Picking the wrong exhaust material means rust spots — or high-temp discoloration and cracking. The three mainstream materials are SUS304, SUS321, and Ti-6Al-4V.
SUS304 — entry choice
Most common, good for ~400-500°C continuous. Mid- and tail-section, naturally aspirated. Not for turbo manifolds — fails above 600°C.
SUS321 — turbo manifold standard
Titanium-stabilized stainless. Handles 700-900°C continuous. Resists grain-boundary corrosion that destroys SUS304 at high temps. Costs ~1.3-1.6× SUS304. Don't skimp here.
Ti-6Al-4V — premium
~56% the weight of SUS304. Excellent corrosion resistance. The "rainbow blue" heat-tint is the tuning aesthetic. Material costs 15-25× SUS304; total fabricated cost 5-8×. Used for race cars and hyper-car kits.
Decision flow
- Turbo manifold? → SUS321 (don't cheap out)
- Budget for premium weight + aesthetics? → Ti-6Al-4V
- Street use, NA or light boost? → SUS304
Common mistakes
Using SUS304 on a turbo manifold (will crack at welds in 6-12 months). Running Ti exhaust at high load without heat shielding (loses the rainbow tint). Accepting "stainless" exhausts that are secretly SUS201/430 — always require mill test certs.
