In a high-performance engine, the gaskets and hardware are the soldiers on the front line of power production. Your $6,000 CNC-ported cylinder heads aren’t going to make enough power to pull a fat kid off a tricycle if the head gaskets can’t handle the pressure of combustion, and your high-dollar aluminum engine block is soon going to be ventilated if the connecting rod bolts decide to take a break (pardon the pun).
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Of course there’s no such thing as parts that are too good for your engine, but the fact is you can get away with budget bolts and gaskets for certain parts of your Rat motor, but the cylinder heads, rotating assembly, and valvetrain are not among them. Even if your intake manifold is happy with hardware store Grade-5 bolts, you are going to be happier with precision reduced-head or 12-point manifold bolts that are designed for proper tool clearance when it comes time to snug them down.
Cylinder Head Gaskets
Head gaskets are the most important gaskets in your engine; they have the responsibility of sealing very high combustion chamber pressures. Any leakage does not only reduce your power output, it also quickly leads to expensive damage to the head and/or block from the hot exhaust gases eroding away the deck surfaces with cutting-torch temperatures.
Other than proper gasket selection, the most important factor in achieving a good head gasket seal is that both the block and head deck surfaces be clean and flat. Standard specs call for no more than .0025 inch of warpage, and some gaskets require even less run-out. Additionally, some gaskets require a specific surface finish, or RA (roughness average), for a proper seal. This is especially critical with iron block/aluminum head combinations because of the different rates of expansion as the two dissimilar metals heat up.
There are three general types of head gaskets: solid metal (included embossed steel and dead-soft copper), composition, and multi-layered steel (MLS).
Embossed steel shim gaskets should only be used on cast-iron blocks with cast-iron heads. The best thing about steel shim gaskets is that they are thin, usually around .020 inch compared to the stock gasket’s thickness of about .040 inch, and represent a quick and easy way to increase the compression ratio on your street performance big-block. Depending on your combination of piston dome and combustion chamber size, this could amount to at least one-half point of compression increase, typically from 8.5:1 to about 9.2:1. Remember that this also reduces piston-to-valve clearance, so you need to recheck that if you are using a high-lift cam. Mr. Gasket still offers a .020-inch-thick elastomer-coated steelshim head gasket (PN 1131G) for Mark IV engines with bores up to 4.370 inches and iron heads.
Dead soft copper gaskets used to be the exclusive choice of Top Fuel and other extremely high-horsepower engines due to their robust construction, but they were hard to seal.
Things have improved today, and there are several specialty companies offering copper head gaskets with elastomer coatings that seal the water passages quite well, and some incorporate steel O-rings into the gasket itself, requiring no special machine work to the heads or block. With modern manufacturing techniques, they can be custom-made to fit whatever application you want. You can get them from Copper Head, Clark, Milodon, SCE, Hussey, and others.
Composition gaskets have good sealing properties for the coolant passages and formed stainless steel around each bore to handle combustion pressure. Most head gaskets you get from the local auto supply store fall into this category, but the performance gaskets from Fel-Pro, GMPP, Mahle/Victor Reinz, Mr. Gasket, and SCE are well suited for high-performance big-blocks up to around 14:1 compression. Some companies, such as Edelbrock, offer composition gaskets specifically designed to fit their products for street highperformance applications.
Multi-layered steel (MLS) gaskets are the latest design in head gasket technology, and utilize three layers of stainless steel sandwiched together. The outer layers usually have some sort of elastomer or other sealing agent for a positive seal around all coolant passages. High-performance MLS gaskets are able to withstand very high compression ratios, and do not need O-rings. Surface preparation is crucial, but that has always been the case with very-highcompression engines. A surface finish of RA 50 or better is required for MLS gaskets. MLS head gaskets for Mark IV and Gen V/VI big-blocks are available from Cometic, Fel-Pro, Mahle/Victor Reinz, and Mr. Gasket.
Big-Block Engine Gaskets and Seals
Mark IV engines require a two-piece rear main seal such as Fel-Pro PN 2904 and PN 2918, and 1990-and-later Gen V and Gen VI motors use a one-piece seal such as Fel-Pro PN 2920.
Most oil pan gasket sets are the traditional four-piece set with cork/composition side gaskets and formed rubber end seals, such as Fel-Pro PN 1804 for Mark IV oil pans. I prefer the new one-piece pan gaskets, especially if you have to change gaskets with the engine installed in the vehicle. Fel-Pro PN 1884R and SCE PN 213090 are formed one-piece gaskets that fit Mark IV pans. GMPP offers a onepiece pan gasket for Gen V/VI engines, PN 10106407. SCE also makes one-piece pan gaskets for Gen V/VI engines, plus exotic blocks like the DRCE/Merlin, AJPE 481X, KB Olds/New Century, and the Donovan 700.
There are as many intake flange gaskets as there are cylinder heads, so refer to the head manufacturer for recommendations. For production 1974-and-earlier large oval-port heads, Fel-Pro PN 1212 or Mr. Gasket PN 5827 are readily available. For production rectangular port heads with a center bolt-hole between each pair of runners, Fel-Pro PN 1211 or Mr. Gasket PN 5828 are popular choices.
Stock Chevy main cap bolts, head bolts, and 7/16-inch connecting rod bolts are adequate for most street performance applications up to 600 hp, but higher-output engines need to upgrade to aftermarket hardware to keep everything where it belongs. Stock 3/8-inch connecting rod bolts should be upgraded as soon as possible for anything other than a very mild Rat motor. ARP makes excellent fasteners for all forms of motorsports competition, and replacement WaveLok connecting rod bolts are on my list of things to procure as soon as possible for a 3/8-inch rod motor.
All stock big-blocks use bolts to attach the heads and main caps to the block, but for high-horsepower engines studs should be used for their superior clamping power. Stud kits are available from A1 Technologies, ARP, Milodon, Mr. Gasket, and several cylinder head and block manufacturers, which offer kits specifically for their products. Studs should only be tightened to a snug fit in the block using either a thread lubricant like oil for blind holes, or a thread sealer for through holes that open into the water jacket, such as head-bolt holes on a production block.
Also note that many head stud kits cause interference with the header flange and the four short studs on the outside of the head. You may have to shorten those studs to clear your headers, and that’s much easier to do if you test fit your headers on the engine before you install it in the car.
Written by Tom Dufur and Posted with Permission of CarTechBooks