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engine speed drops 1500 to 2000 rpm in less than .05 seconds. This rapid change in engine speed can disturb the entire intact tract, so it is essential to keep the velocity of the intake charge as high as possible during these transitions. That's why I advocate a conservative approach when choosing cylinder heads, intake manifolds, and carburetors. Smaller is often faster.
I also believe that you should buy heads that match the
engine you are racing now, not the engine you plan to
build in two years. For example, one of our customers
who races a 468ci big-block recently purchased a pair of
heads that would have been just right for a 555ci
engine. Naturally, he was disappointed when the new
heads did not produce the dramatic improvement in e.t.
that he had anticipated. I pointed out to him that the
big heads were a poor match for the relatively small
short-block he was using now. Until he had the cylinder
displacement that could take advantage of his new heads'
higher airflow capacity, he wasn't going to realize
their benefits. If you are serious about building a
bigger motor, then it makes sense to buy big heads - but
if you're not really committed to a new short-block, you
should choose heads that are right for your current
combination. |
Sharp throttle response is essential in bracket racing.
Oversized ports can make an engine sluggish and
unresponsive, and that's not what you want when you're
trying to judge both your opponent and the finish line.
If you're a heads-up racer, you need an engine that's
sharp when it comes off the throttle stop. Having the
right cylinder heads is as crucial for consistency as
using the right converter and carburetor.
I think it is
a bad investment to spend a lot of money on porting
cylinder heads for a bracket racing or heads-up engine.
That statement may sound strange coming from a
professional engine builder, but it's the truth. We can
order heads for big-block Chevrolets with port volumes
ranging from 260cc to nearly 400cc, with dozens of steps
in between. If you need heads with 345cc runners, it is
more cost-effective to buy heads with the correct
as-cast runner volume than to port a pair of 320cc
heads.
You should also have a clear idea about your objectives
before you spend big money on cylinder heads. If you
have any thoughts about racing in a fast eliminator, I
urge you to consider the Pro Stock-style big-block heads
that are available from Dart ("Big Chief") and
Brodix. ("Big Duke"). You can spend thousands
of
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