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Front Subframe Measurements - Car Craft’s ’71 Dodge Demon

How to measure for a new front subframe

By , Photography by , Grant Peterson,

Here is the plan. We want to run 9s in the quarter-mile, look really cool, and drive this car on the street as much as possible. The last two are simple enough, but the first one is going to take some finesse if we want to keep this thing fast for beer money. Using the calculation for quarter-mile times, RWHP = (MPH/234)3 x weight, our 2,600-pound Demon’s engine needs to make about 750 flywheel horsepower to go 145 mph in the quarter-mile. Or we can lighten the car.

When we introduced this Demon in the Mar. ’11 issue, we mentioned that it was a back-halved car with a ’cage and some good chassis work that seemed to have stopped at the firewall. Everything forward of that was stock. We had peeked under the car and discovered a Chris Alston Chassisworks four-link frame package with Battle Cruiser suspension that had already been installed. So naturally, we called Mr. Big himself to see what we were up against.

“There are thousands of these (back-halved) cars out there, so we make a front frame kit that gets rid of the stock front suspension,” Alston says. In addition to deleting the torsion bars and the related issues, Alston claims his A-arm frame kit will remove up to 300 pounds from the front end of the car, connect to the rear subframe, and make things work the way they were intended. To further the weight loss, we are also going to add some fiberglass parts from Glasstek and other lightweight goodies. Using totally hypothetical numbers, if we can drop 400 pounds off the car, we can reduce the required engine output to about 630 hp. That is a number we can achieve from a junkyard 5.7L Hemi with a shot of nitrous or a blower and still run it on pump gas.

We can already imagine rolling through the drive-thru on wrinkle walls and blasting through the quarter-mile, but first we need to do the math and order the front frame system. Here’s how to do it.

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