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MG MGB GT V8 Factory Originals Technical - Roll Bar to increase chassis stiffness?
|I seem to remember hot rodders in the past often added roll bars to their cars to help keep the body from twisting under hard accelaration. Is there a bar made for the MGB for the same purpose? Or is the decorative one MOSS and others sell effective at all along these lines? What about welding it in place as apposed to bolting? I love the looks of a roll bar, and plan on adding one anyway, even if it offers no additional strength. Just curious what others think. I'm going to be using a stock roller block FI 302 Ford for power, BTW. My car is a roadster.|
|The big problem at least for me) with a rollbar comes to haing one that is functional, fits under a top and allows me to be in the car. At 6'4" I found the "standard" rollbars for a MGB go right thrue my head. SO, my vert does not have one and with our rainy climate, I have to have a top so it probably never will.|
That said, a rollbar only will not increase stiffness that much. Now if you did a cage meaning it has loops that go forward and mount up near the front of the doors or under the dash as well as behind the seats, then you are building a box and that will add rigidity. The key is making "boxes" that are welded to locations on the frame to increase rigidity of the chassis. For the mustang guys I hang with they also usually add subfram connectors at the same time or before they add in a cage. these box section pieces are welded in under the car to add more framing and rigidity to the chassis between front and rear frame sections.
Hard acceleration? You mean hard turns, right?
If your primary intent is to increase chassis rigidity cheaply and simply, I expect you could do a lot better with rather straightforward fabrications of your own design.
You might start with a MonteCarlo bar... i.e. a stout piece of tubing side-to-side across the engine bay. Few MGB's seem to have them, but they're proven in other cars. You could design the bar so it bolts in... or you could do what I did and weld it in far enough forward that it's not in the way of engine removal. (Mine is made out of 1" x 2" box tubing, and includes radiator mounts and front hood pin mounts.)
A similar side-to-side horizontal bar mounted just behind the seats would help too. (I have a cage, with a cross-bar back there, and collectively the cage DRAMATICALLY improved how my GT handles). Whatever tubular chassis reinforcements you install, they can only hope to help if you make sufficiently large, stiff brackets to transfer force into the car's sheet metal without a lot of flexing. It typically helps if you can get BEHIND the car's sheet metal and install doubling plates (i.e. to sandwich the sheet metal.)
|The commonly seen 'loop' roll bars which fit behind the seats and only have rear braces won't help chassis stiffness much. Most of the flex is through the rocker area, this is the smallest cross sectional area in the car. You would have to run some type of bar or brace to the cowl area to have much effect.|
|If you want a roll bar in a street car you must use padding. |
Imagine if you were hit from behind, your head snaps back and hits the roll bar. There is special padding made for this purpose with the hole for the roll bar offset, so more padding is on the front surface to protect you.
Not used as much in race cars because of the helmet, but essential for road use.
Just my advice, Simon.
|You might want to check with Glenn Towery. I bought mine from him and am very satisfied. I'm 6'2" and can lean my Miata seat almost all the way back. When in my normal driving position, the only part of my head even close to the bar is the top. The bar came from a guy in Alabama and is custom made to fit the B. It is thicker (larger dia. tubing) than the Moss bar I had previously, and mounts in the same four places with backing plates supplied. The soft top frame on my '72 barely clears the bar when putting it down and certainly not with the roll bar pad in place. My Snug Top hard top fits as well. As far as increased stiffness, I think it adds some to the overall feel.|
This thread was discussed between 16/11/2003 and 19/11/2003
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