Mazda rotaries - Morley's World 449

By: Dave Morley, Photography by: Mazda, Unique Cars archives

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Morley raves about rotaries

So, word on the street is that Mazda is bringing back the rotary engine for 2022. But don’t get too carried away, because the rotary will only form a range-extender engine to recharge the MX-30 hybrid’s batteries. I can hear you turning the page already, but stay with me.

Mind you, there’s more bad news: That means that, crucially, the chook-cooker will not power the vehicle’s wheels. Equally inevitably, the vehicle itself will be yet another cross-over/SUV. Yawn.

Resorting to a rotary engine for what amounts to a stationary engine is like marrying Scarlet Johannsen because she whips up a mean spag-bol. It’s an utter waste of far greater talents.

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Rotaries came in all shapes and sizes

I dunno about you, but I’ve always dug rotaries. I like the way they sound, the way they feel to drive, their willingness to be tuned and, of course, the way they rev till forever and make big mobs of horsepower while they’re at it.

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As a kid living in a country town (that I won’t, for reasons of self-incrimination, name) we used to have a pretty regular Saturday night between-the-traffic-lights derby going on. It was, to be fair, a pretty quiet town. At first, I was running my RA23 Celica with a warmed over, SOHC two-litre. At that point, there were two regulars I couldn’t get past. The first was a two-litre Escort and the second was an RX-4. And I remember that damn Mazda like it was yesterday; red with a tan vinyl roof and a set of disco-looking alloys. And it had those four square tail-lights…and I should know, I spent plenty of time looking at them.

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Eventually, thanks to a policy of winding it up till it snapped and then backing it off half a turn, my brother and I managed to tune the old Celica engine to a standstill. Boom. Up she went one fateful arvo, miles from the nearest town, leaving a trail of con-rod confetti and 10W40 down the road. Booted a rod clean out the side of the block and even managed to smash what was left of the piston into the cylinder head. I managed to salvage the manifolds and the camshaft. No kidding.

I began to study Engine Swaps 101 and bought an imported, Japanese-spec 18RG twin-cam from a mob down in the big smoke. It arrived on a pallet and my brother and I managed to jiggle it into the engine bay, ripped off the pollution gear, cobbled up a throttle cable, sleeved the old exhaust on to the new headers and pretended it was all legal.

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Morley’s tempted by the RX4

Next Saturday and who should turn up but that two-litre Escort. Which was despatched well before the braking marker for the next red light. Poor bastard didn’t know what hit him. One down, one to go. Finally, the Mazda turns up and we find ourselves P1 and P2 at the lights. Old Mate in the RX-4 has no idea that I’m now packing about double the neddies (I hadn’t even washed the car since blowing the engine to smithereens) and I’m feeling confident. Until about the top of first gear when I shifted and he just kept pouring on the coals.

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I never did beat the bugger and had to be content with the fact that I had the second-fastest little coupe in the parish. And despite my admiration for the things, I’ve never owned a Mazda rotary, either. I’ve come close a couple of times, but those brapp-brapp ducks have never quite lined up. Not that I’ve completely given up; every now and then I key ‘RX-8’ into the odd website, but my heart says the cars I really want stop at the first-shape RX-7. My absolute pick would be an RX-4 or RX-5, but fate has stepped in and I now own another 18RG-engined Celica (an RA40 this time).

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R100 started the revolution here

None of which has stopped me learning as much as I can about rotaries and, along the way, I’ve picked up some clues that you may not have run across yet. In fact, there’s plenty of fake news out there when it comes to rotaries, but I suspect that only makes me want one more.

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So let’s tackle some of those rotary myths right here and now. The first is that rotaries rev like crazy and figures of 9000rpom and more are often bandied about. Try that with your Chev small-block and, unless you have a NASA-spec lab supplying the tech and a large merchant bank signing the cheques, you’ll be picking up bits of piston-skirt and con-rod for the next month. But are the rev-crazy rotisserie stories true?

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 A rotary as a range extender in this

Well, yes and no. See, the mistake people make is to assume that it’s those rotors inside the rotary that are spinning at such incredible velocities. In fact, they’re not. The rotors are geared to the output, or eccentric, shaft (what acts like the crankshaft in a piston engine) to the tune of about 1:3. That is, the crankshaft spins three times for every one tour the rotor makes of the engine housings. So, sure, the crankshaft might be shoving the tacho needle around to 9000, but at that point, the rotors are spinning at a lazy 3000rpm or so.

The other porkie-pie that has become fact is that a 13B rotary has a displacement of just 1.3-litres. That number was calculated using just one of the three combustion chambers on each rotor (each one is about 650cc) multiplied by the number of rotors (in the 13B’s case, two). And that’s where 1.3 litres come from.

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Morley’s nemesis from younger days

The fact is, of course, is that each rotor has three sides that each form their own combustion chamber and each one fires every time the rotor performs a lap. But, because of that 1:3 gearing thing, the output, or eccentric, shaft spins a full turn when just one combustion chamber of the rotor goes through the suck, squeeze, bang, blow deal. So, only one side of the rotor actually fires for every rotation of the output shaft.

But doesn’t a 1.3-litre four-stroke piston engine need two rotations of the crank to fire every piston that makes up its capacity. Er, yes it does. So now, the same two turns of the rotary’s ‘crankshaft’ mean that two sides of the rotor will fire. So that’s 650cc times two, times two rotors. Let’s call it 2.6 litres shall we? Which is where all that power comes from and all that fuel goes to.

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A rotary in a Kingswood, what would Ted Bullpit think?

None of which alters the fact that, if you’re yet to drive a rotary engine Mazda, make sure you do it before they ban ’em. Or turn them all into stationary engines.

 

From Unique Cars #449, February 2021

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