Education comes fast when you're first starting out. I think that education is also expedited when you're working alone. Last year I did this to my frame, attempting to make header clearance. Pretty awesome, huh? Well at least I recognized I had totally just 'effed things up. I made the following repair and thought all was well. But now I'm wondering if while I was at it I should have gone ahead and boxed the area I cut out. I'm about to pull the engine again, and hopefully for the last time until paint, and I thought while I had the chance I'd box that portion. I can't box it fully for various reasons, but would boxing just this portion (appx. 1 1/2 feet) add any strenght or create stress points and weaken it further?
-Glad you brought this up...it has probably been covered in other threads, but I haven't seen it. I have a '26 Henney Hearse that I was going to also "partially" box the frame in some weak areas, but I too wondered about creating artificial stress-points. I'm definitely not an engineer, so I'll also be interested to read responses.
Norm Jones has a sweet '32 roadster with a Hemi, was @ HAMB drags. Frame is partially boxed in the front. This is the smoothest riding '32 I have ever ridden in, and we went fast thru some really rough road.
It's been common practice to box a frame from the firewall forward on a mildly powered rod. BIG horsepower and/or torque is usually best served with a fully boxed frame. Frank
I would only be concerned with stress concentrations if you are removing material. It is difficult to add material and make the frame weaker. In short, I couldn't make an educated guess on frane durability with out more info, but any boxing is good in this case.
I am not an engineer, so this is only my opinion..... I am guessing this is a ford frame...They were designed to be part of the suspension, the cross members are rivited in place to allow things to move. When you box part of the frame, you are not allowing everything to move, therefore, adding stress to the metal right next to the welded box area causing possible failure. In your example, it looks like your running a big block. It that is the case, your are really gambling, and should box the whole frame. Don
In my opinion, partially boxing a frame does absolutely nothing except add a bit of support in the motor mount area by helping transfer the localized loading of the top frame web to the bottom frame web. To really reap the benefit of a boxed frame--less torsional frame flexing, less "wrap up" under hard acceleration, then you must box the frame full length. All that a partial boxing does is to transfer the accumulated torsional distortion caused by the engine trying to rotate counter to the crankshaft rotation to the unboxed section of frame which starts at a critical point halfway between the front and rear axles, where it is actually the weakest.
it's a chevy frame. my main motivation in the partial boxing is to strengthen the areas that I cut out and rewelded. if i had never cut them out i wouldn't really be considering the boxing right now. does the benefit of boxing areas that have been altered by cutting and welding outweigh the risk of partial boxing creating stress points?
failure occurs where weak meets strong. in this instance, where the boxing plates finish. stagger the cuts (angle cut) of the plates you insert to spread the stress along a greater area. sometimes we add "keyhole" cutouts to the end of plates to let them give a little more and let the chassis rails move around some more
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