Blue Bell, PA
1968 Plymouth Road Runner
Engine: 426 Hemi
11.54 at 125.31
Making the biggest headlines of the meet was Rick Mahoney's Dark Midnight Blue '68 Hemi Road Runner, an original Hemi/four-speed car. After a fresh build by Scott Tiemann's Supercar Specialties, it debuted this spring with a four-speed and Dana 60 rear, running a best of 11.73 at 125. But, at this event, and for consistency, the four-speed was temporarily exchanged for a TorqueFlite.
The Road Runner was an all-out effort, with a Ray Barton Hemi under the hood, built to blow away anything that's ever run at the Pure Stock Drags. It's a state-of-the-art powerhouse, having clocked a blazing 10.92 at 126.93 on a 1.71-second short time at Maryland International Raceway last October with Rick at the wheel.
At the Pure Stocks however, the Friday spin-fest netted a best e.t. of 11.82, making him the number six qualifier. That night, a couple of changes were made to boost traction and dial back the Hemi a little.
Ignition is standard Chrysler electronic, but they bring several distributors that have varying advance curves, and at this event, they swapped for the slowest curve. It still gets full advance, but not until 4,500 rpm.
They also added 175 pounds of weight to the trunk.
"Right off the trailer on Saturday, Rick ran 11.54," Scott told us.
In the afternoon shootouts, Rick drew Larry Kirkum's aluminum-headed, Tri-Carbed 427 Corvette. In Round One, he backed up the 11.54, running just a blink away from an 11.49 (11.49 and quicker must have a rollcage or be DQ'd for this year and next). But it was Round Two when it all came together.
"I could tell as soon as I stepped on the gas that this was our best run of the weekend," Scott said. "It hooked up perfectly and shifted clean. I slammed on brakes at about 1,000 feet...that would have been low 11.30 or high 11.20," Scott reports.
"What's amazing is that the car weighed 4,025 pounds—I had 175 pounds in trunk when it did that."
Calculate in that their best 60-footer was a modest 1.95, and you can see the Road Runner's blockbuster performance. That's quicker than much of the heavily modified F.A.S.T. racers.
Scott is adamant that the car is rules-compliant, and he's forthcoming about most of its details, but a few things are classified, at least for now.
The block is .030-inch over, with a Chrysler forged crankshaft, offset for .013-inch more stroke, which is less than the legal maximum of .015-inch. Displacement works out to be 433.34 cubic inches. It's built with Diamond pistons and aftermarket steel rods in the standard Hemi length.
"No one thing makes it great," says Scott, "but a lot of little things make it great."
For example, after observing the oil pressure gauge behaving badly during dyno runs, the oil's return path to the pan was changed. with help from a fellow racer, tubing now diverts the oil to the sides instead of it draining onto the spinning crankshaft. That prevents the oil from foaming, stabilizes oil pressure, and removes an obstacle from the crank's free rotation.
Scott and Dave also specified a cam with wider lobe centers, believing that Barton's Hemi may work better on the dyno, but a slightly more modest grind (.480/.475-inch intake/exhaust at valve) would be better suited to the OEM exhaust manifolds and closed exhaust that Pure Stock cars run. A smaller cam seems counter-intuitive, but a stocker is a different animal, and normal rules of race-engine building don't necessarily apply.
Rules cap the exhaust pipe size at 21⁄2 inches, but cross over pipes are allowed. The Road Runner uses mandrel-bent tubing, the same stuff that everybody runs, and the mufflers are Walker long ovals.
The recipe worked, as the engine dyno'd at over 700 horsepower at 6,900 rpm.
Besides the signature glow of a Scott Tiemann restoration, Mahoney's Road Runner has a unique sound as it screams down the track heading for the traps at a howling redline.