3.23 vs. 3.55

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stimpy29

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Happy Saturday to you all! :)

My 69 Cuda restoration saga continues and I wanted to get some advice on rearends. I have two 8 3/4 rearends available to me of equal quality. One with a 3.23 ratio and one with a 3.55. The car will have a 4 Speed with a 408 motor giving about 380HP and 455ft/lb torque. It will be mainly a cruising car, with some highway driving. What rearend gear do you recommend?

Thanks for your help as always.
 
Stimpy29, you left out an important part of the equation. How tall are your
tires? Guessing they are around 28" on up go with the 3.55. With all that
torque sounds like you are going to have one mean tire shredding machine!
P.S. A 28" tire w/3.55 = approx. 2530 rpm @60, 2740 rpm @ 65mph and
2950rpm @ 70mph. Hope this helps.
 
Orv Grote said:
Stimpy29, you left out an important part of the equation. How tall are your
tires? Guessing they are around 28" on up go with the 3.55. With all that
torque sounds like you are going to have one mean tire shredding machine!
P.S. A 28" tire w/3.55 = approx. 2530 rpm @60, 2740 rpm @ 65mph and
2950rpm @ 70mph. Hope this helps.
Click to expand...

Thanks for the quick reply. I just checked my current tires and they are 26" diameter. I'm probably going to go with a different tire. But I can't imagine going with much bigger than 28".
 
There are factors to consider other than gear ratio. Sure grip ?, Clutch or cone type ?, Original A-body housings or modified to fit ?, Still straight or need straightened and back braced ?.
 
RedFish said:
There are factors to consider other than gear ratio. Sure grip ?, Clutch or cone type ?, Original A-body housings or modified to fit ?, Still straight or need straightened and back braced ?.
Click to expand...
Thanks for the message. It's a sure grip, not sure what type. Everything else is stock, no modifications to my knowledge.
 
Just a follow up question to what we've been working on. We decided to go with the 3.23 setup. After installing everything, we realized that the backing plates from the old rearend (4 holes) don't match up with the new axles. Does anyone know where to source appropriate plates?

Thanks as always.

EDIT - Bah, we ended up finding them in the back of the garage...disregard
 
Just got back from a 1,000 mile trip with my 3:23 geared 68 Cuda with 28 inch tall tires. 70 to 75 MPH all the way betwen 2500 RPM and 2800 RPM. Loved them! It's nice to go with the flow of traffic and not feel like I'm killing the motor...
 
QWK FSH said:
Just got back from a 1,000 mile trip with my 3:23 geared 68 Cuda with 28 inch tall tires. 70 to 75 MPH all the way betwen 2500 RPM and 2800 RPM. Loved them! It's nice to go with the flow of traffic and not feel like I'm killing the motor...
Click to expand...

You think you have it bad... I'm running a 4.10 gear. I think it makes the car slower to be honest.
 
My car has 3.23's and 26" tall tires and if it had any more gear it would be screaming driving down the road at 65.

You apparently had a 7 1/4 axle before. you need backing plates for your brake size and type from an 8 3/4 or 8 1/4 rearend, which might be a bit difficult if you still have the small bolt.
 
RedFish said:
There are factors to consider other than gear ratio. Sure grip ?, Clutch or cone type ?, Original A-body housings or modified to fit ?, Still straight or need straightened and back braced ?.
Click to expand...


redfish, can you elaborate on this? I'm a differential dunce and I've just picked up an 8 3/4 over here in Australia (they are extremely rare here), 489 carrier, cone type sure grip, 3.23 gears. The axles and housings will need to be shortened to fit my 68 cuda. Im running tall tires (275/60 x 15).

Why would factors such as sure grip, type of sure grip, and whether or not it is an original Abody housing influence choice of gears, or have I misinterpreted what you are saying?

cheers
 
I have an A518 in my Dart, 27" tall tires, 3:23 gears. I think its neat to cruise at 70 MPH and only be running about 2000 RPM!!! My 408 stroker starts its torque curve at about 1800 so it will pull right on up without any downshift. EFI engine and I averaged 19.7 MPG on my first outing a few days ago. Put 215 miles on it. FUN.

Larry
 
There is a marginal diff between the 2 in cruise rpm, but the 3.23's already get you 3000 rpm cruises going 70mph so with only a marginal diff in rpm and performance I would recommend to you to go with the 3.23
 
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