Believe it or not, the really fun cars to test are the low-end models, not the ultra-luxe jobs most of us only dream about. Down in the bargain basement, compromises are evident, and it's interesting to see what corners were cut to meet a price point. Sometimes there are delightful surprises. Case in point: this week's guest, the all-new 2000 Nissan Sentra. (It's being relabeled as a 2001 model already, with only trivial changes.) I always had a fondness for the Sentra, for being an utterly unassuming subcompact that got the job done with little pretense of being anything more than basic transportation. Viewing driving as necessity seasoned where possible with enjoyment, I never would have bought one - there were too many competitors that did a better job of emphasizing the fun in functionality. Many buyers agreed, reducing Nissan to a fringe player. Well, let me tell you, with the 2000 Sentra . . . they're baaaaack. Dramatic Sentra sales increases show the word is getting out, good news for the struggling company which required a cash infusion and equity stake by Renault to avoid bankruptcy. This is the fifth generation of the entry-level small car, and it's the first designed exclusively for the North American market, by Nissan's California studio. Implicit in that sea change is that it's bigger than any of its homonymous predecessors. It has edged into the compact ranks (as measured by the Environmental Protection Agency), now offering 100.1 cubic feet of interior space (cabin plus trunk). The most noticeable change is in overall length, up by a significant 6.5 inches to 177.5. It's now an inch higher, and nearly an inch wider than the fourth-generation machine, the better to accommodate our bulky American frames. The exterior styling, while far from dazzling, makes the car look far more substantial, and with its inoffensiveness, is likely to hold up over the long pull. With its excellent paint job and fine overall fit and finish, it looks as if it belongs a notch or two upmarket. (Sentras are made in Aguascalientes, Mexico, some 300 miles northwest of Mexico City.) Sentras are offered in four series. The base is called XE, the next-fancier GXE, and the most congenial, SE. Naturally Nissan foisted an SE on their sometimes-harsh critic. The XE starts at $11,649, the SE at $14,899, with the GXE in between. Given the three-grand spread, don't expect the XE to measure up to the test car. (A fourth series called CA is available only in California. It is the first gasoline-only vehicle to be accorded super-ultra-low-emissions status by the California Air Resources Board, and features zero evaporative emissions. Nissan claims it generates less pollution running than other low-pollution vehicles do when turned off.) The SE interior is clean and functional, with attractive materials and shapes that are well integrated. With harmonious cloth inserts on doors, the ambience borders o n elegant. But it's what is not so visible that really impressed. Torsional rigidity across the model line is said to be 30 percent better than on the prior platform. That concept translates into one's feel of how well a car seems screwed together. The more rigid the platform, the better the handling, all else being equal. It "gives" less when dynamic stresses are applied. A 30 percent gain is impressive, and readily perceptible. The challenge when increasing rigidity is to do so without hurting ride quality, and also to make sure that the bits attached to the chassis don't go loose. Nissan has accomplished the mission well. Road-shock isolation could be a bit better, though it's as good as one typically finds in this class. Over very distressed roads, potholes and bumps are a trifle jarring, although such ordinary events as expansion joints are no cause for concern. There's a little hip-hop on washboardy surfaces, not unexpected with a wheelbase less than 100 inch p> The power-assisted steering is fairly quick and not overly numb. The test car benefited from the addition of optional 16-inch wheels and tires, which are monsters for this weight class. The XE gets adequate 185 - 65 - 14 rubber on steel wheels, while the SE performance package entails a 195 - 55 - 16 contact patch. Handling might best be described as competent. You'll not mistake this for a BMW, but the Sentra does what's asked of it without complaint and without surprises. Especially with the "performance" package, the car is capable of more energetic work than one might reasonably expect. Power comes from four cylinders, the lower orders getting a 1.8-liter 16-valver that makes 126 hp and 129 foot-pounds of torque, while the SE rates a 2-liter twin-cam job. It makes 145 hp way up at @6,400 rpm and 136 foot-pounds at a still-lofty 4,800. The 1.8's torque peak comes at 2,400, which suggests it might be better suited to a less-involved style of driving, especially with the optional automatic transmission. The test car had the five-speed manual transmission. It functioned decently, if not sportily, never getting in the way of a swift change nor encouraging same. The clutch is fairly long-throw, and quite sudden in its actuation. This would be a bear to learn on, though more experienced drivers will soon adapt. The throttle is tightly wired, producing a leap-ahead feel when the accelerator pedal is pushed. The way the engine is tuned, there's not much brio below 3,500 rpm, and the game really begins at 4,000. The redline is at 6,800, followed in short order by a hard engine cutoff, which I experienced a few times because of the engine's willingness to zoom toward the stratosphere. EPA estimates are 24 mpg city, 31 highway, on 91-octane. I recorded 26.6, with the powerful air conditioner blasting and the engine humming in its upper reaches most of the time. Braking was impressively good. The SE has disc brakes front and rear, while the other series get drums aft. The SE's front discs are also larger than its sibs'. Stopping distances were relatively short and the brakes were easily modulated. I wouldn't hesitate to get the optional antilock, especially since it comes bundled with side air bags at a decent price. The instruments are big and easy to read, affecting the Maxima-style black-on-titanium look by day, reversing at night, with reddish-orange needles. The upgraded stereo in the tester was very pleasing. It had better than average tuner sensitivity, excellent clarity and tonality, and enough power to satisfy anyone but those who relish seismic effects. The optional rear spoiler, pure eyewash, is an imposing presence in the rearview mirror, and the aft window is not that big anyway. As a new model, Sentra has not established a reliability record, nor has it been crash-tested yet. Base price on the tester was $14,899. The SE Performance Package adde d $899, and contributed the 16-inch alloy wheels and tires, rear spoiler, viscous limited slip front differential, 180-watt, 7-speaker audio system, body color side sill extensions, lighted visor vanity mirror, overhead storage, map lights, upgraded seat cloth and an immobilizer system; the moonroof cost $599; floor mats, $79, and side air bags and antilock brakes, $699. Total, with freight, was $17,695. It definitely should be on the take-a-look list if you're contemplating a Honda Civic, Dodge Neon, Ford Focus or Mazda Protge. "The Gannett News Service"