Spray bolts with pb blaster and wait for about 30min before trying to remove the bolts. May require more than one application. Still need to be careful.I doubt you're under 300 on that set up. You should pretty easily see double digit gains on both HP and TQ out of a downpipe with that you're already got. Just beware of breaking studs while taking the downpipe off, thats a fairly common issue when removing exhaust pieces on just about anything.