kariayam

Hi all.

I own a FD3S and the chassis seemes to be too old now (year 1992 and 19 years old of age..). I am thinking to refresh the aging chassis and reduce as much flex. So I am planning to do spot welds on the chassis for refreshing the old chassis.

My target of spot welds :

1- just to have 'new' chassis feel and solid handling on normal road since this is on-the-road car.

2- 70% will be driven agrresively on normal uneven poor quality roads and 30% track day.

3-to eliminate body flex. Can be easily seen when i jack up the car at one corner and creaking sound is everywhere..


I dont know if i have to weld the whole body or only at some critical point of the body to get the purpose as i mentioned above. I also dont know where is the critical part of the body to do the spot welds. As I know, the main area of spot weld are:

1)door jamb area
2)front windshield area
3)Rear hatchback opening and spare tyre well
4)Firewall
5)Engine bay,
6)suspension tower Front and rear..

How about:
7)transmisson tunnel area?
8)Floor area?

Really need opinion from you guys on the sufficient weld areas to meet my target/purposes as stated above.



Some of my friends suggested spot weld the whole unibody. But I am afraid it will be too stiff and hard for bumpy roads and sacrifice my traction or handling and crack the body over days.

( As i know, the chassis still needs some very little flex for good traction and handling). Please correct me if i am wrong...because i never involved in a professional motorsport, I just read in the internet..

adam c

iTrader: (2)

That sounds like a bad idea to me. You would be far better off by getting yourself a good suspension upgrade that suits your needs.

dgeesaman

iTrader: (7)

Steel body panels and welds do not lose stiffness over time. If anything happens, they crack and break. The only reason why chassis welding would be important is if the factory spot welds are fatiguing through and have broken. But I've not heard about cars being stripped down and finding cracked welds. If you want to go into this type of thing I would begin with inspection for cracked welds first before you take a welder to it.

I agree with Adam, suspension bushings, pillowballs, engine mounts, springs and dampers do lose performance over time and can be improved substantially with replacement. Drivetrain braces have been shown to help to support the diff as well.

Wompa164

iTrader: (4)

It's not a bad idea, just kind of extreme. Someone watching too much Wangan Midnight?

The obvious answer is invest in your suspension and maybe a cage first.

Rxmfn7

iTrader: (4)

Invest in a good quality roll bar instead. There was a night and day difference after installing my raceshop bar.

patman

iTrader: (3)

I'm with them^

A cage will add more stiffness than spot welding ever could, it is easier to install a cage than spot weld, and if you also get good seats and harnesses and make sure the cage is well designed to give driver headroom, the car will be much safer too.

ptrhahn

iTrader: (9)

Yup,
Rattling/creaking is likely accessory stuff, or bushing, not the unibody itself. A good roll bar is probably your first/best bet, perhaps along with a brace for the front that ties to the firewall if you're really concerned.

GodSquadMandrake

I am on the opposite side of the fence. I agree that a chassis loosens up over time. Anyway I don't want to debate about that so I won't go into it, op asked some questions about stiffening the chassis.

Here is a great thread by a friend of mine in Alaska who is working on a Rabbit:
http://www.akeuro.com/forum/index.php?topic=5244.15

You will notice that he put a lot of attention into the pinch weld area. You can stitch, spot, or seam weld it. Just make sure that you alternate sides. If you seam weld an entire side at once, you run the risk of warping the chassis. This is welding 101 for large assemblies.

Front end:
You have the basic idea already. In addition you can weld in a small piece between the firewall and the frame horns to triangulate them. This area is a crumple zone and is weak for a very specific safety reason. Normally this kind of modification is done in addition to a roll cage. When you strengthen this area, you are actually decreasing your safety in a frontal impact unless the passenger compartment is also strengthened. So use some wisdom here. But you could put a small piece to strengthen it a little bit. Also there are the fender braces which go on the outside. Here's a picture of the basic idea:


You could argue the fender braces aren't as important on the FD because it has double wishbone suspension, I don't know. That's up to you. But the basic concept is that the frame horns are weak because they don't have much support. After the firewall all you have is the bumper bar, radiator support, and the subframe. The subframe has larger holes than the size of the bolts as you know if you've ever installed one. These are a weakness. Here is an explanation of that concept:
http://www.youtube.com/watch?v=zWyUD...layer_embedded
Anyway that is why I believe in strengthening the front frame horns. The strut tower brace addresses the issue from the top, but the bottom is more important.

Bottom to top:
Ichishima Tatsuru, President of Spoon Motorports (they make the rigid subframe collars from the video above) has done a couple lectures on this on the Japanese TV show Best Motoring. He goes in depth explaining why chassis stiffness is more important on the bottom, starting with a base, rather than focusing on tower bars and stiffness on top. Basically his theory is that stability is created on the bottom. He talks about examples where they couldn't quite make a car stable at certain spring rates, but after increasing the chassis stiffness in the bottom area the car became more stable and they were actually able to run stiffer springs with more stability. He talks about OE Honda engineering and how they work in layers, and the crossbone chassis. During the interview he shows a Honda Fit chassis fresh out of the Honda factory without any undercoatings applied. So you can easily see the technology they used to make the chassis stiffer.

Noise:
You've got this one backwards. Stiffer chassis's are quieter. The unibody is essentially a giant drum. When you strike it in one area, the sound is transmitted throughout the entire structure and the panels like the firewall and floors are like a speaker. When you stiffen the chassis and decrease flex, the suspension absorbs these impacts instead of the chassis flexing and transmitting the energy as sound.

On that topic, there is a new technique that Yamaha pioneered in 2004 with their Yamaha Performance Dampers. You could actually call them Lateral Harmonic Dampers. This isn't very popular yet, even in Japan. On the aftermarket side a lot of van owners are buying them to make the ride quieter. On the OE side, luxury car manufacturers like Lexus are using them. They are also used on the Nismo 370z because they do offer performance benefits too.
Here is the Yamaha news release on the product:
http://www.yamaha-motor.co.jp/profil.../pdf/ts_01.pdf
The aftermarket is handled by a company called *** and the product is called the *** body damper. They don't have an RX7 specific application and are very expensive, but you can understand the concept and maybe apply it anyway. Here's a review from a Nasioc member:
http://forums.nasioc.com/forums/show....php?t=1215727

He uses them as a substitute for his Cusco braces, these are actually meant to be used in addition to regular braces. Here's a pictorial of the concept that I saw shown by Tien at a trade fair:





The first is a model of your car without a strut brace. You're supposed to hit it with a hammer. It rings like a tuning fork of course.
The second shows what your car is like with the strut tower brace. When you hit it with the hammer, it still rings but not as loud.
The third one is dead silent. It completely eliminates all noise. It's like you're hitting air with the hammer. I was amazed to say the least.

This product isn't doing anything for noise besides road noise. If you have differential whine, this isn't going to reduce it.

Foam:
Also there are 2 part structural foams that have been available for a long time. You pour them into the frame rails from the inside and it hardens, stiffening the members that were hollow before. It's been tested, and proved to work.

You'll notice that some panels, specifically in the engine bay, have an adhesive smeared over them. The idea is that without welding, you can increase the stiffness by simply putting an adhesive between where the fenders meet the unibody at the top. Or where the strut tower is stitched on. This isn't done by accident, there is a reason for it. So if you take this stuff off, put it back on.


Chassis tuning is a fine art and it is very mis-understood. A lot of people have different ideas and they are hard to test because most of the time when someone does this sort of work, they do other modifications that make a before/after test apples and oranges comparison. So take everything you learn with a grain of salt. I'm not an expert, I just try to learn from others.

Also a rollcage would obviously be a great idea, but you didn't ask about that so I just assumed this is not an option.

turbojeff

iTrader: (30)

Didn't read all the thread but I think that most of the looseness felt is actually bushings and trim. The chassis is pretty stiff. Much different than a 70s designed Econbox.

IWINULUZ

iTrader: (10)

so many people have tried to convince me on why stitch welding has a positive effect I still dont believe in it (and by believe i mean feel a physical difference). I have built numerous track and street cars and driven stitch welded cars and non stitch welded cars, i think its a waste of time and money. Unless you want that **LQQK**

dimondjack

I think that there isn't a particular "right" answer here. The bushing and stuff probably squeak louder, but this answer focuses on determining where you need chassis stiffness.

Mandrake is correct that chassis stiffness isn't well understood in the aftermarket, but it is well understood at the OEMs and in forms of racing that are technology based (F1, GP2, Indy). The comment that upper or lower stiffness is "worth" more doesn't entirely fly, as it entirely depends on where the stiffness is being lost. Most production cars are designed to have a good portion of torsional stiffness (the twist you see when you jack up the car) go through the roof. However, many cars are designed to have the stiffness transmitted through the floor (all convertibles, Ford GT, Lotus Elise), which you can see by massive center tunnels and rocker panels, as well as stiffening braces in the floor.

Chassis stiffness is very important for handling, but only to a point. You essentially want all of your chassis control devices (springs, dampers, roll bars) to be the dominant movement, not the chassis. This allows you to change the properties of the springs, dampers, and roll bars to change the chassis handling. The opposite is a go-kart where all deflection is frame deflection. The only way to change suspension reponse is to actually add or remove frame tubes, or change seat points. This works when you only need to soak up miniscule bumps, but loses effectiveness when you need to soak up more energy.

To really understand where and how you want to make the rx7 stiffer, you need to do a twist test. You apply a torque to the car using jacks or something and then measure the angular deflection along the body. You will end up with a graph of angular deflection vs. position on the car, so you know where the most stiffness is lost.

Ideally you would have solid springs for this, but you can do it without it. If anyone is interested in doing a test I can walk them through the process, and we could post the numbers here. We would need race scales, a jack or two, and 6-10 dial indicators.

Once the location of stiffness loss is know, a particular solution can be engineered. This may be seam welding, a roll cage, or stiffeners of some sort. You want to focus your energy in the area of highest stiffness loss, because if you lose 0.25 deg/100 ft-lbs in the front section of the car, but 2.0 deg/100 ft-lbs in the center, the most you can gain by adding torsional stiffness in the front of the car is the 0.25 deg/100 ft-lbs, which is not much compared to the total stiffness loss.

Anyway, that may not be the solution to the kariayam's problem, but it is a little look in to how race team test and then design out chassis stiffness.

kariayam

Dimondjack, thanks for your respond. Appreciate that if you would share us the step by step guide to do the chassis torsional test, so we can compare and collect data for our fd. And we will be clear on area of improvement on our fd. Thanks

j9fd3s

iTrader: (3)

the chassis DOES wear with time, although you actually need to be racing with it, like you need to be putting high suspension loads into the chassis for a long time before anything detectable happens. the FD too is actually designed to see high loads like this, so it will do better than a honda which isn't designed to see any loads at all.

we've been racing an integra for 5 years, and with each increase in grip, we have started to wear different parts of the body, and it actually has popped a few spot welds. on the street this would not be a problem...

that noise thing is interesting, its true you quiet a drum by damping it....

the seam sealer on an FD though is just seam sealer, all it does is keep water out, its not even really an adhesive. not that you couldn't use an adhesive, lotus does among others.

GodSquadMandrake

I guess these guys aren't just cartoons, apparently they actually exist:
http://www.fujimura-auto.co.jp/body_...l/menu_01.html

thewird

iTrader: (8)

If you want your car to feel like new again and better, do a full bushing replacement to polyurethane like the Super Pro ones, upgrade the sway bars, and optionally replace/upgrade your suspension. The fender braces do make a difference on the track with slicks on but only after you've addressed the more important points. Having said that, those welds *might* make a difference but you need to address all other soft points which are significantly more important first.

Also, RE-Amemiya makes rigid collars.

thewird

theorie

iTrader: (31)

nice. i'd like to see that in person.

kariayam

thanks to all of you guys for the input....

kariayam

If i am to improve the rigidity of the unibody, which area on the unibody should i focus for the spot welds? Probably The weak and stress prone area on a fd?
May be there's only few/certain area that i should pay attention for the spot weld...as you know,i am not aiming the rigidity of an extreme time attack machines out there..only to be enough to overcome the chassis 'wear' and able to take the g force abuse in the next 10 years.

Please advice. Thanks.....

j9fd3s

iTrader: (3)

i'm not sure about the FD, with the FD mazda took the FC shell, and put it into the computer and fixed the problems. the FD shell is actually very good as is. i'd think poor accident repair would be the biggest problem

if you can find it, the FD body shop book is actually very good about showing what, where and why the body goes together, down to the spot weld placement. you might try www.foxed.ca

i've heard mixed things about the urethane foams, but mazda uses it on the Rx8 subframes, so if its good enough for them, it should be ok, as long as you can get all the oil out