Indicators of a 1971 Big Block Car

[Patrick B.]

Re: Indicators of a 1971 Big Block Car

Patrick, Maybe I’m missing something can you show me an example. The code as you know is a three letter code for 1970 and a two letter code in
71-72. It tells you the actual ratio, not if it was a big block or small block. Again, maybe I’m missing something as it wouldn’t be the first time. All big blocks, LT-1’s, L-46’s, and automatic transmission cars used to heavy duty cast caps whereas all others use the metal strap to secure the joint to the rear end yoke. Also the cars that utilizes the cast caps also has their axle shafts shot permed with a number 31 size shot. Can you show me an example. Thanks.

Ron -- I am much more familiar with 70's where the code is indicative of the big block rears (also used by LT-1's in 70). I see now that the codes don't have much meaning in 71 beyond the ratio. Perhaps the distinction between the AX and LR 3.36 rears have some meaning, and a 3.70 or 4.11 would likely preclude a LS-5 even if it had the HD caps. I have never seen anything written that L-46's used HD rears, but they were not available in 71 anyway. The subject vehicle is clearly a small block, but if it had a 3.70 or 4.11 rear with a plausible date it would likely be an LT-1 which would be of interest to the OP.

[Ron G.]

[Joe L.]

Re: Indicators of a 1971 Big Block Car

All-------

Keep in mind that the differential codes define the complete configuration. They do not merely indicate a ratio. The elements of configuration include what type of stub axles are installed. This was true for ALL Corvette differentials regardless of year. This means that there was never a case in which a single axle code was produced with both types of axles (i.e. u-bolt and cap). As I say, the code defined the complete configuration.

So, I would say that for 1971 codes AA, AB, AC, AD, and AW represented differentials with cap type axles (otherwise known as HD axles). Very likely, code AX was the code for 3.36:1 with cap type axle and code LR was the code for 3:36:1 with u-bolt type axles (the reverse is also possible). L-48 with base engine, 4 speed, and 3.36:1 rear ratio was the standard combination for 1971. So, it received the 3:36:1 with u-bolt type axles. All other engine/transmission/rear ratio combinations received the cap type axles.

[Nick P.]

Re: Indicators of a 1971 Big Block Car

thanks for everyone's feedback! Once the car is back on the lift, I'll post the code if anyone is interested. Attached are a few photos of the engine mounts. Although it already seems clear the car is a small block, out of curiosity....where there different engine mounts for small vs big block? Do the welds on these mounts appear factor correct? thanks! mount2.jpgmount1.jpg

[Ron G.]

Re: Indicators of a 1971 Big Block Car

Nick,

There is one other indicator of a big block car versus a small block that I probably inadvertently did not mention. The brake lines coming out of the rear brake calipers on a big block have spiral armor to protect the lines from being damaged as opposed to small blocks did not have the spiral armor protection on the brake lines coming out of the rear calipers. This was due to the torque of a big block. Just an FYI. - Ron

[Joe L.]

Re: Indicators of a 1971 Big Block Car

thanks for everyone's feedback! Once the car is back on the lift, I'll post the code if anyone is interested. Attached are a few photos of the engine mounts. Although it already seems clear the car is a small block, out of curiosity....where there different engine mounts for small vs big block? Do the welds on these mounts appear factor correct? thanks! [ATTACH=CONFIG]101082[/ATTACH][ATTACH=CONFIG]101083[/ATTACH]

Nick------


There was no difference in the motor mounts or motor mount brackets for big blocks or small blocks.