Joe,
If you are contemplating dual-exhaust on an Alpine with two pipes
replacing the existing exhaust collector, you will drop your power output
considerably.
As each of four exhaust pulses (per cycle) enters the collector and
continues down the single pipe (you currently have), each of these pulses
cause a negative pressure to exist behind them, and they help to draw the
next cylinders' exhaust pulse away from the engine: this is called exhaust
scavenging.
There is a partial vacuum (negative pressure) present at your exhaust
manifold or header due to scavenging, and this helps draw more fuel into the
combustion chambers while both valves are open during their period of
overlap, or as Isky calls it "the 5th cycle".
Secondly, you will not develop a high enough temperature to chase away
humidity in either side of your new exhaust systems, and they will rust away
quickly. Because the temperature is so low, the density of the exhaust
gasses climbs quickly, and their velocities drop, again reducing scavenging.
Jim Leach Pacific Tiger Club Seattle
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