I'm building my car up to run roadcourse events primarily at this point, but I want to be able to take teh car to test and tunes and woodburn drag strip and PIR nights. Will these tracks allow me to run a SCCA rollcage as long as my tubing is 1 5/8" X .125" mild or 1.75" X .095" chromely?

So I've been doing a lot of reading trying to figure out the requirements of SCCA and NHRA cages. I'm looking at building a cage that satisfies both requirements so that I can take it to the drag strip and run fast, but also have no issues passing tech for track events.

SCCA Tubing Requirements for Roll Cages:

Up to 1500 lbs. 1.375 x .095 DOM / Seamless / Alloy
1501-2200 lbs. 1.500 x .095 DOM / Seamless / Alloy
2201-3000 lbs. 1.500 x .120 DOM / Seamless / Alloy
1.625 x .120 DOM / Seamless / Alloy
1.750 x .095 DOM / Seamless / Alloy


NHRA Tubing Requirements for Roll Cages:
1.625 x .118 DOM
1.625 x .083 4130 Chromoly.

With these requirements in mind I created a table to show the weights of different materials when used in the cage:



The two lightest options are 1.625" x .125" mild steel at 132lbs and 1.75" x .095" 4130 chromoly at 108lbs. So for $100 difference I will have a cage that 24lbs lighter and will pass tech in both NHRA and SCCA. I am capable of tig welding and feel 4130 is the best option in this case.

My only major issue is how to sport the main roll hoop as NHRA and SCCA do it differently:

SCCA:


NHRA(I will run straigh rear bars unlike this cage):


I figured I could take the SCCA main roll hoop with diagonal bar and add the feet like the NHRA have going in. Would this satisfy both requirements? Input welcome.

Heres a good link I've found regarding welding 4130:

http://www.netwelding.com/welding%204130.htm

Seems mild steel filler is what you want to use to make the joints flexible enough not to crack with 4130.

The main concern for me is the safety of 4130 in a crash:

"While AISI 4130 steel typically has a higher tensile strength that is only a part of the picture. All steels have a very similar stiffness (modulus of elasticity) and Mild steel (AISI 1020 for this example) will deform 600% more before fracture than Chromoly.
(My reference is the ASM International Metals Handbook H.E. Boyer, T.L Gall)
What you should discuss is energy absorbtion. A stiff but brittle metal will not absorb as much energy before fracturing as a similarly stiff but more ductile one."
-Niles


Regards,
Justin


Modified by Justin Olson at 11:31 AM 8/30/2006

 

What types of times do you expect it to run? If it's borderline, I doubt they would bother to be picky as long as there is a cage in it.

 

Well when its all sorted I'm shooting for low 10's high 9's on drag radials.

Still trying to decide which direction I will be going on the motor. 2JZGTE or LS2 402CI.

Regards,
Justin

 

In that case they would be picky If you run that quick they may even require a chute.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin Olson &raquo;</TD></TR><TR><TD CLASS="quote">. All steels have a very similar stiffness (modulus of elasticity) and Mild steel (AISI 1020 for this example) will deform 600% more before fracture than Chromoly.
</TD></TR></TABLE>

no wonder chromoly cost so much more

 

CroMo tubing ultimately has less ductility then DOM but the material itself is not brittle. Ductility of 4130 is only 15% less then 1020 tubing (typical DOM) as bare material yet you are getting a 75% increase in yield strenght. Where problems crop up is when 4130 tubing is improperly welded.

 

What kind of car are you building?