NISSAN has released its second-generation Z-car droptop with product, performance, safety, and value-for-money improvements over the old car that are designed to keep the convertible competitive against the Audi TT and BMW 135i soft top.

On sale now from $74,990 (auto: $77,990), the Z34 370Z Roadster represents a $7000 premium over the virtually identically equipped Coupe version.

But that’s $2000 less than the old (and less well specified) Z33 350Z Roadster if we’re comparing manuals, although the new auto costs $1000 more than before.

The Z34 retains its predecessor’s front-engine and rear-wheel drive layout, with a 53/47 front to rear weight distribution. If you look at it from above the classic 1950s double cockpit configuration should be evident.

However, like the closed car, the 370Z Roadster is a shorter beast than the 35-Ouncer ragtop. Length is reduced by 65mm to 4250mm, and the 2550mm wheelbase is some 100mm stubbier than before, with the rear half of the car taking all of the cut. Yet the width and tracks have been widened – coming to 1845mm, 1540mm and 1565mm respectively.

An all-new electro-hydraulic roof – which is 176mm longer even though it works within a smaller space due – usurps the old electrical item, and dispenses with the manual latching system for a one-touch full-automatic operation.

It results in a 20-second operation via a relocated (to centre console) toggle, folding away beneath a body-coloured steel tonneau behind the seats. For convenience a button on the door handles allows it to be also lowered from the outside, making entry easier in confined spaces.

The roof also loses the old canvas item for what Nissan calls a “high quality” fabric, while the interior material and finish are also much classier. Improved noise and weather insulation were key objectives.

The Japanese company says it went for soft – rather than a hard – roof design for the former’s lower mass, improved weight distribution and packaging advantages, making for a bigger boot – which can swallow a full-sized golf bag and “some weekend luggage”.

Three key objectives were behind the new roof: to create a sleeker coupe profile with it erect to offer easier and simpler operation and to reduce wind turbulence for better all-climate comfort.

To that end a glass wind deflector lives between the twin rollover protection bars, while the roof’s ceiling is fully lined. The windscreen is shorter than before but the electrically-heated glass rear window is now bigger. It’s also on a greater rake, for improved aerodynamics sake – 0.33cd is the quoted figure.

Abandoning the old model’s horizontal lines for a Ferrari California-esque bulbous profile, Nissan says the 370Z Roadster’s silhouette continues with the cantilever theme first seen in the R35 GT-R.

Decapitating the Coupe and the subsequent lost rigidity required significant structural reinforcements in the A-pillars and side sills, as well as around the door and boot openings.

Obviously based on the 370Z Coupe, the convertible shares all of that vehicle’s chassis and mechanical components – including its VQ37VHR 3.7-litre V6 engine with VVEL Variable Valve Event and Lift.

Floor it and it delivers a maximum 245kW of power at 7000rpm and 363Nm of torque at 5200rpm, channelled to the rear wheels via a carbon-fibre composite driveshafts.

The droptop also features the six-speed manual gearbox that blips the throttle for upshifts and downshifts, and also adopts the Coupe’s new seven-speed paddle-shift operated automatic transmission in lieu of the 350Z’s five-speed device.

In manual guise, the 370Z roadster rushes from zero to 100km/h in 5.5 seconds (auto: 5.8) while fuel consumption drops from 12 litres per 100km to 11.2 (auto: from 12 to 10.8). Carbon dioxide emissions are 265 grams per kilometre, or 257 if in the auto.

Weight rises over the Coupe are 55kg (to 1608kg) and 60kg (to 1618kg) for the manual and auto respectively, but the 350Z Roadster was 32kg heavier.

Among other parts, the bonnet, boot lid and doors are made of aluminium to help cut the kilos.

Suspension is via a double wishbone up front and an independent multi-link arrangement in the rear, while a vehicle speed-sensitive hydraulic rack and pinion steering system is employed.

By the way, a Nissan insider says the Porsche Boxster served as the overall benchmark for the 370Z Roadster.

Also helping keep things check are Nissan’s Premium Braking System incorporating 355mm front and 350mm rear vented discs with four-piston front and two-piston rear aluminium callipers, while a viscous limited-slip differential, anti-lock brakes with electronic brake-force distribution and brake assist, and electronic stability control are found on both models.

Present also are dual front, front-side and new door-mounted curtain airbags, along with seatbelts with pretensioners and load limiters.

For their outlay the 370Z Roadster owner also gets keyless entry and push-button start, one-touch power windows, remote central locking, automatic climate control air-con, a pair of 12-volt outlets, 6CD BOSE audio with eight speakers and dual subwoofers, radio/MP3/WMA capability, Bluetooth hands-free phone operation, satellite navigation with DVD and iPod USB connectivity, and Roadster-specific ‘net seats’.

Nineteen-inch alloys shod with Bridgestone Potenza RE050A P245/40R19 tyres up front and P275/35R10 rubber in the rear are fitted, and will be added to the 370Z Coupe from April at no extra cost, replacing the old 18-inch wheels. However, the aluminium spare is an 18-inch T145/70D18 item.

Sadly, the integrated heating and cooling functions fitted to some overseas 370Z Roadsters has been deemed to expensive and unnecessary for Australian-bound Z34s Nissan probably wants to avoid its new baby being branded with the same bulky boulevard cruiser label as the old Datsun 280ZX and first 300ZX.

Nissan hopes to shift about 800 to 900 Coupes and Roadsters in 2010, with the latter’s sales accounting for up to about 25 per cent. Unlike the closed version, where buyers are pretty much evenly split when it comes to gearbox choice, automatic versions of the open top will dominate, to a 60:40 ratio.