Sorry guys I'll try this again. It would not post!
My question was how could a guy make his FB a more solid car. It is hard to explain unless you have had the fortune to drive the cars I have. Audi, Porsche, Jag, Lexus
and a couple of others. My favorite though is my Brothers 944. If anyone has had the pleasure to drive a good one you know what I mean, it is such a solid car. You just know your driving quality, It's tight and go's thud when going over railroad tracks. What could a guy do to make a 7 feel tight and solid? Weight is not a consideration it does not matter if we added some. I have had 4 first gens and driven one when new so I know how good they can be but would like to take it to the next level.

 

Dynomating the interier would reduce the sheet metal sound.

 

I like the feel of the car.

What do you mean "goes thud when going over railroad tracks?" Unless it's just mine, the suspension isn't set up to be very forgiving on bumps. Railroad tracks are an extreme example I think.

Guess what "thud thud...thud thud...thud thud" is?

It's me driving in a turn lane, riding over the turn arrow painted on the road.

 

That's funny, I understand what your saying. I mean that there are no serious rattles or just an overall loose feeling. Like I said if you have driven a 944 you would know what I mean. It is hard to explain.

 

My '88 MX-6 drives very solidly among the cars I've driven. No I haven't driven a 944...among many cars I probably will never drive.

 

What year is the 944?

 

grrrrrrr damn double posts.


And how many miles on the 944?
(compared to your 7)

 

Rack and pinion steering kit, Racing beat springs, tokiko hp blues up front and kyb gas adjusts in the rear, or if you wanna spend more dollars, coil overs. 14 inch GSL SE rims with good z rated tires. Thatll make it bump over railroad tracks, handle awesome, and have perfect steering feedback. As far as speed, that a new thread for another day.

 

It is a 1987 944 with 100,000 miles. I am currently 7less.

 

Adding a front strut brace should help a lot also. I know what your saying about 944's, they handle sweet. Couple more weeks until mud season is over!

 

I know an '87 with 100k miles on it will be significantly "tighter" than my '81 with 170k miles on it :-)
That's just the nature of driving a car over time.

But I like the suspension & R&P suggestion above...

 

Seam weld the chassis, and use sound deadening. And you can foam fill the chassis too.

 

Im using sound deadening and putting in a 4 pt roll bar.

 

Full cage.

 

I was considering seam welding my current project, but was advised not to, because the welds would probably crack(higher stress areas) leaving it worse than before. And it wasn't worth the trouble.
I've also been told that brazing them with brass is the correct way to do it so they give a little and don't crack, but that seams kinda pointless.
Any comments/suggestions?

Foam fill? Why not just cram wet sponges everywhere you can find? I hate taking that stuff out of cars.

 

Sometime the feeling of solid...having spent a little time in jags and porsche's myself..comes from the feeling like your glued to the road. Downpush. I have found that the RX7 has a tendency to be a bit flighty in the rear.

A tail can make it seem more solid to the road and i believe is even dealer recommended.
I feel that solidness, like rattles and such are less common then the in the porsche.

 

Suspension work and wider/bigger tires make a huge difference in how solid the car feels on the road.

 

Thats why you stitch weld it. Short like 1-2 inch welds with approx 1-2 inch gaps inbetween. This way if a weld develops a crack, it stops at the end of the weld and doesnt progress. This is what rally guys do, cant imagine street driving being tougher on a chassis than what those guys do.

No, theres a special foam used in high end cars to stiffen the chassis, reduce noise, and deaden vibrations. They say it makes a unibody car like ours as stiff as if it had a full rollcage.

 

There are a few basic properties of your car that will affect the way it feels regardless of the suspension, tires, and sound deadening you put in the car.

The first is torsion. Think of it as you being a giant and grabbing your car -- by the front with your left hand and by the rear with your right. Now you try to twist it like you're wringing out a towel. How hard it is to twist is the static torsional rigidity -- the higher the better.

The second is bending. This time, you're trying to bend the car in the middle until your hands touch. This maneuver is called static bending rigidity (or beam). Once again higher is better.

I don't know the numbers, but I would suspect the Porsche 944 is significantly stiffer than an FB in both of these measures. This stiffness is felt as a "solid" feeling to the car. When you hit a bump, it goes "thud" and that's it -- no aftershocks. When you drive one wheel on a curb you can still open both doors without any problem. The car feels like it was carved out of one block of steel -- it feels, well, "solid"!

If you want to increase the solidity of your FB, here are the things you can do, in order of effectiveness.

1. Add a well-designed roll cage. This can double the torsional stiffness of the car. Not for everybody, but undeniably effective for any car. Note: A 4-point roll bar won't do nearly as much as a full cage, and the full cage must extend to the front strut towers and be well executed to get full effect.

2. Stuctural foam. This stuff isn't soft. If I hit you on the head with a chunk of it, you wouldn't laugh. It is a high-density concoction that "cooks off" in the high bake paint ovens and makes the car stiffer. There are also low-temp versions available that are epoxy-based. The downsides to this are weight, and that you must know where to put it -- not easy without some finite element (FEA) analysis. BTW -- this stuff is effective in both stiffening the body (for torsion and bending) and for improving crash performance.

3. Seam welding. This will add moderately to the stiffness of the car. I believe more is more when it comes to welding car bodies. If you're gonna do it, go crazy. Any place metal parts join, weld them together. The trick is making good welds that don't burn through the thin sheetmetal. This is a job for a TIG welder in experienced hands.

4. Dynomat, Undercoating, Shoddy, etc. These are all acoustic bandaids. They come in two basic types -- those that block noise transmission by increasing the mass of the barrier (i.e. that tar-like stuff, called mastic that OEMs apply to floorpans) -- and those that absorb noise so it won't continue to bounce around inside the vehicle (cotton shoddy that is behind carpets and trim pieces). I call these bandaids because they'll make your car quieter, but won't help the wet noodle aspect that I think you are referring to.

 

What about strut tower brace or good solid polyurethane bushings. Good springs, shock/struts, sway bars, good rubber on the ground, preferably 205/215-50-15's. Aero dynamics, Iam sure their is more?

 

I have a strut tower brace on my car. Can't honestly say I can feel the difference. Some OEMs put them on cars, so they have some merit, but the effect is secondary, at best. Think of it as putting perfume on a pig -- it'll smell a little better, but it still stinks.

As for the other stuff, read the first sentence of my other post.

 

Does anyone know if your local body shop can get that foam, or is it a special order hard to find thing? Then like the previous post stated how do you know where to put it?

 

We use a foam simalar to this to hold tellophone poles insoft ground or in place were there was not enough dirt to fill the hole again it is unbelievable how hard this suff is. W e put a short piece of pole in a 55gal drum and used the foam in the drum. When it dried we tried pulling it apart it just tore the barrel apart, got like concrete it took the guys at work an hour with a masonry saw to get the foam off the pole.

 

You can get it from a company on the web. ITW foamseal is the stuff. Do a intarweb search. They are the only place I know of that makes it. Dont use the expanding foam from the home improvement places. Its not rigid enough, and wont dry cause it wont be exposed to the air. Youll just have a goopy mess.

 

As far as where to put the stuff -- here are my guesses, based on FEA motion models from other cars (I've never seen one for an RX-7 FB). Starting from the front of the car and moving rearward:

Upper Load Path Beam Roots -- where they come into the cowl sides (up at the dash board) usually sees a lot of vertical and lateral bending.

Front rail roots -- where the rails meet the dash panel and kick downward. This area where the rail section gets smaller usually sees a lot of vertical bending.

Cowl side to sill joint -- where the lower door hinge bolts, down through the front portion of the sill or "rocker" usually sees a lot of bending in the 'Y' plane.

Torque box -- that hat section that runs underneath the car, beneath where you normally put your feet, from the rails out to the sills. As the name implies, this part usually sees a lot of rotational force, like a driveshaft would.

The sills -- to save weight, I wouldn't fill the whole thing, but use enough of the stuff to close off the section every 1 1/2 feet or so. They see both Y-plane bending and torsional forces.

The 'yoke' that runs cross-car above the floorpan, just behind the front seats. Fill the outboard areas near the sill and the zone above the rear rails. This thing ties the sills to the rear rails and will see similar forces to the Torque boxes. (These really are the rear torque boxes on an FB)

Rear Rails -- where they transition from underneath the front floorpan to up the "waterfall". These will see 'Y'-plane bending.

The concept is simple -- you want to stiffen up the skeleton. The most important parts of the skeleton are the underbody points between the suspension force input points. For example -- the car's stiffness out at the front bumper beam isn't as important as the stiffness where the rails meet the dash panel.

Car underbodies (sedans, wagons, convertibles, and coupes) are basically three chunks joined together:

1. The engine box, which includes the dash panel and everything in front of it (front rails, upper load path beams, radiator surround, cowl/plenum).

2. The front floor, which includes the front floorpan, sills, etc.

3. The rear floor, which includes the rear floorpan, rear rails, etc.

Where these three main chunks join is where the car is normally the weakest. These are therefore, the points that need the most attention.