From the calculator in the other post it sounds like 3.36. In either case his cam isn't that big and a performance distributor curve will make a big difference. I picked up almost a full second in the 1/4 mile with a recurve in my old camaro. That time improvement pretty much all came at the bottom end.
I walked VictoriaVette through this a while back and he had similar results. Stock emmisions curve sucks on a stock engine. It gets compounded the more mods you make and a high rear ratio really makes it noticable. A couple hours work and $20 for a recurve spring kit and a vacuum can will get you more sometimes than a thousand dollars and a week's work.

 

I'm gonna do the measurement again. Does it matter if you mark the driveshaft from the motor or one of the 2 small ones after the diff?

 

Check out the total cost of changing the gears, parts, labor, taxes etc then look at the TKO 500 with the 3.27 first gear and see how much more that would cost. That is the best mod for a C3 no matter what engine or rear end IMHO.

 

when I built my 70 Nova, I was running a 355 with a turbo 400. I broke in the motor using the factory 10-bolt gears which were probably 3.08 or perhaps higher. While he had plenty of muscle, and it was a terrific highway cruiser, I wanted lower gears and bought a 12 – bolt housing From a 70 Camaro.

I should have used the gears that were inside of it when I bought it but I chose to buy Richmond 4.11 gears for it and when it was done, I felt like I ruined that car!

I was so used to having a highway cruiser (it could peg the speedometer in second gear!!!) and driving the car all over the southwestern states, which I did for years. Now all of a sudden, the car was too squirrelly at full throttle, and my maximum comfortable cruising speed dropped to 70 miles an hour.

I could no longer take the car on long trips as I had for years prior. When I sold the car the buyer loved it at first. But when I saw him two years later, I asked if he made any changes to the Nova... he said those gears were the only change. I was really proud that the engine I put together 10 years prior was still running strong. ( when I owned it, 6500 RPM burnouts and 1-2 shifts were daily occurrences) But obviously he agreed with me that the 4.11 gears were too low for that car.
PS the tires I was running were P 215/65r15 on rally wheels that came from a '85 S-10 pickup.

 

If you want tire smoking launches forget gearing change. buy a 9.5 inch 3000 stall Precision Ind. torque converter. Back when I only had 355 ci I built a motor to spin 7200 rpm with a big single plane manifold. It didn't have much off the line with a th350. So I bought a 3200 stall 9.5. When you floored it I was instantly in the power range. street tires had very little traction and I has to use Goodyear drag racing slicks at the track

http://www.converter.com/vigilante.htm

 

I just redid the test and with one revolution of the wheel the drive shaft turned exactly 3 times. Is that still a 3.08, I wouldn't think so.

 

sure it is

 

It's close enough to 3.08; since there are no corvette ratios of 3.00, that's close enough to be certain of 3.08s.

BTW, my '78 with 3.08's has run a best of 11.59 sec in the 1/4 with a 406 SBC and a 10" converter similar to what gkull suggests. And, on a 2,000 mile trip last June to Florida, it got 17 mpg with the AC running!