A-833 2.47 1st gear change to 3.09

My 65 Barracuda originally had a 3.09 low gear and 3.23 rear gears. With an almost stock 340 in it, it was fast off the line just letting out the clutch and giving it gas. No hi-rpm clutch dumps, just go. Well at 150,000 miles or so, the main shaft got a groove worn in it, under the needle bearings. I was told that replacement shafts weren't available (this was mid-seventies), so I switched to a late sixties four speed. Bolted right in, just needed to get a driveshaft.

That's when I found out my original trans had the 3.09 low gear. Later trans had a 2.66. The difference was unbelievable. You could still take off reasonably quick if you revved it up and dumped the clutch (it was still two tenths slower in the quarter), but it was a dog off the line with normal driving. I hated it. Later found out that the original 3.09 gearset that I had saved out of the original trans would fit in the newer case with the newer main shaft (no ball and trunnion). So I swapped. Have never regretted it.

With 3.23 gears, the overall low gear ratio with the 3.09 trans is 9.98. With 2.66 low gear, you only have an overall low gear ratio of 8.59. To get a 9.98 overall low gear ratio with a 2.66 low gear, you would need 3.73 rear gear.

The 2.47 low gear is even worse. Its overall low gear ratio with 3.23 rear gears is 7.98. To get a 9.98 overall low gear ratio with this trans, you'd need a 4.04 rear gear.

Now you could of course change the rear gears instead of the trans. 3.91s would work. But the OP is complaining about how many rpms he's turning at 70 mph with the 3.23 gears he has now. It would turn 20% higher rpms with 3.91 gears. Top speed would be 20% lower (if that's a consideration).

To those who suggest that if it's kinda sluggish of the line with 2.47 gears the OP just needs to tune his motor up, I say BS. Maybe a stroker crank. More cubes can handle taller gears. A 340 needs gears. Either at the trans or in the rear end, take your pick.

And don't give my any crap about how well an automatic works with 3.23 gears. Automatics have torque converters to multiply torque. Manual trannies only have gears.

Strictly for drag racing, or road racing, the close ratio trans would work better. For the former, choose the rear gear you need, and the close ratio trans would keep the motor in the power band better. For road racing, same deal except you don't worry about standing start acceleration.

FOR THE STREET, with streetable, relatively tall rear gears, and only 340 cubes, the 3.09 gearset is absolutely the way to go. Its not even a close question.