Assuming a 350 hp street motor, auto trans, repo '32 rails under a Brookville body, full fendered, any opinions on partial boxing at the engine mts and X-members vs. full boxing? Sure would seem to be a lot easier to fit fenders, brackets and running boards. Did full boxing come into vogue with drag racing? Most of the mfg. frames seem to come that way but is it really necessary? Figured I might get a few "Dear Stupid" answers but just had to ask. Thanks
32 frame in my opinion is strong enough for a mild engine/weight configuration. after all,they had good sized weighty engines in them.
Its definently stronger if not more cosmetic especially on fenderless cars if your concerned about access assemble the car with fenders and all that attaches to the frame and weld nut certs where needed inside the rails and then box it, boxing is as you mentioned a necesity with more powerful engines. The only stupid question is one not asked.....rod on!
Are you going to use a Repo body or a Henry Body?? The twist of a street driven Rod is a factor on body choice. Dead weight of the engine flat head/small chevy doesn't matter torque does .Build it to last,it doesn't cost any more money if you are doing it your self!!
I'd box it . . . but also think about what type of x-member setup you're going to be using. An original 32 style K-member leaves the frame a lot more susceptible to twist/flex than does a later style front-to-rear x-member (like a 34 and later chassis). Even if I had an x-member, I'd still at least box the front area -- from the front cross-member to the x-member. Another consideration is that many of the replacement/aftermarket cross members are designed for boxed frames . . . so make sure you know which route you're going before you order frame parts. Boxing is some work -- and you definitely need a frame jig to do it correctly (the frame will "move" from all the welding - so be forewarned). If you're just doing the typical SBC in a 32 trick, then you'd probably save a lot of time and money just buying a frame that is already setup, boxed, etc... (Trust me on this one!). Or just order a complete boxed frame and have them NOT put in the motor/trans mounts . . . you'll still be ahead of the game.
350 hp is a tad more than dear ol' Henry intended. Boxing in stressed areas (firewall forward, K member mounts, rear kick up) would be needed. I like 3/16" to weld motor mounts to, everything else can be 1/8".
If you can get your hands on an orig frame un-boxed, lay it on the floor and try and lift it from one of the front horns............you will decide to box it
Buddys deuce factory frame was boxed in all but 2 spots on each side ,6" open section where the firewall bolts on,guess where it started to crack.
i agree, even though i did'nt box mine the flex is massive on a stock frame i would be doing it is i put an ohv in it.
I have had 3 unboxed gennie framed 32's with steel bodies. My highboy roadster had good cross members and was boxed only in the area of the cross members. The motor mounts were on a tube cross member that reached from one rail to the other. The hood was a top only. No problems. My channeled coupe had no boxing, a modified K member and Hurst front mounts. Hood was top only. This car repeatedly broke the radiator support rod mounts on the Walker radiator. My avatar full fendered car has a motor mount cross member, like my highboy, tying the rails together and it chips the paint in the hood area occasionally from flex. My current project has a boxed frame.
A Chassis Engr. real X member will stiffen it up several times more than boxing. Boxing from the X mem. forward is required for the cross steering. This is to reduce torsion flexing due to off center steering loads. C notching the rear will require local boxing there. I put in 1/2" thick C sections to reduce bucking and move the neutral axis down. Boxing the center of the frame does little. Retired engr.
I ran a test some years ago. I three pointed a stock frame and applied a torsion at the front with the rear restrained. From center line to the side of the front crossmember I got a 2" deflection. I installed a X member in a set of ASC rails and applied the same load. I got a 1/8" deflection. I boxed the frame and got the same 1/8" total deflection. These were rough measurements and were just for curiosity at the time. It has been a long time since I built a boxed frame without a X member ,but I am sure it would have twisted much more than the 1/8
I would box it full length. The weight of the engine is not the issue it is the torque of the engine. Mine is boxed and still twist under good to full acceleration.
Thanks guys..Some great first hand experience responses. I forgot to mention that I'm running a 37 Hudson side, not cross steering. Seems some thought I meant no boxing at all. My thought was partial boxing vs. full boxing. Andy confirms that the most important factor in rigidity is a well designed X-member.
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