I am going to make a 4 point bar to go behind my 2 front seats so i have a place to mount my harness to. I was wondering if anyone knows of a good place to get lightweight steel tubing that i could use to make this out of. I have priced them online and i can make one for much cheaper than what i would pay for one and i can make this one exactly how i want it.

 

I used a harness bar from Stable energies ($99.00) and connected the shoulder harnesses to the rear Seat belt points. why reinvent the wheel?

 

That harness bar needs to have a center brace. A BIG impact will pull the center, bowing the bar and pulling it free from the attaching ends.......leaving you loose in the belts WITH a piece of loose steel for company.............I have seen it happen, and it was NOT a happy ending........

Also, I noticed something else - the Porsche seats do not have "shoulders" or "loopholes" to hold the shoulder harness on top of your shoulders. Someone makes a slip over cover that goes on the headrest to hold the shoulder belts. I say this because, during a drivers school a few years ago, I was driving a students 911, and had the shoulder harness slip off my shoulders onto my elbows - trapping my arms at my sides.....while going down the straight at about 100 mph.....giving myself (and my student !!!) quite a fright !!!

Not trying to trash your car or your preparation, I am merely passing on my experiences, and saying BE AWARE.

 

I would use the mount points for rear seatbelts, except in PA we have stupid *** safety inspections of our cars every year in order to get them licensed and if you modify the factory restraint system in any way, they will not pass your car.

I am just using the harness for autoX so a big impact really isn't likely so a small 4 pt bar would work fine for what i want to use it for.

 

OUCH!

Since I use the 4 point setup only for AutoX I am not too worried but it's good unformation to keep in mind.

 

I just made a harness bar for under $15. The tubing is 1 1/2 OD with a thickness of 4mm. The plates that is welded to are 1/4 inch thick. I'm really not worried that the welds will break as sufficent metal is built up around the cross pipe. Grade 8 bolts secure it to the top back mounting points (like Porsche installed them on the 968 Club Sport). I might weld another bar that attaches behind the driver and additional braces that would attach to the factory rear seat belt mounts. This should be strong enough for autocross!

 

Hi I understand your message but bear in mind that: 1) The bar is attached via adjustable plates to the upper shoulder belt mounts with Grade 8.8 bolts; and 2) the threaded part that attached the the plates tot he horizontal bar extends almost two inches into the ends of the bar.

Not only will the bar need to deform, the bolts will need to break and/or the bar will need to pull out of it's threaded imbedment. I figure a tremendous amunt of failure would be required to caus tthe bar to fail as you describe.

If the bar was butt welded to the plates I can see it deform and pull out as you describe, this arrangement seems more stout as numerous failures will need to happen befroe the bar gets released.

Certainly possible but, I owuld think very low probability.

I do agree with you on the risk of the shoulder belts slipping and Stroth advises against using my belts with my seats, most likely for the reason you cite. I only use these belts for AutoX where my top speed, on a really unusual day, is 50 mph. For DE days, I use the 3 point setup.

 

Sounds nice, I am not a structural enigneer but I would ensure that you have more than a butt weld of the tubing to the plates. It is too easy for the weld bead to fail at this point due to stress. I would think you should have a piece of solid rod 2-3 inches into the tubing and the rod is also connected tothe plate to prevent a fracture of the weld from turning into a falure of the holddown.

 

My next bar will be a little different. I will pass the bar thru the plate and weld both sides. I thought about on the one I just made but did not have the means to drill a 1 1/2 hole.

 

Guys: I am not talking in absolutes, all I am saying is be aware of potential problems when you are building something......

 

Back to the orig. question, I also have to deal with safety inspections, use my 6 pt harness for AX and my stock belts for DE and even have the same chassis. I have a Stable Energies bar that mounts at the C-pillar using the threaded holes that were later used for the upper part of the rear seat 3 shoulder belt. My shoulder straps are attached to the rear seat lap belt mounts using longer bolts (bolts are same spec as stock) so that both the stock rear lap belt and the harness can be installed. My lap bely is installed to the same points as the stock 3 point belt, also using longer hardware so that both systems are present and my sub-strap is mounted under the front of my seat rails. All stock belts are retained including the rear seat (my 5 YO niece sat there a couple times), all harness straps are attached to factory installed moints that were designed to hold the occupant in place and all 4 bolts that were replaced are the same spec as the factory parts.

 

Might try "Aircraft Spruce and Speciality Co." They sell 4130 chrome molly steel for the home built airplane industry, also 4130 plate. Sell it by the foot too. Don't know if they have a web site, pretty sure they do. Just do a search.\
Bill