NSU Spider Wankel

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NSU Spider

1964 - 1967
Single Cylinder Wankel (rear)
500 cc
64 bhp @ 5000 rpm
4 spd. manual
Top Speed:
100 mph (claimed)
Number Built:
4 star
In the heady days of the 1960's many believed the Wankel rotary engine would find it's first application to be that of powering a super-car. But instead of a Ferrari-esque sports car, NSU instead introduced the Wankel to the world via the construction of fifty hand-built prototypes which the company then loaned to selected families for market evaluation.

Those lucky enough to score a Spider soon realised the engine was going to be a serious rival to the piston variety, the NSU Wankel Spider being much more than a "gimmick" to promote further licensing agreements for the rotary piston engine. Early licensees included Curtiss-Wright and Toyo Kogyo (Mazda), each company paying a reported $2,000,000 each for full manufacturing rights, and about ten other firms including Daimler-Benz, Alfa Romeo and Citroen paid NSU around US$50,000 for the right to share experimental information prior to negotiations about manufacture.

At first glance, the NSU Spider looked like nothing more than a "topless" Sport-Prinz. In the chassis, the two were really quite different. The front and rear suspension was taken from the Prinz 1000 (which differed from the Prinz 4 and the Sport-Prinz in having semi-trailing arm independent rear suspension in lieu of swing axles). The result was a far better-handling vehicle, giving moderate oversteer and higher ride comfort than you would have expected from 12-inch wheels and a 79.5-inch wheelbase.

At the time NSU was determined to remain a car manufacturer in its own right, as the Swabian firm used to be during the period 1906-1933, and had been again from 1956 when the Prinz was announced. The first Wankel-engined production car, however, fell short of the expectations which early communiques from the factory and independent technical analysists had predicted.

Instead of finding the rotary a magic 15,000-rpm V8 killer, the Spider was instead a rather ordinary and un-temperamental small sports car with the performance of a normal 1100cc roadster. When NSU built its first Wankel-engined prototypes, they were fitted with Volkswagen transaxles which were not ideally matched to the power range.

The Spider had a new all-synchro transmission designed for the Wankel engine, and the factory limited the maximum rpm to a very disappointing 6000. This was obviously in the interest of longevity, as experience by 1965 had proved that seal tip wear increased sharply with a rise in rotational speed. The result, of course, was a car that could be driven just as a conventionally-powered one, with the same controls and the same functions.

In order to get similar results, some driving adjustments were required, because the Wankel had virtually no torque below 3000 rpm, and besides, running it under that rpm would cause excessive engine noise and vibration. In effect, when driving the Spider you needed to keep the herbs to over 3000 rpm, although at idle drivers noted that 750 rpm seemed to be the "sweet spot". From there, you would need to increase revs to at least 1100 rpm where it would sound as though it was about to stall, but it wouldn't. From there to the 3000 range would come to be known as the "shake period", engine vibration being accentuated by reportedly the softest motor mounts known to man.

Many road testers, used to having their ears transmit engine revolutions rather than relying on a tacho, were to find the engine actually spinning at around 3000 rpm at what sounded like 1200 rpm - although they quickly adjusted as they needed to find torque to get the Spider going. And that was the difficulty in driving the NSU Spider - you needed to "learn" how to hold the engine speed high enough to get Wankel-style power, yet low enough to achieve reasonable longevity.

Caught at the traffic lights with the revs below the magic 3000, you could do nothing but wait for them to build up - or slip the clutch. Road testers of the day found that, while the Spider was not so pleasant around town, on the track was an entirely different matter. Here it was much easier for the driver to keep the revs permanently above 4000, just right for showing the Wankel at its best. Better still, the engine wouldn't break if taken beyond the red-line - instead it would just rev and rev to about 7500 with the existing carburetion, feeling smoother and healthier as the needle went deeper into the red.

Of course the Wankel was undergoing constant development, the engineers working hard to find more torque, or at least to spread what they had a little lower on the scale. It could be argued that the Spider was seemingly released a little too soon, and was always destined to failure. Perhaps correct on that count, but if you take a moment to look in the direction of Japan, you would need to consider that Toyo Kogyo had just released a prototype Mazda sports fitted with a two-chamber Wankel engine (while NSU had stuck with the single-chamber unit). While NSU did not object to the excellent progress Toyo Kogyo had made with the Wankel system, especially since the licensing agreements called for a two-way flow of information.

Naturally, however, NSU wanted to be first on the market with the engine on which it had Iiterally staked its future. The 500cc unit of the Spider was very compact and weighed only 275 pounds complete with flywheel, starter, generator, carburetor and air cleaner, giving an unusually high power/weight ratio (4.29 lbs per bhp). It had two cooling systems: the engine housing was water-cooled and the piston was oil-cooled. The oil Iubricated and was then consumed. No oil changes were necessary, but the engine needsed occasional replenishment (approximately one quart per 1000 miles). The oil-water heat exchanger was located next to the engine, while the water radiator was conventionally placed behind the grille. A thermostatically controlled fan was engaged if the airflow failed to keep water temperature within the normal operating range.

During the 1960's Renault and Fiat (as just 2 examples) usually placed radiators for rear-mounted engines in the back, but NSU interestingly moved it in front, in the avowed interest of improved weight distribution. The sheer size of it indicated that weight was at least one of their motives. During testing most reviewers noted the cooling capacity as "adequate", though some described a "hot smell" around the tail after a couple of hours' driving. Ease of service was one of the major sales points of the Spider. The best information we can find on that matter indicates that new seals and bearings would be needed after about 30,000 miles, despite the NSU factory claiming 60,000 trouble-free miles. At issue were the seals at the tips of the rotor - apparently running the engine at its full capacity could cut their life in half.

The engine had only one spark plug, and Bosch and Beru produced special types that were capable of handling the continuous hot exhaust bath to give normal plug life. One way of keeping the revs within reason was to fit a very long top gear, giving 107 mph at 6000 rpm. Aerodynamic drag wouldn't permit the car to exceed 95, and road testers of the day found even that figure couldn't be reached except on a long and empty freeway. Cruising at a steady 75 mph in top gear would keep the engine churning at an easy 4220 rpm - a point where it was free of vibration and the wind rioise drowned it out completely.

NSU Spider
The NSU Spider - on song when spinning at over 3000...
Winding up through the gears, the Wankel reportedly sounded almost like a high-revving air-cooled two-stroke, which was probably not such a bad thing, but on the overrun it was reported to be a persistent backfirer - so the novelty of the unique sound would have quickly worn off. Incidentally, road testers noted the rotary engine gave almost normal four-stroke retardation on the overrun, and generally behaved like a normal four- stroke unit except for the uncanny smoothness once it got on the spin ("on the cam" is perhaps a better term to use, but with an engine with precisely two moving parts: the rotor and its shaft, we will go with "on the spin").

Under most highway conditions, the Wankel engine was practically inaudible, except for a slight whine at high rpm when the whistling of the wind and the gear-box clatter abated enough to let engine noise into the interior. Conversation in the Spider was a shouting match above city speeds, and the general noise level of the car was enough to make both the driver and passenger physically tired after three hours or so.

The chassis combination, with disc brakes up front and light but firm rack and pinion steering, was more than capable of handling anything the 500cc Wankel engine could produce in the way of speed. Fitted to the Spider were new semi-contoured seats with good thigh and back support, some lateral steadying, and excellent fore-and-aft travel. The rake, however, was adustable only by thumb-screws at the bottom of the backrest.

Obviously the Spider was strictly a two-seater, although the room behind the seats was quite useful storage space for packages (or a small child). As in all other production NSU cars, footroom in the front is restricted by the wheel arches, so that the driver's clutch foot must be tucked under the pedals. But there was (reportedly) enough headroom for tall drivers, and the doors opened wide to facilitate entry and exit. Vision was reported as good except to the rear quarters which were totally blind. The sloping hood hid a fair-sized trunk. Instrumentation was generally aircraft-functional with large white-on-black speedometer and tachometer as the center of attention - although both were reported as being wildly inaccurate.

The Spider was the net result of nine years of research on Wankel engines by NSU and was deemed by most to be an acceptable automobile for anyone interested in small sports cars. It was a brave decision by any manufacturer to join forces with Felix Wankel - NSU doing so in 1957. The marriage had always been a rocky one, reaching a peak in 1960 as a consequence of premature press reports, dropping after bankers' verdicts, and reflecting each subsequent license contract and each stockholders' meeting. That the Spider even made it to limited production was a miracle.

Large sales volumes were never envisaged for the car, and this was reflected in a relatively high retail price. 2,375 were built between 1964 and 1967. In 1967, the model was withdrawn and NSU's second rotary engined production saloon was presented. The Ro80 would notch up 37,398 units during its ten year production run. In 1966 Al Auger of Richmond, California USA became the first person in the world to race a Wankel-powered production car in officially sanctioned races. With only installing a mandatory roll-bar and racing tires an NSU Spider raced in 1966 and 1967 in Sports Car Club of America sanctioned road races throughout California finishing second overall champion both years in Class H Modified. Because SCCA had no technical information about the Wankel engine it was placed in H Modified racing against lighter, more powerful 850cc highly modified pure race cars.
NSU Spider

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Also see:

NSU Spider Specifications
The History of NSU
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