gdh@rcpinc

Hello, I am just finally finishing my car this week and have replaced everything mechanically with the exception of the driveshaft, differential, and half shafts. I would really appreciate any help with choosing proper parts to make this final upgrade soon. They need to be able to handle a 725hp bbc that was just installed. I have seen upgrades from the 2.5in to 3in halfshafts, and heard of shops selling "built up" diffs, but am kinda lost, and afraid to make a purchase with my limited knowledge of the subject. This may be a horribly dumb question, but I have heard of upgrading to a ford 9in; do I have to convert to a solid rear for that? I would really appreciate any examples of proven combinations of parts for this conversion. Again, please forgive my ignorance, and thank you all so much for your gracious help, and thanks in advance for any help on this subject.

gdh@rcpinc

Sorry, I guess I should have also added that it is a 71 with a B&M th400 and nitrous holeshot 3500 converter. The car has 4.56 ratio now, but what would be the best diff gear for this setup for quarter mile performance? Again, thanks!

Goody

There are a couple people on here that I know of that have rear ends designed to live under extreme use so hopefully one of them will provide some help. Tom's Diffs come to mind but I don't know if he builds them any more or not. See if you can contact Snowman.

Don't expect this ordeal to be cheap though.

gdh@rcpinc

Thanks for the help! Yeah of course I want to do this as affordable as possible, but am ready to spend whatever amount it takes to have the proper setup. The car will likely be useless on the track at this point, as if it ever hooks I will have a driveshaft up my butt lol

TheSkunkWorks

Tho I don't drag race my shark, after a number of 10-bolt diff failures over the years (on DOT's, no less) here's what has worked for me...

Henry's Machine Works/Eaton 12-bolt posi IRS diff w/31 spline Hy-Tuff side yokes, solid Spicer U's, 3" HD half-shafts (I probably get away with the OEM ones because I don't launch at 5000 RPM with slicks), and Guldstrand modified high-nickel HD stub axles w/0.5" x 3" lugs (setup at 0.001” bearing runout). Other additional items include a solid diff x-member locating kit (3 point) and heim-jointed camber struts w/lock plates in lieu of eccentric adjusters. (For the strip, set them parallel with the half shafts.) I also went to a 15# flywheel, but that's not applicable in your case.

Henry's hasn't responded to a recent inquiry of mine as to whether or not they still do Corvette stuff, but Tom's no longer builds them. FWIW, the famed (within the field) Pepe Estrada designed these setups for both companies, and Tom's had a 12-bolt IRS setup NHRA certified to 7.50', IIRC. http://www.hotrod.com/techarticles/0...tup/index.html

IMHO, if you want a super HD 10 or 12-bolt IRS diff built you ought to get with Gary Ramadei (PM or email me if you need contact info), or with tracdogg2 who also has a very good rep here. FYI, there are a few guys running around with Strange/Dana 60 IRS and even Ford 9" IRS conversion setups, but with "only" 725 HP and an auto that probably isn't necessary. In any event, other than for budgetary reasons you really shouldn't have to consider a live axle, tho if you need to be certified I don't know what that might entail...

Also, if you're dedicating your C3 to drag strip duty, you might also want to check out the DragVette 6-link setup, tho IMCO it doesn't yield optimum geometry should cornering remains somewhat of a priority. Sorry, you have to compromise one or the other, or both, as there is no one-size-fits-all suspension setup, desirable as that may be. http://www.dragvette.com/

Hope that's worth $.02

Clams Canino

I agree here - Gary is "Da Man" now.

-W

tracdogg2

Your best upgrade would be the 12 bolt but with an automatic a fully built 10 bolt should hold up. You will definitely have to upgrade to the 30 spline stub axles and the 31 spline spindles. You will also need the thick wall 3 inch halfshafts and 1350 series spicer joints. You could also upgrade to the 3.5 halfshafts with the 1480 series joints, spindles, and stub axles but you will have to cut away some of the battery and storage compartments.
No one builds the Dana 60 conversion anymore that I know of. But with enough money it can be had. It would require removing the entire storage compartment area and relocating the battery.
shoot me a pm if you need any more info.
Mike