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Real world benifits of frame boxing and stiffening

40369 Views 30 Replies 20 Participants Last post by  UMI Tech
Hey Guys,

Wondering if going through the trouble of boxing the a Chevelle frame and putting in "K" supports have a real world benefit. I know it can't be a bad thing but am I going to see any difference in the handling dept, will it give the car a harsh ride? I am trying to decided if i should do it to the frame on my 67 since I have it apart right now, if i do it I will have to re-powder coat the frame. Any before and afters out there with no other mods as a variable?


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What are you planning to do, and why would you want to would be my questions first. The old Chevelles have a pretty decent frame now, and when the Big Boys do a build they never seem to do anything to the frame. I have Hotchkiss suspension under mine now, and can put the jack under the car infront of the rear tire and lift the whole side of the car up. But I like you will be interested to hear from other members.
My frame was twisted badly from being transported and skull dragged from the container, so having it straightend was the first thing needed to be done.
The guy doing the mods showed me how easy the frame still could twist after boxing the side rails, so after spending good money on suspension gear it seemed a waste not to go that little bit further and not give it all a strong mounting point to get the most out of what I'd bought.

Looking forward to it's first track day:D


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In-general anything you can do to keep the suspension pick-up points where they belong in relation to each other is a plus. That's the concept behind strut tower bracing, subframe connectors, etc. It's pretty difficult to quantify just how much help boxing and stiffening provides. My recommendation would be to try it (if you're willing to re-powder coat) or go with some bolt-in products.

We offer a connector to reinforce upper and lower rear pick-up points as an example:

Customer feedback indicates their rear suspension "just feels better". We can't place a number on it per se, we just know it works!
Hey Wayne. That looks like a great start to your project. I really like the gusset action. Let us know how it performs!
I was thinking of doing something more along the lines of this
That's a kit form HPI CUSTOMS in Winnipeg, Manitoba, Canada.
About $600 if I remember right. Comes with everything in that pick including the precut boxing sections.

Or you could just come up with your own...Plenty of threads in this forum of people's home designs.
That's a kit form HPI CUSTOMS in Winnipeg, Manitoba, Canada.
About $600 if I remember right. Comes with everything in that pick including the precut boxing sections.

Or you could just come up with your own...Plenty of threads in this forum of people's home designs.
I was hoping to hear some good before an after results with just these types of reinforcements as a change. every car reacts different to less flex and I am (i think most are) are so used to these old cars that twist around on every bump I am afraid what I am creating... a modern performance car with a 67 chevelle body! My old 300 srt8 would lift a wheel off the ground going into the driveway at my shop at an angle, I will be damned if I have ever seen an old muscle car do that pulling in.

I thought about going that HPI route, figured with the time it would take to fab it up and the materials I would be better off.

So I called HPI today to get the details and I was disappointed to find out that these kits are made with NON DOM tubing the frame mount reinforcements raise the body of the car up 1/8 inch and the trans cross member is 1/8 inch higher then stock as well. Everything is MIG welded.

The standard kit now runs $650 +$150 shipping ($800) and you can custom order the trans cross member at stock height and request DOM tubing & Tig welding but now you are starting to get into some serious money, but I don't think I would want it any other way.

I don't want anyone to take this as a bash on HPI, these guys sound top notch and you can get it anyway you want (materials or otherwise) and I think they are a great option if you are willing to spend the bucks!
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Thanks Ramey, I'm really stoked you like it, I'll be getting some of your HD front swaybar mounts soon.

The HPI Customs kit is worth the money and I would of went that way if it wasn't for the cost and time involved in shipping it here.

My frame work set me back $1500 all up, I was quoted between $3000-$4500 by the top custom shops over here as it was such a rare oddball chassis (why did I buy an Olds), that isn't the same as a Chevelle as one guy told me. The guy that did all the fabrication and welding worked at Bunnings Hardware, the downturn over here has all the top tradesmen working there. He was great and even borrowed a laser level to check it before I got it back.

My body needs to be lifted 1/8'-1/4" as I made sure the drive line angle was near perfect before the gearbox crossmember mounts were welded in.
Because I wanted to run the Olds crossmember and have a stock look it hits the floor on either side.

I was even surprised at how much the frame weighs even with all the extra steel in it.


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It's pretty difficult to quantify just how much help boxing and stiffening provides.
Customer feedback indicates their rear suspension "just feels better". We can't place a number on it per se, we just know it works!
Anyone that sells any product that adds strength can quite easily and inexpensively quantify the numbers by conducting beaming and torsional tests. I'd find this useful if I was wanting to verify that something added chassis strength, rather than just "looking" strong.
Hey Craig. I totally agree with your request for quantification of numbers as pertaining to chassis rigidity. We're working on gathering and communicating that type of data.

By the way, your screen name is fantastic. I remember reading old Hot Rod magazines my dad had stored away when the Yenko Camaro's were new. They were awesome machines.

Hi Ramey. Sounds great! I understand that it's a bit of work when your catalog covers so many different makes and models, but I'm a sucker for data when I'm making a purchase.

My screen name (and my car) is a bit of a misnomer, as it relates to a 68 Chevelle. Yenko sold 99 Chevelles in 1969, making them even rarer than the famous 69 Yenko Camaro.

So, mine's just a fake with some cheapo Yenko stripes, and it's not even the right model year :)
Anyone see the new Hot Rod mag with the old school '55 Chevy on the cover? There is an advertisement for a kit to box stock Chevelle frames. Also, they will soon be releasing a mini tub kit for the '64-'67 Chevelle.

Here is the link:
I'm sure that bracing and boxing the frame will help a bit, but if you are really looking to increase torsional rigidity you will have to work on the y-axis as well, AKA, a roll cage that ties into the frame.
You really have to look at this from a structural perspective...

Yes the frames to twist very easily by themselves. Simply boxing the open frame channels will make a noteable difference in the frame rigidity.

Adding more tubes down the middle will make a lot less difference.

However you should not look at the frame by itself when evaluating stiffness as it is only one part of the overall structure. You must also consider the affect of the body as it is a major structural member here.

First stage stiffening would be to move to solid body mounts, albeit at the expense of a LOT more noise and vibration transfer. Then if you really want to stiffen things up plan on a full cage with extensions to tie into the nose and tail. You can eliminate virtually all flex with a proper triangulated structure.
I think the frame flexs the most at the point where the cowl mounts. At this point the frame goes from being boxed to unboxed, and fenders don't offer much stiffness.
Lift up your vehicle on a four point lift and notice how your fender gaps change. This is part of the reason why I chose to keep the inner fenders as they add alot of structure to the fenders.

Our frames also suffer from torsional rigidity. The frame is pretty wide and does not have any beneficial cross members between from the the engine crossmember and the cross member at the rear wheels.

IMO its old technology and every build has to have a good enough point (inless your making/buying a tube chassis)
For example my DD is a 2008 Cobalt SS, it weighs 3,000 lbs, and is the fastest FWD production car around Nurburgring 8:24. So that being said will my chevelle handle better? no chance! But I did install higher rate springs, 17 inch wheels with good tires, better alignment, and good shocks.
Ill let you know how my gto chassis with the hpi parts works once i get my car back together.

the parts definately added a LOT of strength to the frame and they are designed and built very well. the kit also includes everything and the people from hpi are also very helpful.

mine is off being galvanized as we speak. pretty excited to get it all back and have a car again soon!
Think about this...

When GM built a convertible they needed to deal with frame twist due to a lack of strength from the body. They did this by boxing the frame.

That alone should answer your question. Im sure you know they use this boxed frame in BB cars to handle the torque. They used them in wagons and the EC's due to the fact that they would see additional load and needed additional strength. Its SORTA like the HD chassis available for GM trucks nowdays since the frames on the trucks are much more closely engineered than they were back in the day.

If you want any more real world proof, look at any aftermarket frame available. They ALL use a boxed frame WITH a ladder style bracing system. They arent going to add that weight without a noticeable improvement in tortional rigidity.

Sadly, you arent going to get a super tortionaly stiff chassis without a roll cage. Theres no way to make a flat plane stiff, you c an try but they are only attempts at improving a geometric shape that is floppy. 98% of car owners arent going to add a cage or even a roll bar so you take waht you can get at that point.

Bottom line, all of the trussing and boxing is done cause it does work. Needing torsional tests to make up your mind or methodical pre and post boxing road course tests are probably not going to happen. First one cause (albeit simple on paper) requires strapping a frame to the floor or a frame rack which most guys dont have and as such wont be able to do the test. Second is that most anyone that does the pre post tests also do A WHOLE LOT MORE UPGRADES than just the frame. In that case it surely isnt apples to apples. Then it would be Watermelons to Squash.

If you have the means, do it. It will help where you need it. One thing it may almost definitely do is highlight deficiencies in your suspension parts. Crappy shocks, sway bars ect will magnify their issues with a chassis that isnt acting as an additional spring.

Last words, START WELDING!!!
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I'm with a few of the veteran members who posted towards the end of this thread... To truly stiffen a frame you have no choice but to cage it if you want to yield any significant

Here's what I would do and stop when it's good enough for me. Afterall, we've all got different levels of frame stiffness tolerances (i.e. my butt dyno is not as sensitive as yours :))
1. Box the frame. This probably already gives you say... 35% stiffness improvement (i'm pulling these number out of my butt to prove a point.. bear with me)

2. Solid or Poly body mounts... 20%.. probably your next best bang for buck stiffness mod. If it was me i'd stop here...

2. Tie in the front section of the frame better where it mounts to the front bumper and do the same for the rear crossmember...15% improvement

3. Do those weld on side rails... 5% improvement if any in regards to torsional stiffness. It can certainly add a little bit to front-to-rear compression stiffness but virtually does nothing to the twisting forces. They sure look cool though too bad they probably add some 50-75bs+ of weight too.

4. I also like the weld-on transmission crossmembers. Anything to solidify the side frame rail to the other side will help so much more than #3 imho.

5. Then you can do smaller add on like the bar/link that connects the top/bottom rear suspension links together. 5%?

The point is... if you do all these improvements on the flat plane your improvement will yield significantly diminishing returns the more you try to do.. all you end up doing is adding a bunch of weight. The ideal setup is to triangulate the front left suspension mounting points to the rear right and vice versa. There's no way to really do that unless you do a cage. Not a half cage.. but a full cage.

Mark at SC&C wrote a book on chassis stiffening for the old cars.. I've yet to pick it up but i've heard good things about it.
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For those that don't want a full on cage, wouldn't you be able to add SOME "hoops" in the y-axis other than the traditional cage?

At the front,Especially for those with LT1/LSx or a more traditional turned distributorless, add a hoop that starts at one frame rail just in front of the firewall, goes up vertically at least far enough to clear the transmission bellhousing, or higher to travel horizontally just below the transition from firewall to cowl, then attach to another vertical member attached to the opposite frame rail. Then add the front "strut bars" that traditionally go from a cage's A-pillar bars and attach somewhere on the forward frame rails, except here we attach them to the hoop instead of the A-pillar bars.

Yeah, I know, there's brake components on the "left" side and possibly A/C stuff on the right. Get creative, mount the brake stuff to the hoop instead of the firewall, use a different A/C solution.

Haven't paid close attention of the layout of the rear frame in relation to the body in the rear "firewall" area, but maybe something similar could be built back there. A hoop that basically runs up the sides and along the top of the area beneath the package tray, tying the rear frame rails together, with strut bars of course, kind of like making a smaller "mainhoop" structure behind the rear seat instead of in front of it.

And maybe even build a vertically shorter pair hoops to mount the seats to. Takes some creativity here. And you would definitely get some extra NVH mounting the seats directly to the chassis, might feel like a vibrating massage chair though!

Cut out two sections of the floor board all the way across the floor that correlate to the positions of the seat mounting points. Make them wide enough to match the tubes you'll use to build the "hoops". Make the horizontal sections so that they follow the shape of the floor, up and over the trans. Verticals attach the frame of course. Fab up mounting points for your seats. Mount the seats, then fab up sheetmetal covers to weld the floors over the horizontal tube section, leaving an opening at each seat mounting point, which will be sealed with some sore of grommet.

Okay, the seat one is really ambitious, but on a car that will be blown completely apart and needs work on the floors either way, it might be feasible.

Just food for thought from a "spectator" who has never built anything like what I'm talking about.
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