Posi Rearend???

[buckeyecharger]

I figure i would ask the experts....What do you guys think???

What is the best factory mopar posi rearend gear ratio? I want to put a factory posi rearend in my Charger and need some advice.
Thanks!

[Troy]

#1 a "posi" is a Chevy term. In the Mopar world, the limited slip unit is called a "Sure grip".
#2 are you asking about the "posi" or the gear ratio?

Either way, your answer is probably "it depends". What do you want to do with the car? How and where will you be driving it (1/4 mile track, road course, cruise-ins, highway. etc.)? How much power? Automatic or stick shift transmission? What size rear tires?

I personally have 3.23 rear gears with a Sure Grip and 28" tall tires in nearly all of my cars. I spend a lot of time on the highway and none at the track (any track). A 3.55 is another good gear on the street but I've found that I still rev too high (for my taste) on the highway and my mileage takes a hit. If you want to race (1/4 mile) you'll probably want 4.10 or more gears - especially with tall slicks. Expect to have to keep it under/around 60 mph on the highway though. If you care about gas mileage more than acceleration you'll want to try 2.76. No need for a Sure Grip then as the engine will have some issues even trying to get the tires to spin (unless you have LOTS of torque).

Troy

[68X426]

Mopar rear ends include the Dana 60, though not actually made by Chrysler. The Dana had limited slip designs called Powr-Lok for 1966 to 69, and called Trac-Lok in 1970 and up.

Ratios for the Dana go as low as 3.54. Like Troy said, it depends on what driving you do. Lower for highway, higher for hot rodding. 3.23 is a great compromise, but it still depends on what you expect from your overall driving experience.

[buckeyecharger]

Thanks for the info. thus far.

First off, Yes I should have said "sure grip"....Sorry! and I consider myself a Mopar guy.

Second... I will be highway driving not the 1/4 mile. My Charger has the original 383 with the 727 tranny. My car is all original so I don't want to deviate from that to much and put some exotic rearend in the car. Gas mileage is not a concern, but I don't want to be driving to the car show at 5,000 rpm either.
Thanks!

[Chatt69chgr]

I'd think that you would be looking at a 8-3/4 rear end.  Available gear ratios are 2.76, 2.94, 3.23, 3.55 and up.  For what you want, I believe that the 3.23 would be the best.  You can buy sure grips from several sources now.  In fact, you can buy the whole 3rd member (pumpkin) set up and ready to go with the sure grip in it for around a $1000 as I recall.  Use the calculators online to determine your tire diameter.  Then use other calculators to determine engine rpm with various rear end ratios.

[Piston_Freddy]

http://vexer.com/automotive-tools/speed-rpm-calculator

[68X426]

You say mileage isn't an issue, so go 3.55. Nice driveability, performance, and was a factory ratio for the 383.

[Troy]

What year is your car? What rear axle does it have in it now (8 3/4")? What size are your rear tires? If your car is stock you don't want a race type gear ratio any way because you'd need to change the torque converter. A 2.76 or 3.23 gear will be fine for cruising - but knowing the tire size will help. A 3.23 will accelerate better but get slightly worse mileage. The 383 will rev pretty high too which will work well with the 3.23.

Troy

[Cooter]

If the car is stock, why would anybody need a Sure Grip? I mean, if all your doing is driving on open highways and NOT "Drag Racing" the car, I can't see dumping $600.00 PLUS into a used up, worn out, slipping, one wheel peel without a rebuild Sure Grip chunk myself....