i have a 68 camaro with 4 speed muncie 2:52 first gear and 15 inch tires/rims. what rearend gearing do you recommend?

You didn;t really give enough info. I will assume it is a street car and will see the highway. IF that assumption is correct, I would suggest 3.55's or 3.42's depending on which rear end you have. If you want a little better milage and lower RPM's on the highway you may want to try 3.36 or 3.23's. If it's a small block car I would go tith the 3.55's or 3.42's.

Agree with Camaroman7d,..not really enough info. What cam and type of driving?

If you decide on 3.55's let me know,..I have a barely used (less than 100 miles) ring and pinion set for a 12 bolt. I went to 4.10's on a car that had a cam that was much more rowdy than planned.

What size rear tire do you have?

Do you plan to switch to a 5spd any time soon?

What are you looking for? Low end torque or top end speed?