63 fuel car

[Bob R.]

What HP engines could be ordered with a 3:08 rear in 63. The rear differential in my car is stamped CJ and correctly dated for my car. I believe it to be original to the car but wondered if it could be ordered for a fuel car.

[Jack M.]

Re: 63 fuel car

Here's a composite excerpt of '63 rear axle data from the FREE Information Kits available at the GM Heritage Center.
If you are unfamiliar with these items, take a look at this old thread: CLICK HERE

[Bob R.]

Re: 63 fuel car

There was a lot of information there thanks for posting that. I noticed that there are two optional rear 3:08 gears one is noted as G81 and is available on 250 and 300 HP the other is G91 and is available on 340 and 360 HP. The Black Book notes that there were only 211 cars delivered with G91 but it doesn't note how to identify the parts any idea what CJ would be?

[Jack M.]

Re: 63 fuel car

On page #3 of the initial document posted, take a look at the top/right corner... CJ is listed as a Positraction Axle.
Also, page #1 lists the G91 for 250 & 300 HP vehicles.

In addition, this attachment illustrates the same info for G91:

[Jack M.]

Re: 63 fuel car

NOTE: Model info can change during the year... there is no guaranty regarding the data in these Info Kits (but nice FREE stuff).

[Bob R.]

Re: 63 fuel car

I do not follow you. G91 is noted as 250 and 300 HP with 4 speed and was a $2.20 option. G81 doesn't list the engines but is noted as a $43.05 option. I know that CJ is a 3:08 posi but I don't see any notation explaining if it is G91 or G81 and whether it was used for a fuel car.

[Jack M.]

Re: 63 fuel car

Hummm, maybe I'm confused (sorry - as I'm dyslexic). Let me revisit the data provided in the Info Kits.

[Loren L.]

Re: 63 fuel car

G91 is a non-posi 3.08 available with the wide ratio 4 speed that came with the 250/300 HP motors. If I recall correctly the '63 Z06 convertible that was ordered by the GM employee and discovered a few years back came with a 3.08 Posi - the owner called it a "contributing factor" to the number of speeding tickets he acquired in the first 18 months of ownership.......

[Michael J.]

Re: 63 fuel car

I have two C2s with 3.08 rear ends. My '64's (FI tanker) window sticker shows the 3.08 posi (2G81AA) a $43.05 extra cost option. I am not sure how many rear end ratios were extra cost options.

[Jack M.]

Re: 63 fuel car

I noticed that there are two optional rear 3:08 gears one is noted as G81 and is available on 250 and 300 HP the other is G91 and is available on 340 and 360 HP.

G91 is noted as 250 and 300 HP with 4 speed and was a $2.20 option. G81 doesn't list the engines but is noted as a $43.05 option.

Perhaps those two statements are messing me up (they seem to contradict)... what engine do you think the G91 was associated with?
According to what I'm reading (and I'm NO expert), it appears the G91 was an open axle (3.08) available with the 250 & 300 HP engine ($2.20 option).

In addition, it appears the 3.08:1 positraction axle (G81) was a $43.05 option... and it was available with the 360 HP engine.

[Timothy B.]

Re: 63 fuel car

I always believed that posi was a option and with posi you could specify any ratio. With the standard open rear you got 3.36 with wide box cars and 3.70 with close ratio cars.

[Michael J.]

Re: 63 fuel car

In '63-'64 M20 was the only option in a manual Muncie.

[Duke W.]

Re: 63 fuel car

G91 was an open 3.08 axle only available on 250/300 HP engines with M20. The standard axle was open 3.36. G81 was the optional Positraction axle available with all engines, 3.36 or 3.08 on 250/300 HP engines, and six ratios from 3.08 to 4.56 on 340/360 HP engines. As far as M20 was concerned if you ordered it with a 250/300 HP engines you got the wide ratio version, and CR with 340/360 HP engine. M21 came along in '66 when on some engines you could order either the CR (M20) or WR (M21).

[Leif A.]

Re: 63 fuel car

G91 was an open 3.08 axle only available on 250/300 HP engines with M20. The standard axle was open 3.36. G81 was the optional Positraction axle available with all engines, 3.36 or 3.08 on 250/300 HP engines, and six ratios from 3.08 to 4.56 on 340/360 HP engines. As far as M20 was concerned if you ordered it with a 250/300 HP engines you got the wide ratio version, and CR with 340/360 HP engine. M21 came along in '66 when on some engines you could order either the CR (M20) or WR (M21).

Duke,
I'm sure you meant CR (M21) or WR (M20)

[Michael J.]

Re: 63 fuel car

Yep, and there is nothing more difficult than getting a '63 or '64 Corvette with an M20, and one of the SHP engine, moving from a standing start on a hill with a 3.08 rear end.......