Do I need clamps to install this hose?

Yes. This hose ships without clamps — you'll need worm-gear or T-bolt clamps sized for 1.50" and 1.75" diameters to secure both ends. Size them based on your hose barbs.

Will this handle coolant and intercooler lines, or just boost?

Silicone is rated for both high-temperature coolant and pressurized boost lines. Works equally well in either application — just match your clamp pressure to the operating pressure of your system.

Can I use this on an existing system, or does it need to be part of a new build?

Either way works. If you're patching an old line, cut and remove the old hose, then slide this reducer onto clean barbs. If building new, route it in place before attaching your radiator or intercooler.