1970 Plymouth Duster 340
13.37 at 102.75
Tom Cannon is a Mopar guy from way back. He runs an orange '70 T/A Challenger and a red and white '71 Super Bee in the F.A.S.T. races. For Tom, the Pure Stock Drags, competitive as they may be, is a chance to kick back and relax.
When we told him that he had the quickest Mopar small-block at the Pure Stock Drags, he was surprised. "I don't know what to tell you," he said humbly.
The numbers-matching block was removed and set aside, and a replacement '71 block was blueprinted along NHRA guidelines and installed with the '70 heads, intake, and carburetor. The '71 block is identical to the '70, but there are differences elsewhere.
"The 1970 engine has the Carter AVS carb, and the '71 has the ThermoQuad," Tom points out. "The difference is that the AVS is 625 cfm and the Thermoquad is 800." That's a sizeable difference in ratings, but it may not translate into more power because of changes elsewhere.
"The '71 340 has a different passenger-side exhaust manifold," Tom explains. "It has a smaller, more restrictive 17⁄8-inch outlet. The 1968-1970 manifolds had a 21⁄4-inch outlet." So the bigger carburetor and smaller exhaust manifold probably offset each other. Swapping the carburetors for testing is on Tom's to-do list, but he hasn't done it yet.
Tom says that the rest of the engine is very near stock. "I run the factory Prestolite dual-point distributor. I've never tried anything else." He sets it up on a vintage Sun distributor dyno, with Accel high-performance points (they have a stiffer return spring to prevent bounce), and 35 degrees of advance that are all in by 1,200 rpm. Unlike the high-powered Hemis and 440s, that reduce timing to preserve traction by slightly curbing engine output off the line, the 340 is not riding the ragged edge of traction, so he brings in full advance very early.
The air filter is a run-of-the-mill paper unit, and the Carter AVS has the stock jetting, which Tom says delivers the optimum air/fuel ratio, or very near it.
340 Dusters also have an issue where the driver's side exhaust pipe snakes through the engine compartment. The pipe has to be crimped for clearance at the starter, Torque shaft, Pitman arm, and torsion bar.
"It's squeezed down to 17⁄8 inches for around 3 inches," says Tom, who adds that there's just no way around it, even with a custom pipe, which he runs.
The balance of his exhaust is 21⁄2-inch duals, with no balance tube, and a pair of Walker Dynomax Super Turbo mufflers.
If you're expecting to find hidden tricks under the hood, they're just not there. "E.T. is all about the starting line," says Tom, and to that end, he runs a four-speed with 4.30:1 gears in the Sure Grip differential. Driving technique is also simple. "I just hold 1,500 rpm, ease the clutch out, and when it's fully engaged, I mash the gas."
That simple, basic launch gets the Duster off the line with low 1.90 short times. From there, Tom makes the 1-2 shift easy, a little harder for 2-3, and leaves his foot on the floor for 3-4.
The 3.91 gears put it across the line at the top of 3rd gear, while the 4.30s go through the traps at the top of 4th. The suspension is stock, and while the high-powered cars launch better on over-inflated rear tires, Tom's experiments with tire pressure proved one thing. "I've tried from 23 to 42 psi, and the Duster just doesn't care."
Tom makes his runs with half a tank of 110-octane racing fuel in the tank. The high-powered cars on the edge of traction like to run a full tank, and even add weight to the trunk as the improved traction more than offsets the penalty of weight.
All time low ET for the Duster is 13.20. That's over a tenth quicker than its very consistent 13.30s, thanks Tom suspects, to a water burnout there, which was not available at the Pure Stock Drags. Its lower elevation (320 feet at Cecil County vs. 919 feet for the Mid-Michigan Motorplex) may have also been a factor.
It sounds like the biggest difference between the big-cube B- and E-Bodies is that while they have to take steps up to and including reducing engine output for their limited traction, with the small-block, you can pretty much let 'er rip.
"It could go faster," Tom says. "There's a smidge of compression left on the table. It's got a little less than 11.5:1 and rules allow up to 12.0:1. Also, if it had an automatic, it would probably go in the 12s. Looking at the race results, there are cars in the 12s or close running my trap speed."
"Stepping out of those 11-second cars into the low-13s Duster is like watching paint dry," Tom quips. Yeah, maybe a quick dry.