Anybody  remember what the 3rd gen RX7 EPA mileage rating
was? Mazda is claiming the RX8 will come in at 18-19
city and 23-24 highway according to the Jan Motor Trend article.

Is this the 40% they claim?

Paul Lamar

Marc Wiese wrote:

That is almost exactly what my 94 twin turbo gets!! The city is a bit
higher than mine. (driven conservatory-little boost).

Marc Wiese

As Jeff Spitzer pointed out several years ago and Mazda mentioned
in their tech papers a turbo charger can improve the compression
ratio in effect. Jeff called it the overall pressure ratio.
The Wankel configuration is not amiable to high compression
by mechanical means because the combustion chamber is in the
rotor. The shallower the combustion chamber the higher the compression
but the worse the combustion chamber shape diverging further from the
ideal spherical shape. Therefor the turbo charger can boost the
overall compression ratio leading to lower fuel burn per HP
generated.

I don't know if Jon Lauter noticed this effect in his
supercharged rotary boat engines.

It will be interesting to see what a turbo charged RX8 engine
does as far as fuel consumption is concerned.

Paul Lamar

Thermal efficiency of the cycle is really the effect of expansion ratio
generally this is the same as compression ratio. Super charging increases
the effective compression ratio, but not the expansion ratio, and
decreases efficiency. That is why turbo compound can work, and
turbocharging can increase power with little impact on sfc. Vance

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