Umm, not sure I agree with you analogy. Not to bring rotary stuff to
the Dakota List, but, the rotary displaces 654cc per face, times 2
rotors, for a total of 1308cc, or 1.3 liters (if you round down).
Rotary engine displacements and Piston engine displacements are measured
the same way. Displacement is the sum total of positive combustion
chamber volume increases for one complete revolution of the main shaft
(crank or eccentric). In a piston engine, this means the total amount of
space swept by its pistons. In a rotary, it is easiest to think about
the difference between the maximum and minimum volumes for a single
chamber multiplied by the number of rotors (where each rotor has 3
chambers).
Remember that the rotor actually revolves at one third the speed of the
eccentric shaft, which is the reason only one chamber's displacement is
used in the calculation. The difference in power is due to the fact that
the rotary uses its full displacement to produce power for each
revolution of the eccentric shaft while only half the displacement of
the piston engine is producing power for each revolution of the
crankshaft. When you consider the facts above, you will see that on a
rotary, each rotor fires once per eccentric shaft revolution. In a
piston engine, only half of the combustion chambers fire for a given
revolution.
This means that a 2-rotor engine fires as often as a 4-cylinder engine.
However, the power stroke duration in a rotary is 50% longer, it being
3/4 of a main shaft revolution to the piston engine's 1/2. This makes a
2-rotor engine similar to a 6-cylinder.
A 20B displaces 654cc times 3 rotors, or 1962 cc, or 2.0 liters (if you
round up)
This is not meant as a flame war, but a clarification. Please send any
responses off list to me.
Carl
99 Dakota
88 Rx7 GXL
84 Rx7 Base
On Tuesday, October 16, 2001, at 12:47 AM, Crit Bennett wrote:
> The twin Hitachi units on the 93+ RX-7s are a real pain in the ass,
> plus a sequential twin setup wouldn't be the way to go. The
> compressors are too small for a parallel twin V8. Also, the 1.3 is a
> little misleading. Rather than displacing 1.3 liters for every two
> revs, like conventional reciprocating engines do, the rotary displaces
> 1.3L per face and two faces pass per rev. It's essentially a 5.2L
> engine but doesn't burn as effectively. I'm a rotary nut and would
> gladly drop a Mazda 20B into the Dak if I could, but it's not a fair
> analogy.
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