I dont have any actual dyno numbers for you but.... I run a bolt in straight pipe on my b16 except for about week around emissions time every year. Then i put in a high flow cat. I will tell you that it is considerably louder and raspier with the straight pipe. However i am in a hurry to get it back on there every year because there is a noticeable difference in top end pull... like 7k and up. With the cat on there the powerband seems to flatten out up top, and with no cat it keeps pulling harder. Pulls harder on the butt dyno anyway.