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.