Our era is often referred to as the Information Age, but
not all of the available information is necessarily
useful. I am beginning to think that flow benches should
be labeled with a government warning: "Caution!
Excessive reliance on flow numbers may be harmful to
your engine!"
I'm kidding,
of course. Used wisely, a flow bench can be a useful
tool in engine development, just like a timing light or
a dynamometer. Unfortunately, some racers believe that a
flow bench is the ultimate answer machine. When
the subject is cylinder heads, the four words I dread to
hear are, "What do they flow?" Novice racers
and magazine writers share a fixation about airflow. The
mistaken belief that "more is better" is often
the false assumption that produces an underperforming
engine.
I learned
this lesson myself when my partners Buddy Morrison and
Lee Shepherd built our first flow bench in the mid-'70s.
It was a great contraption that could just about suck
the windows out of our rented shop on Arkansas Lane.
While this homebuilt test bench boosted our racing
program, it certainly didn't make us engine experts
overnight - even though we initially thought we had
found the key to the |
vault
of knowledge.
We had been
racing 287-cubic-inch small-blocks in various Modified
and Comp classes before we decided to make the move to
Pro Stock with a 331ci engine. (Students of Pro Stock
history will recall that the '70s was the era of weight
breaks for various engine and chassis combinations.) We
were determined to be "scientific" in our
approach, and reasoned that a 15 percent increase in
engine displacement demanded a 15 percent increase in
airflow. We dutifully enlarged the ports, increased the
valve diameters, and hit our airflow targets. We set off
to conquer the world of Pro Stock - but our pride and
joy was a dog.
After struggling to even qualify in our initial outings,
we pulled an old pair of Modified heads off the shelf.
Lee worked on the ports for an afternoon, we bolted them
on our Pro Stock short-block, and we qualified fifth at
Englishtown in our next race.
If you went strictly by the flow numbers, those heads
would hardly enough air to satisfy a respectable
big-inch bracket racing engine - and yet they were magic
on the race track. That was when I realized that cfm
isn't everything. It's a lesson that I have seen
repeated
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