To chop top, or not to chop top? That is a question hot rodders have been asking since the inception of the genre of car enthusiasm in the 1930s. Back then, hot rodders would do anything to gain more speed—more powerful engines, removing weight, improving aerodynamics—all of it served to make a car go faster. The Motor MythBusters (hot rodders at the core, by our definition) love the idea of improving aerodynamics, but they question the fathers of hot rodding and their choices to chop and lower the roofs of their cars.
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Building a chop top hot rod is fun and one could end up with a great looking car, but does cutting the roof off a car actually help with it’s aerodynamic performance? To test this automotive myth, the Motor MythBusters are breaking out their 1976 Dodge Tradesman van—one of the least aerodynamic car shapes, ever—to see if lowering the roofline has any benefit to the straight-line speed.
How to Make a Chop Top Car
With the help of lead fabricator Rose (who trained under the legendary Gene Winfield), the Motor MythBusters want to cut a full 12 inches out of the roof of their old Dodge van. If you’re wondering if you’ve seen this van before; you have! This is the same crusty green Dodge B-series you saw the Motor MythBusters test the “three pump brake failure” myth earlier this season.
Cutting the roof off any car isn’t as simple as busting out the sawzall, throwing a couple weld beads down then calling it a day. Cars—even “Ruster,” the lovable green Tradesman Van that is about to get a haircut—are generally egg shaped. If you look at a car head-on or from the side, it’s easy to see that the roof is not as wide or as long as the body below it.
Chopping the top off a car is as much sculpture and art as it is fabrication and engineering. Once the roof of the van comes off, one of two things need to happen: 1) the roof then needs to be selectively cut apart to add patch panels to make it bigger, or 2) the sides and pillars of the van need to be massaged inwards so the roof will line up properly. Rose suggests the former and also says the dramatic chop of 12 inches is ideal on a 1976 Dodge Tradesman like this.
Testing the Aerodynamics of a Chop Top Van
The Motor MythBusters try to follow the scientific method as much as possible. It would be fun and entertaining to cut the roof off Ruster and do some quarter mile passes, but the result could be misleading if the crew doesn’t take into account all of the variables.
The Motor MythBusters Tradesman van is no performance machine; weighing in over 4,000 pounds and powered by a 225ci slant-six, but a weight loss program like a 12 inch chop out of the roof could have a huge impact on Ruster’s quarter-mile time. That’s where the scientific method comes in—The Motor MythBusters only want to test the variable of aerodynamics, so they need to weigh the van before surgery and add all that weight back in.
To test if lowering the roof of a car has a measurable effect on aerodynamics, the Motor MythBusters need to make sure Ruster, the old Dodge van, is exactly the same in every way possible, just with a shorter roofline. Horsepower, gearing, weight, tires—all of it has to stay the same or the data could be corrupted. Even if it doesn’t perform any better, Ruster definitely looks better with a chop top roof. Want to find out if the hours of sculpting and fabrication paid off? Then you need to watch Motor MythBusters, only on the MotorTrend App. Click here for a free trial!
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