Diff for my 73 Charger

[Pouria]

Hello friends;
I own a 73 Charger with upgraded 340 motor. The output is believed to be around 400+HP at the rear end. The diff is a 8-3/4 with welded housing. how can I identify the ratio? Is it a Sure Grip? If it is not, do you recommend Auburn Gear LSDs for my application? I care about high speed more than initial accelaration because I believe that the motor is powerful enough to move the car fast even with low ratio gears. Which ratio do you suggest for me? I live in Iran, far away from US. I may be able to find stock diff out of other mopars of the same age here, but Chargers are really rare! Which car I can use for this? There are plenty of Coronets and darts mostly with 6Cyl . motor.

Yours - Pouria

[mikesbbody]

i dont know too much about them but i will tell you what i know im sure there are others that will correct anything wrong i tell you. a easy way to check if its a suregrip or not is to jack up the rear and turn one of the wheels. If the other wheel turns the same way, its a suregrip also the most common types were the 741, 742, and 489's these are the last 3 numbers of the serial number on your 8.3/4.
there are 2 types of 8.3/4 sure grips the cone, and the clutch the clutch is often looked upon as more desireable and often more expensive both can be rebuilt. also, if you want top end speed go for higher gears (lower numerically) i.e 3.23's 2.90's etc good luck. i just looked at my 8.3/4 which is a 489 suregrip (cone type) i had a 742 which isthe clutch type and i sold it! (stupid!)     

[mikesbbody]

one more thing, you mentioned the 6 cylinder cars? the probably dont have the 8.3/4 (i could be wrong) but i think they will more likely have the smaller 8.1/4 or smaller rears.

[doctorpimp]

one more thing, you mentioned the 6 cylinder cars? the probably dont have the 8.3/4 (i could be wrong) but i think they will more likely have the smaller 8.1/4 or smaller rears.

Hi Pouria,
Here in North America, 6 cyl Mopars were equiped with 7 1/4 or 8 1/4 rearends.  Both of those types don't have the same differential and gears etc as the 8 3/4.  Now that being said... Export cars going to the Middle East and SW Asia might be different, you'll have to check out the car graveyards to be sure (at least all the donor cars will be rust free  )

The easy way to tell the ratio of your car is to:
1. Place car in Neutral on level ground with park brake off.
2. Chock front wheels and raise rearend onto Jackstands (safety first)
3. Crawl under your car, and have a friend slowly turn a rear wheel one full rotation, while you watch the rear U joint - counting how many times it rotates.
4.
2 3/4 times = 2.76
Almost 3     = 2.93
3 1/4          = 3.23
3 1/2          = 3.55
etc etc etc

5. You can also notice if both wheels turn in the same direction (suregrip) or opposite directions (standard).

[Pouria]

Thank you both for the valuable information

[doctorpimp]

Thank you both for the valuable information

[mikesbbody]

your very welcome good luck!