Sean Johnson’s ’70 Chevelle

It’s a little too fast for the rules. Sean’s sitting in the staging lanes at the Los Angeles County Raceway (LACR), helmet on, waiting for the signal to fire the Chevelle and pull into the bleach box. At first, the driver didn’t want to say too much to the guy who walked up and asked about the engine. “It’s just a little 350,” said 18-year-old Sean Johnson, the car’s owner. The stranger sensed something was up. Sean seemed a bit guarded about the motor. Usually, you can’t shut these guys up about their engines.

Sean fires the Chevelle and pulls into the bleach box. He lights up the healthy-sized M/T street tires and hazes the tires as he eases out of the water. He doesn’t bother with squirrelly dry hops or other monkey motion and gently nudges the blue A-body into the staging beams. The Tree flashes down and the Chevelle leaps off the starting line. Somebody nearby says, “That thing leaves hard.” It does, yet something’s not right. The launch looks much quicker than the 12.20/104-mph timers indicate.

Back in the pits, the visitor returns. Sean says, “I thought you were one of the track officials gonna kick me out. We don’t want ’em to know how quick this thing really is.” After a few more questions, he admits it’s really a 406 with iron Bow-Tie heads. It’s clear he’s proud of the fact that he drove it 90-plus miles from his home in Camarillo, California, to the track despite the 3,600-stall converter and 4.10 gears.

After checking the plugs and the timing, Sean’s ready for another blast. His cohort, Brendan Murphy, slides up to the visitor and says, “Watch it this time, he’s gonna run it out the backdoor.” Again, Sean performs his burnout and stage procedure smoothly, like he’s done it a hundred times. The Tree clicks down to the last yellow, and the deep blue Chevelle plants the tires and launches. This time there are no brake lights and the finish-line lights blink out an impressive 11.72/116-mph numbers. This is a testament to the Chevelle’s true aspirations. Corrected for LACR’s 3,000-foot altitude (the density altitude was 4,550 feet), that’s a sea-level 11.30 pass at almost 120 mph. But that e.t. and speed also means trouble.

Before Sean can return to the pits, track officials invite him to leave because the Chevelle has no roll bar. NHRA rules are clear; if you don’t have a roll bar, you’re not supposed to run quicker than 12.0 seconds. “I spent all my money on the motor,” Sean says. “But as soon as I can afford it, I’m gonna put a roll bar in it so I can come back.”

It’s clear that Sean enjoys the sleeper image. Sure, the Chevelle has a nice paint job with no rust bulging out from underneath the rear quarter-panels. But neither is this a show car. If you’re going to sniff out this car’s intentions, then you’d better pay attention to the clues. The biggest giveaway is the tires. Those are 28x12.5-15 Mickey Thompson E.T. Street tires on the back mounted on a set of 15x10 Weld Pro Star wheels. But anybody can play the game with big tires. A glance at the rear reveals something interesting. There’s a fuel cell protruding through the trunk floor sporting a pair of fuel outlet ports. The 12-bolt rear is not unusual and the rear suspension looks almost stock with only polyurethane bushings locating reinforced lower- and stock upper- control arms. A stock driveshaft connects the 12-bolt to a Turbo 350 automatic built by Cottman Transmissions. Sean shifts by way of a B&M Pro Stick.

All of these attendant systems are aimed at putting the 406 small-block’s power to the ground. Sean works as a machinist and discovered this motor at The Block Shop where a customer had abandoned it when he couldn’t pay the bill. Sean worked a deal to buy the engine for the reasonable price of $2,000 and stuck it in the Chevelle.

Mark Jones at The Block Shop built the engine around a two-bolt 400 block bored 0.030-over with Keith Black hypereutectic 10:1 pistons and a stock, nodular iron 400 crank. The rods are also stock 5.7-inch pieces fitted with a set of ARP bolts. The real fun starts with the Chet Herbert mechanical roller cam that specs out at 242/250 degrees of duration at 0.050-inch lift that pop the valves open to 0.580/0.600-inch lift specs.

The cam is a good match for the iron Bow-Tie heads, which feature 2.02/1.60-inch valves and a Mark Jones valve job. It also runs a set of 1.5:1 roller rockers. Sitting on top of the heads is an Edelbrock Victor Jr. single plane with a Holley 750-cfm double-pumper (PN 0-4779) carburetor. On the exhaust side, Sean chose a set of 1¾-inch Hooker Super Comp headers blended into a 3-inch set of Hooker Aero Chamber mufflers installed by Muffler Time in Camarillo.

While the engine has not been dyno tested, we worked backward using the Quarter Jr. dragstrip computer simulation to come up with roughly 475 hp for a power figure. Since this was Sean’s first real pass with the Chevelle, it’s clear there’s some e.t. and speed left in this combination. Sean feels the car could run low 11- to high 10-second times with a little more tuning.

Overall, this is a great first effort for a high school teenager. Sean still has more plans for the Chevelle—mostly centered around going a little quicker.