Real world benifits of frame boxing and stiffening

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

Paul-ish said:

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.
http://www.hpicustoms.com/index.html

Or you could just come up with your own...Plenty of threads in this forum of people's home designs.

Click to expand...

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!

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.

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!!!

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.

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.