Firebrid: The Prius v Powered Hybrid Convertible

Never seen an oval tube roll bar, probably because it's weaker than round of similar diameter so nobody uses it (definitely not sanctioned for racing). Worst case you could fab it up from ovalized 4130 as long as you could get someone to bend it for you (requires special mandrels, both inner and outer).

You can try to make your own oval tube from round tube but it's not as pretty as the factory oval stuff.
http://www.jim-haubert.com/Flat-tubes.jpg

Bit harder to find that tubing but you could try someone like these guys:
Louisiana Steel | Welded and Seamless Oval Steel Tubing

Bending flat oval tubing:

 

I wasn't thinking you'd be racing it but mentioned it since that rollbar profile would be quite rare (if not custom) since all the other off the shelf stuff will likely be meant for racing (ie round tube). It will be good for lap belts but not sure how well it would really be for rollover without more bracing although it's certainly better than nothing on a convertible.

 

Strikes me that for a roll bar hoop to be effective, it has to have some for and aft bracing. Strong enough to hold the entire weight of the car. And be attached to ultra strong mounting points. The whole idea is to hold your head off the pavement. If it folds even a little bit, so does your head.

 

Just another thing to throw out there but make sure to do the math on the system you design if you are really going to attach seat belts to the roll bar because really you should have some fore/aft bracing due to the possible forces involved in a car crash (which could easily end up in several tons for both passenger and driver acting on that roll bar). Not sure how well that other one was designed in the photo you shared but make sure the bar is sufficiently thick (oval profile will actually be helpful in this situation due to direction of bending forces), attachments have at least a 6" x 6" x 1/4" 4130 plate to weld to (get good penetration on your welds) and that hopefully you can find a way to working in some bracing fore/aft (even if it's down low behind the trim panels).

Example of plate attachments for roll bar on unibody cars:
http://www.stangtv.com/wp-content/blogs.dir/1/files/2012/06/white_falcon_011.jpg

 

I'm not an engineer, but I can tell you there are lots of unibody convertibles with a single "rollover bar" that have shoulder belt mounting points on said bar. VW Cabriolet and PT Cruiser come instantly to mind.

 

Installing a rollbar is OP's opportunity to te it in to fore and aft structure, carrying static and dynamic loads, and stiffening the entire chassis.

 

He wants to keep it looking as stock as possible. That would ruin the convertible top down look.

 

Understood, and I haven't followed this extensively, but convertibles already suffer from structural rigidity deficits and could use more bracing above the floor plane.

 

I’d take a convertible any day .

But always good to have someone to swap bulls stories with.

 

How about messing with the spelling and call it "HYBIRD Drive" instead?!........it is a Firebird afterall.

 

It should be HYBIRD drive on the FIREBRID It is no longer a Firebird.