Plymouth's new Acclaim appears to be one of Chrysler Corp.'s best-kept secrets. Perhaps some big advertising blitz is in the making, but as of now, this family sedan might just as well be in the twilight zone as far as potential buyers are concerned.

No doubt, though, the word will be spread on this car as soon as more people become familiar with it. It is just too good a buy in that old Plymouthtradition.

The Acclaim can best be described as the 1990s' version of the old traditional Plymouth sedan. Meaning it can be had in several trim versions (from nice to luxurious) and in several engines (from mild to wild). And all the time, carrying the family around in style and comfort.

Although Plymouth already has a good family car at an attractive price, theReliant, there's really nowhere to go from there when a buyer wants to go upscale. (There's still the old rear-drive V-8-powered Gran Fury, but that's adifferent story.) Now Reliant owners have another family sedan in the Plymouthline-up. And Plymouth also has another car to attract the attention of owners of other cars.

The test car (supplied by Scott Chrysler-Plymouth, 2120 33rd St., Allentown) was a bottom-of-the-line Acclaim model (the LE model is a little more expensive and the LX is quite a bit more expensive) but it certainly didn't look or act like an inexpensive car. There are many who say that there is no such thing today as an inexpensive car. But the mid-size Acclaim with a base price of $9,920, which includes more than 50 standard features, certainlycomes very close to it.

Styling is closer to the slightly smaller and sporty Plymouth Sundance thanthe Reliant. It has a contemporary aerodynamic look with softly rounded lines.Nothing off the wall but not stodgy, either. Styling highlights include a small frontal area with egg-crate grille and flush headlamps, sloping hood, raked flush-mounted windshield, semi-flush side glass, flush backlight, high trunk deck and integrated bumpers. Convenient features of the design include atrunk lid that opens down to the bumper for easier loading and unloading and wide rear door openings for ease of entry and egress.

With contoured front bucket seats with full console, a contoured rear seat,full instrumentation including tachometer, an AM/FM stereo radio, padded headliner and thick carpeting, the test car had the look and feel of a more expensive car. Room is good both in the front and rear. The trunk measures more than 14 cubic feet and a 45/ 55 fold-down split rear seatback allows for even more storage.

Driving the test car proved to be a real blast. Here is a car that Chrysleris pushing as a family sedan but with the optional engine in the test car, it is one of the quickest family sedans around and perhaps the quickest for the money. Just as the old Plymouth Fury had its 440 V-8, the new Acclaim also hasa surprise under the hood.

It is a turbo-charged 2.5-liter/153-cubic-inc h four-cylinder engine that runs and runs and runs. The 2.5-liter engine is a slightly larger version of Chrysler's 2.2-liter four (both have the same bore but the stroke of the 2.5 is longer). In its turbocharged version it produces 150 horsepower at 4,800 rpm and 180 foot pounds torque at 2,000 rpm. And this is 150 horses with no detectable turbo lag, even with the three-speed automatic transmission.

The engine uses multi-port fuel injection and features a single overhead cam and dual counter-rotating balance shafts. The turbo is designed with a low-inertia turbine and compressor, which, according to Chrysler, provides higher sustained peak acceleration, substantial low-end torque and quiet, low vibration idle. But you don't have to take Chrysler's word for it; just step on it to prove it. Notice, this turbo does not have an intercooler. But the lack of it certainly doesn't seem to bother it.

Power just doesn't let up. But then 150 horses are a lot of horses for a car weighing a little less than 2,800 pounds. Acceleration is very quick - 0-60 in less than 9 seconds - and very true. For all of its power there is just a hint of torque steer. And while fuel mileage isn't exceptional, it certainly isn't bad. The test car averaged 15 miles per gallon for city driving and 22 mpg over the highway. Unleaded premium must be used.

Standard engine for the Acclaim and Acclaim LE is the naturally aspirated 2.5, rated at 100 horsepower at 4,800 rpm and 135 foot pounds torque at 2,800 rpm. The luxury LX comes standard with a 3-liter/181-cubic-inch V-6 rated at 141 horsepower at 5,000 rpm and 171 foot pounds torque at 2,800 rpm. A five- speed manual transaxle is standard and a three-speed automatic optional on both the turbo and non-turbo engine four-cylinder engine. The LX uses Chrysler's new and innovative Ultradrive four-speed automatic transaxle.

Although Plymouth makes no claim that the Acclaim is a sports sedan, it certainly does handle well. The suspension features nitrogen-charged struts upfront and beam axle trailing arms in the rear with nitrogen-charged shocks. Anti-sway bars are used on both ends.

As mentioned, base on the Acclaim is $9,920. The test car had a bottom lineof $13,016, including a $425 destination charge. Options included the Popular Equipment Discount Package (air conditioning, center armrest, rear window defroster, tinted glass, 4-speaker system), $1,168; Deluxe Convenience Discount Package (floor mats, ignition light with time delay, speed control, tilt steering), $345; Premium Equipment Discount Package, $314; automatic transmission, $536; turbo engine, $678, and P195/70R14 Touring tires, $30 factory-ordered with car. Package discounts amounted to $400.

The Acclaim is protected by a 12-month/12,000-mile basic warranty, a 7- year/70,000-mile power train warranty, and a 7-year/100,000-mile anti- corrosion warranty.