Finally found a 489 SG case with 3.91 Richmond Gears.
Its gonna go into my 67 383 Fury wagon.
Any idea what my highway driving might be like with a Factory 727?
Any tips to improve it if needed?

Assuming you have not so tall tires, at 3000 rpm you will be in right lane with most folks passing you?

How fast do you want to drive and for how long at a time?

definitely not highway friendly.

I had 391,s with a 440 and 30 inch tire.No tack but i can tell ya at 70mph it was wound up pretty tight

One I drive often is a 4:56 and a 28 inch tire, 3:91s a great overall gear, the more limp wristed prefer a 3:55.

Many forget the gears alot of us ran in the 70-s and 80-s on the street 4:56, 4:88, 5:13, just build it right, not tight, and drive.

A 3:91 is still enough to upshift to 2nd at 55-60 and let it sing.

back in the mid 70's, early 80's, i ran 5.38's in my charger on the street with 29" tires. talk about singing ! 3.91's now.

I have a 65 Plymouth Sport Fury 383 with 3.91 gears and it does fine on the highway. I prefer two or four lane roads but the interstate is OK too, you wont be holding at 100 mph for long stretches but cruising at 65-70 isn't bad. I wouldn't want to drive it from Miami to Seattle or anything though, that would be a long trip. I had 3.23 in it before, really prefer the 3.91 but I mostly drive around town and stuff.

Having a taller tire will help when using the deeper gear.

With a 28" tire it is ok on 2 lane roads, I personally hate it above 60-65.
Fun around town yes

It's all a trade off.
The 70 Satellite has 3.23's and 30" tires...Hate it around town but out on the freeway it doesn't even run good until 70 mph and up.
The 69 Dart has 391's and 28" tires...much more fun around town but starts to turn more RPM's than I like above 60-65 mph.
This new 72 Duster were putting together is 4.11's with 28" tires...should be even more fun but will I'll need to stay off the freeway with it...

Yep. I think with 275/60s/auto and 3.91s I was doing 65 at 3500 rpm. Too hard on the motor for any extended driving for me. Now, if you're talking a couple miles to get ice cream and back, you're probably ok.

Put the in and have some fun. You can always swap your original gears set back in in a few hours before a long trip.

You'll be looking at the tach more than the speedo.

Go to an empty parking lot. With car in Park, rev the engine to 3200rpm. Hold it there for a half hour. Did you like it?

OR,

Get on the interstate and put it in Second gear. Accelerate to 70mph. Hold it there. That's what 75 would feel like with 3.91s, assuming your original ratio was 2.92 or close.

When I'm driving 600 to 900 miles in a day, I sure don't want to be assaulted by a high revving engine. It actually increases fatigue and leads to unsafe driving.

Back in the day, there were those jerks who bought Porsches and then drove them in Second gear at 5000 rpm because "that's what the engine was designed to do". I sure don't think they were manly because of that. When I changed my '64Dog from 3.91s to 3.23s it lost that quickness around town but on the road at 80 it was a lot easier to make that 900 mile day. And my sexual orientation didn't change.

R.

This is what it was like in my 68 D100. 318, auto and 3.91 gears with 235/75/15s...

3.23 with lots of freeway miles & 15" tires.

3.55 with 15" tires around town, hills & some freeway.

3.91 mostly for racing or a low geared truck with pulling power.

Sat nite cruise car, ok
Everyday car, it'll get old fast. Unless you live in the middle of NY city.
Good time for a 518 change. Best of both worlds.

Exactly, I "only" have 3:73s and it sucked driving in the right lane at 3700rpm with every minivan passing you.
518 swap was the best thing I've done.

For a wagon, 3.23 would be my gear of choice for street car. Build more power and don't worry about the gear.

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?

Not all of them do.

A firm wrist can handle a car as it was originally made, no modifications needed.

Because all you limp wrists cried about the noise.

Here's a clue. MoPar had OD trans in the 40's. Not like it's something new.

Thats a negatory there Ghostrider. Reduced RPM @ cruise equates to lowered emissions and improved mileage
every.
single.
time.
Overdrive has been enhanced with lockup convertors for the same reasons.

Ba.... Its all good if people like OD trans, obviously I like the old deep geared 1:1 stuff and I can drive slow until I need to drive fast and I could not give a --- about the cost of gas.

I live in the dry heat, if it hits 40% humidity im drippin so I do understand the ac part also.

One day I will give in, but I hope its not soon.

Can't believe how little the 3.55-1 is mentioned here. In a thread about 3.91's.

In the days before OD, ALL ratios were a compromise in a car driven both in town and at speed.

The 3.55 (3.54 for you more fortunate folks) was/is a GREAT multi-purpose gear!

so keep the stock 391 and trailer it?

Had a car for a while with 4.10:1 gears and 26" or so tires Also had no PB or PB but it did have 4 wheel drums,was my daily driver and went for carshows and such everywhere and the only thing i would have changed on that car if i had keept it would have been discbrakes in the front. Sure i wasnt going fast on the highway but no problem driving the posted limit even thought it was alitle hard on fuel on highways.

And not one limp wrist cried about worse mileage and emissions. The cried about "the engine screaming as you tootle along in the right lane getting passed".

Engines also wore out faster before overdrive.

The stock 318 in the D100 I mentioned before would not keep up with traffic with the pedal to the floor.

My first 69 SuperBee had 3.91s back in '74 and 3.91s have been my go-to gears ever since. Even today, my Cuda has 3.91s. But now, it also has a 518. So blasting down the hiway at 75 or so is no big deal......for me or the car.

3.91s are a lot of fun but are very hard on the engine on the hiway. I have popped more than one big block screaming down the hiway. But that was back when these cars were disposable and I could go to the local wrecking yard and pick up another 440, swap my parts to it, and go beat on it some more.

Today, blocks and stuff are harder to find, more expensive, and I am older and lazier. So, no 3,000 or 4,000 RPM screaming down the hiway for my stuff anymore. It may take it.....for awhile. But there is no doubt that it is hard on the engine. And we have choices now that we didn't have then. We can enjoy 3.91s and have reasonable engine speed on the hiway. Kinda like having your cake and eating it, too.

It's 2018, not 1974.

lol, that wasn't it's job. Imagine that same ride with a /6. Wee.

As for wearing out faster, more likely it had to do with the rings used and the oil formulations than OD. I still have the 318 out of my 87 Diplomat, 200k+ miles, bores look pristine. Moly rings, good oils, regular maintenance. No OD. back in the musclecar days, well oils sucked and cast iron rings.

If you are taking the time to ask then I believe you would be happier with 3:55. I had an E body with 440, 29.5" tall rear tires and 4:10s. I was not happy on the highway. Holding everyone up in the right lane.

I have 3.54 gears in my pile,and was thinking about switching up to 4.10s for racing.
Will my wrists become any stronger?
If Passon could kick out those 5 speeds he could sell a bunch.

I ran 4.10's for years in my wagon with 28" tires. I finally had enough of slow lane cruising and the engine singing above 3k. I swapped in 3.55's and my only question was why didnt I do it sooner! It made driving everywhere much more enjoyable. Granted, it did also have a healthy BB stroker, so still plenty of tire roasting at will . But w the 3.55s, I could actually keep up with the majority of highway traffic for once, without buzzin the heck out of it. Prior to the 4.10s I had a Charger with 4.56's, and yes I see the pattern of gear ratio change with my age .

At hiway speed, the difference between 3.91s and 3.55s is a little over 300RPM. That isn't that big of a difference.


http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

Don't know if it's possible or not, but if the OP was able to run a tall tire on his Wagon, say 29 inch or better it mite not be to bad.

That was my first thought. Approximately 10% difference. Not worth it in my opinion. There is no gear ratio available that will allow you to cruise at 1500-2000 RPM like you are used to in modern cars with 2 overdrives and lockup converters.

Back in the late 60's early 70's many muscle cars from Ford. GM. and Mopar came with 4.10 gears and 26" tires. However a 383 Fury Wagon was not then, is not now a muscle car. It probably had a 2.93 originally. People drive faster now than in 1967. with a 2.93 gear at 75 mph the RPM will be 3000 plus but with no tach and a quiet exhaust system who noticed? 3000 RPM is not going to hurt a 383 unless it is already hurt.

The way I see it a 2.93, much less a 3.55 will not get you were you want to be. Several people have suggested an overdrive transmission. That is the only way you are going to cruise at 70-80 MPH at comfortably low rpms.

ME? 4.30s with 28" tires. Has only been on the interstate longer than 10 minutes at a time once in 20 years. If I ever get around to switching to a Dana it will probably get a 4.10.

I ran a D200 PU back in the day. All over the place with a lot of highway miles. 4.10's and 29" tires. It did OK on the highway. I would cruise 70 and sometimes 75 max. It was probably turning 3300-3500 RPM on a sustained basis at higher speed. That is as much as I would want to run and even then noisy even with turbo mufflers.

With car size tires (25-26"?) I think 3.91 would be too much. Also speeds are higher now.

My current classic PU runs 4.10's and 31" tires. OK to 70-75 MPH and spinning pretty well at that speed. As much as I want.

My '70 Challenger ran a 318 and 3.23 as original with 24-25" tires. The original powertrain did surprisingly well. Decent acceleration and OK on the highway. Now runs a 496 and still 3.23 rear. Also OD transmission. It runs well.

If highway driving is part of your plan, I would suggest a 3.23 rear. It will do fine on the highway and the 383 should handle it fine at low speeds. Plenty of go.

Got 4.30's in my Charger and they're fine cruising around 70mph. People magically move over when I come up behind them for some reason. Still, in the next few years I'll build a 400 based stroker and swap in my 3.91 pig. I think that will do for anything less than a cross country tour. YMMV...….

Back in 68-70 my 64 Plm had 2.76 and a 4 speed (a little hard on the clutch) oval sprint track tires on 15 inch mag wheels, kinda tall and had to massage the well a little. Even at 80 mph it was still under 2000 rpm. Back in those days I knew where the radar traps sat so we went whatever mph we wanted. The 70 Z would run 3000 at 60 but I have no idea what gear it had, buzzed around the 95 interstate 3500-4000 or more all the time. To get a ticket one had to be real stupid, not like today.

I currently have 3.54 gears in the Dana 60 under my '65 Coronet. I'm getting ready to swap a new Dana 60 with 3.23 gears in there. The 3.54 gears are okay but I think I'll like the 3.23 gears even better.

Us limp wrists must sit behind desks and earn enough money to afford OD

Yeah, that's the problem.

I just love how people reminisce about the "good old days" when men were men.....
People used to have dentistry performed without anesthesia too.
Sometimes the "good old days" just weren't that good, they're just old.

Was it here on moparts years ago that I viewed a picture of
a foreign overdrive unit bolted to the rear of a 727 in place of the OEM tailshaft?

If my fuzzy memory is not fooling me this overdrive had what seemed like a small diameter.

I am not talking about a Gearvendors unit
or the overdrive add-on designed by Chrysler for the 518/46 automatic.

Less than an hour ago I was listening to Red Eye Radio on 820 WBAP out of Dallas and heard a commercial repeatedly for 2.18 ratio big truck differentials now available.

In 1968 I had 4 teeth pulled by my small town dentist without pain killers.
To his credit it did all four very quickly.

Did you know the tooth brush was invented in West Va?
Any place else it would have been called a teeth brush.

Might add in late 60s a tank of gas was $5.00. Two 4s, 5.86 gears, cruising Friday and Saturday nite would take 2 tanks. Didn't matter back then, $100 or more does today on wall mart greeters salary does.

If you have a small block that swap to a 518 only set me back $1,000 using the factory TC that came with it. Looking at $1500 or about if you need an Ultrabell to fit it to a big block. As long as you can make your own mount - no problem.

In the year 1967, the average retail price of gas in the U.S. was $0.33.

This is equivalent to $2.47 in 2018 dollars. National Average Price of gas as of 8/20/18. $2.838. It's $2.69 around here.

Lol , In the early 70's I absolutely refused to buy Sunoco 260 because it was an outrageous 45 cents per gallon.

Typical Walmart greeter probably does not use 2 tanks of gas in a month.

I did not live in WVa.
I had no cavities and the 4 teeth were in good shape and not wisdom teeth.
My jaw was too small.

I also remember 31 to 33 cents per gallon gasoline when CocaColas from a vending machine was 10 cents.

The ratio of gasoline price to vending machine Cokes has stayed pretty stable.
The ratio of a Mars MilkyWay bars to gasoline has also stayed relatively constant.

The above ratios have been more stable that the ratio of the price of crude oil to either a troy ounce of silver or Gold.

Unless,. I still have that car! LOL
I pumped 260 for $.38 @ gallon (my weekend job) pumped 190 the most, $.29

Sorry, must have hit a nerve.

Doesn’t having 4 teeth removed from a small jaw prove that legally I cannot be a
“Big Mouth”.

Touché LOL

I dont know any typical walmart greeters that even own a older performance muscle car.

Ive never understood how some can own a 30-60k mopar muscle car that is really a luxury/toy vs a necessity in life and complain about the cost of a tank of fuel but yet never balks at there 40k new truck needing a $200 oil change.

However at the same time I wont pay $1.70 for a candy bar thats 40% smaller then when it was 25 cents in 1975.

Sarcasm with priorities

3.91's are in, I used right stuff to deter the 3.23 swap......

5:13's and 88's here, also ran 56;s and 4:30's 😁

We have gotten used to our OD's and loafing down the highway doing 75 at 2,000 RPM. So it'll be different. Will it blow up? likely not as that's what they did back in the day.
Myself I'd probably go with a 3;23 or 3:55. Some even find the 55's to steep.

I went 3.73s + Gear Vendors.

Car is nice on the highway now.