gears

[LanceB]

My brother was getting the rear end fixed on his 77 L82 and I suggested getting new gears while it is being worked on. He would rather have more low end than top end, and from reading this forum and talking to the mechanic we went with 373 gears. The other work done to the car in the past 6 months includes a rebuilt carb, headers, and true duals. Will there be a noticeable difference on the takeoff? It already runs pretty solid and will leave my 81 at the stoplight. If it is much better I may have this done to mine.

 

[81 Corvette]

he will notice the change. Not sure the gear he has now, but i'd guess 2.9-3.1. IMO, 3.73 is too much unless you have an over drive tranny, or only drive on teh street.

My 81 is scheduled for a 3.54 swap later this week. I thought about a 3.73, but the rpm's at 70 were way to high.

 

[yellow77]

My L82 (1977) came with 3.55 gears, and I believe this is the correct gear for that year and model type (assuming automatic). If this is the case, he wont be gaining much at all.


Cheers

Richard

 

[LanceB]

Talked to mechanic, and the 77 has 331 gears. This tells me a couple of things. This car may not be an L82

 

[LanceB]

Does anyone know what gears came on the L48? Also I remember a post somewhere in here that tells how to find out if vehicle is a true L82 or not. Does anyone remember where it is? So far in the last 2 weeks I have found out that my 81 was originally white (not the current red), and my brothers 77 may not be an L82. Oh well, they look good and run good.

 

[Glensgages]

Does anyone know what gears came on the L48? Also I remember a post somewhere in here that tells how to find out if vehicle is a true L82 or not. Does anyone remember where it is? So far in the last 2 weeks I have found out that my 81 was originally white (not the current red), and my brothers 77 may not be an L82. Oh well, they look good and run good.

According to a source-book I have, the fifth symbol of your V.I.N. designates engine code:
"L" -is the 'base' L-48, while "X" is the optional L-82.

The same book lists for '76, gear ratios of 3.36 for L-48/4-speed, 3.08 for L-48/auto, 3.55 for L-82 w/ WIDE-RATIO 4-speed, 3.55 OR 3.70 for L-82 w/ CLOSE RATIO 4-speed, and 3.36 for L-82/auto.....
but in '77, only 3.36s are listed, WITH an 'optional/highway axle ratio' (possibly 3.08s?) are shown, at $14.00.

 

[Culprit]

LanceB - here is a data point for you to add another piece of info to your investigation for comparison.

My 78 L-82 has stock 3.70 rear gears and close ratio 4 spd tranny.

At 60 MPH I'm running approx 3000 RPM (I haven't done the math, just remembering what the tach said - the real number is probably somewhere between 2800 and 3100) on 255 60 15 tires.

 

[Glensgages]

Culprit:
the actual formula for calculating RPM at a given MPH with a stick-shift, 1:1 transmission is:
MPH x GR div/by .006 div/by 1/2 TH = RPM
GR = Gear Ratio
1/2 TH= 1/2 Tire Height

60 MPH x 3.70 div/by.006 div/by 13.5" = 2740 RPM.

Is that about correct?

 

[81 Corvette]

Culprit:
the actual formula for calculating RPM at a given MPH with a stick-shift, 1:1 transmission is:
MPH x GR div/by .006 div/by 1/2 TH = RPM
GR = Gear Ratio
1/2 TH= 1/2 Tire Height

60 MPH x 3.70 div/by.006 div/by 13.5" = 2740 RPM.

Is that about correct?

Works for me....and to think i took the tire size and calculated the circumfrance to determine the number of tire rotations per mile, then took the engine rpm's and divided by teh gear ratio to get the tire rpm's and then divided by the tires rpm's per mile to get mph. :L

 

[Glensgages]

Works for me....and to think i took the tire size and calculated the circumfrance to determine the number of tire rotations per mile, then took the engine rpm's and divided by teh gear ratio to get the tire rpm's and then divided by the tires rpm's per mile to get mph. :L

81Corvette:
Yeah, you can 'go' that route, figuring tire circumference, tire/axle RPMs, yada-yada-yada...
but that is what the " .006 " is for; it is a factor, incorporating all 'those' type things into consideration...

I learned it (and memorized it) years ago from an old racer...

 

[mr mctavish]

Glensgages ------ I figured you,d pop into this thread Im going to go 3.54 also.
Thanks for the input.

 

[Glensgages]

Glensgages ------ I figured you'd pop into this thread Im going to go 3.54 also.
Thanks for the input.

mr mctavish:
If that thing hooks with 3.54s.......it'll be like in the opening scenes of "Back To the Future"....

"Mahty... when this thing hits 88 miles-per-hour.....
you're gonna see some serious chit!!!"

 

[Culprit]

Glensgages - Thanks for crunching the numbers - I have other things going on here than to pull out the calculator right now. I appreciate it.

Semper Fidelis,
Culprit

 

[Fishman]

I have other things going on here than to pull out the calculator right now

What in Iraq could be more important than calculating ratios for Vettes? :L

 

[LanceB]

I am waiting to get the 77 back to do some investigating on whether it is an L82 or not. Getting off of the subject a little, I looked at my 81 last night with my handy black book. The VIN says it was made in B.G., so there is no way red is the original color. According to the book there were no solid colors, so white may be out of the question too. I looked in the door where the paint stamp is but I haven't deciphered it yet. I suspect maybe it was a two-tone, white being the top color. Anyone know how to read the paint stamp in the door?

 

[81 Corvette]

http://corvetteactioncenter.com/specs/c3/1981/index.html

just pick your year from teh drop down box and look at the production info