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Gas Works

An LP gas-fuelled rotary? No, it's not an old RX4 that Grandpa's converted to save money at the pumps - it's a 320hp-at-the-wheels high-octane turbocharged RX-7!

Words by Michael Knowling, Pix by Julian Edgar

Click on pics to view larger images


As the co-owner of Victoria's SelectMaz workshop, you'd kind of expect Issy Sveticic to garage some pretty unique rotaries. So we didn't fall over backwards when he gestured to a swarm of highly modified Wankel exotica and told us "Yeah, these are my toys". Amongst his workshop's collection is a total of three Sports Sedans (in various stages of completion), a Club Car, a wild triple rotor MoTeC-managed Series 3 RX-7 and, of course, this innovative LPG-fuelled turbo Series 1 Mazda RX-7.

With bubbling enthusiasm and character, Issy explained that the main reasons he made the move to LPG was to both showcase what his company could do and demonstrate the potential in running taxi-cab juice.

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One of the biggest plusses of using gas (other than its cheap cost and EPA advantages) is in its wonderfully high anti-knock properties. Depending on which service station you buy it from, LP gas is often rated to around 100 RON or more. That means Issy can run mega-high combustion pressures inside the rotor chambers of his beloved rotary without hassle - and this, naturally, means more power.

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Singled out for its cost-effective performance and excellent compatibility with LP gas, a Japanese imported 13B turbo engine was chosen as the base to give the company's 1979 Mazda sporty enough grunt to gain some cred amongst the go-fast lads. How does this 320 rear wheel horsepower in an 1100 odd kilogram sports car sound to you? Impressive when you consider that the stock 12A-powered RX-7 (with only 103hp) could cover the quarter mile in low-17s... Rest assured, when we drove this red rocket it had more than enough to make for some major entertainment - all the way through first and second gear was simply lost traction if you wanted it that way!

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Once freighted, the ex-Japan motor was immediately pulled down and re-assembled to SelectMaz's "race engine specs" by dowelling and slotting in low compression Series 4 rotors. These were balanced, clearanced and equipped with the extremely reliable factory 3mm seals. While it was pulled apart, the flow through the housings and potential for big power was also improved markedly with an extend-port job. After assembly, the package then found shelter under the nose of the RX-7 by fitting a 13B sump, 12A turbo front timing cover and a special cross member.

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The turbocharger unit is built up from stock core and is brought up to "high-flow" specs by conversion to a T04 compressor cover pulled from a racecar. It forces in up to 17-18 psi of boost pressure to get things boogying. To ensure the turbocharger is always fed a free-flowing stream of cool air, a long length of convoluted tubing makes its way from a front mounted K&N pod filter to the mouth of the compressor. And, making the most of co-owning a rotary workshop, Issy welded together a pair of unused 13B intercoolers to both boost cooling efficiency and reduce intake restriction at the same time.

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Always a pleasant sight to see under a bonnet, a nicely fabricated SelectMaz tubular exhaust manifold feeds the turbine, with bypassed gasses escaping via the stock wastegate. These parted exhaust gasses meet in a 3 inch dump pipe off the turbo and the pipe continues in 3 inch mandrel bends through custom a straight-through resonator and rear muffler. But combined with the extended porting, the car's still not exactly as quiet as a mouse.

Moving on to fuelling, the engine only ever drinks LP gas - there's no petrol system hooked up at all. Issy first tried gas out on rotaries years ago and had success in "flogging one out for 160,000 kilometres" - so he already had a good idea of how to set a gas system up and tune it for optimal results.

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This system uses a standard type Mazda adapter plate to mount a Gas Research carb (with Issy-modified fuel rods) and a Century converter. Issy's dizzy (?!) is a re-graphed Series 2 electronic device working with the conventional twin coil set-up, but also a set of Magnecore leads and chilly NGK plugs.

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At the end of it all, he can sleep well at night safe in the knowledge that the conversion is fully road and EPA legal - thanks largely to LP gas. And in the fuel economy stakes, the 13B turbo/gas combo shines through by returning around 450km per 48 litre tank ("if you can control yourself" says Issy). And don't forget (in Australia) gas is about 40 cents per litre as opposed to about 80 cents per litre for premium unleaded... Ultra high performance doesn't come much cheaper than this. The trademark smooth torque delivery of the rotary can be felt too - and there is even slightly improved drivability over a petrol-powered variant. That's because with such high-octane fuel, the ignition timing is further advanced for maximum response and bottom-end torque.

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As part of the imported engine/5-speed package that slid into the RX's void, a new 4 paddle brass button SelectMaz race clutch was inserted along with a SelectMaz heavy duty racing pressure plate. Add to this a SelectMaz short shifter and the "dead time" during gearshifts is near-as-dammit to zero - just the thing to keep the turbo spooled up on a charge through the gears.

Further back is a Series 2 RX-7 arse-end with a factory-spec race LSD spinning a 4.1:1 ratio. Attached to the other ends of the heavier duty Series 2 axles are a pair of Series 2 RX-7 discs, which stop the car reasonably when teamed with the stock front discs and good pads.

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Kicking off this 5 year project, the body was the very first part of the vehicle that needed attention. Some run-of-the-mill body prepping, a respray in bright red and the fitment of a full Euro body kit (available through SelectMaz) remedied this situation. And it sure does make the curving lines of the 0.36 Cd RX-7 look a hell of a lot tougher! None-too-subtle is also the best way to describe the "TURBO LPG" stickers that run down the front guards and splash across the rear. Wear and tear from over 15 years of use had also had an adverse effect on the intimate interior of the 'Seven. But rather than opting for the usual re-trim, Issy simply installed the interior from a Series 2 U.S. model.

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Australian rotary fans will recognize this as the same as a Series 3 interior with its power windows. But in addition to this there's now a colour-coded Nova steering wheel, VDO boost, water temp and oil pressure gauges and a Sony radio/cassette.

Giving the car both a purposeful stance and good handling is a combination of KYB gas dampers, SelectMaz custom springs, Nolathane bushes and a front castor kit. Interestingly, Issy says he ditched the rear swaybar to give the combo less snap oversteer. But with near 50/50 weight distribution, the RX-7 is a fairly well balanced package at most times. And Issy's no boof-head when it comes to making handling judgements: he's won 6 and 12 hour races, taken out lots of second places in the State Club Car championship, and has had class wins in Sports Sedans and a second place in the championship.

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Filling the standard wheel arches out to the max is a hot-looking set of 15 inch Simmons V4s and 225/50 and 205/50 Falken rubber. And don't those gold Simmons rims bring back images of the highly successful ATCC cars of the 80s? Oh, and the spare wheel area that used to contain the RX-7's emergency ride home is now consumed by that 48 litre gas tank. But who in their right mind would complain about that slight loss of function? The more exciting driving time you can squeeze out of this car without needing to stop for fuel the better!

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Just ask Issy about some of his on-road antics...

Contact:

SelectMaz:
+61 3 9401 1155
www.selectmaz.com.au

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