Yes, an upper and lower intake gasket is a critical part of the engine. This gasket works to seal off the top of the cylinder head from the bottom, preventing air, fuel and coolant from entering or exiting where it should not be. The upper intake gasket sits between the manifold and head while the lower intake gasket seals off any potential leaks that may occur between the block and manifold. Both are essential components in ensuring your engine runs smoothly without leaking vital fluids or allowing unwanted substances into your vehicle's combustion chamber. Without these two key pieces, you could experience major problems with your car's performance as well as damage to other parts over time due to improper sealing.