What is the best choice for street strip.......
1970 Duster 431 stroker roughly 550 horse, auto, 4:10 gear.

Running a spool isn't the best idea if the car is going to be street driven at all. I'd go with Detroit Locker/Truetrac (I believe that they're the same company now). That's what I have in my '68 Plymouth and it's good for both street and strip. If you aren't planning on building the rear end yourself, you might consider Dr. Diff.

Call Cass (Dr.Diff).

He will explain the differences, the Locker is the toughest but is also noiser.

I have basically the same car and combo (71 Duster 426 SB, manual trans) as you and decided to get the nodular iron 489 case with forged steel caps, billet adjusters, 3.91 gears, Eaton True-Trac, crush sleeve eliminator and forged steel 7290 U-bolt yoke. I doubt I'll ever hurt it.

My buddy bought his slightly Stronger Detroit Locker setup, he has a (Demon) with a 500+HP stroker SB and a 4 speed. This is the strongest 8.75" differential available (by a small margin), but not everyone likes how it drives, as there in 1/8" internal lash in the ratchet mechanism. About $50.00 more overall compared to the Auburn setup I bought.

All of the parts from Dr.Diff have been top notch!

A friend of mine used Dr Diff stuff in his 68 bigblock Dart....said he was great!

Another vote for Detroit Locker

I used Dr diff to order my Dana 60. He recommended the true trac for my 650 hp four speed street car.

Locker here too, I like it but it did take some getting used to. Not the noise though. As loud as my car is, if you can hear the noise from the rear end in my car something bad's about to happen....

It's that play in them that feels weird, the car will wiggle a bit if you coast then get in it again , even going normal speeds.

I thought my Cal Tracs were causing this at first. It takes a little getting used to but it's fine for me.

Another vote for Dr Diff and a Detroit Locker.

I find it hard to believe so many suggest the locker, I can see it some cases, but its awfully annoying in many street applications especially when exiting corners in a hurry. I suggest OP make sure he gets some seat time in a friends car with a locker before putting down any money.

Right Jcc, driving my buddies Demon (and our Duster race car) with the Locker made going with the Tru Trac an easy choice, especially since we are not talking about a big difference in strength.

I also run a Detroit Locker in my 63. Ron

What I meant to say in my previous post was that they're both made by Eaton now. I have the Truetrac in my car, not the Locker, and it does just fine on the street.

Absolutely love my Truetrac! Works like an open diff when not needed and performs great as a Sure-grip when needed. No noise, no need for LS additive, does not wear out. Great piece!

Whatever you decide on AVOID any type of CONE TYPE differential , they are absolute garbage .

Thinking of going with True Trac....alot of good things said......thank you. Everyone here is always a great help. Take care all!

True track here

Here is the one I got from Dr. Diff, first class piece all the way.