You'll be fine. If you want your car to make hp, then open the exhaust. If you want to make torque add back pressure by closing it up. It won't hurt your heads or anything internal. I ran open headers for many years. I have had 3 inch on my street truck for 7 yrs including cat and mufflers and neither have had any problems. The only thing that will hurt your heads is improper installation, or your occasional internal parts failure. I would suggest making sure that your timing is correct and set properly. Don't make any mistakes with that cause you could burn a piston or overheat and blow a head gasket. I would run what you have now. If you feel your lacking torque then maybe ad a step down before the mufflers.