The Nissan 300ZX Turbo may be built in Japan but it is as American as sushi. Of course it was the American market this company was after when it introduced the grandfather of all ''Z'' cars, the Datsun 240Z, back in 1970.

There are many more sports cars available these day but the ''Z'' still remains one of the best-selling sports car in this country. No doubt one of the secrets of its success - besides looking very much like a sports car - is that Nissan can't keep its corporate hands off the design. The old American automotive manufacturers' adage that new sheet metal sells was certainly taken to heart by this Japanese company.

Although the 300ZX only hit the market for the 1984 model year, it has had sheet metal changes every model year since; and this was on a car that started out as one good-looking sports car. Sometimes just rearranging sheet metal does nothing for a car. In fact there is a good possibility that it could end up not as good looking as the year before. But the '87 300ZX is even better looking.

Through some neat rearranging of sheet metal, the newest ''Z'' has a slightly meaner look. There is still a good deal of resemblance to last year's model but both the front and rear have been smoothed and refined for an even more aerodynamic look. It is the type of car that is a real pleasure to look at.

Otherwise, the '87 remains about the same except for some other changes. For example, the suspension system has been recalibrated for what Nissan claims iscrisper handling; the air dam and rocker panels are now fully integrated into the body; high-output halogen auxiliary road lamps have been relocated under the front bumper; the fuel injectors are now bottom-flow design for smoother idling; newly designed alloy wheels; the turbo model has charcoal window moldings and rear air spoiler with a subtle ''turbo'' graphic on the lower door and rear panel, and there is a new reduced-friction turbocharger.

Slipping behind the wheel of the 300ZX Turbo quickly establishes one of the other reasons the car is so popular: It is quite roomy and comfortable for a sports car. It is one of the larger sports cars with a wheelbase of 91.3 inches, length, 170.7 inches; width, 67.9 inches; height, 49.7 inches, and curb weight of 3,265 pounds. The two seats are not only spacious but have enough adjustments to make sure just about anyone can be accommodated.

The test car had full analog instrumentation that is attractive to the eye and easy to read. A digital instrument panel is available for $650 but I would advise saving the money and sticking with the standard and much sportier gauges. Knobs and buttons are well marked for easy use. The parking brake is located on the passenger side of the driveline tunnel, which may cut a little bit into the room on that seat leaving more for the driver. Storage space behind the two seats is excellent and is easily acces sible from the rear hatch.

The 300ZX Turbo is not really a casual car to drive. It takes some concentration and effort, meaning you can't daydream and turn the steering wheel all over the place. Steering is very responsive, the car turns quickly; whether or not it is the driver's intention. Of course, sports cars are suppose to respond quickly.

The four-wheel independent suspension features MacPherson struts up front and trailing arms in the rear. Springs, bushings, power steering pump and stabilizer bars have been beefed-up for firmer cornering; in the rear there is now a 24mm stabilizer bar for a flatter ride in hard cornering. A somewhat unique feature of the system is that the driver has the choice of selecting the firmness of ride, and subsequently the handling. The three-way adjustable shock absorbers (dial-a-shock) can be selected by the driver while the car is in motion. The three setting are firm, normal and soft. If you buy the car, you ofco rse are free to set the shocks anyway you want, and I somehow feel that the real driving enthusiast will use the firm setting; the boulevardier the normal setting, and the mid-age crisis buyer the soft setting.

This year the settings have been recalibrated to go along with the overall recalibration of the suspension system. Compared to previous years, the settings are definitely firmer in all positions. Handling, as can be expected, is excellent. If you have the skill, the 300ZX Turbo will do just what you want it to. Even if you haven't the skill, it will make you look better.

To go along with the looks and handling is a fair amount of power supplied by a turbocharged fuel-injected V-6 measuring 3-liter/180-cubic-inches. This overhead cam engine is rated at 200 horsepower at 5,200 rpm and 227 foot pounds torque at 3,600 rpm. This is certainly more than enough juice to make the daily run to work an exciting experience.

There is a slight turbo lag in off the line acceleration but once it gets rolling just hang on. The lag throughout other ranges can be just about eliminated by a little anticipation and keeping up the rpm. And with the five- speed manual transmission, it really isn't all that difficult to do. The engine also has a nice healthy sound to it and it isn't that apparent unless the roof panels are removed or you happen to be standing on the outside and watching it drive away.

Fuel mileage turned out to be quite decent for a 200 horsepower sports car. The test car (using unleaded premium) averaged 25 miles per gallon for highway driving and 16 mpg for city driving.

(The non-turbo 300ZX engine is rated at 160 horsepower at 5,200 rpm and 174 foot pounds torque at 4,000 rpm.)

If by this time you are beginning to suspect that the 300ZX Turbo is expensive, you are right. It is not only expensive but weak-in-the-knees expensive. Long gone are the days of the cheap yen. Base price for the car is $22,699 and it includes a long list of standard equipment such as the T-roof, air conditioning, 40-watt, four-speaker AM-FM cassette stereo, and a variety of functional and convenient features.

The test car, with a delivery charge of $240 and its one option, the electronic equipment package at $1,300, had a full price of $24,239. The electronic package includes cruise control, power driver's seat, a premium 80- watt stereo system, automatic temperature control, defogging outside mirrors, and audio and speed controls built into the steering wheel.