Click to enlarge This is one of the pages from the SFI 25.5 booklet I ordered. The various different colors relate to different sizes of tubing required. Lots to look at.

Once I was satisfied with the hoop and supporting tubing I moved on to the rocker panel sill bars. The 25.5 specs allow for different sizes of tubing to be used on the driver’s and passenger’s sides of the car. Basically, the driver’s side gets the stronger stuff. I had previously installed an outrigger bar from the sub-frame connectors to the rocker panels at the front, so I only needed to join the outrigger with the rear main cross member to satisfy the 25.5 requirements. I made the drivers side sill bar from 1 5/8” tubing and had to cut a notch in the factory Ford front seat mount crossmember to allow the bar to sit nice and low. I then welded the cross member to the bar.

Next thing to tackle was the door X braces. The X part is made from 1 ¼” tubing and is intended to add support to the windshield “A” pillar bar and help keep the driver’s legs from getting outside of the cockpit. The diagram showed the brace in the perfect form of an X but if I did that I don’t think I could safely get out of the car in an emergency. The text states that those bars simply need to start high at the front and end low in the rear. After calling SFI for confirmation I decided to install them at about half way up in the door opening. Apparently, this is a “grey area” and the final decision of legality is up to the NHRA inspector at the time of certification. Great. Leave it to me to work in a grey area! I did go Internet surfing and found numerous examples of cars with certified 25.5 chassis and some of them I wouldn’t have passed! I guess it depends on whom you get at inspection time.

After I was satisfied with the X braces I moved on to the dash bar. It was fairly simple to make using my bender and it is made of 1 ¼” tubing. The next bars I made are not required but I feel they are needed, especially in a car that does rather large wheelies! These were also a couple of the toughest bars to fabricate and mount. I wanted to tie the front shock towers to the roll cage to help keep the front end of the car, cowl forward, from flexing up and down when I do wheelies. You know how I like my wheelies! The Comp Engineering kit had actually come with two of these struts and they were quite long and had a nice big bend at one end. I kind of thought I would end up making my own, but I was pleasantly surprised when, after some cutting to length type fabrication, I was able to use them. It really couldn’t have worked out any better!

The stock Mustang firewall actually had a hole in the firewall that wiring used to go through on each side of the car and they were in almost the exact location I needed to pass my support bars through to the shock towers! A very small amount of die grinder work on the driver’s side hole and I was good as gold (or is it good as gas these days?).

I made some square reinforcing plates to weld to the towers and cover a couple of holes and then welded the bars to the plates. The inboard end of the bars are welded directly to the windshield bars behind the dash. Nice, clean, simple, and effective installation.
I do need to back up a little on something I forgot to cover last issue. After I had the rear frame rails installed I made some custom sub-frame connectors out of 2x3 boxed tubing. I have done this before on Fox chassis cars and it really works neat. It takes a little bit of time but by using a die grinder with a parting wheel and my pneumatic chisel, I opened up the factory sheet metal sub-frame connectors and finished cutting a strip about two inches wide front to back from the firewall to the rear cross member. The inside of the factory connectors is a perfect fit for two-inch wide tubing!

This is the almost finished driver’s side view. Notice the placement of the Funny Car hoop and door X braces. Should be legal? Ha!

I cut the front end of the rails at a 30-degree angle and after cutting the right amount of the floor away I was able to pound the new connectors forward as far as they would go inside the sheet metal connectors.

After cutting the rear of the new connectors to the right length they got welded to the rear 2x3 cross member. The stock floor was then welded to the new rails the entire length. This makes for a very strong and nicely fitting sub frame that doesn’t hang down and look ugly.

Well, my time this month is up. I hope you learned something or at the very least got a spark of enthusiasm to get to work on your project. I know that as much as I enjoy doing this I am really getting tired of working on it on my limited time frame. But, no one will finish it for me so I’ll keep plodding away! Until next time…

Remember, there is always hope,
And, when in doubt…Do a WHEELIE!!!