Do I need to weld this on, or does it bolt up?

This is a catback system, so it bolts directly to your factory catalytic converter — no welding needed. You'll connect at the cat flange and secure the tip at the rear.

Does this come with all the bolts and clamps I need?

The assembly includes the core system. Confirm you have clamps and fasteners on hand before install — mounting hardware spec not detailed, so a test-fit will tell you exactly what you need.

Will I need to modify anything under my car to fit this?

This system is designed as a catback bolt-on, meaning it connects at the stock cat location and routes out the rear. No cutting, drilling, or suspension work required.