Greets!
Spacers create an expansion of 'x' volume (Vb) in the
fuel/air 'pipeline' called a plenum, which acts as a
low pass filter (aka muffler), smoothing out the
strong pulse 'train' that otherwise disrupts flow.
This increases volumetric efficiency with increasing
Vb (only up to the limits of the system and
unavoidable pumping losses of course), with the
trade-off being a reduced power band with increasing
Vb centered around whatever the new intake/exhaust
system tuning is.
IOW, yes it increases power over 'x' rpm range, so for
good street driveability you don't want a very large
plenum, and considering the limited hood/inlet
clearance, any minor gains from increasing the plenum
Vb is quickly offset by increased inlet turbulance of
a lower profile air cleaner system if not properly
designed to 'bend' the air around the carb inlet
sufficiently to maintain good metering action.
Bottom line, without improving the rest of the
'pipeline', increasing the plenum's Vb much over stock
can potentially disrupt metering enough to decrease
performance/driveability, so unless a particular
spacer has been recommended based on at least some
testing, Caveat Emptor.
I did the Holley cum electric choke swap on vin 1609
back in '75 on the weekend after I bought it IIRC and
don't remember using a spacer and don't have easy
access to look at it right now, but I'm confident I
just used whatever minimum thickness was required to
ensure that the linkage and accelerator pump arm
travel wasn't compromised. The improvement in overall
performance/driveability was well worth the $$/effort
without the need for any extra jet or power valve
experimentation, but as always YMMV.
Anyway, a number of others have done it, so hopefully
they will chime in with more specifics of the
conversion than I can remember.
GM
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