would have wound up with a cam just like the
factory cam, but at a premium price.  Why bother?  Sometimes it's best just to
leave well enough alone and go with the tried and true.  But if a person is
totally confused and wants to leave the cam selection process to an "expert",
then a custom cam grinder may very well be the best all around choice.

But as far as your question about cam selection in rebuild kits... yes...
usually a kit supplier is willing to let you leave items out of or upgrade a
kit as desired.  The price will be adjusted accordingly.  The kits are set up
to appeal to as wide a customer base as possible, but if you're building a
engine destined for tractor pull contests, then of course you need to pay
close attention to what you're getting and make different choices.

Happy camming,

John L.
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jlandry AT halcyon DOT com      |
Conservative Libertarian        |  Scout(R) the America others pass by
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