Ok guys I have a few questions for guys here who have had this done or did it. I'm taking my 72 off the frame to box it and address a few weak spots. Nothing bad but it needs to get done before I drive it anymore. I have priced out steel and the .120 thickness hot rolled is 90 bucks for a 48x 48 sheet and the cold rolled .104 is 107 bucks. Now the cold rolled is about 20 percent stronger due to the process of cold rolling. I saw boxing kits where they come in .125 but for 64-67 a body's. My question is will the .104 be sufficent my thinking is the 104 thickness sheet will be stronger but lighter than the .120 . I want the frame to be rigid but I don't want to add a whole bunch of wheight. I'm also looking at aluminum bushings . Any help is appreciated I'm not racing a 10 sec car here but I want this to be as strong as possible for future upgrades and not add a ton of wheight.

 

Frankly, I think you'll be a lot better off getting the boxing sections from a convertible frame than just using flat plate. If you turn this into a convert frame, the convert crossmember is a bolt-in, you can get pre-bent brake and fuel lines, and the resulting frame has both increased torsional stiffness AND increased bending stiffness. Note that you should not confuse strength and stiffness; the frame is plenty strong, but you want it to be stiffer.

If you simply add flat plates to the inside of the open channel frame, you will create "collateral damage". First, you'll need to fabricate custom crossmember mounts (likely tabs like those on the 64-67 converts), and you'll need a custom-width crossmember. Second, you'll be custom bending all your fluid lines. Third, and most importantly, while you will provide some increase in torsional stiffness, you'll be adding a lot of weight for very little increase in bending stiffness. The bending stiffness comes from the top and bottom caps of the frame rails, not the sides. That's why the convertible box sections add to the top and bottom caps.

 

I'm well aware I wil need to re plumb all my lines and that's ok to be honest. What do you mean by the caps ? I planned on making c channels and welding them on the frame so that welding would be easier. I know guys have done this with out the convertible frame I'm curious as to what they are doing or what is done. If its really not worth it then ill just fix thw eak sections gusset some corners and call it a day. I really doubt I wil run in the 10's ever . My frame is actually still pretty solid but I wanted to box it because if its coming off then now is the time. A frame is 500 bucks and steel is cheaper so id rather swing the work my self. I have extra aluminum fuel line and re bending my break lines won't be to bad. Is it worth even boxing my frame ?

 

My worry when anyone talks of boxing a frame is the engineering. These things were designed with a certain amount of flex in them. Stiffening them haphazardly can end up moving stress to points not strong enough to take them. Imagine driving without springs .... chassis flex is just one big relaxed torsion spring.

 

Convertible frames are boxed to counteract flexure due to the lack of a roof. If you want to stiffen up a frame for a hardtop put a cage in it. That way you'll get torsional resistance. You're not going to get an appreciable amount of additional stiffening by boxing the frame. (yeah, I know they boxed 442 hardtop frames in 64-65 but I'm sure they stopped because it didn't add any value).


If you insist on doing it you can weld 3 or 4 two inch wide tabs, spaced evenly from front to back, from the top flange to the bottom flange to support the flanges and it will get you the almost the same strength. The web of a beam (or sides of a box) don't really add strength, they only serve to support the top and bottom flanges from deforming under load. It's the top and bottom flanges that do all the work

 

I guess then I'll just fix the weak spots gusset a few corners in and get new bushings. I apreciate the input guys. I'll just invest in some rear suspension stuff. I know that most cars I have seen with flat plate have a cage so I can see where flat plate is essentially a pointless attack of plan. Now my next question. Aluminum bushings or the poly bushings. Both priced the same. I have never done any of this so excuse my total lack of experience.

 

There are some decent threads on some of the Chevelle forums where it shows how to gusset the lower control arm frame connection points.


Aftermarket frame braces (if you don't have them already) that go from the upper control arm frame mounts to the lower control arm frame mounts do a decent job at stiffening the frame to prevent the flex and rotation of the frame.

 

Im going to get the braces , the relocation brackets for the real lower control arms and adjustable uppers for the pinion angle, and I have 50 / 50 shocks from lakewood. The front is all set up with moroso trick springs and 90/10's. I will do some reaserch on the chevelle forums for areas to gusset. Thanks allyolds68.

 

I would consider finishing the factory welds through out the frame and gusset the suspension pick up points. That way you are only adding minimal weight and reinforcing the factory design.

 

The convertible frame adds considerable stiffness and about 42 pounds. Jack up a corner of a sedan with the F35 HD frame aka convertible frame and you will see.

 

Here is how I boxed mine. I used 1/8" steel sheet.

 

Very nice ! . I think I'm going to just fix what I have to and gusset the areas I need to and call it a day. I think for my use I'll be alright.

 

http://abcperformance.net/frame%20boxing%20kit.html

ABC Performance also uses .125 plate. You can also see where they have to change the cross member as Joe stated. Which of course they offer also.

 

If I did box it I planed to cut my cross memeber and weld in nut plates on the inside then weld plates on the cut ends of the cross memeber with gussets and holes drilled in the corresponding locations.

 

FYI, I just stopped by a fab shop and bought some sheetmetal drops. I only have about $20 in material invested.

 

Hellwig Frame FX, wish I did it before I painted everything...
http://scandc.com/new/node/943

-Michael

 

wayyyyyy toooo steep on price. Im pretty handy with steel so fabbing stuff up and cutting is no issue. Specially since chadman reminded me I can buy scrap drop off from fab shops. I though 100 bucks was a deal but he has me beat with the 20 bucks lol. Im deciding to not box my frame. In reality it is pointless unless I have a full cage. I have a 4 point welded to the body braces. Im not looking to go that fast and im thankful I got great info on the boxing and advice it saved me some coin but the info is still appreciated.

 

We boxed my 65 442 frame in the same manner that Chadman did. Here is what I can tell you..
When I pulled the body off the frame (no accident car) the frame was tweaked, sitting on a level concrete floor the left front of the frame and right rear of the frame were touching the ground, the other two sides were not, just out of curiosity we blocked the frame up and one person standing of each end actually had enough weight to take the tweak back out of the frame. I took it to the frame shop where they got it back perfect but I was told that they were very prone to twisting.
We boxed the frame using .125 and it made a significant difference in the rigidity of the frame. Took it back to the frame shop to make sure we didn't cause an issue with alignment when we welded, it was spot on.
I am very pro-strengthening the frame. Those cars were not made for big tires, suspension that actually hooks, and the amount of power that can now be made out of whatever power plant you choose. Its a well known fact that there is a lot of power to be gained through the frame and chassis. Also consider the fact that we are talking about 50 year old metal!

 

Great post real57,
x2 agree 100%

 

I really don't think I'll ever be running faster than maybe mid 11's ever lol. Currently in the 12 sec range with my small block.

 

I saw this at Carlisle. Hellwig sells a frame boxing kit for the 68-72 A-body. I don't know the price, but it seems like an easier way to go.

 

Thanks joe p. I looked it up and the price is 346 from JEGS . Kind of pricey if I decide to box it Id rather make my own panels to fit within the frame.

 

A little off topic but relevant.
FYI~ We designed frame strengthing plates for OUR A-body chassis(and many other components) when I worked for a well known(long gone) chassis shop in the late 80's in Chicago area.
At that time our chassis was really flexing, even with the Cro-moly cage, we found stress cracks in the old chassis frame rails and around the hard points, so we boxed the frames which helped.
Bottom line is, the fatigued 40+Y/O frames were never intended to be race cars, corner carvers, or anything but street cars, so in order to help the above stability/strengthing measure are highly recommended.
Pics below are examples of before and after, 1st from the early 90's, 2nd from 2006 era. clearly the car has made great strides, but the chassis was and is the same today. before.
after.


I do offer a kit designed for the GM body's along with many of the other components. We fabricate most of this in house.
I have been doing this on a customer based needs, but if this is something others may need/want? I'll start posting all the chassis components we designed on my web page as soon as I find time.. or just call.

 

Shoot me a price. I just want to box it. If the money is there for me then I will do it but I'm trying to have caviar on a cheetos budget here lol.

 

IMHO you should do everything you can to stiffen your chassis including attaching the role cage to it. You are not improving the chassis performance one bit by having your cage welded to the body. Your car's really not fast enough to warrant a roll cage, so if your not going to weld the cage to the frame, you may as well get rid of it.

 

The roll cage does add a bit of protection. On unit body cars its ok to weld it to the floors where there is stuctural steel such as sbove the rail. In my case I did it on the areas where the body braces are. One other reason I did it is to have a reason to not put an interior on it. I could weld the cage to the frame but right now that's one less **** butter sandwhich I don't need to get my self into. I realy doubt I wil see any gains by addidng all that strength so I feel the effort will be kind of pointless. Biggest gains will be suspension. I doubt my car can produce enough torque to loose time in the suspension travel / body twist .specially if I add lift bars which is all I need car should be set for what I'm using it for.

 

Check out Jt race craft they have some cool braces http://jtracecraft.com

 

I agree that your roll bar does add some safety, but it does nothing for your chassis. When you stiffen the chassis you reduce twist. This will give more consistent launches every time. If you are going to remove the body to box the frame, why not just tie in the roll cage to the chassis at that time? You say your current power plant will not generate enough HP to see any real benefit from stiffening your chassis. I think you are mistaken. I also think you should plan ahead for when you do install a 500 HP mill. I'd hate to see you wrinkle the roof line from body flex after going through all that body work.

 

Not too worried about the flex im not really looking for gains through the chassis work. I don't have the cash for the tubing to cut and drop my roll bars I would need to cut and replace it. Just not really worth it. Boxing the frame is still in the air. Don't need to take the body off the do the roll bars just cut the floors and patch around the tubes as needed so down the road that can be done.

 

Also I don't really want to run faster than 12's. Car needs to be street driven on pump gas and just fast enough to run pro at the local brackets and slow enough to have a leg up. Once you get closer to 11's it cost more than what I really want to spend

 

You're only going to gain so much from boxing the factory frame. Boxing will only stop frame twist where it is. What I mean is, is the frame member twisting relative to itself, or relative to other frame members. It is the latter that causes more twist. Gussets are one thing to add at the corners, but the important things to do are reinforce the load points and the corners. The best way to reinforce a 90 degree joint between beams is via a truss forming diagonal between the two, because the new member is using the distance from the joint as leverage for its force, and thus can be lighter.

That will accomplish stiffening in XY plane, as in the plane of the ground. The two Z planes, XZ (arbitrary axes here) as in front to back and up and down, and YZ left to right and up and down, are limited by the fact that the frame is basically flat. You can gusset where elevation changes, and you can go from the bottom of a cross member to the top of a side beam, but that's about it, other than boxing. That's why roll cages help, because you now have a 3D frame that you can reinforce in all dimensions.

Copper, if you put a cage in, and don't want to weld to frame, BOLT to frame. Do not just go to floorpans in a body on frame car. It's pointless and dangerous. I can explain why it is dangerous if you'd like.

 

In short I was asking if it was worth it to box it or if anyonehad done it or if its worth it I'm my case. I'm well aware of how tying the cage wil reduce twist its simple physics and geometry kinda simple. I'm not looking to add a cage. I didn't just weld my 4 pt. To the floor I welded it into boxed and channeled areas of the body. Since I know floors are only so strong. Truly this is being more complicated than it should. Sweet and simple wil boxing really help my high 12 sec car is it even worth the effor considering I don't really want to run faster than maybe high 11's . That's all I was really asking. If I don't need it why the hell do it. No need in wasting money on the MAW if they really won't do jack squat. Wil I see a gain in et.'s probably not like I said. I went from running anti hop bars essentially like lift bars then took them off and saw no diffrence in et. So even in that aspect with the power levels I'm running there will be little to no gains . I got a lot of great info and I'm still on the fence . I might and might not box it. It comes down to price and if I want to. I don't mind my car doing the twist lol.

 

WELL I might kick and scream sometimes but sometimes things happen. My friend dropped of a ford 9in. rear for my dad to strip and de grease at his work. We where catching up and I mentioned what I had going on and he mentioned he has a tube bender and 200 feet of .120 DOM tubing and if we don't use more than 3 20 ft pipes he covers it since I painted 2 motorcycles for him for nothing. Now If I decide to cage it im obviously chucking the 4 point in the scrap bin and we will be starting from scratch. Im only doing a simple 8 pt. Now that I have laid that out as a possibility my question is should I do aluminum bushings ? Where on the chassis should I weld my points for maximum strength . This is still up in the air but its a big possibility.