Rotary engine capacity miscalculation

John Avis by | December 16, 2011 | New Cars

I can never understand why the automotive world has gone along with the way that rotary engine displacement is calculated.

The 13B and RENESIS engines claim a capacity of around 1.3 litres.

My opinion is that these engines have a capacity of around 3.9 litres.

Let's look at the facts for the engine from the Mazda RX-8.

1. The combustion chamber size is 654cc.
2. There are two rotors.
3. Each rotor has three combustion chambers.

So 654cc times two rotors times three combustion chambers is 3,924cc... 3.9 litres!

I guess Mazda (and other Wankel engine manufacturers) are claiming this capacity because it is only possible that two combustion chambers are combustible (in contact with the spark plug) at any time. That's fair enough, but I don't know any six cylinder engines that fire all six cylinders at the same time.

Need more facts...

The RX-8 produces 170 kW of power, 211 Nm of torque, and has a combined fuel consumption figure of 12.9 l/100km.

A Ford Falcon with a 4.0 litre 6 cylinder engine has 195 kW of power, 391 Nm of torque, and has a combined fuel consumption figure of 9.9 l/100km.

A Toyota Yaris with 1.3 litre engine has 63 kW of power, 121 Nm of torque, and has a combined fuel consumption figure of 5.7 l/100km.

Do the RX-8 specifications look closer to the Falcon or the Yaris?

Hopefully you will now agree with me and join me in my (fairly silent) protest against this injustice!

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