billlee

Can anyone tell me what final gear ratio's were offered in 81, the 2.72 for the manual trans, and a 2.87 for the standard auto, but what was the performance ratio offered?

81vette

I believe it was the 3.07

Duke94

Good question. All the Corvette referance books I have show the 2 ratios you list along with a G92 Performance Option but they don't say what the ratio is. A few internet sites seem to agree that it is 3.15 but I couldn't find anything "official".

Gary

81vette

1981 Corvette from Road & Track

Curb Weight................................33 95 lbs
Test Weight................................35 90 lbs
Weight Dist (with driver), f/r...........48/52 %
Trans................................... ......4 spd manual, 2.72:1 final ratio
0-60 mph...................................9. 2 sec
Standing 1/4 mi...........................17.0 sec
Speed at 1/4 mi...........................82.0 mph
Stopping Distance from 60 mph......130 ft
Interior noise at 50 mph................73 dba
Lateral Acceleration......................0.790 g
Slalom Speed..............................61.2 mph
Fuel Economy..............................16. 0 mpg


1980 Corvette from Road & Track

Curb Weight................................33 45 lbs
Test Weight................................34 30 lbs
Weight Dist (with driver), f/r...........46/54 %
Trans................................... ......4 spd manual, 3.07:1 final ratio
0-60 mph...................................7. 7 sec
Standing 1/4 mi...........................16.0 sec
Speed at 1/4 mi...........................86.5 mph
Stopping Distance from 60 mph......130 ft
Interior noise at 50 mph................73 dba
Lateral Acceleration......................0.790 g
Slalom Speed..............................61.2 mph
Fuel Economy..............................14. 5 mpg


Mark

gbvette62

The 1981 optional G92 Performance Axle Ratio was 2.87.

G92 was ONLY available with RPOs YF5 (California Emission Equipment) and MX1 (Automatic Transmission). 49 state emission cars came with a 2.72 ratio with the 4 speed and 2.87 ratio with an automatic. Both auto and 4 speed trans Calif emission equiment cars came with the 2.72 ratio, the 2.87 could be ordered with Calif automatic cars. This information is from the 1981 Chevrolet Dealers Order Guide, Corvette page. The Performance Ratio was a $20.00 option and was installed in 2,400 cars.

The 3.07 ratio used in 1980 will work in the 81 Dana rear, but was NEVER offered by Chevrolet in 1981.

81vette

After reading your reply I realized that I have heard this before. I went back to my Road & Track which is a special issue that contains various articles from Road & Track over the years on Corvettes. I started looking at the 1980 and 1981 spec sheets and realized that they had switched the specs in the two articles. They don't have the car year on the spec sheet, so you can't tell by looking for a title. The give away was the pricing for the two cars on the spec sheet which was also referenced in both articles. Anyway, you are correct.... the performance ratio was a 2.87.

I've corrected my earlier post.


Mark

gbvette62

That Road & Track info would have been taken from the Chevrolet Long Lead Press Preview, which would have taken place in the spring of 1980. Chevrolet MAY have planned to offer the 3.07 ratio as an option for 81, but that never happened. June 1980 Corvette Parts Books list the 3.07 for 80 & 81, but September 81 books only list the 2.72 and 2.87 rears.

I have a Chevrolet "Inter-Organization Letter" dated April 28, 1980 and titled "1981 Plan Book - Corvette Coverage Revision". It states the following: "Rear axle ratios changed to 2.72:1 with manual transmission and 2.87:1 with automatic. Previous ratio was 3.07:1 for both applications".

Another 1981 Corvette Plan Book Inter-Organizational Letter I have, this one dated September 23, 1980, states "California Rear Axle Ratio For Automatic Transmission Changed To 2.72:1. 2.87:1 Ratio Retained As Performance Ratio".

The actual "1981 Corvette Plan Book", dated 9-15-80 and marked "GM Confidential", "Chevrolet Motor Division", "1981 Corvette" and headed "Product Program" has the following information on page A2. It says: "New 2.72:1 axle ratio to be used with the 4-speed manual transmission in all 50 states and the automatic in California. The 2.87:1 ratio to be used with the automatic federally and as a performance ratio with the automatic in California".

The "1981 Corvette Plan Book" makes repeated mention of the "Gas Guzzler Tax". Most of the changes made to the Corvette in 1981 were made in an effort to avoid the tax. This is probably why the 3.07:1 was dropped.

gbvette62

Sorry, you updated your post quicker than I was able to locate (and type) the additional information I just posted.

The important thing is that the correct information has been posted!

81vette

Good info.

Mark

billlee

Thanks for all the information guys, Am I reading it correctly that the 2.87 was only offered for the CA auto cars?

gbvette62

The 2.87 was the only optional rear and it was only available on California cars with auto. The standard rear in CA was the 2.72 with the auto.

The 2.87 was already standard with automatic cars sold everywere but CA.

larryg3

gbvette62 is right on the money. I had mine changed from the stock 2.87 (verified with my build sheet) to a 3.54, and boy did that really wake up the car!!

foundvettelifeisgood

This morning, before finding this great old post, I took a ride to determine my axle ratio, logging RPM at various speeds from 50 to 75. I have a 4 speed 81 and the math confirms the 2.72 axle ratio...