Mazda investigates hydro-hybrid RX-7

MAZDA remains cagey about when, or even if, a next generation RX-7 performance car will appear and is even tighter-lipped about what will power it.

But senior factory officials at the Frankfurt motor show have ruled out a number of possibilities and confirmed Mazda is investigating many other high-tech solutions, including hydrogen/rotary hybrid power.

Chief Mazda product planner Joe Bakaj confirmed previous reports that a next generation RX-7 would not feature forced induction versions of the RX-8's effective Renesis rotary engine.

"We are not prepared to give up (acceleration) response, which effectively rules out turbo (charging of the RX-8 engine). And supercharging could be a solution but it has efficiency issues," he said.

Mr Bakaj also ruled out a triple-rotor version of the Renesis engine on the basis of cost, the same reason he said would prevent Mazda increasing its capacity.

"Going larger displacement would require a basic redesign of the Renesis, which we'd have to be careful about given the volume limitations," he said.

This is despite previous reports that suggested increasing the Renesis engine's rotor size by 10mm, in much the same way that Mazda's popular earlier rotary engines grew from the original 1967 Cosmo Sport's 10A engine over the years, would be the most practical solution to increasing the new generation RX-8 engine's output.

Similarly, peripheral porting solutions similar to those that eventually brought about the demise of Mazda's previous rotary due to high emissions are not believed to produce significant enough power increases, nor is other ancilliary technology like direct injection.

"We're looking at something entirely more sophisticated," said Mr Bakaj, who conceded hydrogen-rotary hybrid power had been investigated.

Hydrogen power is considered less costly than fuel-cell cars and more environmentally friendly than petrol vehicles, while rotary engines are less fuel-efficient than internal combustion engines when running on petrol, but are expected to be more efficient than standard engines when powered by hydrogen.

Mazda began a two-year trial period for an experimental low-pollution hydrogen rotary engine vehicle in 1995 and has produced a number of hydrogen-powered rotaries, including an MX-5-based hybrid that weighed 400kg more than standard, mostly due to its 300kg hydrogen fuel tank.

Japan's fifth-largest car-maker has already flagged its intention to unveil an RX-8-based hydrogen-powered rotary prototype at the Tokyo motor show in October, and aims to put it on the market in around five years.

It is unclear where a hydrogen/rotary-powered RX-7 would fit into Mazda's range, if at all, but in its simplest form as a lighter-weight two-seater coupe with similar power to RX-8, a new RX-7 could simply be positioned between MX-5 and RX-8.

Mr Bakai said a decision to produce a successor to the RX-7 depended on the sales performance of RX-8.

Although early sales were promising in Australia, Japan and the US, RX-8 is yet to go on sale in Europe and Mr Bakaj said the market success of RX-8 would not be known in its first year.

"The RX-8's success can't be judged this early, so we're in no hurry to push into an RX-7," he said.

A new generation RX-7 will therefore not be seen at next month's Tokyor motor show, which will instead be headlined by a concept that forms the basis of an all-new MX-5, which is expected to go on sale within two years.

Mr Bakaj ruled out the fitting of rotary engines in Mazda cars other than RX-8 and a possible RX-7 on the basis of cachet value. "We want to keep it exclusive," he said.