All good suggestions. One thing that you can do to increase the strength of the sub frame connector is to weld in some gussits say 3 to 4 inches long from the connector to the floor pan in 3 or 4 places. This will spread the load of the connectors and give you a more ridgid connector. The way I am going to do mine is as stated above. I did this on my last drag car and it worked like a dream. Cut the floor pan fromthe end of the front to the end of the back sub frame the size of the connector. Lets say 2", Then cut the top side back into the sub frame about 3". Lay the connector in the channels that have been cut and weld in place. Then weld the floor pan to the connector the entire length on both sides. Very strong and does not hang down lower than the body. Then I welded the roll bar loop to the back sub frame where the connector was welded to it. With a 8 pt cage in the car you could jack up either side rear tire and pull the front tire off the ground with no flex in the body. You could open and close the doors just like when it was sitting normal. Just some more options for you to think on. Don
Nothing. He's just trying to "spread the load out" by using the C shape metal instead of welding the connector directly to the frame rail. It's redundant. The connector is still held on with it's circular/oval shape weld. If it gets twisted enough to tear away from the frame rail it will still tear away from the channel section. If you're looking to "spread the load out" then you should probably just start with square or rectangular tubing. I'm also not a big fan of "under-ride" subframe connectors. Everything we build around here gets the "through the floor" design. Even if they are round tubing. It's much stronger!
I was not initially worried about the weld letting loose, but more that the weld heat would weaken the frame rail, and eventually the connector might either tear a chunk of the frame rail out, or begin to bend it inward, like a can being crushed, but not so dramatic...just a little bending over time. Using a plate or wrap-around would allow the stresses to be spread out over 6-9+ square inches of the frame rail, and not just the 3 or so sq.in. of the tubing welded directly to the frame. Should be able to take more stress before potentially deforming the rail. Regardless, this all sounds like a bit of overkill, especially for my application. I may as well just weld them right up...
This is exactly the reason that the NHRA requires the tubes of the roll bars to be welded to a plate rather than to the trunk flooror the floorboards, even in cases where the bar is directly over the frame rail. Remeber that our "Frame" is in reality just slightly thicker sheet metal bent into a "U" shaped rail. Go with your first instincts and use the thicker metal formed as a u-shape and weld around all the edges. The piece of mind will be worth the extra pound of metal in the car. Just be sure that the rear mount will clear any suspension mods you plan to make in the future before you weld it up.
i like this idea... sounds like a great idea.. i wish i would have thought about it when i had my floor boards out and welding all them in... it would have been so much easier to weld the subframes in with the floors out
question for all those that know when you weld in the subframes.... obviously you want to do it with the car on the ground... but you cant get under... do you just jack the car up and put jack stands under the rear axle and one under each front wheel? or drive the car up on ramps and weld it that way
i am going to do it while it is on a lift, 6 foot up at a friend's muffler shop...That is if I can keep him sober one saturday afternoon.
If you do it the way that I suggested most of the welding (90%) is done from the top. After you get all the top stuff welded it will be strong enugh to jack up and finish the bottom. If you are putting them on from the bottom you can jack the car up and support it with jack stands on the rear end and the lower control arms. Just make shure that all the jack stands are of the same type and they are all on the same lock position located in the same site side to side on a flat floor. That way you will have no body flex and the car will be straight when you are done. Hope that helps Don
