The battle for the ultimate weapon on the touring car circuits of the world is producing an interesting side effect. Hitting the streets are a tantalising succession of race-bred production cars of stunning potency.

The latest to emerge is Nissan's Skyline GTS-R, a limited-build quickie which forms the basis of the Group A touring car which Fred Gibson's Melbourne team will be racing next season.

International Group A eligibilty regulations require manufacturers to first produce 5000 identical cars, and then a minimum of 500 of any subsequent evolutionary model.

The recent 167 kW Ford Sierra RS500 Cosworth is an example of a Sporting Evolution. Next year's Group A Commodore from Holden's is another.

Nissan has plans to follow Ford and BMW into international touring car racing, meaning Europe, in 1988. The Skyline GTS-R represents its idea of the perfect platform upon which to develop a racing car.

The evolutionary changes to the existing mass¬produced Skyline coupe (sold in Japan, but not here) are extensive and are intended to overcome any deficiencies in the original version. The turbocharged and intercooled two-litre in-line six-cylinder, 24-valve engine now produces 154.5 kW, an improvement of 15 kW. The new car gets the same Garrett AiResearch T-04E turbocharger as fitted to the Sierra RS500 evolution car, and an intercooler four times larger than before. Under next year's Group A rules, intercoolers must be standard.

The bigger blower and intercooler, and a new tuned stainless steel exhaust manifold provide the potential - within the regulations, of course - to around 300 kW in track trim.

Nissan has also learned its lessons on the importance of sympathetic aerodynamics. The present Peter Jackson Skylines, which don't have the benefit of wings, show obvious awkwardness on fast corners.

This deficiency has been rectified with the new car. Unlike more plebian versions of the Skyline which have automatically retracting front bib spoilers, the GTS-R's front air dam is fixed. This is partly to save weight, but probably because moving aerodynamic devices are banned in Group A racing.

Gibson also reports that the suspension pick-up points on the GTS-R have been relocated to maximise the race car's handling and its ability to utilise all its considerable power.

The street package also has racer-inspired monoform bucket seats, and an Ital Volante leather-bound steering wheel. But, according to those who've sampled it, the appeal of the road racer is the wallop it packs.

There's no denying performance sells up a storm in Japan. Nissan built 800 Skyline GTS-Rs, 300 more than required. All were snapped up on the day of release.

Now rumours abound that BMW, smarting from recent touring car defeats by the Sierra, is set to bolt a blower onto its 2.3-litre, 16-valve M3.