On any engine, when each cylinder fires, the head will invariably want to take off and fly away from the engine. Of course this never happens (at least we hope not) because the cylinder head is secured with a series of head bolts (or studs) properly torqued to the engine. Average cylinder pressures are over 1,000 psi on high-performance engines and can be as high as 2,200 psi. Incidentally, detonation can raise that pressure to 3,500 psi and higher. Of course the higher the pressure, the more separation, and the head gasket is unloaded. MLS gaskets are designed to maintain gasket loading under severe cases. The embossed bead on the gasket acts as a valvespring that will expand and recover. The multiple layers and polymer coatings are purposefully located to surround the combustion and coolant passages.
Clamp And Load
Critical to any head gasket's perfor-mance is that an engine will only have a certain amount of clamp load available. This load is determined by the amount, size, and thread type of the head bolts or studs divided across the surface area to be sealed. By using beads, combustion armor, or wire inserts the sealing force can be increased. This improvement in sealing force may counteract another portion of the surface, so like all other aspects of engine building, there must be a balance of engineering to effectively seal the entire head gasket from the forces the engine exerts during operation.
Before You Install
Installing a new head gasket may be easy-simply position it over the dowel pins and press into position-but before you get that far you'll want to be certain that you've prepared and checked the surface correctly. This means you'll want to first clean the surfaces of both the head and the block and check them for straightness. For a high-performance engine the maximum out-of-float, as measured with a straightedge and feeler gauge, should not exceed 0.0025 inch.
With traditional performance head gaskets the surfaces should be very clean and in the 60-100Ra (rough average) range. Fel-Pro's PermaTorqueMLS typically requires a surface of 30 Ra or smoother. Before installing any performance head gasket it's best to check with the manu-facturer for the suggested surface finish as well as aluminum and iron applications.
The wrong torque value or improper torque method can cause head-gasket problems. Obviously if the head gasket is not torqued properly between the head and the block, combustion gases and engine fluids can leak past the gasket. To achieve the correct clamp-load, the head bolts or studs must be stretched properly. This will not occur if the fasteners have too much friction during installation. Before installing and torquing any head bolt, coat the threads with the manu-facturer-recommended lubricant.
High-performance head gaskets...
High-performance head gaskets properly installed to clean, flat decks will provide adequate sealing with properly installed and torqued head bolts. This engine makes about 400 horses, so the Fel-Pro Performance head gasket is a good choice.
Fel-Pro's Perma-TorqueMLS uses specifically located sealing beads to lock in the combustion chamber and coolant passages, thus concentrating the clamp loads in critical areas.
Fel-Pro's PermaTorqueMLS gasket...
Fel-Pro's PermaTorqueMLS gasket is made with four or five stainless steel layers manufactured with special polymer coatings. This all helps to seal an engine that may experience head/block movement resulting from aluminum head-to-iron block installations.