Opinions on rear gears

[BSB67]

If most of your cruising is 55mph highways and back roads, the 3:23 is a nice all around gear. If you do a lot of freeway cruising, the 2:94 might be better. As someone else said, if you have both, try the one that's in there and see how you like it. If it seems doggy on your cruises, change it out to the 3:23.

This. I had 2.94 in my 440 car and thought that they were fine and would do it again, and I don't do a lot highway driving. The motor and cam matters.

 

[91r/t]

Thanks for all the response. I will be running 275/60/15 about 28 inches tall and stock 727.

I have 3.55's with a 28" tall rear tire and I run 3000 RPM at 70 MPH in my Roadrunner with the 4 speed. In between gears it matters, but using an auto or a 4 speed your final drive ratio is still 1:1, so final RPM's will be the same. (Unless your using an OD 4 speed) I find it to be the perfect combo for mostly hilly areas with some highway driving.

 

[JimKueneman]

My vote if for 3.23. In my 68 coronet, mild 383/727, 275/60 rear tire .... I went from 2.76 to 3.55 to 3.23 and love the 3.23. I do lots of long cruises , just did 200miles this Saturday. I definitely lost some off the line punch from the 3.55 but its much nicer at Hwy speeds. 3.55 wasn't terrible on the Hwy, but I felt was a tad high on the rpm ( also didn't have a tach at that time so who knows, I was going by sounds of the engine !) ......

With a 904, 2.94 gears and 15" wheel with tires that are almost a perfect diameter match to the original F78 14's my Coronet turns 3000 RPM at 80MPH on the freeway. I believe when I did the math 3.23 would turn almost 4000 RPM on the freeway which seemed too high for me on extended trips (like hours at a clip).

 

[jz61]

mine is much like yours! 65 belvy 440 727 auto 3,55 in the rear same size tires that you are running, mostly stock motor, happy zone for the motor is 2200 to 2500 rpm. with the 355's that's about 45 55 mph if I do a lot of highway 3000 rpm is about 62mph according to reading on wifeys smartfone app at wich point im looking for another gear! all of the options for getting some kind of overdrive are costly, and need quite a few mods, if I came across a 323or lower like 294s or whatever id be tempted to try it just to see if it killed the responsiveness

 

[747mopar]

Doesn’t the transmission affect highway rpm. OP did not say what trans. My TKO 5 Cruises 72mph @ 2150 rpm w/3:54 Dana.

Almost all transmissions at that time were 1:1 ratio in final drive, you and I have the best of both worlds

My vote is 3:23s if your driving a good mix of backroads, town and freeway. I love 3:55s myself but I have 2 extra gears, having said that I spend most of my driving in 5th with 4th being 1:1 ratio so without the O.D. I'd be swapping out the 3:55s.

 

[747mopar]

Don't forget to take into account the motor, how the motor is built (cam selection) will play a big rule in choosing the right gear. Something that is very handy is downloading the Tremec app, it allows you to quickly figure rpms based off of gears and tire diameter. Just above 2,000 rpm for a mild big block on the freeway is wonderful IMO but that means sacrificing low end, choose your poison lol.

 

[bee71]

3:23's. Original on our Bee,great for cruising and just enough punch to get started.

 

[65-440]

With a 904, 2.94 gears and 15" wheel with tires that are almost a perfect diameter match to the original F78 14's my Coronet turns 3000 RPM at 80MPH on the freeway. I believe when I did the math 3.23 would turn almost 4000 RPM on the freeway which seemed too high for me on extended trips (like hours at a clip).

1000 rpm difference with 1 jump up in gear ratio ? That seems a bit much, maybe a few hundred .. but that depends on your tire diameter I guess..
I just swapped out 3.55 for 4.56 in my jeep and rpm changed 500 at 65... with OD puts me at 2300, I can live with that !

 

[JimKueneman]

1000 rpm difference with 1 jump up in gear ratio ? That seems a bit much, maybe a few hundred .. but that depends on your tire diameter I guess..
I just swapped out 3.55 for 4.56 in my jeep and rpm changed 500 at 65... with OD puts me at 2300, I can live with that !

Your right, thinking of something else. This is a 10% change in ratio so change is about 300 RPM (3300). To a 3.55 is 21% or about 630 RPM (3630) increase.

 

[BSB67]

........, but using an auto or a 4 speed your final drive ratio is still 1:1, so final RPM's will be the same.

The auto will rpm higher due to converter slip. About 5%.

 

[GrabberOrange69]

Here's my take on gears, it's not science, just MHO.

If you really like driving it on the freeway, don't go any deeper than 3.23 with a 15" rim. The "tweener" gears 3.40-3.70 are junk. I've had 3.70s in my small block 4sp car for a decade and I'm removing them. I thought I could straddle the cruiser and drag car use. What I found is they are too low to happily cruise on the freeway, but not deep enough to fully enjoy on the drag strip. In the lights I'm right between 3rd and 4rth gear so I have to over-rev my power band, or choose 4th and loose precious moments in a shift. I'm thinking 4:11s or 4:30s.

Figure out what you want to do with the car. Cruiser = no deeper than 3.23. Drag strip = start at 4:11. Dual use? Get an overdrive

 

[Larrry B.]

Thanks for all the response. I will be running 275/60/15 about 28 inches tall and stock 727.

I have 255/60/15's on the rear with an upgraded 727, with 3.23 I'm able to make most people on the street look slow (without flooring the pedal) and still able to fly down the freeway.

 

[91r/t]

The auto will rpm higher due to converter slip. About 5%.

Good call never thought of that!

 

[65-440]

upgraded 727.

Please elaborate on this ....

 

[fratzog lover]

What are the cam specs for your motor?

 

[Cranky]

My 383 Challenger went from 12 mph with the 3.23's on the highway (65-70) to 16 with the 2.94's! Some called me a lair but not one of them would take me up on a bet. Put yer money where your mouth is! My dad got 17 with a 74 440 New Yucker! Didn't believe him at first but he said the same thing. Put yer money........

Anyways, a big block has plenty of low end even with the tall gears. After all, what's that saying about no replacement for displacement? My whimpy 383 Challenger would fry the tires at will if flooring it off an idle and it was only a 330 hp motor. Letting it roll off the line just a bit and then flooring it was no problem. Never took it to the track to see what it would do though which was one of the very few cars that never saw the track

 

[mopar 3 B]

With a 904, 2.94 gears and 15" wheel with tires that are almost a perfect diameter match to the original F78 14's my Coronet turns 3000 RPM at 80MPH on the freeway. I believe when I did the math 3.23 would turn almost 4000 RPM on the freeway which seemed too high for me on extended trips (like hours at a clip).

somethings wrong with your math. 4000 rpm 3.23 gear 26" tire = 87 mph

the 80 mph can be done with 3400 rpm 3.23 gear 28" tires. Compared to the same with 4.10 gears at 63 mph. MY Charger RT is built for the 63 MPH range with 4.10 gears. it really likes that 3400 rpm range. Top mph is 126. If speed limits continue climbing the 3.23 will get real attractive.

That's why it all in the build.

 

[Larrry B.]

Please elaborate on this ....

2800 stall converter, shift kit, deeper pan with cooler.
8.75 rear, Auburn Sure grip with stock axles.

What are the cam specs for your motor?

Not sure if this was intended for me but here you go.

No, this is not the op's combo but the 3.23 works for me currently.

 

[andyf]

I'm working on a 1965 Belvedere II that will be used solely as a cruiser. The 273 will be swapped for a 440. It currently has its original open rearend with stock gears (don't know ratio). I have a sure grip center with 2.94 gears. I also have a set of 3.23 ring and pinion gears. Should I use the center with the 2.94 that I have or switch to the 3.23? Thanks

Really depends on a bunch of factors such as the cam and the transmission. The 3.23 gears area safe choice but you might be happy with 2.94 gears if the cam is stock and the torque converter is stock. You didn't provide enough details so it is hard to provide a complete answer.

I just switched to 3.23 gears in the Dana 60 in my '65 Coronet from 3.54 gears. The 3.23 gears drop the RPM by roughly 10% and give me 10% better fuel economy going down the road. The car is a little softer leaving the line and with the cam I have, the car doesn't like to cruise in 5th gear at anything under 70 mph. The cam is super critical when you're talking about freeway cruising with tall gears since you might be running 2000 rpm. A lot of performance cams don't work efficiently until 2500 or 3000 rpm. So that means you're cruising down the freeway with an engine that isn't working very efficient.

 

[fratzog lover]

No, this is not the op's combo but the 3.23 works for me currently.

Gotcha. That sure isn't the cam to live in harmony with a 2.94 rear! It was indeed meant for the OP.