I agree with the others that have said that 3.91s get really tiring on the highway.

That said, I don't daily drive my Super Bee, so I just cant bring myself to swap the 3.91s out for 3.23s. Despite 90% of my driving being on the highway, I just cant give up that extra kick in the butt that the 3.91s give!

Keep the 3.91s and put a 518 transmission in it. Then you can have the best of both worlds.

I hated my 3.91s [28.5"] tire when I got on the highway, it's pretty bad. Now that I have a double-overdrive...they're pretty good.

In 1985 I drove my 71 Cuda 340 4 spd 3:91 rear, 7 hours with only gas stops, to Ann Arbor Mi and the Mopar Nats on nearly brand new F-60-15 Goodyear Polyglas tires I'd found.
As someone stated, I do recall watching the tach a lot.
Would I do that trip today......not even if I was held at gunpoint

Well, I'm running 3.91's right now in my Roadrunner with 26-1/2" tall rear tires. The suburb highways are 70 mph & I'm running right at 4000-4100 rpm in the slow lane...… my well-built, balanced, all forged motor sounds like it's going to spit a connecting rod out the side of the block on the highway. I personally wouldn't recommend 3.91's for the street.

I don't remember my 70 340/4 Cuda w/3.91's being all that bad going down the highway, but it has been a lot of years since I did it (30?). I'm thinking of sticking a set in my beast, just haven't had enough energy yet. Of course I can always swap the 3.23's back in if necessary..

In 1991 I drove from Memphis to San Diego in my 64 300. 4.10 gears, three speed stick, N50-15 tires, dual Flowmasters. Roughly 3500 rpm at 70, speed limit was 55 back then.

No problems and no I did not hang out in the right lane cowering

Yea, I dont know how some even get there doors shut without there walker getting bent up.

So much for performance cars with performance car axle ratios.

Whats next a C-body Prius?

Worked for me

340 auto with a 28" tire and 3.91. I was doing 3500 RPM at 70. Switched to a 2.76 for the Nats. 2500 RPM at 70 and 3000 at 80. It became a blast to drive on the interstate.

How many 2-3 hour hiway drives do you take with those 4.56’s?

In the 70-80’s how many people were doing 80mph on the hiway? Y’all were stuck doing 65 screaming along.

If you need a lot of gear, you have a limp wristed engine.
Plenty of guys in the 10’s with just 3.23’s.

115mph @ 3,330rpm
73mph @ 2,141rpm

I had 3:91's in my 69 383 Dart with 27 inch tall tires back in the day. I can tell you from experience it does not make a good highway car. You won't like it. I recommend 3:23's if you are going to do much highway driving with the car.

You may not like it but fit the tallest tire you can and it wont be to bad. I am from the 60's and 70's when we ran 4.10's and 28" tires so it don't bother me. I run 4.30's in my 63 with a 30" tire and I turn about 3200 around 60 to 65 mph. Myself I may drop to 3.91's as I don't think it will slow me down any in the 1/4 mile with all the torque my 493 makes. Ron

Running 3.91 gear set with 31.7" tires and TKO-600 5-speed.

- EM

OK Im livin under a rock ova here.
What is this magical 518 Tranny swap

Overdrive....wish I had the money for one.

Must of hit a nerve with the limp wrist part, but fyi in the summer time I drive 175 miles each way one time a month for a club meeting, 4:56 on a 28 inch dr.

I love it as thats what these cars were built for, the cars can take it, its the spoiled disillusioned owners that seemingly cant.

As for the BS "Plenty of guys in the 10’s with just 3.23’s" im a 100% confident these are not N/A old school stock stroke STREET muscle cars but rather small block turbo cars or big block strokers.

Id have to ask you to post some of these stock stroke street driven 340-s or 440-s that run a carb or two or three running 10-s with these 3:23.

Face it, some just cant/wont run our old cars as they were delivered or for there intended use, since when is a 4:56 gear on the street extreme, oh I know, when some get too old to cope.

So maybe a scatpack with od/cruise and ac is more fitting for some seeing how that now a classic muscle car with deep gears, no ac as they were intended to be and as delivered from ma mopar is not acceptable to some here.

Hey, I hear alot of corvettes came with 3:31 rear gears, might be a good option for some.


And another thing im confused about is whats the big flippin deal of running the speed limit? Why not run 60-65 and enjoy all the thumbs up from the passer buys. Ive never got a ticket for running in the right lane at the posted limit.

I must have an old heart, I'm 30 and thought my 3.91s were annoying...We typically run 80-85mph here on Texas tollroads.

The 3.91 in my Runner sucks on the highway, even with 275 R60 15 tires.

My Boss 302 with 3.91s wasn’t much better 25 years ago. Great for getting ice cream, but not on the highway

Unless you have an overdrive transmission, stick with something like 3,23 gears.

As to the limp wrist comment, why do you think all the performance cars have overdrive transmissions now?