C4 X frame brace
Thread Starter
Heel & Toe
Joined: Jun 2007
Posts: 16
Likes: 0
From: St. Albert Alberta
C4 X frame brace
Just looking for opinions on weather the X frame brace added to the C4 convertibles added much to frame stiffness. I removed mine temporairily as it rubs against the exhaust with a god awful squeak at idle. I was talking with another C4 vert owner who also removed the X brace and he said he didn't notice any difference. I was reading on the GM Heritage sale at Barrett that the ZR-1 vert prototype was built to see if the C4 vert could handle the power of the LT4 and they found that it couldn't. As my vert is close on HP to the early LT4's, I'm wondering if I should be concerned......
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
The factory brace did add some stiffness to the frame but not in twist. It helped in a front to rear bending movement. Because there was no attachment between the windshield frame/firewall and the rear of the bocy, the 'vert was prone to more twisting than the coupe with the targa top removed.
The factory X-frame not only bolted to the corners of the frame, but there were 3 studs on each side of the body floorpan that held the back half of the X-brace to the body. The OEM exhaust was close to the x-brace but there was enough clearance around the pipes and the center resonator. When I had my '92 vert, I added a B&B system with 3" pipe and never had a clearance issue.
What does stiffen the 'vert body considerably is the factory hardtop. The hardtop has an internal "halo bar" just like the coupe. When you attach the hardtop with the two metal brackets and use the encapsulated bolts in the windshield frame to connect the front of the hardtop, it will make the 'vert stiffer than a coupe. In addition, the car becomes quieter inside and resonance is reduced.
The R-D Cross-Frame does not attach to the floorpan, only to the 4 corners of the frame. For a coupe, it will probably help, but it would not provide any real support if it was going to replace the OEM X-brace.
The factory X-frame not only bolted to the corners of the frame, but there were 3 studs on each side of the body floorpan that held the back half of the X-brace to the body. The OEM exhaust was close to the x-brace but there was enough clearance around the pipes and the center resonator. When I had my '92 vert, I added a B&B system with 3" pipe and never had a clearance issue.
What does stiffen the 'vert body considerably is the factory hardtop. The hardtop has an internal "halo bar" just like the coupe. When you attach the hardtop with the two metal brackets and use the encapsulated bolts in the windshield frame to connect the front of the hardtop, it will make the 'vert stiffer than a coupe. In addition, the car becomes quieter inside and resonance is reduced.
The R-D Cross-Frame does not attach to the floorpan, only to the 4 corners of the frame. For a coupe, it will probably help, but it would not provide any real support if it was going to replace the OEM X-brace.
Drifting
Joined: Jun 2007
Posts: 1,478
Likes: 4
From: Formerly from the Great White North but now residing in the Desert Southwest NM (The Land of Dis-Enchantment?)
Use the cross brace! I wrapped the pipes with header wrap where they passed over the brace and that eliminated any contact issues.
Race Director
Joined: May 2008
Posts: 10,742
Likes: 629
From: Manheim Pennsylvania
My 1995 vert., with the X brace, seems to be stiffer than my 1990 cp was. Also I have no rattles with the vert, to my surprise. I don't like to change factory body support components, the factory put them on for a reason.
