i've seen a turboed Prelude go from 210 to 260hp by removing the cat and replacing it with a straight pipe. it was right on the dyno. did a run of 210. un-strapped the car. replaced the cat. strapped it back down put out 260 something on the next run. i would spend $40 for 50hp. i agree with you that it wont make any power on an NA 4cyl. you'll lose a lot of low end power. but it does nothing but help on a turboed car. i've also seen a turboed civic go from 145 to 170 with putting on a straight pipe and pulleys. now that was like 3 weeks apart from the 145 to 170 but no other mods except the straight pipe and pulleys which would gain like 2hp. the cat makes a huge difference on a turboed car. but to answer the mans question. no you dont need a high flow cat unless you go with forced induction