Pick the gear

[81 Corvette]

So what gear would you choose and why. I mostly use the car to drive back and forth to work (about 2 miles) and the rest is spent dinking around town with a few trips home. I'd say the non work driving is about half highway and half city.

The choices are 3.31, 3.54 and 3.73

Right now I think 3.54 seems like a nice compormise.

What say you?

 

[Ken]

Manual transmission or automatic? :confuse

With the limited amount of daily driven miles, I wouldn't hestitate to go with the 3.73s - you'll love to response!

 

[81 Corvette]

its an auto. current gear is 2.87

 

[Glensgages]

As Ken stated before me, with such limited mileage, and almost all of that being stop & go city, I'd throw as much freaking gear at that '81 as I could afford, 'specially if your '81's locking TC is still functioning properly.

3.73s'll really 'scoot', and scare those ricers, too.

 

[81 Corvette]

I'm starting to lean more towards the 3.73. The torque lock up does work, or at least the car sounds like its shifting into a 4th gear. I'm going to sleep on it for a few days and make the decision next Monday. Thanks for the input and I look forward to more.

 

[Scott Winebarger]

For the traveling that you are doing , the 373 will be a blast !

 

[Culprit]

The choices are 3.31, 3.54 and 3.73

Right now I think 3.54 seems like a nice compormise.

Why compromise? With a statement like that, I think you know what you truly want.

I have the 3.73's (or 3.70/3.71, whatever it was in '78) and I have absolutely no complaints - other than wanting a 5 speed Keistler with OD, but it sounds like I do considerably more highway driving than you do.

Semper Fidelis,
Culprit

 

[Glensgages]

FYI.....

if your TC is locking-up, and you choose 3.73s, you'll be turning approx 2800 RPM at 60 MPH with 27" tires (BFG 255/60R15).

Your speedo/tach ratio will be slightly more than 2:1 (60 MPH-to-28 {hundred} RPM) in 3rd gear w/ lock-up.

My '82 Corvette (stock) ET/MPH went from 15.704/86 to 15.004/91 with nothing more than a swap to 3.73s from 2.87s.

By Corvette-standards, it's still a pig, but it is much more fun to drive without the motor 'lugging and chugging' at city-speeds.

 

[81 Corvette]

thanks for the info....most of my highway driving is in the 70-75 mph range. I don't recall the rpm's but seems like at 70, the rpms are at 2700~ If i go to 3.73, my highway speed will probally have to drop. I figue its gonna be an extra 600 rpm or so to pull the same speed.

my current 1/4 is 14.58 @ 100.1 I'd like to see a sub 14 second time with the 3.73

I couldn't sleep last night while debating between the 3.73 and the 3.54 lol

 

[Glensgages]

thanks for the info....most of my highway driving is in the 70-75 mph range. I don't recall the rpm's but seems like at 70, the rpms are at 2700~ If i go to 3.73, my highway speed will probally have to drop. I figue its gonna be an extra 600 rpm or so to pull the same speed.

I'm figuring you'll turn approx 3600 @ 75 MPH

my current 1/4 is 14.58 @ 100.1 I'd like to see a sub 14 second time with the 3.73

14.58 @ 100+ MPH?????
:confused
With 2.87:1 gears?????
:confused
"Somebody's" not playing with their OEM L-81.....
:nono
Care to tell me more?
:BOW

If you're making that-much smoke, traction may-be a problem with anything deeper than 3.31s, which probably wouldn't be worth the cost or effort.
If you can hook, you'll run high-13s, maybe quicker.

My friends have 2 'rules-of-thumb' regarding swapping gearing and ET-reduction:
#1: each .25 of gear-ratio = .1 in ET; or
#2: each .1 of gear-ratio = .06 in ET.
I've seen each work (on occasion), meaning you'd pick-up between .344-seconds, and .051-seconds.
I think I picked-up so-much more ET (.701) because the 2.87s are almost 'off-the-chart' (the CFI was so woefully under-geared from Bowling Green).

If you'd like, I can show my before/after incremental times.....

I couldn't sleep last night while debating between the 3.73 and the 3.54 lol

The difference at 75 MPH will be less-than 200 RPM; get the .73s and be done with-it...

 

[LanceB]

After reading thread, I may be interested in changing my 81 stock gears one day, what is a ballpark figure for something like that (in KY)? I take it this is not an easy do it yourself job either. There are a lot of riceburners here that try to see what I've got.

 

[Glensgages]

LanceB:

I have no idea what the fee would be to have the gears swapped-out;
my guy charged me less than $400 labor & miscellaneous parts & gear lube, including swapping-out both (drive & driven) speedo-gears in my 700R4.

I got my gears a year ago from:
"Ronnie" at POWER-TRAIN
631/589-7020, on L.I., N.Y.

They are 'Precision Gears', and cost just $125 less S&H

 

[LanceB]

I recently had the spindles and bearings replaced in my rear end by my mechanic. I should have asked him his thoughts on the gears when it was there, but I didn't even think about it until I read the thread. He has a 79 with legit 390,000 miles daily driver. Pretty fast car too.

 

[81 Corvette]

It looks like I'm taking it to a 4 wheel drive shop.

http://www.4wddiv.com/indexhome.htm

they are going to supply the parts. I might be able to save a buck or two if i ordered the gear myself, but i don't feel like messing with it. They are also doing the removal and install, u joints, diff bearings seals etc.

The diff leaks pretty bad at the yokes, so this all started as a required rebuild, but since its apart I figure now is the time to do the gears.

Their estimated cost for all labor and parts is $1300-$1400.

I guess I should clariffy my times. It is on the dreaded g tech so you can debate the accuracy. lol

the mods are light so far but include rpm air gap, 625 demon carb, new distributor, dynomax headers, hi flow 3in cat and dual flowmaster 40's. the clutch fan has been removed and replaced with flex-a-lite set up, and no smog pump or ac compressor.

 

[Glensgages]

I guess I should clariffy my times. It is on the dreaded g tech so you can debate the accuracy. lol

the mods are light so far but include rpm air gap, 625 demon carb, new distributor, dynomax headers, hi flow 3in cat and dual flowmaster 40's. the clutch fan has been removed and replaced with flex-a-lite set up, and no smog pump or ac compressor.

THAT might explain it.....

If you are still running 8.2:1 CR, the stock heads and cam, you might be very disappointed in your ETs.

I had a similar bottom-end in my '79 Z28 (LM-1), swapped to 64cc heads (9.3:1 CR), .450"/218* hydraulic cam, 650 dbl-pump, open-headers, etc., and I could run 14.40s/97 with 3.42:1 gears.

While your '81 Vette may weigh less than my Z28, I can't really see it running almost the same ET, at a higher MPH, with LESS gearing, and no cam/compression (but I hope I'm wrong...)

Just for chits & giggles, why not see what your '81 runs at a REAL track before the gear-swap?

 

[81 Corvette]

like i said, feel free to debate. Its not a real track time, but its in the ball park, and right now thats whats important to me.

i'd be afraid the back end would fall out if i stomped it at a track or any where for that matter. the outter u joint on the drivers side is shot.

 

[Glensgages]

like i said, feel free to debate. Its not a real track time, but its in the ball park, and right now thats whats important to me.

81 Corvette:
I meant no-disrespect; just seen a lotta people take their "13-second G-Tech cars" to the strip and run solid, high 14s many times....

You are correct; how it FEELS is just as important, 'specially if you have no plans on running it often.

Keep us posted on progress...

 

[norvalwilhelm]

if your TC is locking-up, and you choose 3.73s, you'll be turning approx 2800 RPM at 60 MPH with 27" tires (BFG 255/60R15).

With 4.11's and a 700R my rpm at 60 was 2200 and at 70 was 2500. I just found the combination of 411's and 307 first gear in the transmission too much gear in 1st.
I have done a back to back comparison of 308's and 4.11's in the same afternoon and the 411's sure woke the car up. That was in a small block, not my bigblock

 

[81 Corvette]

81 Corvette:
I meant no-disrespect; just seen a lotta people take their "13-second G-Tech cars" to the strip and run solid, high 14s many times....

You are correct; how it FEELS is just as important, 'specially if you have no plans on running it often.

Keep us posted on progress...

Its all good. Its just something to benchmark agaist. As a second bench mark, before anything was done, it ran 16.5ish on the same road and same gtech.:L

I take the numbers with a grain of salt. but a grain of salt is better then a glass of air.

 

[mr mctavish]

Im interested in the final results also. Thinking of going to 3.31 from 2.72
I ran 13.99[best] looking for mid 13's Intend to get a tko w/od at the same time.