3.23 or 3.55 rear end?

[sir_veza]

Hello Everybody, This is an excellent forum and can't wait to jump in! My ride is a 1974 Challenger with a 360 stroked to 408. A833 - 4 speed with 3.91 (8 3/4) rear end. Thinking of changing to either 3.23 or 3.55 so I can enjoy driving more at cruising speeds etc. Interested in reading some opinions of what others have done...Thx Steve

 

[TC_Cuda]

First Welcome to the site and Nice car

I had 3.23 in my Cuda for a few years and it is a good all around gear but, last year I went to 3.55 and I like it a little better. Just a little more acceleration.

Just for a little info I have a stroked 440 ( 493 ) and my RPM on the freeway at 70 MPH with the 3.23 was about 2930 RPM and with the 3.55 it is now about 3215 RPM with 26" tall tires, which is a little more than I would want for a long drive but for the short time that I drive on the freeway its just fine.

So my opinion is... go with the 3.55. You been using 3.91 and the drop to 3.55 will be noticeable but either gear will be good.

Just my 2 cents

 

[fasjac]

Welcome to the site from Arkansas! Nice looking Chall. If you're wanting to do more cruising at 65-75, the 3.23's would be my choice. The 4 speed gives you some advantage around town.
The 3.55's are very popular and fun around town and light (shorter distance) highway speeds. I run 3.91s with a 500 stroker but, I have a 5th gear for the highway cruises. How about a couple more pics of that car when you get time. Glad you joined up!

 

[marks ebody]

3:55

 

[Ralph]

I like the 3.55 gear in my 73 cuda. Had 3.23 before. But I do not drive on the highway much and then about 55 so it works well for me.

I have a 3.91 in my challenger with a 5 speed and like it alot

 

[sir_veza]

Welcome to the site from Arkansas! Nice looking Chall. If you're wanting to do more cruising at 65-75, the 3.23's would be my choice. The 4 speed gives you some advantage around town.
The 3.55's are very popular and fun around town and light (shorter distance) highway speeds. I run 3.91s with a 500 stroker but, I have a 5th gear for the highway cruises. How about a couple more pics of that car when you get time. Glad you joined up!

Really appreciate your input. Here's a couple of pics from last summer...

 

[fasjac]

Really appreciate your input. Here's a couple of pics from last summer...

Sure thing, just letting you know, I can't see the photos on my side.

 

[sir_veza]

Not sure what's going on...the site is telling me the photos are too large?? Also tried one at a time...

 

[sir_veza]

Welcome to the site from Arkansas! Nice looking Chall. If you're wanting to do more cruising at 65-75, the 3.23's would be my choice. The 4 speed gives you some advantage around town.
The 3.55's are very popular and fun around town and light (shorter distance) highway speeds. I run 3.91s with a 500 stroker but, I have a 5th gear for the highway cruises. How about a couple more pics of that car when you get time. Glad you joined up!

First Welcome to the site and Nice car

I had 3.23 in my Cuda for a few years and it is a good all around gear but, last year I went to 3.55 and I like it a little better. Just a little more acceleration.

Just for a little info I have a stroked 440 ( 493 ) and my RPM on the freeway at 70 MPH with the 3.23 was about 2930 RPM and with the 3.55 it is now about 3215 RPM with 26" tall tires, which is a little more than I would want for a long drive but for the short time that I drive on the freeway its just fine.

So my opinion is... go with the 3.55. You been using 3.91 and the drop to 3.55 will be noticeable but either gear will be good.

Just my 2 cents

Thanks for your thoughts. So I could just swap out the 3.91 for the 3.55 in the 8 3/4 rear end correct?

 

[Mopar Mitch]

I run small blocks.. highway driving 4.30, 3.91, 3.55 and 3.23. I like the 3.23 best choice for highway cruising (as well as pylon autocross racing and hi-speed road course HPDE/HSAX events). The faster mph you go... the more you will want to go faster... 60-65-70-75-80... and I like to highway cruise at ~70mph. Actually, I intend to try a 2.94 to replace my 4.30.

You can find rpm and mph charts, per tire diameters and transmission gears, etc on the web. That will help to give you a good idea where you'd be comfortable on the highway rpms.

 

[fasjac]

Thanks for your thoughts. So I could just swap out the 3.91 for the 3.55 in the 8 3/4 rear end correct?

Sure can. Make sure the cases are the same casting numbers? Sure grip units? I alway add LSA in mine

 

[Ralph]

Find a good OEM set from the site. the new aftermarket ones seem to make noise in my opinion.

 

[sir_veza]

Sure can. Make sure the cases are the same casting numbers? Sure grip units? I alway add LSA in mine

Sorry - casting numbers??
Sure grip definitely !!

 

[fasjac]

Sorry - casting numbers??
Sure grip definitely !!

Yea, like on the side of the third member ( chunk) the last three number should be
742, 741, 489

 

[sir_veza]

Yea, like on the side of the third member ( chunk) the last three number should be
742, 741, 489

ok Thx

 

[Cojohnso]

I have 3.54:1 in a Dana with my B-body slightly built 440. (4-speed) And I believe the ideal street rear gear. Going from 3.91:1 to 3.23:1 will be significant. I have a 28" rear tire. On 15" rim. And it's a highway commando. She"ll bury her 150 speedo approaching 6500 redline. If you need to go faster? Then you have some serious skeletons in that closet.

 

[sir_veza]

I have 3.54:1 in a Dana with my B-body slightly built 440. (4-speed) And I believe the ideal street rear gear. Going from 3.91:1 to 3.23:1 will be significant. I have a 28" rear tire. On 15" rim. And it's a highway commando. She"ll bury her 150 speedo approaching 6500 redline. If you need to go faster? Then you have some serious skeletons in that closet.

Thanks that's some serious power. I think that would do the trick - (The skeletons don't pay speeding tickets around these parts) LOL

 

[Cojohnso]

Thanks that's some serious power. I think that would do the trick - (The skeletons don't pay speeding tickets around these parts) LOL

Actually the 440 is probably only in the 425 HP range. But for some reason it seems to put out it's power later in the RPM range. I had a very simular built 440. Same gear and trans. (Basically same car) But very different personality. Was quicker thru gears. But at 130 MPH? It was done pulling. This guy is still chugging hard. And glides much better at higher speeds. As I said. Different personality. The point? I think you will like your 3.55:1 gear option.

Quick walk around vid of my street car.

 

[sir_veza]

Yea, like on the side of the third member ( chunk) the last three number should be
742, 741, 489

Crawled under the car yesterday afternoon. 489 casting.

Sure can. Make sure the cases are the same casting numbers? Sure grip units? I alway add LSA in mine

Sure can. Make sure the cases are the same casting numbers? Sure grip units? I alway add LSA in mine

Crawled underneath yesterday. Casting is 489. (BTW - still can't upload any pics) - keep getting error message the file is too big??? Strange...

 

[NoCar340]

If you're taking pictures with your smartphone, check your resolution settings. Phones love to take ultra-max resolution photos so those with data plans burn through them quickly. A friend is constantly running into this issue on another board, but won't listen to me that there's absolutely no need for photos that are 10240 x 7680 pixels and 15MB in size. Try resizing your photos to 2048x1536, 1200x900, or 1024x768. I don't think anyone intends to print a poster of your car from a website posting.

As far as gear selection, tire diameter plays an important part. My Valiant runs around 2,600RPM @ 60 per, but I've only got 25"-tall tires on it (P235/60R-14).

Here's a simple, easy calculator to determine your RPM at a particular speed, with a given gear ratio and tire diameter. Play around with it a bit... see what tickles your fancy.

If your tire size is P-metric, size is easy to calculate. Using my Valiant's P235/60R-14 as an example:

235 is the cross-sectional overall width of the tire in millimeters.
60 is the height of the sidewall, expressed as a percent of the width.
14 is the rim diameter.

235/25.4 (mm to inches) = 9.25"
9.25 x 60% = 5.55". Multiply that by two, since there's sidewall on either side of the wheel, to get 11.1".
11.1 + 14 = 25.1" tire height.