What difference would I see if I change my rear gears in my 67, now I have 3:08s 12 bolt no posi (will have posi if I can find one)4 speed, I was thinking 3:55s or 3:73s the engine in it is a 366 truck motor ( was in it when I bought it) car ran strong but no low end, may replace the motor with a 396 in time, car will be for street use only.

Off-hand I would guess a 500-600 RPM change. You want to run in the powerband of your cam. 3.08's may be just what you want with a 396.

Be carefull with that 366. I don't know how much you know about them, but they don't like high RPMs at all. They have very heavy pistons with 4 rings. If you can find a 396 block you can use the 366 crank, rods and heads on it to make a pretty good engine. The 366 has a steel crank with the same stroke as the 396 and 427, heavy duty rods, and the oval port heads are similar to the 325 and 350 HP 396 heads. You just need a block and a set of pistons.

You will see a major difference if you swap gears. I changed the 3.08s in my 67 out for a set of motive 3.73s and it was night and day. The car is so much more responsive now and it gets into the powerband a lot faster. The motive 3.73s make no gear noise, and they were easy to set up.

If it's going to be street duty only I think you'll be much happier with 3.55's. There not too bad at freeway speed, and give you a good launch out of the hole in town. Also if you decide to get the 396 and stay with the 3.08's you really should look into getting a Powertrax Lock-Right Locker. Summit has them on sale now for $240. part # PWT-1910-LR They work real well and if your not changing gears you can swap this out with the spider gears in an afternoon without having to pull the entire diff. That way you don't have to worry about the backlash in the ring gears. It's a pretty basic swap.

Darn, darn, darn!!

PLEASE think hard about converting your 366 tall deck motor over to a standard deck 396 or larger motor before you ruin some good motor guts!!

pdq67