I've been looking at my '47 Ford frame for a couple of years now and wondering just what's involved with removing the x-member. I realize that if removed, the frame will need alternative reinforcing. Why remove it? It's exhausting... With the x-member in place, that severely limits your exhaust choices. You're pretty much limited to stock manifolds, shorty headers, fenderwell dump headers, or drop the headers to under the frame. My car is lowered, so that last one is out and fenderwell headers on a lowered car is a can of worms. I'd like to be able to fit tri-Ys or even four tube headers without hanging below the frame. My pedals are already firewall hung, so they're not in the way. I've also got a welded-in crossmember for the IFS, so there should be plenty of stiffness there. I assume that at a minimum I'll want to box the frame rails, it's the transmission crossmember that I'm mostly concerned about. Anybody done this? (Pics would be fabulous!) Or have any insight? I'll be a trail-blazer if I have to, but I tend to over-build stuff so I'm hoping for some working examples to avoid overkill. TIA!
You will be removing most of the frame's stiffness, maybe close to all if you hack out the doublers. In more modern cars (say, 78-81 B-body chevys) the front ans rear of frame is held together by massive crossmembers that also hold suspension locators. These occupy a substantial amount of the frame's length. The center in these is simply pathetically weak u channel, but the main body is MUCH stronger than a '48 Ford body. Building stiffness back will be very clumsy compared to original X because you probably cannot put in complex curve sections that dodge your mufflers. High supports like a full roll cage might be best, along with any reenforcing you can do within cowl... I would start by acquiring a spare frame.
Remove and not replace it with another full X member? Boy, you sure do understand electrics, but you need a lot of chassis learnin'. The X member is the main strength adding factor that keeps the Ford frame from twisting. Just boxing the outer rails won't cut it. Just welding in a big front crossmember won't cut it. Maybe you will always drive on smooth roads, and never enter a driveway at an angle, but maybe not. If that frame twists, there goes all that front sheetmetal you spent so much time aligning. And cracks at all the corners of the door and trunk openings. Not pretty.
You'll need to modify frame rails to install this generic tubular X-member, it may solve your clearance issues; just don't install the under floor brake assembly? This has a simple bolt in transmission cross-member. There would be torsional flex with this style unless you reinforce it. I used similar in my Chebby however I used a shaped 3mm thick plate welded to the top parallel tubing above the transmission to limit the torsional flex. A notch provided transmission clearance and I was able to retain OEM floor. As a sideline I installed a 46 Olds centre X-member (Similar to 42-48 Ford) and IFS into a friend's 42 Chevy PU, it was a lot better than the OEM ladder frame.
If the X member were removed couldnt you just add some crossmembers to mimic a newer chassis? My F1 pickup chassis is nothing but C channel and a few crossmembers and is designed to twist, although I have not ever seen it twist or knew it if it did.
That's why I'm asking... And to answer Bruce, I have a spare frame... LOL. It's the forward legs of the x-member that are screwing me. If I could get those out of there or at least moved back about 18" I think I could make something that would work. The current head pipes that are in there look like they were designed by a drunk (with all the short, sharp bends for fit) and you'd have to pull the motor to get them out or use a Sawzall. Each side is made of three pieces, so it's obvious that they were built in place. I definitely want to retain the torsional rigidity of the OEM frame, I just want some room for exhaust...
There's already holes in the x-member, but they're too small for a header collector. If I cut it big enough for those, it mostly won't be there anymore...
Sounds like shorty headers, or some custom made that might fit through the enlarged holes in the X are going to be your answer.
Shorty headers are the obvious answer (or a set of 289 Hi-po manifolds), but I'm planning on a big-inch 351W and don't want to choke it any...
If it was me I'd box the frame and then re-install the cross-member rearward to better fit your engine/transmission/ exhaust. For those who think this won't work ask yourself how many pro-built 32 to 48 Ford frames have you seen where they: (1) Boxed the frame the entire length (2) Welded in a front crossmember, either straight axle or Mustang II (3) Welded in a rear crossmember for a cross spring and/or rectangular tube shock/coil over mount (4) Welded in aftermarket round tube transmission crossmember, and that's all the reinforcement they installed?
IF you cut holes in the X-frame for header collectors....(even though the holes will be huge)..if you weld a collar around the holes of equal size/thickness of the existing X-frame...I would think that would re-establish the integrity of the X-frame. Just have a couple of big-old holes in it! Then run your exhaust thru it. Why wouldn't that work?! 6sally6
Steve: I wouldn't recommend it. A friend of mine installed a 351 C in his 47 Ford and chose to move the foreword mount of the "X" to the rear approx. 6" to give him the additional clearance that he needed. After that, they experienced the frame flex every time you turned the steering wheel, ( you'll note that the "X" ties into the side rail right behind the steering mount / box.) with the car on the ground. You could both feel and see it move.!
Another suggestion, shorten the front legs where necessary to gain sufficient clearance. I added top and bottom reinforcing plates to better spread the torsional load when I did that 42 Chevy PU. Still retains beefy strong centre and torsionally rigid?
I don’t understand the exhaust clearance concern. I had to widen the center of the X for transmission clearance for a 700r4. You can open up a couple holes in the frame if you need to gain clearance with out removing all your structural rigidity. I run 2 1/2 inch exhaust front to back- tucked up into the rails- nothing hanging down- with no issues. Sent from my iPhone using The H.A.M.B. mobile app
The X-member works by resisting angular deflections between the rails in the longitudinal plane. The torque about a lateral axis at the centre of the X-member is the same for any given angle regardless of where the X-member is located along the length of the frame, so moving the X-member back is indeed a viable option – provided it doesn't then interfere with the rear suspension. The front part of the frame is, however, now required to do more, cantilever-wise, to resist torque, so boxing might be a good idea (though strictly, it would make more sense to beef the flanges than duplicate the web of the rail. Weld angle or square tube inside the upper and lower flanges to create small box sections?) If you do the exercise you'll find that the torque about a lateral axis at the centre of the X-member is huge compared to the torque about a longitudinal axis the frame has to deal with, due to the much greater moment arm lengths. That part of the assembly should ideally be particularly beefy. An X-member is really a clunky way to deal with the problem, but doing it a different way would mean very wild engineering tangents. For instance, with IRS there would have been the opportunity to use a torque arm or similar to tie the diff unit to the engine/gearbox and thus keep engine torque out of the frame. Likewise a rear transaxle would limit engine torque to peak torque rather than peak torque times first gear ratio. However, these do nothing about torque inputs from suspension loads, which can easily exceed multiplied engine torque by some margin.
why cant he oval two holes as previously suggested right where he needs em, box that section of the x member and frame and reinforce it also similar to pics above? the xmember stays put, he gets two bigger holes and the weak points potentially created by making the holes bigger is fixed by boxing and reinforcing the x
Lots of interesting information (some of it conflicting! LOL!) and all food for thought. Let me reiterate what I'm trying to do. The problem with the x-member is if left as-is, I can see service on any long-tube header design being very difficult. I suspect that the headers would have to be installed/removed with the engine out of the car; I'm trying to avoid that if at all possible. But not being a structural engineer, I'm hoping to tap the collective wisdom here on the HAMB for a solution. And it's the torsional frame twist that most concerns me; I figure if I can minimize that, the rest will take care of itself. Looking around on the 'net, very few aftermarket frames are available for the '41-48 Ford cars, but those few still use an x-member. Once you get into the '50s, they mostly disappear, I suppose by accounting for the increased structural contribution of the body shell as Bruce mentions. Although most late '40s/early '50s truck frames do without x-members, which somewhat puzzles me. But a few possible solutions have come to mind, let me run these past everyone... One would be to box/reinforce the front legs of the existing x-member, cut a 'U' into it for the header (opening facing down), then have a bolt-on lower rail (3/8" thick?) to replace the structural integrity. Another thing I noticed is the majority of aftermarket frame feature round-tube x-members, using relatively small 1" or 1 1/4" tube. Does round-tube resist twisting better compared to square cross-sections i.e. would this be equal to or better than square tube? I saw one aftermarket frame that staggered the front attachment points of the tubes, that would aid in installing headers. And @Ned Ludd brought up a very intriguing idea; reinforcing the flanges. This got me to thinking; one of the most rigid structures for it's weight is the honeycomb. Maybe a series of 'W' shaped inserts welded inside the frame channel as diagonal reinforcement (along with boxing plates) would stiffen the outer rails enough to eliminate the need for the full x-member. Fabbing/installing the boxing plates would be a PITA though... Thoughts?
Side pipes! I am actually finding this thread informative as I too have to make mods to my 41 frame to clearance for the transmission. So please, continue.
[QUOTE=" Another thing I noticed is the majority of aftermarket frame feature round-tube x-members, using relatively small 1" or 1 1/4" tube. Does round-tube resist twisting better compared to square cross-sections i.e. would this be equal to or better than square tube? Thoughts?[/QUOTE] There's a reason round tube is used for roll cages in cars and I think you just answered your own question
If you shorten the front legs and remove those support brackets, you can replicate the gussets at the rear and fit them on the front legs replacing those small open channel brackets. I did similar to my 46 Olds to increase torsional rigidity; I only had gussets on the front legs but not on the rear legs. To gain exhaust clearance I opened up exhaust holes in X-member legs front and rear, tipping the edges allows more clearance for tubing to run through. I have an X-pipe between rear legs and nothing hangs below frame rails.
I'm all about nothing hanging below the frame. I also want to be able to remove any exhaust bits without dismantling the car... I'm curious; I know you guys down under have all sorts of rules/regulations you have to conform to, is there any guidelines on frame mods that may apply in this case?
There's a reason round tube is used for roll cages in cars and I think you just answered your own question[/QUOTE] Difference between round and/or square/rectangular tubing is that round has the same deflection for a given load [like bending] in all directions where square or rectangular will vary depending on direction of load..Main frame rails [morrison/alston] are generally 4" tall by 2" wide as the most ability is needed in the vertical direction..Now in an X member even though it is to provide torsional rigidity it still really just resists bending..An aftermarket x member won't do shit for rigidity unless the legs are solidly connected where they [should] cross like the original x member; and no a tube across for a trans mount is not sufficient..
We have lots or rules, regulations and a 3-stage inspection process in this state, it would exceed NSRA standards. Other states here require a formal inspection by an engineer prior to registration / licensing. I'm going a different route and using an engineer who knows his stuff unlike some of the current people involved in the process. Every state is different however most adhere to National Guidelines (Section 3), which I believe were based on this states guidelines, which some states have not have adopted so far. I'm using bolt together flanges and 'V' bank clamps so servicing the exhaust is straight forward if necessary. Insofar as frame modifications are concerned, they need to be structurally sound and based on proven engineering principles, some HAMB modifications I've seen would not pass down here. Any modification needs to be safe, well engineered and designed with structural integrity, quality fabrication with welding etc taken into consideration. I've done some OT work on my Olds frame and have had it inspected already by an engineer who was happy with what I'd done and how I'd done it after I'd explained the rationale for the modifications and how I'd gone about them.
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