I came across the following simple description of intake and exhaust valves. "Think of the intake valve as the wide front door of the cylinder-it's made larger to let the maximum amount of air and fuel in on each stroke. The exhaust valve is the smaller, more fortified exit. The most critical distinction is what they're made of. The exhaust valve has the tougher job by far, as it has to withstand the fiery blast of post-combustion gases. To survive this, it's built from special high-temperature metal alloys. The intake valve, on the other hand, gets a nice, cooling spray of air and fuel with every cycle, so it doesn't need to be quite as robust. For this reason, they have different part numbers and are absolutely not interchangeable. Using an intake valve in an exhaust port would be a very short, very unhappy experiment." Here are the valve diameters for the four modern HEMI engines, compared to the legendary 426: 5.7- 2.05 inches Intake; 1.55 inches Exhaust 6.1- 2.075 inches Intake;1.58 inches Exhaust 6.4- 2.14 inches Intake; 1.65 inches Exhaust 6.2- 2.10 inches Intake; 1.55 inches Exhaust 426- 2.25 inches Intake; 1.94 inches Exhaust
