I've had my 81 C3 for about a year and a half and it has ZZ4 with 375-400hp with a 3 speed and stock rear end. Ive been looking to make some better times and a little better fuel economy. I found a 5 speedmanualtrany kit to bolt up on it and was wondering if anyone knows how much my stock rearend could hold and what should i do to beef it up a bit and also does anyone know whatthe stock gears are? and should i go to a 3.73 rearend? Any ideas would be greatly apreciated. I'm justtrying to get a plan set formy baby so ican do everything at once. Thanks guys!

 

Hi and welcome to the forum.
I think the stock rear is 2.72 for your year. A 3.73 will give you more get-up and go off the line.
As far as how much power it can take, my guess is 400 to 500 HP. PG.

 

ahh thanks for info. So a 5 speed with a 3.73 would make a good combo for getting off the line with some decent top end yet? How hard is it to do a gear swap and where would be a good place to find info on how to do it?

 

I'm thinking that somewhere I read that there was more than one gear ratio available in '81. I just looked throughafew books quickly and found nothing on it, but I may be going through them too quickly or not in the right ones or read it on the NET somewhere. I'm sure that one of the "regulars" here on the site could tell you right off whether or not there were. Don't take it for granted if you're not sure as the final outcome will be determined by those numbers. On my code print-out for my '81, it says that I have a "2.87" to 1 ratio, but theaxle ratio is listed belowin the "options" block along with cruise control, power door locks and seat, etc.. makes me think that ration was optional.

 

According the '81 factory sales brochure, the manual came with 2.72 and the auto with 2.87.

The really neat thing was you could get an 8-track player & a CB in the radio.

 

haha i want the 8 track and CB Should the rear end be able to hold up to that power or am i going to start breaking things if i up the horsepower on it? anyone have any ideas about that?

 

Unfortunately for you, you have one of the weaker rear ends in the C3's because it is aluminum. The earlier units were cast iron and could handle more power. I do believe that you can adapt an iron rear to work in your car, but I am not the expert in that area.
What can yours handle? I wouldn't go over 300 hp. I broke my iron rear at just about 400 hp.

[sm=icon_cheers.gif]

 

well thats good to know. Would a rear end from an early C3 bolt on to mine?

 

Didn't they make a few changes to the way the alum. crossmember attaches to the frame? The steel one was attached via a couple of rubber iso-mounts on the ends plus another on an torque reaction arm in the center. If they left the mounting details on the frame, then it might be doable.

 

What ratio was the optional gear ratio that's refered to in all the ordering info. Listed in "Corvette museum" website. It listed one (code) ratio for the automatic, one for the 4-speed and an optional ratio that was available. The number isn't listed, only the code for it-like the other two.