The owner of the 7’s Only Racing shop, Tom Dragoun, built a successful racing series in the NASA SoCal region with its GT RX-7 cars, which featured a fiberglass body over a tube-frame chassis using first-generation RX-7 drivetrain parts. The series and the cars enjoyed a respectable lifespan, but as the fields thinned, the cars themselves began to reclassify among the Super Touring 1, 2 and 3 classes — and they were struggling against competing cars.

7’s Only Racing is updating the tube-frame RX-7 GT chassis, original designed for competition as a one-design class, and turning into something lighter, more modern and more balanced.
7’s Only Racing is updating the tube-frame RX-7 GT chassis, original designed for competition as a one-design class, and turning into something lighter, more modern and more balanced.

“We knew the cars were deficient because we’re getting beat by the Corvettes in ST2 and ST3 and the Porsches are beating up on us,” Dragoun said. “But it was a spec car. It was only designed to run against itself. So when we decided we wanted to go faster, we had to start thinking of what to do.”

What he did was take an unused chassis from behind his shop located at Buttonwillow Raceway Park, clean it up and set it on a jig in his shop and reimagine the car. For starters, he knew the McPherson front strut-type suspension and rear live axle were weak points in a class that fields Corvettes, Vipers and Porsches. He considered reconfiguring the frame to accommodate Miata front and rear cross members, but as he started looking into it, he went with the cross members from the MX-5, which are the same as those used on the RX-8.

“It’s going to be about 97-inch wheel base,” Dragoun said. “The MX-5 is 83 and the RX-8 is 107, so we’re kind of in the middle. They say the RX-8 is a little bit too long for racing and the MX-5 is a little bit short, so we’re hoping we’re going to hit a happy medium.”

All the components are unique to the new car. For example, the front control arms are hand-fabricated as are the tie rods for the multilink rear suspension. The new parts cut a lot of weight off each corner of the car, but, Dragoun is quick to point out, the geometry is the same as the factory specs.

Dragoun also saved a lot of weight using sculpted brake rotors, 7 pounds at each corner. Rather than using the MX-5 hubs, Dragoun went with the hubs from the RX-8. They are a little heavier, but they are more robust. Weight savings was tantamount to the new car, and if Dragoun has his way, the car will tip the scales at 1,800 pounds with a driver on board. “We’re going after a light weight,” he said.

“We’re really trying to focus on making everything on the car as light as we can possibly make it.”

In addition to a low weight, Dragoun is also trying to distribute that weight as evenly as possible. To achieve that, Dragoun offset the engine and transmission to the right and rearward. The orientation of the engine means the shifter will have to use intermediate shafts with heim joints. It also means the driveshaft likely will be shorter than a yardstick and the differential also will be offset to the right.

“The whole thought process behind the whole thing — and I’ve already done some corner-weighting on the car and moved the motor around to where I thought it was corner-weighted the best I could do —as you probably well know, most cars, whether they’re tube frame or not, the left front corner is the heaviest corner, and it’s very difficult to get the weight shifted off that corner back to the other parts of the car,” Dragoun explained. “Now, by moving that motor back equal to the driver, now we’ve equalized the front of the car, we’ve moved the motor over to equalize it left to right and we’ve moved it a bit back to try to put more weight on the back of the car.

“The biggest problem in making a really good racecar is getting more weight on the rear so you can get more braking in the rear,” he continued. “The Porsches just kill us under braking, because the weight’s in the back of the car. So when they get on the brakes, the car just squats, it comes down, whereas the more we get on the brakes the more the back end lifts up. So I’m trying to counteract some of that by moving the engine back.”

The car is still under development, but most of the hard work has been done. Building the first car takes the longest because all the parts need to be designed and built as do all of the tooling and jigs needed to build the chassis.

The first chassis will be powered by a Mazda 12A rotary engine with a six-speed transmission out of an RX-8. In ST2 trim, the car will make 230 horsepower. For competition in ST1, power output bumps up to 280.

Speed News will doing a follow-up story on the car when it gets its new fiberglass body and hits the track. As a little tease, the renderings Dragoun showed to us look like a nice evolution of the FD RX-7 and the RX-8.

“I wanted to build something really fast and really fun for a long time,” Dragoun said. “The spec car was a great learning experience in how to do things, but they were just never that fast.” The evolution has begun.

Owner:

7’s Only Racing

Year:

2014

Make:

7’s Only

Model:

RX-7

Weight:

1,800 lbs. w/driver

Engine:

12A or 13b Mazda Rotary

Transmission:

6-speed from RX-8

Suspension:

Front: dual A-arms with Penske adjustable coilovers Rear: Multilink with Penske adjustable coilovers

Tires:

Front: 15-inch Rear: 15-inch

Brakes:

Front: Sculpted rotors with Brake Man two-piston calipers Rear: Sculpted rotors with Brake Man two-piston calipers

Data system:

NA

Sponsors:

NA
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Images courtesy of caliphotography.com and Brett Becker