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Prioritizing Seam Welds


182kartracer

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I'm getting to the point in my 2002 race car conversion where i would like to seam weld the chassis before i add in the cage. I was wondering if i could get some advice in which seams are the most important/provide the most benefit. I would like to be as efficient as possible in my seams to save myself time while providing the most benefit. Any help would be appreciated!

 

P.S. Diagrams are very beneficial!

Go Boilermakers!

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The important parts are the junction of the front frame rails and inner fenders, and firewall to inner fenders. It's also advisable to run some square tube between the upper footwell portion of the firewall down to the frame rails, right at the entrance to the no-mans-land pocket formed where the frame rails dive away downward from the firewall (no-mans-land is the place where all of your 10 and 12mm sockets disappear into when liberated). If you're keeping a full nose panel/core support on the car then running the vertical seam between core support and inner fenders is also good.

 

There's not much amidships or in the rear that your cage won't already be doing. Gussets/reinforcements at the top of the rear subframe mount kingpins and stabilizer link locations in the floorpan probably aren't a bad idea though.

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Before you do any of that, make sure it's not prohibited by the class you want to run.

 

Seam welding's all well and good, but it would suck, in 3 or 4 years, to finally make

the podium only to discover that your car is not class legal, and you have to find

another shell.

Gussets and adding material to the shell will put you in an unlimited class, against VERY fast cars.

 

If seam welding is legal, there aren't too many places where the 2002 is overstressed.

I agree with Dross that the front, from the tops of the struts to the rocker panels, and that

door aperature at the a- pillar are worked pretty hard.

 

The question that you SHOULD ask is, how much can you do with your cage?  Most classes

above (and maybe now including) IT allow an attached front inner fender contact point, AND allow a pad up to 

100 square inches.  THIS is your winner.  Make that contact point as high as you can on 

the inner fender, make it attach right into the fold where the inner panel heads back, and then

do everything allowed in the rules to tie that cage bar to it, including a triangulating brace in the cage.

Then do the same thing at the floor.  Boxing is almost universally allowed- do it!

THEN use your door bar to make the side of the cage as rigid as you can.

-

You've just taken most of the vertical, and some of the lateral, loads off of the shell and put them into the

(infinitely stiffer) cage.  Legally.  100% legally.  Every car has advantages for racing- BMW's stout

front strut/ inner fender construction is one big advantage it has, as it ties nicely into how the cage rules are written.

 

The rear of the car is less stressed (less weight) but try to get the main hoop tied into the rocker very hard.

(boxing, again)  You can't catch the rear subframe mount- the geometry doesn't work- but you CAN catch

the rear wheelhouse, and that's good for taking suspension loads into the cage.

 

t

sometimes knows what he's talking about.

  • Like 1

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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20 minutes ago, TobyB said:

The question that you SHOULD ask is, how much can you do with your cage?  Most classes

above (and maybe now including) IT allow an attached front inner fender contact point, AND allow a pad up to 

100 square inches.  THIS is your winner.  Make that contact point as high as you can on 

the inner fender, make it attach right into the fold where the inner panel heads back, and then

do everything allowed in the rules to tie that cage bar to it, including a triangulating brace in the cage.

Then do the same thing at the floor.  Boxing is almost universally allowed- do it!

THEN use your door bar to make the side of the cage as rigid as you can.

 

I was going to get the cage from https://rollcagecomponents.com/bmw-2002-roll-cage-kit/ in 1.75 x 0.90 It will some with the X style door bars, Triangle foot bar, Rear down Diagonal Kit, and i will be adding tie ins to the front shock towers from the cage.

 

The class im racing in does not have any prohibitions on seam welding. Gridlife Touring Cup

"10) Chassis
a) No major modifications are allowed to the chassis, frame, unibody, floor, firewall, etc. unless
clearancing is required (must not benefit performance in any way), or strengthen/bracing is
needed. Non essential body/unibody items and trim may be removed for the purposes of
weight reduction. Major unibody (or frame for non unibody cars) structural items may not be
compromised or lightened. Material may be added to reinforce problem areas or known weak
areas on chassis, or repair crash damage, but full reconfiguration/”tube frame conversion” to
structural areas of unibody cars is not permitted.
b) Radiator supports may be replaced with fabricated items for purposes of fitment or repair to
chassis area, but general location of radiator must not be altered from factory.
c) Chassis suspension locating points may not be altered or modified. Reinforcement of pickup
points for longevity purposes is allowed, as is seam welding, but location shall not be changed.
In the case of live/solid axle RWD vehicles, suspension pickup points may be added to facilitate
converting to alternate axle locating method style (watts link , 4 link, panhard bar, etc) and
alternate spring/shock mounts may be used.

Go Boilermakers!

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If the cage construction allows unlimited points, then, yes,

top of the strut inner fender (you'll find the thick inner fender)

use that x- brace, and put an upper bar at its top.

 

You'll be good.

 

I have one prefab cage, and one 'made to fit' cage, locally, by Godspeed (gratuitous plug for Robb- https://www.facebook.com/pages/Godspeed-Fabrication/367589889969262 )

 

The 'cost' up front of the custom cage was more than twice the prefab- but over the construction of 

the car, it was a lot less than that (Robb put it in, so that saved days) and it fits SO MUCH BETTER

that it's saved a lot of figurative and literal headaches since.

And since it picks up the car at the stress points much better, it makes the car a lot stiffer.

 

I learned me lesson- custom for me, from here on out.

 

But that's me.

 

t

 

 

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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