When i bought my rx7 the owner gave me a pettit AST and told me to install in but my rx7 doesnt have have one in the stock location. Is it okay not to have one?

 

I have the same issue, my motor is missing and I know there is know AST do I just install the pettit racing one. Good question man

 

OP,

You can delete the AST; however, it needs to be done properly.

Lots of good info can be found in the Frequently Asked Questions "sticky" in the 3rd gen forum

Air Separation Tank / AST / Coolant Expansion Tank:
Often fails due to heat and pressure. Many people replace them or remove them from the system.
Coolant Air Separation Tank
Coolant Air Separation Tank Elimination