X-Mozilla-Keys:
Turrbie@aol.com wrote:
In a message dated 8/7/99 3:07:59 AM Eastern Daylight Time,
rotaryeng@earthlink.net writes:
> I was under the impression that non-turbo II engines earlier than 93
> (i.e.
> cast
> rotor depressions) had a compression ratio of 8.5:1, and that the CNC-
> machined
> turbo II 93+ rotors were 9.0:1. Did Tracy make a typo above, or did I
> miss
> something somewhere? I'm guessing that the combination of turbo rotor
> housings
There two things that you are probably missing: First, Mazda switched to CNC
machined rotor depressions in 1989. The rotor depression is the only thing
that dictates compression ratio differences between 1986 - 1995 13bs, whether
they are turbo or normally aspirated. This may sound too simple because the
manufactures of reciprocating engines usually set compression ratios by the
head combustion chamber size in conjunction with the piston dish volume and
the head gasket thickness.
Second is the combination of parts used: The Iron end housings and rotor
housings are 89 Turbo II parts. The rotors are from a 90 13B 6 port normally
aspirated engine which has a 9.7 to 1 compression ratio. The simple act of
installing these rotors gave the engine it's new compression ratio of 9.7 to
1 compared with the stock 9.0 to 1 ratio of an 89 Turbo II.
There were many other mods and parts swaps done such as: a normally aspirated
oil pump was used, the intake and exhaust ports were ported lightly and
blended, the rotor housing water jackets were grooved, the heat risers were
plugged and the oil main in the rear housing was modified to eliminate the
oil filter boss. And some other little details... Everything was done with a
purpose in mind, but that's too much to discuss in this thread. Tracy will
be writing about the design strategy in his newsletter.
Bruce Turrentine
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