Rotory engines are large externally, and while they can make very high power levels per ci, they need turbocharging to really be strong because of the very small displacement of the engine. I do not feel the rotory engine is superior, they are very inefficient as far as fuel usage for displacement, they are short lived (especially when turbocharged), they have difficulty passing emissions, and due to externally large size they are impractical in many cases.
The Mazda RX-7 was the most successful rotory powered car in history, the later versions making 255hp from a small 80ci engine (2x 40ci engines together). With twin turbocharging the car was very quick in a 2800lb chassis, but once you begin putting on poundage, the results would have been less than stellar. Very poor torque production would seriously hamper acceleration of a large mass car.
The RX-7 managed a terminal velocity at the end of the 1/4 mile significantly below that of the Mustang Cobra approx 101 vs 104, and slightly slower times as well. With a 600lb weight advantage you'd expect a 255hp car to perform better, but lack of low end power, and little reciprocating mass hurts the engines performance.
Dispite having a high top speed, the RX-7 was not an impressive performer in my personal experiance between 80-120mph. Only after 120 does the RX-7 have the edge due to aerodynamics when compared to the average stock 5.0. While it can reach a terminal velocity higher than the 5.0, it's slow getting there. I have walked more than one Gen III RX-7 TT from 80-120mph in a stock Mustang 5.0. The times posted for the car from Motor Trend is 0-60 5.2sec 1/4mile 14.1@101mph. I'm not normally one to say Motor Trend does a good job driving cars at the track, the 0-60 time is evident of a very good launch. While a tremendous 0-60 performer, you can see as the speeds begin to rise, the RX-7 slouches off. The only thing that allows the car to attain such an impressive top speed is it's very good drag coefficient.
Speaking with many RX-7 owners you may find that the performance of the car drops dramatically with increasing mileage, most TT RX-7's are well on their way to rebuild stage by the time they accrue 80,000 mi. The very nature of the RX-7's engine requires it to be under boosted conditions much more than a standard piston engine, which is one of the reasons the wankel has longevity problems. The overall maintenance record of the powerplant is problematic as well. The RX-7 is not a reliable car, this may well have to do with the complexity of the design. Maintenance costs are also exceedingly high due to limited production runs and parts availibility.
I used to be a tremendous fan of the rotory design, but now that I've looked deeply into the complications around it, I've come to the conclusion that while the engine may have extreme performance potential for it's size, it's fallbacks outweigh it's advantages at this point.
All in all you could bet that if Mazda thought they could make a superior product with a different kind of engine, they would have marketed the rotory in other cars as well.
There is a set of 4v heads availible for the 302. Or at least there was. The heads used the existing OHV design, simply adding more valves. They were/are called the Dominion 32v heads. They make a ton of high rpm power with tremendous breathing capability. Due to the extreme stress on the cam, I doubt they are too reliable.
As far as desmodromic valving are you talking of the design used on Ducati motorcycles that uses a valve closing part to control valve floating at high rpms?
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