only way it hurts in extreme cases will you lose horsepower those rice burners with way to big of an exhaust and nothing else done tothe engine yes you can lose 5hp or so what happens with to large of an exhaust and no extra air flowin the motor with the correct functions "exhaust valve opens there is a suction there to pull all that out of cylinder head and out the end of the pipe with an extrememly over sized exhaust that suction isnt nearly as strong and your cylinder gets pollutied with exhaust particles
okay here is the thing with exhausts
auto tech school basics a large aftermarket exhaust has literally no affect on the engine and to large the engine will lose horsepower
thats if this is the only upgrade the term is called "volumetric efficiency " this is what your attempting in increase if you put a large exhaust onyer engine tru duals or the split deal is irrelavant you must increase the amount of air flow into the motor there are several way to accomplish this. so increased airflow and larger exhaust will increase the engines volumetric efficiency . Larger throttle body, some sort of after market high flow cool air intake ,high flow air filter larger intake manifold . cam with higher lobe life at duration preferably roller cam and not a flat tappet
anything increase the amount of air that goes in the engine helps dont forget to headers also makes a difference to