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1991 Chevrolet Corvette 427 Small Block Grand Sport - Intimidating Imitator

Witness the only '91 small-block 427 Grand Sport

Jerry Heasley Jul 1, 2005
Corp_0507_03_z 1991_chevrolet_corvette_427_grand_sport Back_left_view 2/1

Joe Polai's '91 Corvette runs on good, old-fashioned small-block power, yet the 427 badges give it a slightly skewed first impression. "The big-block is 130 to 140 pounds heavier, and it doesn't lend itself to handling at high speed as a small-block does," Joe admits. Leave it to Corvette builders to get big-time horsepower in a lightweight package.

Joe chose the '91 because it was the "last year of the standard small-block." With all the hoopla about performance, some of us might have lost track of the classic Chevy V-8, introduced in 1955 and phased out at the end of the '91 model year. Option code L98 was the classic 283/327/350's last stand in the Corvette. The venerable LT1 was a whole new ball game in 1992.

Joe began with a 250-horse coupe with faded, cracking paint, and hopelessly in need of brakes, tires, and "a lot of fixing." He never considered keeping it stock. What drew him in was that familiar 350 that launched so many thousand ships. With this classic 350, Joe could draw on the wealth of small-block parts at a "reasonable" price, such as high-performance cylinder heads.

"I got AFR heads. Motown makes the engine block. It's a casting replica of the 350 small-block. Then they bore it out to 411/48 inch and put in a 4-inch crank. It comes standard with four-bolt mains and the priority oiling-all the good parts that a regular GM 350 block does not have.

"Externally, the 427 looks like a 350. You can't tell the two apart. It hooks up to the standard 1991 ECM. We just had to modify the chip to accept more fuel, air, and so forth. But it runs off the standard computer that is in the car." TPIS, short for Tuned Port Injection Systems, modified the chip and assembled the 427 small-block. It balanced and blueprinted the internals to the tune of 575 hp at 5,800 rpm and 540 lb-ft of torque at 4,800 rpm.

Joe says, "I originally ran the GM fast-burn heads, which only gave me 525 horses. When I switched the heads, I got 575! It's the only change I made since then. And I'm running the TPIS camshaft, which is roughly .590-inch lift. I'm running 11.5:1 compression using 93-octane gasoline."

TPIS also built the intake manifold, which Joe says is "almost like the LT1/LT4 intake." Higher rpm and flow also dictated the 68mm throttle body in place of the stock 48mm. Joe felt the car had earned a set of stripes, since it needed new paint anyway. Choosing the Grand Sport paint scheme of 1996, featuring red hash marks and a white, over-the-top wide paint stripe, Joe made himself a homemade Grand Sport.

We met up with him at the National Corvette Museum for the ZR-1/C4 Gathering. Joe arrived on a Thursday, and his coupe was streaked with water stains from the rain. We didn't realize until the following week when we called to ask details about his coupe that he had driven 840 miles each way to his home in Maple Grove, Minnesota.

"You made it fine with no problems?" we asked.

"Yeah, sure. Oh, I had a little moisture in the distributor cap. All that rain, every day. It was misfiring a bit. Once I got it home I took the distributor cap off, put some alcohol in there, and it runs fine."

The Real DealThe basic car is a '91 coupe (L98 engine, 250 hp), six-speed, with a glass top, power sport seats, and an FX-3 suspension. It's a daily driver with roughly 90,000 miles. Modifications on the car are as follows.

Engine* 427ci, assembled and tuned (on engine dyno) by TPIS* Engine management by TPIS (computer chip)* 575 hp/5,800 rpm and 540 lb-ft/4,800 rpm; over 500 lb-ft of torque at 3,000 rpm* 427ci four-bolt small-block with priority oiling, by Motown; 427 block, (0.060 over, a total of 440 cubes), internally balanced* Rods, 6-inch H-beam, by Eagle* Crank, 4-inch, 4340 forged, by Eagle* Pistons, 11.5:1, by Diamond* Oil pan, 7-quart with kick-outs, by Canton* Oil pump, by Melling* Distributor, stock* Cam, ZZX Cam, (0.588 lift with 1.6 rocker arms), by TPIS* Rocker arms, 1.6, by Comp Cams* Aluminum heads, (AFR 220, with 2.080 intake and 1.60 exhaust valves), ported by TPIS* Intake, Mini-Ram with 26-pound injectors, by TPIS* 58mm billet-aluminum throttle body, by TPIS* Ignition, MSD* Water pump, aluminum* Radiator, aluminum, by Griffin* Fluid damper* Flywheel, clutch, and pressure plate, by Fidanza* Headers, long-tube and ceramic-coated with 311/42-inch after-cat exhaust, by TPIS

Suspension, Rearend, & Brakes* GS calipers with stainless steel pistons front and rear, from DRM* New Sport rotors and brake pads, from Vette Brakes & Products (13-inch front, 12-inch rear)* Rearend, 4.09 gears* Camber Brace, from Eckler's* Sport Suspension, from Vette Brakes & Products:32mm front sway bar26mm on the rearMono composite springs front & rearSmart strutsPolyurethane bushings

Interior* Ripper shifter* Seat covers, by Eckler's* Seats embroidered (with 427 Grand Sport), by Fast Track Products Inc.

Exterior* '96 Grand Sport (GS), white stripes, hash marks, rear fender flares, and black paint* Paint by MACCO* 427 red emblem/lettering, from '67 Impala Super Sport* Grand Sport emblem/lettering from '96 Grand Sport* Chrome ZR-1 rims, front 9.5 inches, back 11.0 inches* Tires, Goodyear GSC tires, P275x17 front with P315x17s out back

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