View Full Version : First generation unibody strengthening

11-19-2007, 11:40 AM
Howdy. I’m trying to figure out the best way to stiffen up the zero-generation unibody on my 1966 Ford Fairlane GT with a 390 FE. It’s mostly for street with some light strip, and my main goal is to make it handle decently. I’ve done pretty well so far, it’s got Global West upper a-arms, Edelbrock tubular tie rod sleeves, 1-1/8” front anti-roll bar and ” rear, QA1 adjustable shocks front and Bilstein Heavy Duty rear, new stock springs, and mix of new poly and rubber new bushings, as well as a shock tower brace and subframe connectors.

I’m not asking about suspension setup stuff, though: what I am trying to do is get information on general unibody strengthening tips that would be applicable not just to me but to others with older nose heavy muscle type cars. I’ve looked through this board as well as other web resources and parts that are available for my specific car. The parts and techniques I’ve found, in order from front to back are listed below. I’ve also listed what I think are the key attributes of each:

Vertical Radiator V brace: reduced front end parallelogramming (from Evolution Motorsports)
Shock tower brace (Mustang Monte Carlo Bar): torsional and beam stiffness via triangulation
Firewall to shock tower braces (Mustang Export Brace): torsional and local beam stiffness by providing a load path between the two individual strut towers and between each strut tower and the firewall. A post here said that bolting an export brace on a classic Mustang brought deflection from 1.062" down to 0.319", a 70% improvement over stock. This clearly seems to be the single best improvement to make based on multiple sources.
Subframes: A post here said that Maximum Motorsports said that testing on Fox body sub-frame connectors revealed that they help improve beam deflection of the frame rails, but have little to no effect on reducing torsional deflection.
Driveshaft loop tied into subframes: some torsional stiffness if done right?
Driveshaft tunnel brace (used on convertibles): reduces overall parallelogramming by closing the bottom of the driveshaft tunnel thereby reinforcing that portion of the floorpan
Vertical sheet metal panel closing open area behind rear seat: improved torsional resistance? A post here stated that the structure to the rear of the driver’s seat is much more stable than the area in front of it.
Seam welding: Probably too pricey for me, but many benefits.
Doublers: Any ideas where in general would be good places? From the drifter community.
Structural Foam: Best places seem to be A-pillars and runners under door sills
David on this board said that he thought a stock 73 Camaro he had tested measured at about 4,000 ft lbs/deg of torsional rigidity. With Herb Adams style braces from firewall to upper A arms bolted to each side torsional rigidity was raised to about 6,000 ft lbs/deg, and that about 10,000 ft lbs/deg is a good goal for a tube chassis race car. So I guess my goal would be somewhere in the 7,000-8,000 ft lbs/deg range, and my question is if I finish doing steps 1 through 7 above will I get close? If not, what kind of additional steps would make sense?

For reference David also noted that the major torsional members in order of sensitivity to torsional loads translated from NASCAR to a unibody are:

The roof structure that runs from the "A" pillars at the windshield to the "B" pillars behind the drivers door.
The strut towers and any reinforcement that runs from the tower to the firewall at the "A" pillar.
The "A" pillars themselves.
The front frame rails from the firewall to the core support.
The rockers and the torque box structure.
The structure at the top of the windshield.
The structure at the bottom of the windshield or cowl area.
The frame rail extension that runs from the firewall to the seat pan structure.

Some of the references I found:












Thanks for any help, Scott

11-19-2007, 12:24 PM
Hi Scott, with all that info above I believe you answered your own question. All good info there, now just put it to use.

On a side note, go over to Lateral-G.net. Theres a guy (Libby) with a nice Fairlane but its a bit over the top.

David Pozzi
11-21-2007, 08:48 PM
I didn't provide the list of torsional rigidity areas in order of importance. It was Bob - SN65

One problem with stiffening is you are adding more weight so you can't go crazy adding too many braces. But I'm a firm believer in beefing up the chassis for better handling on these old cars, they really need help.

Damn True
11-21-2007, 10:30 PM
A new member that uses the search function?

Yes virginia there is a Santa Claus.

Welcome Scott. Looks like you have the data to get started. Plenty of know how around here to help you through the tough bits.

11-23-2007, 05:38 PM
Folks, thanks for the encouragement and for not chewing me up. Over at cc.com I found the following SAE paper on torsional stiffness of a NASCAR chassis:

http://www.ces.clemson.edu/~lonny/pubs/journal/sae983053.pdf (http://www.ces.clemson.edu/%7Elonny/pubs/journal/sae983053.pdf)

It's got some nice real data and a bunch of trials with measured results of each. It looks like the only additional thing I might consider is a pair of diagonal bars going from the front of each subframe connector to the back of the Mustang-style front engine cradle/subframe horns - the front cradle has two bars going back and it looks like a couple feet at a nice angle back to each sub, and the SAE paper found some value thereabouts.

The other thing is how much stress the shock tower to firewall bar puts on the firewall. It looks like ideally it'd be good to x-brace the firewall vertically but that's not practical for me.

It's funny, I used to run Volvo 240s, and also did some chassis foolishness with them. It really helped mid-corner stability. They have extra bars that they added for the African market and so on, one pair from underneath the struts back to under the firewall and another pair of standard-type diagonal braces from the tops of the struts to the firewall. I recall being warned that the top braces could cause indents on the firewall, and they bolted in to pre-drilled holes so there was some engineering there.

Anyway, thanks again, I'll keep on chooglin'!

- Scott

David Pozzi
01-19-2008, 09:31 PM
Thanks for that link! A very interesting read.

01-24-2008, 02:50 AM
boxing the space underneath the pedals to tie in the frame and rocker panels adds alot of torsional rigidity..

plate with a 90 deg bend in it, to "continue" the firewall down to meet a horizontal extension of the floor.. make any sense??

01-24-2008, 03:00 PM
Wow, I was just thinking about starting a new post on some of this. I was going to be more specific though and tie into my 79TA in particular. I'll come back and read this as I have time.

One quick question though. XV and Bob(SN65) have inspired me to attempt to hide this bracing as much as possible. Can that be done on a second gen or do they need more help than that body can provide?

02-13-2008, 07:12 PM
Me and a friend a few years back took his 66 mustang, tigged the WHOLE car together, made custom subframe connectors welded into the floor/subframe.
Then we built a custom Xframe/brace that fit under the hood that tied the shock towers the fenders and such all together.
WE did some minor redesign on the front and added in a custom rack.
The trans crossmember helped tie it in and we designed a 4 link sort of like the street challenge stuff ART does. The car can be lifted on one corner and has very little flex.
WE modded it to take a 5.4 last year and it now rides on ShockWaves all the way around.
Surprizing you can stiffen it up by LOTS of welding, plating in certain areas and then installing the cage/connectors.
Good Luck

03-08-2008, 06:27 PM
... Self expanding foam into the rail boxes that make up the unitized sub frame attached to the floor pan.

10-18-2008, 11:08 PM
better late than never... chassis stiffening kit (https://www.mustangsplus.com/tech/chassis/index.html) for '65-66 Mustang.

04-14-2009, 07:34 AM
im new to the site, I guess its okay to post after a 7 month delay and maybe somebody will respond.

what is stich welding the unibody, is that just tack welding the torque boxes?

High Plains Mopars
04-14-2009, 10:41 AM
Stitch welding the unibody is welding up every seam in the sheet pieces that make up the structural parts ofo the unibody.

From the factory these cars were all put together using spot welds. It is like the buttons up the front of a shirt. Stitch welding all the seams creates a more rigid structure that is more solidly tied together, like replacing the buttons on the shirt with a zipper.

04-16-2009, 06:41 AM
Awesome thank you