Hey guys I have a 91 z28 5.7 with the exhaust package where you have dual cats and a 3 inch downpipe to the muffler. Now according to every review I've read this adds alot of power. Of course a 3 inch pipe would but why the extra cat? If i do away with them and replace them with a 3 inch pipe will I lose power because of back pressure or gain alot? Im planning on replacing the stock muffler with a 80 series flowmaster. All input is appreciated.

 

A single 3" will outflow the dual 2.25" cats. Backpressure is bad anyway you look at it. The less you have the better for all RPM's of operating power. The dual cats were introduced to add a bit of exhaust flow but keeping the stock size piping. A sinlge 3" is cheaper in the long run, space efficient for subframes, and can support in excess of 400rwhp.

 

What about 2 hollowed out cats? Everyone tells me to gut em or take them off. I might add a borla catback exhaust to the equation.

 

You don't want to take them off. I know here in IL it's like a 1500 buck fine if you don't have at least 1 CAT visibility on the car (given it came that way from factory). If you have emissions in your area forget about gutting them also. You would need to either make due with what you have or go out and get one of those new high flow 3" CATs just make sure it's emission legal.

My CATs clogged up so I just had them gutted out (hollow'd) and reinstalled course we don't do emission testing in this area either. It was just a quick fix for me.