Roadkill: Budget 12-Second Big-Block 1970 Duster!

Roadkill is the web show about stupid fun with cars, mostly involving basic junk cobbled together to go fast—or at least just go. Episode 40 delivers all of that and more, including a farm-find rescue, a connection to the famed General Mayhem 1968 Dodge Charger, and a cheap-and-dirty big-block swap into a 1970 Plymouth Duster. Result: the Crop Duster, a low-12-second, daily driveable car built with used parts and a motorhome 440 short-block. It’s like the 20th anniversary revival of HOT ROD’s 440-powered 1968 Dodge Dart project car called Cheap Thrills, except the Crop Duster is better executed (it’s a matter of scale there), with an actual transmission mount instead of just hose clamps. Sorry for the spoiler.

There are 40-plus photos in the gallery below that tell the story in living color, but for those with a longer attention span, here’s the bigger story. It begins with Roadkill episode 23, wherein a stripped-naked 1968 Dodge Charger rolling carcass is transformed into a Mad-Maxish, General Lee-invoking beater of a street-and-dirt blaster using the guts from both a 1977 Dodge motorhome and Roadkill’s 1973 Plymouth Fury that embarrassingly and predictably failed at a 24 Hours of Lemons race in episode 22. The Charger was dubbed the General Mayhem, and went on to star in episodes 25 and 32, the latter of which has true Dukes-level sideways action at a rally-race school. It made the Charger the most popular car on Roadkill.

So what’d we do? We took it apart. Roadkill is now sponsored by Dodge, so naturally we used that as an opportunity to mooch a brand new 2015 Charger Hellcat and whack it apart to toss that 707-horsepower, blown-Hemi drivetrain into the 1968. #BecauseRoadkill. You’ll see the result in summer 2015, but in the meantime, the Charger’s old motorhome 440 and Fury transmission were sitting in the shop along with headers, a battery, wiring, a radiator, and a complete exhaust system. It looked a lot like a swap kit.

Enter Steve Dulcich, editor of Engine Masters magazine. About ten years ago he bought a 1970 Duster as a rolling shell for $700, then left it at the HOT ROD shop where we sort of absorbed it as our own. Dulcich eventually picked it back up, but through a convoluted trade scheme that involved Edelbrock heads, a 1968 Dart, a 1972 Charger, and five years of abandonment in the weeds of Steve’s grape farm, the Duster became officially ours. So did a week of Steve’s time, as he joined Roadkill on a five-day mission to install all the Charger parts into the Duster before heading to the dyno shop and dragstrip.

First, the 440 motorhome engine was treated to some used speed parts from the Dulcich stock room, including ported Edelbrock heads and an Isky Supercam that was in his 1971 Charger 25 years ago. It’s a hydraulic flat-tappet with both the intake and exhaust lobes using 232 degrees of duration at 0.050 and 0.484-inch lift, with lobes stuck on a 108-degree lobe-separation angle. Comp Cams lowest-buck lifters and timing set were added to the otherwise stock valvetrain, right down to the pushrods. Other speed parts include an Edelbrock Performer RPM intake that was on a long-lost Imperial derby car and a 700-cfm Holley that’s been on the shelf so long that we suspect it was once used on the Cheap Thrills Dart. The brand-new goodies include MSD ignition and TTI 1-3/4-inch engine-swap headers. The biggest downer with the whole engine is that, with the stock flattop pistons 0.125-inch below the deck surface at TDC, this garbage only has 8.0:1 compression.

The 440 was hung into the Duster using Schumacher Creative Services mounts that adapt the big-block to the car’s original Slant Six K-member, a swap that requires a C-Body oil pan. (In case you’re unaware, the A-body Duster was never sold with a big-block from the factory, and even the small-block V8 K-member uses different mounts than the big-blocks.) The Fury’s old 727 Torqueflite auto trans, with a basic Trans-Go shift kit and a used B&M mystery torque converter, mounted right onto the original trans crossmember. We repurposed the Charger’s driveshaft by cutting it and shortening it ourselves, which (shocker) proved to be a really bad idea. More on that later.

The real problem with the installation came down to the headers. We’ve used TTI headers many times and find them the best-fitting ones available for Mopars—but the caveat is that you have to read the application guide. We didn’t, and learned the hard way that the TTI swap headers for A-body cars (Darts, ’67-’68 Barracudas, Valiants, Scamps, Dusters) don’t fit with power steering when using the tall-deck 440 engine; they say the low-deck 383 or 400 will fit with the power steering. We should have put a manual steering box in the car, but we refused to forego the power unit this time, so the headers got good and mangled with hammers, fire, and torch welding. (Side note: as a result of this destruction, Engine Masters subsequently dyno-tested the affect that bashed header tubes have on power production. On a 530hp, 7,000-rpm small-block Chevy with 1-3/4-inch tubes, every header pipe received a dent at least 2 inches long and ¾-inch deep. Only 16 hp was lost. Se we feel OK about our butchery. Kinda.)

The other parts adapted from the General Mayhem Charger were the exhaust system and radiator. The exhaust was a 3-inch setup using Cherry Bomb mufflers and turn-downs, and it needed extensive hacking and welding to fit, including an S-turn made of multiple wedge cuts to get around the passenger side of the trans crossmember. The radiator mount also needed some fabrication, as the B-body 26-inch-core was never factory installed in the A-body Duster platform, which used 22-inchers, max. Dulcich cut and sectioned the lower radiator support to move the radiator down (while looking pretty stock). There’s a lip on the core support that points to the rear of the car, and it was trimmed ½-inch to move the radiator forward so that twin Flex-a-Lite 11-inch fans would clear the power steering pump. There’s that power stuff shafting us again.

The next step brought another old project car into play, the Hemi Orange 1970 Duster that was on the November 1998 cover of Car Craft, and which was self-evidently dubbed The Orange Duster by readers. It was first built as another budget, 12-second A-body, but with a 360 small-block with ported Hughes iron heads and a four-speed. Dulcich did the bodywork and paint on that car in about the year 2000, and bought it shortly thereafter. Naturally—since it was freshly painted, running, and driving—he blew up the motor, removed it, parked the car, and mostly forgot about it. It would have made the most sense to revive that nice car rather than the homely Crop Duster, but Roadkill isn’t about making sense. Instead, it’s about parting out the perfectly good car to build the beater, which is why The Orange Duster gave up its 4.10-geared 8-3/4 rearend, leaf springs, and Caltracs bars.

Years ago, the rearend wound up with disc brakes for reasons no one can recall. Because of that, and because factory A-body 10-inch drum front brakes offer only a mild suggestion to slow down when faced with 440 heft, we also installed a complete front-disc-brake conversion from CPP. These use B-body spindles and mid-1970s calipers like you’d find on a Cordova. CPP also sells inexpensive, stamped-steel upper control arms with the larger B-body ball joints to make the installation a snap. In the process, you get new upper and lower ball joints and upper control-arm bushings.

Three guys, five days of wrenching, and finally we hit the last step of adding a new gas tank from Year One, and the Crop Duster was ready for burnouts, followed by the chassis dyno at Westech Performance. There, we swapped the 700-cfm carb for an 830-cfm unit and a 1-inch open carb spacer. With 38 degrees of total timing in the MSD distributor (with one blue and one silver spring on the advance mechanism) and an air/fuel ratio of 12.9:1 at peak torque and 12.6:1 at peak horsepower, the old 440 spit 356 horsepower and 419 lb-ft of torque to the tires. We’d hoped for about 450 flywheel horsepower, but didn’t think we’d get there with the pathetic 8.0:1 compression ratio. We made it into that neighborhood, anyway.

Then the homemade driveshaft bit us, shaking so badly that it broke the tailhousing of the transmission in half. If you watch the Roadkill episode, you can see smoke pouring from the car during the dyno pull. That’s ATF on the exhaust. The car went back to the farm for a week for some more work by Dulcich: a new tailshaft, a proper driveshaft, a Six Pack fiberglass scoop bonded to the ‘glass hood robbed from The Orange Duster, new tie-rod ends, 0.920-inch torsion bars, and fresh Cragar S/S rollers with M&H drag radials.

Finally, it was dragstrip time at Fontana, California, on a 70-degree day. After tame runs to make sure not too many parts would fall off, the first pass in earnest delivered a 12.53 at 111 mph. With nothing but changes in shift points and launch technique, the junk went 12.39 at 113 mph! The most encouraging part about that is the generous mph number and the horrible, 2.0-second 60-foot time that can be cured with some carb tuning (it bogs) and a looser converter. The Crop Duster could be in the 11s next time. But everyone says that.

We hope to just drive the thing. We’ve ordered up fresh seat covers in green vinyl with the 1971 plaid-insert fabric, because we like the camp-counselor look. With a new carpet and headliner and a Comet wash, the Crop Duster will ready for prime time. People have asked about the total investment, because the car gives the illusion of being really cheap. Reality is that it’s a challenge to find a 1970 Duster this straight and complete for $700 any more. The Edelbrock heads are $1,800 new, even before you port them. A used 8-3/4 rearend for an A-body with 4.10s and a Sure-Grip is probably another $1,000 these days. There’s nearly another thousand in all the brakes, another in the electric fans and ignition, and nearly a thou in the wheels, tires, lugs, and mounting. The headers are $700-plus. All told, this is probably a $10,000 project. These days, that’s cheap for a 45-year-old car that runs 12s naturally aspirated with a solid engine, trans, and rearend with new speed parts, plus fresh suspension, brakes, and wheels, and tires.

Can you do it cheaper? Of course. But would you have a car with the image, performance, and driveability of everything you’ve wanted since high school 30 years ago? Probably not. We do.

Something to Say?

2 thoughts on “Roadkill: Budget 12-Second Big-Block 1970 Duster!

  1. Great pictures….. One I didn’t like was the picture of the motor mount. You can clearly read “Korea” on it. I would never put this on one of my cars. The other major issue is this mount is not captive. I had a 1970 duster and I know for sure the original mounts were. I thought you guy would be better than this!

  2. Fun project. I kind of want to see what you guys can accomplish with a naturally aspirated slant six. Think modern-era Hyper Pak with efi. I’ve seen properly built examples run the quarter in the high 11s. Who cares if it sounds like a chainsaw was mounted under the hood? They scream, and they surprise the hell out of people.

    Now go read my blog so I can bask in fame and fortune (or at least sate my narcissism).

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