ok so i have two cats. one is a high flow magnaflow. other is a hollowed out cat. question is, does a hollowed out cat give incorrect back pressure? and is it harmful for a engine? thanks.

 

an engine doesnt need backpressure this is a common myth spread about by the "slow" people on forums. What you are worried about however is the exhaust air velocity. The air velocity will change inversely with area. (AKA larger exhaust=larger area=slower exhaust velocity). This is what attributes to the feeling of a loss of low end power or torque after a 3 inch exhaust is bolted up to your stock civic motor.

Truthfully, you will not notice a difference other then sound between your two options so I would say go with the magnaflow and not have to worry about having a loud annoying exhaust.

 

good point. ill slap the magnaflow back on. another question. how does a exhaust leak in any area of the exhaust hurt an engine?

 

other than the annoying noise a small exhaust leak will not negatively impact your engine or it's performance