Date: Fri, 11 Aug 2000 16:09:09 -0400
From: "Jeff Lloyd"
> Lets not forget every chamber fires once per revolution not every other
> revolution like a 4 stroke piston engine
> So in reality it is like 654cc X 12 that's 7848cc regardless of turbo
> charging that is one inefficient motor only putting out
> 250hp from almost 8 liters.
Jeff, the two chambers each only fire ONCE per revolution of the output
shaft. The other two chambers per rotor are intaking, compressing, or
exhausting during the power stroke time. The rotors turn at 1/3 the rate of
the eccentric (crank / output) shaft. So in piston engine equivolence, it is
like a 2 stroke of 1.3 litres, but actually a bit better since it does not
lose 1/3 of the compressions stroke with open ports. If I remember right,
SCCA classes them in prepared as 1.8 times chamber volume change, or 1.8 x
1.3 = 2.34 litres. I don't have my rule book sitting here, but I think it was
another only 1.25 times for turbocharged. So 2.34 x 1.25 = 2.93 litres. That
is definately an understatement of the air flow potential.
In reality, they flow double the chamber volume compared to a piston 4
stroke, so 2.6 litres, and a turbo can double the flow again at about 15 psi
of boost (5.2 litres making 255 hp, sounds about right) , I don't remember
what the stock RX-7's run for boost, but it was probably a bit under 15 psi.
Gary M.
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