Trying to help a friend out with his 98 Spec Glanza V. Car is standard apart from a HKS cat back system/dump valve and air filter. He has described that the car feels incredibly slow, he said you can feel it building boost pressure but it doesn't go anywhere. Had a little look last night and couldn't see any obvious, he has recently had the timing belt changed and the timing double checked. When i started it up last night and gave it a rev it sounded like something was rattling round in the cat? Could the cat be blocked and causing power loss issues? Cheers, Charlie