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.