We guess back when 400-horsepower engines were considered big, chassis flex wasn’t much of an issue. But now that a 500-, 600-, even 700-plus–horsepower engine in a street car is nearly commonplace, it’s something that needs to be addressed. This need to stiffen up the car’s chassis is made even more imperative now that classic cars are capable of pulling well over 1 g during hard cornering.
One way to help tame this flex is by adding tubular strut bars between the factory firewall area and the subframe. These bars triangulate the front clip and help eliminate chassis deflection forward of the firewall. Now, you can grab some bar stock, along with a tubing bender and engineer your own, but we found a kit where all the really hard work has been done for you. The strut kit from CA Chassisworks, once fitted and welded in place to the supplied brackets, offers the added benefit of being easily unbolted and removed for engine work or subframe removal.
1. To stiffen up the front of our ’68, we picked up this strut bar kit from CA Chassisworks (PN 7055-F1-A, $349). It came with the firewall plates and their unique Gemini connectors. To save weight, we chose the 4130 steel version, but they also offer the bars in mild steel for $289.
2. One of the key aspects of this kit is CA Chassiworks’ proprietary Gemini system used to connect the strut to the subframe. The interlocking design enables easy assembly, and the precision slip-fit joint is stronger than a welded joint.
3. The firewall plate was properly located by using the 3⁄8-inch lower fender to firewall bolt. The plate simply replaces the shims used in this area. Using the bracket as a guide, Dick Kvamme, owner of Best of Show Coach Works in Escondido, California, then drilled the three holes using a 3⁄8-inch drill bit. The upper two holes went into the air vent box and the lower hole went through to the inside of the car.
4. The plate was then secured using the three 3⁄8-inch button-head bolts, flat washers, and locknuts supplied in the kit. While we’re pairing this strut bar kit with a CA Chassisworks subframe, it will work just as well on a factory GM front sub.
5. Once installed, the strut bars can be unbolted from the car, but to get them in the first time, some welding is required. This was a perfect time for us to try out our new Eastwood 135 MIG welder.
6. After trimming and grinding each end of the strut bar to get a perfect fit, we started tack-welding the frame end in place. To make this easier, we had another person hold the firewall end in place. Before welding, we also made sure to use a disc sander to clean the surface rust from the CA Chassisworks subframe and firewall plate.
7. We then repeated the tack welding procedure on the firewall end of the strut bar. Once tacked in place, we removed the bar attached to the brackets and fully perimeter-welded both ends.
8, After fully welding the 4130 strut bar to the firewall plate and the upper half of the Gemini connector, we ground all the welds smooth. Eventually, this bar, along with the subframe, will be powdercoated.
9. And here’s the final result. The bar easily cleared our Eddie Motorsports billet hinges, and after test-fitting our Anvil Auto carbon-fiber inner fenders, it cleared them as well. The total install time for one side was under two hours. With this done, we simply repeated the procedure on the driver side.