I plan on building my car in stages:
1) summer/fall would be building a locost with stock mustang everything
2) next summer/fall would be upgrading

anyway, i plan on building with stage two in mind, so i will probably not be using stock 1.0" rhs...

what are the tolerances of each type of steel tubing?

1"?
1.25"?
1.5"?

Also, I believe that if I will be using 1.5" tubing, then it will be able to handle at least 450rwhp

Hicost has run his 430BHP car for 5/6 years without a problem. The chassis is 1" box section.

If you want to increase the torsional stiffness of the chassis then search for Cymtriks' plans- they've been posted a few times. They double the stiffness with a weight decrease.

HTH,

James

assuming identical plans, wouldn't one w/ 2" piping handles so much better than one w/ 1" piping though? its not much more, and worth it

to be frank, no. 2 inch tube weighs twice as much, surely an extra 75ish kgs isnt going to help handling. Plus, as james says, cymtrik's mods are a simple way to strengthen the chassis and it weighs LESS then the book version. Its like compairing brains over brawn.

thanks