The mettle of any sports car is a matter of mechanical genetics. Or, just how much soul has it inherited from the racing cars in its bloodline?

Ferraris have always represented a fine balance between everyday street handling and enormous performance culled from a thunderous past on world racing circuits.

Lotus is heavy on track talent but light on niceties required for boulevard driving. Jaguar has lost most of its racing dash. So have Alfa Romeo and Maserati. The saucy Miata, of course, is nothing more than a re-creation of the way we thought we were.

Then there is the new Porsche 911 Turbo.

It has returned after a three-year hiatus during which Porsche engineers refined the handling and coaxed an additional 33 horsepower (for a total of 315) from its 3.3-liter and thoroughly historic flat six.

And it contains enough pedigree from its racing antecessors to carry enthusiasts worth the seats of their pants to levels of forward motion and maneuvering associated with such towns as Sebring, Le Mans and Indianapolis.

That's where brakes are huge 13-inch discs drilled for additional ventilation as a fundamental form of urgent slowing from 150 m.p.h. Gears, valves, pistons, crank and camshafts must be deliberately overbuilt if only for scarce moments when everything is overtaxed by maximums of heat or dynamics.

In this high-speed, hard-handlingarena, big turbochargers are cooled internally for additional boost because colder air is denser and allows the engine to breathe deeper and easier. The blinding acceleration from professional-strength turbocharging also transforms a driver's breathing--as that lucky soul goes from full control of the car to a wide-eyed Buck (or Beryl) Rogers barely hanging on.

Rear tires are broad and of special composition to hold the road better than Velcro. Suspension technology must forgive us our trespassing and set a bucking car flat and stable no matter thespeed or harshness of cornering, braking and acceleration. Steering should deliver the same wheel set at 30 m.p.h. as it does at 130.

Such is the pure legacy of world-class racing.

Such is the showroom equipment of the Porsche Turbo.

Yet this car is more than matters of speed and daring.

For a Porsche is a Porsche is an icon. The basic bathtub design of the 911 has been around since L.B.J. was in the White House. What is dateless remains desirable and from classics come nothing but class acts.

All Porsches are lean, solid, reliably engineered and reflect one person's personality as surely as any adoption process. The quality of construction is constant, and that high level has evolved into an industry standard. On a somewhat lesser scale, Porsche snob appeal stays perennial, as does its status as an instant collectible.

Most important, despite what goes on in the upper ranges, a Porsche is soft of pedal and easy of steering when dawdlin g around town and freeway jams. Gears understand finesse, not force. The car can be docile beneath even unfeeling hands and feet.

That, too, is the bequest of the Porsche Turbo.

Buying the car, however, might require a more traditional inheritance. Base price--including $8,600 in gas-guzzler and luxury taxes--is more than $103,000.

Bearing in mind that the Ferrari 348, Corvette ZR1, Acura NSX and Mercedes 500SL will deliver similar panache and performance for much less: How long can Porsche argue low numbers, painstaking assembly and a lopsided rate of exchange as justification for six-figure window stickers?

The other problem in all of this is the unquestionable Jekyll and Hyde nature of the Porsche Turbo. Or Penn and Teller. Because it all boils down to a question of not getting hurt by the magic if you know what you're doing.

The slower half of the Turbo is deft and beguiling. It requires no special skills beyond a talent for pumping yo r own gas to quench an enormous thirst (an average 16 m.p.g.) for premium unleaded.

But the higher side of the car is tough and exhilarating. It takes an awful lot of seat time in a broad variety of high-performance machines--also an instinctive familiarity with the handling quirks of rear-engine cars--before poking the Porsche Turbo into a bellow.

So see this as a serious car for performance-schooled drivers who know what to do when a Porsche's rear end breaks loose. (Steer into the slide and back off the power, you say? Your Porsche just swapped ends and $103,000 is heading for the tules. In a rear-engine car, power is eased on to tame over-steer.)

On the straight and level and through fast, sweeping turns, the Turbo is in its element and at peace. Shifting is slick and the game is afoot: Downshift to where the engine is loitering around 3,000 r.p.m. Punch the pedal, hear the turbocharger become an afterburner, feel the push of unbridled acceleration--and then the blood draining from your eyeballs. Suddenly, there you are. Hanging on.

On narrow, tight, twisty roads, the pleasures are reduced. The wide track and big Bridgestones on 17-inch wheels resist manhandling and even stick a little too hard. The car is never a wild thing. But it is quick to show displeasure, and further abuse will see it thrashing about in protest.

The Turbo runs from rest to 100 m.p.h. in about 10 seconds. More impressive is mid-range acceleration among loose traffic when there is a sudden need to depart the immediate scene. Accelerating from 60 to 100 m.p.h. can then be done in a wink over 5 seconds.

Apart from a smoothing of the whole and a softening of the edges, very few visuals separate the size and shape of the 1991 911 from the 1971 911 dripping cobwebs in my garage. Except for that almost traditional Turbo look: Rubber-edged whale tail, beamy butt and flared wheel wells. At rest, from the rear, its a bat-winged bullfrog.

The wheels are to die for. Five spoke. Cast alloy. And taken from Porsche's 959 super car.

Internally, the car is the same old friend of 25 years. Same fragrant leather (there are three dozen leather options, from roof liner to instrument trim rings) on upright seats that hold thighs, hips and kidneys as if ordered by orthopedic prescription. Same big, bald instruments. Same old inexplicable heater/cooling controls and sub-par sound system. But this year, driver- and passenger-side air bags are standard.

Forward vision, with nothing seen but two fender and headlight bulges, is superb as always. But the rearview mirror has become a little intrusive.

Rear vision is less than we remembered. The culprit is a mid-level brake light mounted on top of the rear window frame. It drops just low enough to hide many things dead astern, including the light bars on black and white Detroit cars containing unsmiling people in uniform.

We all know about rear room in the Porsche. This company began all the nonsense of putting upholstered pie plates in the back and calling them seats. Also, don't expect to get much beyond a garment bag and a sack of puppy kibble in the front trunk.

Sadly, our coral-red test car showed several glitches that one would not expect on a car this pricey. The windshield washer light glowed in permanent warning. The cooling fan stuck on low. Then the cable activating the hood release shed its retaining knob.

On the brighter side, said a Porsche spokesman, nuisances of this type occurring on a $103,000 car usually mean local representatives will make house calls.

Times staff photographer Randy Leffingwell was at the Porsche factory and museum in Germany this month. He was shooting new and old cars for a book on the marque. His loaner was a Porsche Turbo.

On the wide-open autobahn between Munich and Stuttgart, he said, there was steady cruising at 120 m.p.h. with occasional quirts to 150 m.p.h. to clear the fast lane for migrating Mercedes. The Turbo showed safety, stability and impeccable manners at any speed. Leffingwell was enthralled to the point of avarice and pondering ways to afford his new dream: "It is the only car that has ever made me wish I was an attorney."

1991 Porsche 911 Turbo

The Good Eye-watering performance. Handling fit for Fittipaldi. Porsche classicism, super-car technology. Intimidating styling.

The Bad Price bordering on cardiac arrest. Fuel slurper.

The Ugly Still looking.

Cost Base, $95,000. As tested, $105,191 (includes gas guzzler and luxury taxes, optional limited slip differential, sunroof, driver-, passenger-side air bags, alloy wheels, climate control and leather seats).

Engine Six cylinders, horizontally opposed, 3.3 liters developing 315 horsepower.

Type Rear-drive, rear-engined,2+2 sports car.

Performance 0-60 m.p.h., as tested, 5 seconds. Top speed, estimated, 168 m.p.h. Fuel consumption, EPA city-highway, 13-21 m.p.g.

Curb Weight 3,270 pounds.