Better heat distribution. The exhaust valve sees a lot more heat.
metal (steel)
there is no such thing as an inlet exhause valve, you have the inlet valve which lets your air/fuel mixture enter the engine for the power stroke and the exhaust valve which allows the burnt out air/fuel mixture to leave the engine after that the inlet valve re-opens and lets fresh or new air/fuel mixture enter to let it be compressed and combust for the power stroke. First, the correct name is "Intake" valve. There are intake, intermediate intake and exhaust valves in some newer foreign made engines.
Most intake valves are made of the same material as the exhaust. They are heat resistant treated high carbon steel, as are the valve seats. The exhaust valve is usually larger in diameter to aid in scavenging of the spent hot exhaust gas. Some more expensive engines have sodium (Na) filled exhaust valves to aid heat transfer to the valve seat to help cool the valve.
This design allows more power to be made available for the 4 stroke 2 wheeler. Multi-valve engines allow the more higher RPM's to be achieved, thus resulting in more power being made.
The exhaust valve runs much hotter than the intake valve, so it has to be made out of a more durable(and more expensive) material. The intake valve can get by with a simpler and less expensive material.
The exhaust valve doesn't get any cooling except to say that there is some cooling effect when the new charge of air/fuel mixture enters the chamber. That's why exhaust valves are extra-thick, and sometimes made from more heat-resistant material such as stainless steel or titanium.
Intake valves run cooler than exhaust valves and they are made of different material, so their thermal expansion is less than the exhaust valves. Therefore, they can have a smaller valve lash clearance, since they won't 'grow' as much due to thermal expansion, and won't present the problem of slamming into the top of the piston as readily as exhaust valves with too-small valve lash clearances will. But, not all engines have dissimilar valve lash clearances on intake and exhaust. Many small single-cylinder engines have exactly the same clearance on both intake and exhaust valves.
First of all, the camshaft's job is to open and close intake and exhaust valves. It's made up of teardrop shaped lobes, and when the lobe turns away, the valve spring closes the valve. This is precisely timed, so the lobes are aligned just so. On a radical camshaft, the lobe shape is exaggerated so the valves open wider and longer, packing more air into the intake, and letting more out the exhaust. The result is more airflow through the engine, and more power.
A 3-port valve typically has three connections: one inlet and two outlets. These connections allow the valve to control the flow of fluid between different paths. Depending on the configuration, the valve can direct the flow to either of the two outlets or to both simultaneously.
dirt into engine is a big problem and the intake are made softer material due to less heat on valve faces
For a 20 HP twin Briggs & Stratton engine, the valve specifications typically include a valve clearance of around 0.005 to 0.007 inches for the intake and 0.007 to 0.009 inches for the exhaust valves when cold. The engine usually features a flathead or overhead valve design, with both intake and exhaust valves made from durable materials to withstand high temperatures. Specific dimensions and tolerances can vary by model, so it's essential to refer to the engine's service manual for precise specifications.
The Cobra's exhaust is made in the USA and is backed by a lifetime warranty. Their exhaust pipes are made to withstand any type of force you can bring to it.