i have a 72 chevelle 307, th350, stock 2.73 open rear. i run a 16.031. i was looking into getting 3.42's 0r 3.73's i drive the car everyday and take it to the track for fun. would 3.42's make me any faster? if so how much? should i get 3.42's or 3.73's?

3.42's would certainly help quite a bit. IMO 3.73's are too much without overdrive for the street.

With 3.42's you might start to find it burns that tire up quite a bit. Might want to think about a posi, also.

3.42's are a great all-around gear, not too over-the-top but certainly a great upgrade from the factory. Beyond that you'll need to start looking at the motor if you want to start shaving 1/4 mile times down.

If you go 3.08 or numerically higher diffinately get a lock or posi because that one wheel will spin a lot. I started with 2.73 went to 3.08, wasn't enough. Went to 3.36 and made a HUGE difference.

I had 3.36 gears and liked it a lot. I did have a new Eaton posi unit put in at the same time. I now have 3.73 gears so I get better low-end performance and I like these a lot better. I also drive on the highway and will be putting in an overdrive next year.

I'd guess the 3.42's would make your car a few tenths faster. The thing is the 307's are pretty much economy engines and not so much performer engines.

At any rate going to a lower gear now will help and will certainly help/can be reused if/when you decide to step up to a bigger engine.

Check out the APRIL 06 issue of SUPER CHEVY mag. They have a full builbup of a 307. 315hp@5200 and 330lb trk @3800

If this is the 8.2 10 bolt then there isn't a 3.42 gear available for it. The 3.55 is the closest thing to it. When going from a 2.73 to anything in the 3.xx range you will need a new differential because your 2.73 uses a 2 series and you will need a 3 series. You might as well go ahead and get a new Eaton posi.