Chevrolet Impala SS, Handbook

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SSHandbook
Modifications: Exhaust
provides this cross-sectional change. The tail pipe length exiting most glass pack installations is also of little
consequence ifa resonator box is used, but is ofsignificant influence ifnot.
Virtually all V-8 exhaust systems can be refined by the addition of a balance or X-pipe. These have two
potential attributes: increased power and reduced noise. Extensive dyno testing on both of these factors has
indicated balance and X-pipes are 100 percent successful at reducing noise. The reductions amount to a
minimum of1 dB to a maximum of3 dB with 2 dB being common. As far as power is concerned, things are a
little less certain. With engines between about 325 to 550 hp, experience indicates that in about 60 percent of
the cases (mostly with balance pipes), the engine can deliver as much as 12 additional hp, with 5-8 being the
most common. The other remaining 40 percent tested showed virtually no change in output either up or down.
Based on such results, we can conclude that a balance or X-pipe is always a positive asset and never a
negative.
Balance pipe sizing seems not to be overly critical. The only really influential dimension is the pipe
diameter. This needs to have an area at least equal to that of a 2.2S-inch diameter pipe (4 square inches) with
2.5 to 2.75 inches being preferable. Though limited to tests on engines up to a little fewer than 600 hp, there
seems to be no measurable benefits to using a crossover pipe bigger than 2.75 inches in diameter. As for the
crossover length, dyno results indicate that 18 inches responds in virtually the same manner as 72 inches long.
The Final System
Take a look at Fig. 10. This is a system I designed for a 700hp normally aspirated non-nitrous street/strip
small-block Chevy that was installed in a 1986 Corvette. It produced acceptable street noise levels without
any measurable drop in power. Although you may have to adopt some slightly different steps toward getting
an acceptable installation, keeping sight ofthe principles involved will deliver similar results. Step outside the
guidelines and you are on your own!
Fig 10 Here is what a complete zero-loss header/muffler system looks like in
finished form. A lot ofwork went into this but the results were worth the effort
involved.