Will this fit my existing 2.50" intercooler piping?

Yes — the 2.50" inner diameter matches standard intercooler hose and pipe connections. Clamp or weld it inline wherever you need directional change.

Can I use this elbow with silicone hose or does it need hard pipe?

Works with both. Slide silicone hose over the outside diameter and secure with clamps, or weld it into a hard pipe run. Test-fit first to confirm your hose wall thickness accommodates the outer diameter.

Does the polished finish need any prep or sealant before installation?

The polished aluminum is ready to install as-is. If you're welding it into a system, clean any dust or oils before the work. If using clamps and hose, no prep needed.