Well I know on Muscle Car they used a spool for their American Iron car. I would think the open diff would work best for turns, but could be wrong.
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1979 Mustang Ghia-302 HO @ 300hp, holley 600 carb, edlebrock intake, under drive pulleys, Bullet proof C4, 8.8 inch rear end with 3.55, Flowmasters Delta 40s American Thunder 2, pioneer head unit with sony speakers.
2004 Mustang Mach 1-281 DOHC @ 305HP, Shaker, 5 speed, 8.8 rear end with 3.55, Mach 460, Sat radio, Flowmaster Delta 50s, Clear Bright Fog lights, alum items for interior dress up, and an eject button.
spooled for AI ????? Maybe drag racing but a locked rear end on a road course..
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1988 coupe race car 2700lbs 366rwhp
1965 2+2 fast back 4 speed tri power
1968 gt/cs 347 5 speed
1970 mach 1 428scj 4 speed v code 410 rwhp stock
1990 gt drag car 780hp on motor
1994 gt, 1998 svt cobra
2003 svt cobra 456rwhp
You would want a limited slip type of rear set-up for road racing. You need to be able to pull strong out of the turns both left and right, without having the inside tire spin. the detroit locker is the ultimate set-up for vintage Mustang road racers, but it sucks on the street, great on the track.
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1969 Boss 302 (Vintage Race Car) Calypso Coral
2002 Saleen SC281 True Blue
1967 Coupe, 5-speed, Grabber Orange
As already said, you want a limited slip for RR/AX for the same reason why you want it for drag racing.....traction. And AFAIK, the AI rules do not allow a spool. Then the only problem is which to choose......Traction-loc, DL, Auburn, Torsen, Eaton, Trutrac......
First: AI may be concerned with the sudden failure of one axle with the amount of power being applied. Specificially, when one axle breaks under power (more frequent with high powered cars) the race car will suddenly veer to the side of the failure. Coupled with the thought that locked (welded/spools) differentials are prone to break more frequently, the concern might be one of safety. I don't actually know what the rule reads, just what the physical results are.
Secondly: Open differentials are useless on corner exit with any car that lightens up the inside wheel. Wheel spin will result, and it will be as bad as the degree of lifting of that wheel. This phenomenon is worse on solid axle cars (they have higher stress while turning at slower speeds) , but will show itself on independent axles, too. I have seen IRS cars also have mechanical breakage due to these stresses...some sheer wheel lugs. It is aways the weakest link that breaks.
Third: I have been told by racers that the mechanical lockers are difficult to drive smoothly thru the corner, due to the constant lock/unlock mode the device takes. This lock/unlock cycling is dependent on throttle applications trying to balance the car at the limit of its tire adhesion. One solution seems to be to literally coast into the apex of the corner (locker will be unlocked), then apply power from there out (locker will lock up under power). I believe that the car with a different type of differential will beat the locker out of the corner, simply due to the greater control at corner entrance and exit. In road racing, corner exit speed is the determinant of how fast the vehicle will be going at the end of that straightaway (assuming equal cars here).
Each type of differential (clutch/spool/gear/locker/hydraulic) has its own quirks, and the driver has to choose what compromises (s)he wants to make to match his/her driving style.
I have raced for twenty five years with solid axle cars with welded differentials. I have always wanted a different type, to make the driving smoother, but have not found the perfect one (cost is included in this statement). I know everyone has different opinions on this subject, and these are mine.
I raced SCCA BS Pinto during the seventies, and continued in ITB with a Pinto (different one), then an '80 Mustang, and lastly an "87 Mustang which was built from the ground up.
I'm currently looking for the "perfect" Mustang to build for ITR (SCCA). "Perfect" in this case is the right chassis for building from the ground up. I'd like to finish a car this summer, so I'm looking.
I raced SCCA BS Pinto during the seventies, and continued in ITB with a Pinto (different one), then an '80 Mustang, and lastly an "87 Mustang which was built from the ground up.
I'm currently looking for the "perfect" Mustang to build for ITR (SCCA). "Perfect" in this case is the right chassis for building from the ground up. I'd like to finish a car this summer, so I'm looking.
Good racing.
Bill
My dad had a '70 Pinto that was a horrible lime green with a vinyl roof. I remember it amazed me how well it drove in the snow. Then in the mid to late '80's, a guy I knew built one for the Pinto GT spec class that he ran mostly at Summit. I was supprised that they not that bad with a modest amount of suspension and engine improvements. Good luck with your "perfect" build.
Best Differantial for racing 
