ok i have a del sol with a b16 sir in it. just one thing after the next! to get a complete 2.5 all the way back i had a jun 4-1 header put on then had a hi flow cat welded on from the header back to the exhaust, i thought it would have fixed my severe exhaust leak i had from before. now when i i'm driving, i get up to about 3 grand the motor feels like it is limmiting me from going any higher, on top of that there is a whistling sound when it restricts me, and it has a clunky sound (similar to the sound of an exhaust leak) right at the cat! could it be that the weld has not held and there are holes, pits or something still allowing a leak. and would the slightest leak cause my hose power to be limited? my check engine light doesn' come on. please help.

yes there could still be a leak at the weld, depending on who ever welded its skill, but it shouldnt be robbing u of too much hp, maybe u have a clogged fuel filter?? id check that.

get exhaust checked

see if you are throwing any codes. do a full tune up