99-01 Cobra IRS

'99 = 28 spline
'01 = 31 spline

'03/'04 = 31 spline

Many 99/01 owners who chose to run with the IRS at the dragstrip upgraded to GKN (or similar) halfshafts because they were stronger, here's a link:

http://www.need-4-speed.com/gkn.htm

I forget the exact details but the 03/04 halfshafts were "beefier" at a certain area so that they weren't as prone to breakage like the 99/01 halfshafts. That being said, an 03/04 halfshaft can still snap given enough power due to wheel-hop & twisting forces.

I know you mentioned opentrack/roadracing material, but the above info should be somewhat useful. Be sure to check out the folowing pages for further info:

1 - Joe Lynch's site (excellent tech info, mostly drag racing related but still great to bookmark if you have an IRS)

http://www.lx.net/jlynch/

2 - The Cobra "R" section of the SVTPerformance msg board (lots of good info among the 2000 Cobra R owners and their experience with the '00 R IRS; looks like their msg forums are currently down though):

http://www.svtperformance.com/forums/index.php

#3 Visit the Corner Carver forums, plenty of info pertaining to IRS & racing applications (search button):

http://corner-carvers.com/forums/index.php

#4 Corral Roadracing forum (search button):

http://www.corral.net/forums/forumdisplay.php?f=304


Between all of the above sources, you should have a better idea about what to expect when open-tracking an IRS equipped Cobra and how to improve it...g'luck!