From the Archive: 1995 Callaway SuperNatural SS Was a Wilder Chevy Impala

From the October 1995 issue of Car and Driver.

Anything weighing more than two tons and casting an 18-foot shadow ought to be a national monument. Or, at the very least, federal law should prevent it from being named after an African antelope that is svelte, lithe, and agile. As if to rectify GM’s reckless stabs at nomenclature, hot-rodders have attempted for 34 years to make the Impala SS at least quick, if not agile.

The latest attempt is the Callaway SuperNatural SS. “We hadn’t thought about modifying this car,” says Callaway Cars marketing director Rick Carey, “until a guy dropped off his own Impala and said to us, ‘Do what’s right.’ We already had the SuperNatural V-8 [C/D, June, 1995], so that was a good start.”

“Doing what’s right” in Callaway-­speak involves depositing your Impala SS—new or used—in Old Lyme, Con­necticut, for about a week. The stock 260-horsepower engine is yanked pronto, of course, and its iron heads are replaced with aluminum versions whose ports have been polished to a Bulgari-quality luster. Larger-diameter valves are fitted. The cylinders are bored out 0.03 inch and a Callies forged-steel crankshaft with a 3.75-inch stroke is dropped into place, swelling displacement by 33 cubic inches. Next, the engine is enriched by Carillo rods, a Chevy MTG camshaft with greater lift and duration, and a 52 mm throttle-body.

So that the own­er will experience as much of the new­found oomph as possible, Callaway recommends that the engine inhale via the company’s inelegantly named “Honker”—a 3.5-inch-diameter fresh-air duct and low-restriction air cleaner. And the V-8 exhales through dual 2.5-inch-diam­eter stainless-steel exhausts. Twin exhaust tips poke curbward just aft of both rear wheel wells, a layout that shortcuts some three feet of superfluous pipes and increases ramp clearance. This means your dramatic entrance into the A&W drive-in no longer generates a hail of angry sparks.

According to Callaway, these minis­trations result in 404 horsepower at 5750 rpm and 412 pound-feet of torque at 4500 rpm, all of it 50-state legal and none of it inexpen­sive. At this point, you will already have shelled out $14,403. For which princely sum, frankly, the increase in perfor­mance—at least on the first SS we mea­sured—was slim. Compared with the stock Impala SS (C/D, June 1994), the Callaway SuperNatural romped to 60 mph just 0.3 second quicker and blinked through the quarter-mile 0.2 second sooner.

Hey, you slam-dunk an extra 144 hp into any vehicle—even one the size of a high-school gym—and it ought to lean more toward Mr. Hyde than that, right?

Part of the disap­pointing accelera­tion we traced to the stock engine-man­agement system and its attendant shift program. Upshifts under full throttle occurred at 5400 rpm—350 rpm shy of the burly new V-8’s power peak. Equally annoying were full-throttle second-to-third upshifts, in which the driver had to lift off the gas briefly to keep the engine from performing a Mel Tillis impersonation as it stuttered under the whip of a dominatrix rev limiter.

Callaway hauled our test car away and pondered all of this. When the car returned, the Connecticut yankees had replaced what they claimed was a faulty engine­ management box. The new one instructed the V-8 to shift at 5950 rpm—now in the meaty portion of the power curve—before imposing rev-limiting discipline at a heady 6000 rpm. (Well, heady for so many cubes.) Overnight, we had ourselves a real street rod. Sixty mph loomed large in 5.5 seconds (1.0 second better than stock) and the quarter-mile was history in 14.1 seconds at 100 mph (0.9 second quicker, 8 mph faster than stock). The moral: Don’t leave Old Lyme without that trick black box.

As it happens, there are other Callaway virtues to consider. A mild $1014 suspension make­over, for example, that includes four adjustable Koni shocks and a set of Eibach springs—the latter a half-inch lower “but not much stiffer than stock,” says Carey. The droop in ride height is obvious, lending the SS a “let’s-stomp­-everything” silhouette that causes bystanders to gush with adoration. The springs and shocks also reduce roll, should you be so brave as to pitch this condominium into a hairpin. Also, they ensure that you will crush the two-inch chin spoiler the first time you nose this W.C. Fields baby over a California speed bump.

Adding to the festivities are four steamroller BFGoodrich Comp T/As—275/40s in the front, 315/35s at the tail­—which are mounted on raceworthy Forge-line wheels. The rears are 11.0 inches wide, 2.5 inches wider than stock. The result—apart from another $4000 assault on your wallet—is a contact patch the size of a small refrigerator and very little wheelspin under even the most radical of brake-torqued launches. Ride quality is slightly degraded, how­ever, and the front tires are now prone to tramline.

Skidpad grip, compared with stock, goes from a not-bad 0.86 g to, ah, a not­-bad 0.86 g. To be fair, the Callaway SS is easier to hold in a steady tail-out pose, assuming you’ve located an 18-foot-wide lane to accommodate its porcine rump. A major runway or half of New Jersey will do.

Working far better are the big-daddy Brembo brakes installed at the front. (Cough up another $4000.) This modification includes four-piston calipers and Pagid semi-metallic pads, hugging cross-drilled 13.1-inch rotors. Here, we measured improvement. From 70 mph, the Callaway SS stops in only 164 feet, which is a mere two feet shy of what a Porsche 911 Turbo can achieve. Holy cats.

What a 911 cannot achieve is an exhaust that bellows, “I am one evil mother V-8!” right into the next county. This is appropriate for street rods. Unfortunately, there’s a part-throttle resonance that, at 2500 rpm, ricochets into one ear, stomps a steel-drum tattoo on your cerebellum, then performs a pounding pasodoble as it exits your other ear at about 2800 rpm. Full-throttle din is up 6 dBA—the differ­ence between Mozart and Megadeth.

It’s like having an old Grand National stock car—“whOP-wah-wah-WHOOP!”—only with better paint and worse seats. (Even the Callaway guys are weary of the poorly contoured chairs and the steering wheel aimed at your left shoulder. They plan later to install Recaros canted per­manently toward the transmission-tunnel hump.)

With the taxes and all options, the price of your new Impala SS has more than doubled. We’re talking about a $50,966 car based on a Chevrolet that GM has just axed from its lineup, very much like the 405-hp Corvette ZR-1, of which I just saw a zero-mileage example for sale in Columbus, Ohio, for just $966 more than Callaway’s Impala. This is somewhat difficult to explain to my 70-year-old neighbor Martin, whose own Caprice Classic, he says, “cost $18,910 on the nose, pardner, plus she don’t need a new muf­fler yet, like yours.”

You know, you could also lay all of these rod mods on a Buick Roadmaster wagon.

Source: Reviews - aranddriver.com