Syco79

Does anyone have any idea what kind of rpms id be turning in my 79 with a th350 if I were to drop in a 4.11 rear? I had planned to go for 3.73s but the opportunity to get a nice 4.11 setup has presented its self and I am wondering if it would still be street able with the 3 speed auto.

Procrastination Racing

My '79 had a 3.08 and I got 12 mpg. Many on here in a thread a year or so ago got about the same with their 3.55 and so on.

If you go to 4.11, you are going to be quick out of the hole, but gas mileage will be down under 10. You won't like any highway with a speed higher than 55. If it is a weekend cruiser to hit the cruise nights and the occasional drag strip night, go for it.

If you want to drive it frequently and on any trips, even the 3.70 (3.73 is a big Chevy ratio) will be too low.

80vette21

Yes its practical........ If you dont plan on going over like 60mph

I had 3.70s and a Th350 before I swapped to a 383 stroker and 700r4 OD trans and 275/60 tires (the 275s actual drop the RPMS a few around!). I couldnt go over 65-70 on the highway without being up to 4k with that setup.... with 4.11s youll probably be turning about 3k @ 55-60mph, but thats just a guess based on what I saw with my 3.70s. Theres calculators online to figure it out, standby and Ill find one.

EDIT: Okay, assuming your running the standard 255/60 15 tire size heres a breakdown of your expected RPMs:
55mph- 2,809 RPM
60mph- 3,065 RPM
65mph- 3,320 RPM
70mph- 3,575 RPM
75mph- 3,831 RPM
80mph- 4,086 RPM
85mph- 4,342 RPM
90mph- 4,597 RPM
95mph- 4,852 RPM
100mph- 5,108 RPM

As a reference, my car with 3.70s and a 700r4 turns only 1,711 RPM at 55mph, 2,177RPM at 70mph, and 3,110RPM at 100mph! OD is great, Im no longer stuck in the slow lane on the highway!!!

This info is courtesy of Bowtie Overdrives RPM calculator. Check it out here:

http://2004r.com/speedoCalc/rpmcalc.shtml

'75

I just put a 4.11 in a 79 last weekend, the owner is happy with the acceleration and doesn't do much highway driving. With 255-60-15 tires 3065 rpm you would be going 60 mph.

Gordonm

I had 411s in my car a few years ago with a pretty healthy 350. On the highway it buzzed a LOT. Who runs 60 on the freeway anymore. You are running 70 most of the time. I was buzzing close to 4000 rpm with 245 60 15 tires. It was great on the drag stipulate and around town but anytime you had to go over 65 it was tough. Fuel mileage forget about it. This was all with a 4 speed m20. I went with 3.70s. Tha twas better but really was much better with an OD trans.

TexasMadMan

You probably got your answer above, but I was going to say at 60mph you should be turning about 3k rpms.

Skip Burney

You are gonna wear out your engine faster and if you like 55 or 60 you will love a 4.11 heck if you like 45 go for a 4.56

Ironcross

Why are people scared of 4 series gears?...the notion that you will wear out the engine is ridiculous....unless you put together junk engines....The 4 series gears were almost always in the performance Vettes or you may as well stay home....Great for street racing too. The 3 series gears were almost always in Dealer ordered inventory cars without horsepower....You cant hurt a well built Vette engine by spinning it a little faster.... even with a hydraulic cam a Vettes performance can be greatly improved by a simple gear change to a 4 series gear...

.Nearly every one of mine are either a 4.11 or a 4.56... and yes with a 4.11 double the RPM`s to get your speed reading that becomes 70 MPH at 3500 RPM....the 4.56 is a little higher at 4000 RPM`s to run 70 MPR. And as far as a automatic and performance, L72`s and more are great with the 4`s gear....

Vette5.5

Think if doing much highway driving, a 4:11 axle with TH350 isn't what you're wanting, as expect about 4000 rpm @ 70 mph depending on converter stall. I'm currently running a car with 3.73's, 700R4 lock up converter, and that's the ticket.

Syco79

Well I honestly do not care about gas mileage I drive less then 1000 miles per year with the car... Its got a 383 stroker in it now and the 3.08s or what ever is in there is just too damn weak. However most of the roads around here are country roads (im in the Poconos) so im usually cruising around 60. Not being able to get on the highway kind of stinks but its not the end of the world either. I think 3.73s would be a better choice but the price is right on the 4.11 setup... Guess I gotta think about it for a day or so heh

Syco79

I think I could tolerate 3k rpms at 60mph... I typically dont highway cruise anyway.

scrappy76

I actually do not know what gears are in my vette, but at 3000 rpm's I am running about 60mph. So either I have 3:73's or 4:10's. But I am fine with that. I daily drive my vette about 3 times a week going to work. round trip is about 90 miles each day. I have sidepipes and love it. I did not buy a vette for gas milage or quiet.

Jughead

I have 4.56's in my 2001 Excursion that I use just about daily.

I have a 4.11 rear waiting to be transplanted into my 70 vette, has 3.30's now. But I don't go on long trips either.

carriljc

I have them in mine and before I got my 0.62 OD ROD tranny the engine was really wound up just going down the road.
It's much more of a pleasure to drive now with overdrive. Just my input.

Belgian1979vette

Basically it depends on the rpm power band of your engine.

If it is stock and with an auto, i would stick with a higher gear.

If you want the best of both worlds, go for an OD. Expensive, but it's definatly the best deal.

Syco79

the 383 stroker is good to about 6500 rpms... I think 3.73s would be ideal for me but if I can get the 4.11 unit I plan to do it. One day in the far future id like to go over drive anyway but its expensive

MIKE80

I have 3.70 with a 4 speed and run between 2900-3000 rpm at 60 mph. My tires are 275/40 ZR17 all around.

Corey_68

practical? No

Fun? hell yes

jabrun

A guy once told me that in high gear, non overdrive tranny the 1:1 tranny ratio you can check your RPM's at 70 mph. to figure out the rearend ratio. The tach will read 1000 times what the rearend gear ratio is. Example 4.11 ratio=4110 RPM's @ 70mph.

bashcraft

That doesn't work out right. Check here:

http://www.keislerauto.com/speed_analyzers.php?sa=gm_5

At 4100 rpm with 4.10 gears and 225-70 15 tires, you'll be going 82 mph.