GTM roll cage modifications and race car build log

[mikespms]

More solid progress this weekend.

I tell you I must have spent 3 hours staring at this problem over the past two weeks. My goal is to add SCCA and NASA legal door bars to a car that can be street driven. Ideally I should be able to cover the bars and make them look less race car and more street car. Finally I don’t want the bars to make entry or exit any harder.

The ideal way to attach door bars to the stock frame would put the bars right in the same plane as the current window and interior door frame. With this situation the door bars occupy the same space as the stock door frame. If you want working windows and doors this option is out. Several racing bodies also prohibit removal of the stock door framework. In order to install door bars you either need to make a bar that squiggles it way around the obstructions and spans a large distance, or you need to create new landing areas for the door bar structure.

After considering all of the pros and cons I decided new structure to attach the door bars would be easier and stronger.

The first problem was the rear verticals. I did not want to break the plane of the firewall and I also needed to avoid blocking my fuel tank install. The tank is so tight, I have no more then 1/8 clearance at the pinch points. I can just glue some rubber on to the frame to cushion the tank and it does not need any other mounting. (but I will mount it firmly)

Now the verticals. The bottom of the tube lands right where stock corvette seat belts attach. I will not use those seat belt mounts so I cut off the plate. In order to make attaching the tube easier, I used the cut off pieces of seat belt mount to weld up a continuous horizontal plate to attach the vertical bar. It makes it easier to slide the bottom of the bar in from the front. It wedges in when its too long. This way I can sneak up on a tight fit.


I cut and bent two symmetrical but mirror image vertical bars for the driver and passenger side.



What’s cool is the vertical clears the stock cross brace but is just touching. I Debated cutting the cross brace out , but there is not much gain and its possible that the frame would pretzel if I took out that support. The frame is jig welded and I found it to be pretty symmetrical, however when its cut apart it will spring to relieve any pent up stresses.



I ended up using the cross brace as another point to attach and stiffen the rear vertical.



Next was the front vertical. I attached the bottom to the 2x2 square that runs across the foot box and the top of the tube to my window frame gusset. The gusset was an easier attachment point because I could more easily run a bead around the joint. I think it looks cool there too. With all this new structure the frame is starting to look like a fortress.



In keeping with my street car/ stealth race car theme I can also hide these supports under the dash .

Finally the whole point of adding the vertical bars is to add the horizontal door bars.

The lower bar is a simple straight bar. It runs just slightly inside the door shell. The top bar is the tricky one. I am going to mock that one up because I think if done properly it might not obstruct the entry into the car at all and yet still meet the safety requirement. I have seen corvette bars where the top bar is an S bend allowing the front half of the door bar to be lower. This is key in the GTM because swinging your feet out is a little tricky. A high set of door bars in this area is going to make it very difficult to get out.



Getting out with the X style door bars would be very hard. Basically you would need to crawl out or be very good at yoga.

All the vertical elements were welded up. Next weekend is mock up, cutting,and fitting the horizontal elements.


John

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Hi John,
Looking at the strings running along the door, and cant tell how high they are. Did you check if the seat is going to fit in the passenger side? In my car on the passenger side I had less than a 1/4 in. clearance between the seat and the door and the tunel panel. I made a new tunel panel and gained almost 2 in.,it allowed me to move the seat to the center so that I could operate the power seat switch on the side of the seat. It may give you the room you need to run that tube and be able to fit your seat.
Mike