Brainstorming the Next RX-7
March 2003

I always like the idea of Wankel engine. It is lightweight and compact, giving engineers more freedom in designing the chassis. Optimum weight distribution is easy to obtain with Wankel engine. You don’t need any expensive transaxle gearbox or aluminum bonnet. You don’t need to place the battery in the trunk. 

The down side of Wankel engine is still fuel consumption, as you can see in RX-8. We don’t know how much potential it has to reduce emission in the future, but at least it already complies with Euro IV, so Mazda has at least 5 more years to improve it to meet the next phase of tougher regulations. 

However, many people can’t help feeling a bit disappointed about the RENESIS engine of RX-8, for it is no where as powerful as the last RX-7. Although we know RX-8 is intended to be significantly cheaper and more civilized than the full-blooded RX-7, we can’t help feeling empty in our heart. Yes, the voice inside tell us that we want the Seven back. Not only us, but the RX-8 engineering team in Japan also dream about that every night. The management also revealed such intention, but whether a green light is given will be dependent on the sales result of RX-8. If the market accept it, Mazda will be confident to spend another large sum to create the new RX-7. Let’s hope so.

Now, let us brainstorm how the RX-7 would look like. We can safely assume that the car will not be sold in the same large numbers as the RX-8. Therefore it must share key components - such as engine, suspensions and steering - with RX-8. As the Seven will be a pure 2-seater, it can be based on a shortened version of the RX-8 platform. I would like its wheelbase to be cut by 250mm to 2450mm. Wheelarches are pushed out a bit to accommodate wider tracks and tyres. The rear tyres grow to 245/35, still at 18-inch rim because the lightweight RX-7 doesn’t need brakes too big. The front tyres are 225/40, narrower than the rear. The fine suspension of RX-8 just need stiffer springs and dampers to cope with extra power. 

You can get more power from a Wankel engine in 2 ways. One, simply add the third rotor. Unfortunately, the side intake and exhaust ports of RENESIS seems preventing the addition of another combustion chamber, at least that would be inefficient in the terms of packaging. Therefore, I would choose to turbocharge the current twin-rotor unit by a pair of turbochargers like the previous RX-7. Running at a light 0.8 bar, the engine can probably pump out 300 horsepower and 250 lbft of torque, sufficient to punish 350Z and Porsche Boxster S. 

On the other hand, the shorter chassis with B-pillars is not only stiffer but can be lightened in other places, such as transmission tunnel. By using aluminum bonnet, boot lid and doors, plus lightweight trimming in the cockpit, in addition to the shorter chassis and the lost of rear seats and doors compare with RX-8, weight can be down to 1200-1250 kg despite of the heavier engine. By placing the engine further back, 50:50 weight distribution can be retained while polar moment of inertia is further reduced. 

So, this is my dream new RX-7, a sports car capable of doing 0-60mph in sub-5 seconds and top 165 mph. It could be priced at US$33,000, compare with the US$26,700 RX-8, or the same as the top-spec 350Z. Sharing so high percentage of ingredients with RX-8, I think this price is feasible.

If Mazda can manage to cope with emission regulations, then the next phase will be 1.2 bar of turbo boost, creating a 360 hp / 300 lbft RX-7. It could have a higher power-to-weight ratio than the 911 GT3 !!! 

Let’s hope such a RX-7 will come one day. But first of all, the RX-8 should succeed.

Mark Wan

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