YODAONE

Several.posts on ways to improve torsional rigidity...such as tying the shock tower braces, etc.

While the overal body integrity of 1999 LS400 is excellent, have noticed several body braces and fasteners employed that leave room for improvement.

The front and rear bumpers (not bumper covers) are cored metal rectangular shaped and clamped to chassis by 3 fasteners on each side.

The bolts are recessed into the bumper, so they only clamp to the inner plate on a single plane...this is not optimum.

Aside from clamping the bumper to the frame, these fasteners do not aid in torsional rigidity.

Am investigating ways to improve torsional rigidity through modification of the bumpers...

Anyone know if there is adequate space behind the front, and, or rear bumper to triangulate it (two metal plates) between frame rail mounting points?

Also contemplating filling the cores of the front and rear metal bumpers with ITW Foamseal to increase its rigidity..it is a two part professional strength polymer injected into frame rails to increase stiffness. (This is NOT the same as spray insulating foam you buy at Home Depot!) Front bumper has hollow cores.
Is there adequate room behind it to triagulate?


Holes in front bumper are recessed, so only flat plate on bottom and not both planes are clamped by bolts to body...not ideal.
Design of rear bumper suggests several ways to improve torsional rigidity...

YODAONE

Located the following article on a Nissan forum where the author obtained postive results inkecting polyurethane foam into cavities of structural components;

http://www.texasnissans.com/tx/forums/showthread.php?p=106308


Structure Foam Injection - Tales Of Magic Foam Revisited.

Years ago when I looked into chassis stiffening, Mike Kojima from Sport Compact Car was already doing it for their 300ZX magazine project. I was so impressed with the well written article I figured I would just throw it up on here for those that never got the chance to glance through it.

Ūn any high-performance car, it is impossible to make the chassis too stiff. The stiffer the chassis, the higher its natural frequency, making the energy imparted to it by bumps less likely to excite the body's structure. A stiffer chassis enables the use of stiffer springs and shocks without hurting the ride. This is because a stiff, non-flexing chassis transfers more force into the suspension where it can be dissipated by the springs and shocks instead of transferring the force to the occupants. A stiff chassis is also more responsive to roll rate tuning for balancing understeer and oversteer. This is one of the reasons why automotive engineers are continually investigating ways to stiffen chassis without adding weight.

In a final bit of reengineering to stiffen the body, we injected the chassis with catalyzed rigid structural polyurethane foam. Structural foam, in the 2 lb per cubic foot density that we used, can stiffen chassis members up to 40 percent.

Higher densities of foam can increase stiffness by up to 300 percent. Since we cannot retool custom parts to redo the Z's body, we figured that this would be an excellent, low-cost way of greatly increasing chassis stiffness. Injecting foam is not a new technique for chassis stiffening. The Infiniti Q45 uses this sort of foam in some of its chassis members to increase stiffness, as do a few other premium cars. In fact, the foam we chose is the foam recommended to repair damaged Q45s.

He also went on to mention Ÿe were amazed at how this simple procedure improved the performance of the car. The chassis now almost feels like it has a roll cage. A sloped driveway can be driven up sideways with nary a creak. Even though the Z already has a pretty tight chassis, it feels more solid. The ride has improved and road noise has been reduced noticeably. We bet that the car will be even more responsive to chassis tuning measures in the future. If you are a slalom racer, a road racer, have a lowered car or even just want a smoother ride; foaming is a worthy, easy-to-do modification.Çô
As far as the process and products available some things have changed since this articles better days. ITW Foamseal is no more but a company called FOMO has taken their place. FOMO has also made the 2 part foam kits available via Grainger, so itÃÔ readily available to the public.


The part that I have used is #2TE59 and is just over $500 but this is enough foam to do 2 cars. The smaller cheaper kit is actually a different strength foam, so your only option is this stuff but remember two things. Take out everything, I mean everything interior wise that you donÃÕ want to get foam on. Prep and cover all your holes as this is expanding foam and will work itÃÔ way into every small wedge of an enclosure. I plan to do a write-up on this later so keep an eye out.

Here is a pic from my Z32 foam injection experience with Project LOWFATZ. Notice the layout of the seam weld lines and also notice the normally empty section now filled with structure foam to aid in rigidity.

Losiracer2

Aren't those meant to crumple in the event of an impact or collision? I don't recommend filling those in case you need them for their intended purpose.

If you fill them with a high density polymer that is meant to increase rigidity, wouldn't the impact then propagate throughout other structures of the car, causing more damage?

YODAONE

You raise an interesting point...the short answer is No.
Immediately in front of the cored metal.bumper (and behind painted bumper outer cover) is sandwiched a high density foam insert.

Aside from increasing the tortional rigidity of the cored metal bumpers (twist lengthwise) filling the open core with a compressible material will.actually improve crash worthiness.

Triangulaing the backside (side facing engine compartment or trunk) does not affect the outer crumple area.

No different than if you had two hollowed out 2 X 4's that were sistered together and decided to triangulate one side to increase resistance to twisting lengthwise (torsional).the wood will compress and break just the same from impact imparted on the flat side.

As I see it, I am adding not one, but two crumple zones.

After looking at the rear bumper and how thin the material, frankly I am horrified.

Have seen several early LS400'S in yards where the rear bumper was no longer held in place by OEM mounting bolts due to separation as a result of breakaway from corrosion on metal bumper where bolt clamps to chassis. (!)

The OEM didn't do this because of cost, and contemporary materials were not available.

The two part material I propose to use is difficult to work with and it cures in 30 -60 seconds.

Auto manufacturers have been using high density structural foam as a way to increase stiffness while reporting increases of 30%, , so I am not reinventing the wheel.here, but targeting a deficiency for improvement.