I'm not exactly sure when they started doing it, but on most later prop-driven warbirds the exhaust manifolds weren't iron or black, they were stainless steel. The black color comes from soot building up on the manifolds from the cylinder in front.
I usually use Model Master Stainless Steel metalizer (I hate airbrushing laquer or enamel so I normally use the buffing kind from a rattle can). Blow some Tamiya Clear Blue and Clear Yellow on the tubes to simulate the heat discoloration and then some Tamiya Smoke or just some flat black on the front sides and around the tops and bottoms to simulate where the airflow would pull the smoke.
Again, I'm not sure about the Hurricanes. They may have actually had cast iron manifolds. If so Burnt Iron would be a good choice, or flat black with some dark red chalk dust brushed on.