Subframe connectors for a driver/cruiser, necessary to weld to floor?
I was talking about it's best to see what the factory might have done. Not necessarily what was strongest. I stand by what I said.
You're assuming the factory did what was
best, and that's rarely true. They typically do the cheapest thing they can get away with, which is probably why the rails weren't continued for the entire length of the car to begin with. The roof structure being present in that location, along with a lack of suspension points in that area, meant the cabin area was strong enough to meet the factory standards without them.
Welding the floor along the entire length of the subframe connector with two dissimilar metal thicknesses like the US Cartool design does is also very different than having a spot welded flange like the factory frame rails do. It might look more factory when finished, but from a stress/load perspective it's very different. If you want it to look more factory, awesome, go for it. But don't mix that up with "what's best".
I have welded in 2 x 3 tubing for frame connectors for years in lots of Mopars and a few Fords. I have never tried to do the thru floors deal as I have to lay on my old back and do it all. I too have no idea what is the strongest way, but what I do sure makes it stout!!! Makes a REAL difference. But then I have heard some "arm chair engineers" say the car needs to flew some!
Don't know!!
:thumbsup: :BangHead:
There is a limit to how stiff you can make that section of chassis as well, especially using two frame rails in the locations where they get added. You could weld in a set of railroad tracks if you wanted, but the benefit to the chassis stiffness might not be significantly better than a 2x3" box tube. The weight, on the other hand, would be drastically different.
There is a level of improvement that benefits the performance of the chassis, and after that everything is diminishing returns. Personally my somewhat educated opinion is that regardless of which kind is stronger, the difference in chassis strength between the two basic types of frame connectors on these cars is small enough that the vast majority of people driving these cars won't be able to tell anyway.
Sorry, I dont agree with that statement. You can never make a bolted in subframe connector as strong as welded in for any length of time. Get a Lincoln, Miller or Hobart MIG, and buzz em in. Call it a day.
Yeah, that's not at all true. Certainly not in theory. There's a reason why bolted connections are used for most engineered structures outside of light duty automotive.
Now, that doesn't mean that the MP bolt in connectors are as strong. Their 2 lag bolts on each end of the connector are definitely not as strong as a welded joint, and definitely not over time. They would need larger landing pads, more hardware and captured nuts in the frame rails to have a chance to be as strong. So for the MP connectors I agree, bolting those in isn't as strong. But that doesn't mean they couldn't be with an improved design.
Your stress is concentrated on the bolt attach points. This is where over time depending how you drive the car you will likely get cracking looseness and failure.
Sure cracking can start at a weld seam, but is less likely because the entire structure is more rigid.
As far as bolts go, case in point, bridges are bolted together and designed to flex so they dont fail. You are bolting together a frame connector to a car chassis with the intent to make it function as 1 solid structure (no flex, or minimum flex).
Will it work? Sure, it will stiffen it up. Will it work as well as a welded in set of connectors ? No over time it will not. It will still allow a bit of flex, and along with that the stress loading and unloading of the bolts.
Over time the clamping force of the bolts will become less as the oem structure deforms behind them, along with cracking from stress loading and unloading.
Making the structure more rigid can actually increase the chances of cracking at the joints/seams. You have to look at how much the metal flexes over the length of the chassis under the loads it will experience. Too much flex can cause cracking from overwork, but too little flex can cause cracking by concentrating more load than the base metal can withstand. Two very different processes, but the result will still just look like a crack to the naked eye. The amount of flex and load has to be matched to the capability of the material used to build the structure.
Here is something for you to think about. Bolts are made for things you want to be able to take apart to repair or replace if needed. Subframe connectors, are not one of those things.
This is false reasoning. Bolts are used in structural engineering because of their load bearing properties, not because anyone is going to disassemble a bridge or skyscraper. That stuff gets taken apart by explosive demolition, so why isn't it welded? Because of the structural properties needed for the joints, that's why.
Yeah sure, in the automotive world stuff gets bolted together so it can be taken apart and serviced, but that is definitely not the only reason. The entire chassis on one of these unibody cars could be riveted together, and very likely with little to no difference in strength if done right. But they're not, and being able to take it apart has nothing to do with that decision. The factory does things for a lot of reasons besides what's best, what's strongest, etc. and that usually comes down to cost.