CELEBRATING 20 YEARS!

I have a 84 Monte Carlo SS Street car 350 bored 40 over with a automatic turbo 350 3-speed transmission with a 2400 stall converter looking for recommendation on gear ratio it's a 10 bolt I believe it has 342 gears in it right now

What's wrong with what you have in it now? 3.42 isn't a bad all around gear.

3.42 is fine with a non-OD trans like the TH350. You don't want to lose MPG and increased engine wear with lower (higher numerically) gears.

I agree too, as long as you're looking for MPG. You could even go 3.55s, but that a lot of work just to go up 1 size. But if you really want performance and don't care so much about the cost
of fuel, go 3.73s. If you ever get a OD, those would still be good or you could go up to 4.10s like I have. That being said, it's a lot of road noise with that low of gear.