x_x And this is why I could never hope to do squats without equipment to guide me. :p Some of us have too much in front to balance right.
Your limitation isn't a big chest. Eqiupment is actually holding back your squat.
Hold a broomstick over your head much like you've just finished a power snatch. Now squat. You'll highlight every weakness you have in one movement.
Most poeple's weakness will be found as inflexibility in the hips. This occurs because of a tight poterior chain.
You know what? Here is a good link that will explain everything:
http://www.extremefitness.com/forum/showthread.php?t=51805My screen name there is the same here.