Seam welding the chassis

[JPmotorsports]

Yeah I think you'd be better off just stitching rather than a full weld. You'd end up with less cracking/warping and get more cycles out of the metal. I could see fully welding the strut tops if your going to tie the cage into them---sometimes we'll create a cap for the tops and fully weld them.

[FE3-323]

care to make me some strut tower caps for the rear
How about a main hoop in chromemoly?

[MD323]

Jim, do you recommend staying away from fully welding the seams. I.E.> going back over the skipped portions after cool down?

if you do the full seams everywhere then the seams wont allow any flex and the base metal will flex and tear.

[JPmotorsports]

care to make me some strut tower caps for the rear
How about a main hoop in chromemoly?

I can if you like---I don't do alot of cromoly in touring cars because the unibodies are mild steel and then tend to crack---but if you were to bolt it in it would work fine. I believe we test fit a hoop in the 323 and it was the same (except for maybe the kickers).

[ajax]

There really isn't any benefit from using chrome moly for a roll cage.

There seems to be a lot of people promoting chassis flex. Chassis flex is bad, period. Race car designers sometimes do seemingly goofy things because they are actually trying to make the car as stiff as possible while as light as possible. More metal = stiffer car = heavier car; so they will put more metal where they need it and less where they don't.

As long as the welds aren't brittle there is nothing wrong with going crazy with seam welding, it's your time and your money. The biggest benefit that I've seen (coming from one of the rally guys) is that the cars hold together better. My friend with the BMW has been having his strut towers rip out because he popped all of the spot welds, same with the motor mounts.

Are you planning on getting into rallying? For serious racing I would definitely recommend seam welding since you start to shake stuff loose when you're stressing a car that hard.

[JPmotorsports]

Also people think that cromoly is lighter because of the alloy blend, and alot of the sanctioning bodies allow a thinner wall because the cromoly has less malaibility (malibility?---it doesn't bend as much)/a bit stronger in comp./tensile/shear. Truth is it's not lighter everytime---it's so close to mild steel/DOM that it depends on the stick...I've weighed 1 1/2 x .120 DOM against the same piece in cromoly that was 2.5" shorter and the cromoly weighed 1.5lbs more...

There really isn't any benefit from using chrome moly for a roll cage.

There seems to be a lot of people promoting chassis flex. Chassis flex is bad, period. Race car designers sometimes do seemingly goofy things because they are actually trying to make the car as stiff as possible while as light as possible. More metal = stiffer car = heavier car; so they will put more metal where they need it and less where they don't.

As long as the welds aren't brittle there is nothing wrong with going crazy with seam welding, it's your time and your money. The biggest benefit that I've seen (coming from one of the rally guys) is that the cars hold together better. My friend with the BMW has been having his strut towers rip out because he popped all of the spot welds, same with the motor mounts.

Are you planning on getting into rallying? For serious racing I would definitely recommend seam welding since you start to shake stuff loose when you're stressing a car that hard.

[tehstocker99]

malleability

good info here!

[ajax]

malleability

good info here!

Yes. Chrome moly is going to be harder to form because of the higher yeild strength. With a nice mandrel bend you essentially stretch the tube on the outside of the bend and compress it on the inside. I've seen a cross section of a bent tube and the difference in thickness is very noticeable.

If someone is still willing to spend their money on "feel good" assurances, spend a little time and the same money on getting yourself some stringently controled DOM steel. You won't be wasting your money on exotic alloys that don't help you at all. I'm sure ASTM has a premium grade mild steel spec. Ask for that from a steel supplier. The only down side is that they might make you buy a whole bunch of it.