LET'S be clear. The rear of the car is no place for an engine.

I know there are a few Porsche 911 moonies now snapping off their rubber gloves and leaping to their keyboards to fire off a strongly worded dissent -- "Ginger! Reschedule Mr. Thomas' 9 a.m. root canal!" But the fact is the rear-engine configuration -- the hallowed architecture of the Porsche 911, the winningest car in endurance racing -- has been rendered finally, utterly, typewriter-ribbon obsolete.

I would not have thought the ultimate 911 slayer would have a Porsche badge on it, but after spending a week in the Porsche Cayman S -- the hardtop version of the Boxster S, though it's so much more -- I am flummoxed as to why anyone would spend an extra $11,000 (or more likely, a lot more) on a 911 when the exotically fastbacked Cayman S is nearly as quick in a straight line and immeasurably more fun in a crooked one.

Slack your rope, 911 hangmen. Civilians may wonder what difference the placement of the engine makes. Let me explain.

It has to do with an automobile's center of mass and the effects of acceleration. When cars accelerate -- as you might charging out of a corner -- the weight of the vehicle transfers rearward, and in rear-wheel-drive cars this increases traction. This is critical, because it really doesn't matter how much horsepower you have, it's how much you can put to the ground.

Unlike front-engine sports cars -- which struggle to transfer weight to the rear wheels and inevitably require a compromise in suspension setup, allowing the car to "squat" a little -- the rear-engine 911 has its center of mass conveniently situated over the rear wheels. Because the car is more mechanically efficient, the engine can be made smaller and lighter, which reduces overall weight. Less weight means the car changes direction more quickly -- less momentum to overcome in any direction. Lighter weight also means less wear on other parts, such as tires, brakes, clutches. A positive spiral of causation.

And yet, for all of these advantages, rear-engine placement is not optimum. The reason: handling. For decades, rear-engined 911s -- and Chevy Corvairs and VW Beetles, for that matter -- handled awkwardly, like a rubber mallet, weighted heavily on the extreme end. This imbalance made the 911s tricky to control at the limit and occasionally downright spiritual, particularly the turbocharged monsters of the late 1980s. Bumper sticker seen on a 911 whale-tail: "My other car is a tow truck."

In the mid-1990s, with the advent of traction control, stability control and various brake-bias interventions, as well as radical suspension redesigns, Porsche tamed the 911, but never quite quelled the car's antsiness. Especially on cold tires, the 911 can feel snappish and prone to oversteer, and little driver mistakes can invoke the guardian angels of the stability control.

None of this is news to Porsche. But by the 1990s, I contend, the company was hemmed in by its own heritage, compelled by a curious kind of logocentrism to continue the rear-engine format even if it was a pain to engineer around.

THE optimal arrangement is, of course, mid-engine, like the Ferrari F430, Ford GT, as well as Porsche's own Carrera GT and Boxster. Now the center of mass is dead amidships, so that the car pivots, swivels and gimbals from the middle. The Cayman S -- with its 291-hp engine, optional 19-inch gumballs and its patently Porsche genetic code -- feels like the 911 the company might have built if it hadn't been so enamored of its own rear-engined reflection.

For one thing, the cars are nearly the same size: the Cayman S is only 3.5 inches shorter overall than the current 911, with a wheelbase 2.6 inches longer. When the cars are parked next to each other, these disparities are instantly swallowed in the cars' visual sameness. Specialists would discern the Cayman's unique front clip, with its floating fog lights and the Japanese fan-style intake ahead of the rear wheels.

The most striking difference is the slope and rake of the roofline. The 911's roofline limns a single volume integrated into the fender lines. In the Cayman, the rear hatch cuts a tapering, flat hollow between the car's rear fenders, raising them as if by bas-relief into sleek, muscular haunches. A scythe-like spoiler deploys from the back of the car at speeds above 75 mph.

The Cayman is a far more charismatic shape, more interesting and acute, than the serenely lovely 911 coupe.

Technically, the Cayman is a hatchback. Lift the rear hatch and you'll find a shallow cargo space and the brushed alloy access panel for the engine's oil and water reservoirs. Under the carpeted and soundproofed hillock between the wheels is the car's 3.4-liter, flat-six engine, a fervent bit of machinery that in the throes of aggressive driving swamps the cabin with a bright, metallic resonance. Imagine the sound of someone cutting up Zildjian cymbals with a Husqvarna chain saw. I'll wait.

According to Porsche, if you combine the capacity of the hatchback hold with the Igloo-size space in the front of the car, it adds up to more than 14 cubic feet, which qualifies as a very big trunk in most car segments. What you give up, vis-à-vis the 911, is the vestigial twin rear seats, which in case of national calamity may be used to carry passengers. In everyday use, the rear seats make a good place to throw jackets and cameras.

The addition of the fixed roof doubles the car's chassis stiffness compared with the Boxster, says Porsche, and sure enough, the Cayman feels as light and stiff as Maria Sharapova's carbon-fiber racket. The 3,130-pound Cayman weighs slightly less than the Boxster S while enjoying, for the moment, a 15-hp advantage in output. The Cayman S costs $59,695, about $5,800 more than a Boxster S.

Altogether, the Cayman has a toned, hard-muscled seriousness and mastery that the Boxster S doesn't quite match, though obviously the convertible is ripping fun to drive. Neither car is refined in the graphite-smooth way that a BMW or Lexus is. The shift linkage in the Cayman is kind of clunky but utterly accurate. At low speed, the Cayman's variable-assist steering has almost no self-centering tendency to it -- which is nice if you're throwing elbows on tight canyon roads -- but as speeds build, the steering becomes more focused.

And speeds will build. One nice thing about the Cayman -- as opposed to a lot of cars with variable-valve, variable-intake wunder-mills -- is that it has a distinct torque character. The engine is a little soft at low rpm but when it reaches about 4,400 rpm, all the torque (251 pound-feet) is on line and it just pulls in a joyfully bellicose rush to 7,000 rpm. The engine actually sounds happier at 6,000 rpm than 3,000 rpm, so it's not unusual to find yourself chatting along at 90 mph in third gear.

USING the cute little chronometer built into our test car, I timed the Cayman to 60 mph in 5.1 seconds -- about half a second slower than a 911 -- but given its mid-engine architecture, hole shots are not the Cayman's specialty. What this car does best is throttle-blipping, corner-to-corner, chased-by-the-devil wind sprints.

The Cayman puts on a clinic in mid-engine dynamics. You can work the brakes and throttle like the pedals of a pump organ, trailing off the brake with your left foot and putting down the power with your right. The car rail-rides the line with perfect precision. The front tires bite beautifully on turn-in and the car, rotating fluidly around the pole of its mid-engine axis, reacts instantly. No ugly weight transfer to cope with, just pure balanced adhesion and tensile stability.

Add to that fantastic brakes and tolerable ride quality -- though the Cayman is still pretty stingy in suspension travel -- and you've got an awesome German sports car that easily out-points that other Teutonic super-coupe ... what was that name again?

Oh yeah, Porsche.

Automotive critic Dan Neil can be reached at dan.neil@latimes.com.

- - -

2006 Porsche Cayman S

Base price: $59,695

Price, as tested: $70,505

Powertrain: Mid-engine 3.4-liter, flat-six boxer-style engine, 24-valve, variable-valve timing and intake geometry; six-speed manual transmission; rear-wheel drive.

Horsepower: 291 at 6,250 rpm

Torque: 251 pound-feet at 4,400 rpm

Curb weight: 3,130 pounds

0-60 mph: 5.1 seconds

Wheelbase: 95.1 inches

Overall length: 170.9 inches

EPA fuel economy: 20 miles per gallon city, 28 mpg highway

Final thoughts: A spiritually centered version of the 911