Plan to succeed. To build a strongrunning engine, you’re going to need a plan and you should put it together before you hop on the Internet or crack open a catalog to start getting parts for your engine rebuild. There’s an old saying, “If you fail to plan, you plan to fail.” This book is written with the intent of success, not failure. In this chapter we’ll go through the steps of managing the parts for netting success with your rebuild.
This Tech Tip is From the Full Book “HOW TO REBUILD THE BIG-BLOCK CHEVROLET“. For a comprehensive guide on this entire subject you can visit this link:
SHARE THIS ARTICLE: Please feel free to share this post on Facebook / Twitter / Google+ or any automotive Forums or blogs you read. You can use the social sharing buttons to the left, or copy and paste the website link: https://www.chevydiy.com/select-parts-big-block-chevrolet-engine-rebuild/
The first step in the plan is figuring out what you are going to do with the car. Are you going to drive the car like your grandparents: slow, steady, and not always in the correct lane? Are you only interested in using your stump-pulling torque to tow around your sand toys? Do you want to add extra power to run down the quartermile? Are there any twisty open-track excursions in the future? You need to build your engine to suit your needs. Be realistic about your intent.
There are many parts available that work best in specific applications. For instance, you wouldn’t put an Edelbrock Victor Jr. intake on a tow vehicle, and you wouldn’t typically put 13:1-compression pistons in your daily driver. It’s not a bad idea to overbuild the engine a little bit, but you should stick to a realistic plan. To get the most out of your hard-earned money, read through the chapter to help you make some educated decisions on what parts to buy.
The various build types to consider are: stock, towing, street and off-road, road course, and drag strip.
When the engines exceed 650 hp, many top engine builders said they prefer to upgrade to aftermarket engine blocks like GM Performance Parts, World Products, Donovan, and Dart. They said upgrading to 4-bolt main caps, which are stronger than the stock cast-iron caps, helps the strength of the Mark IV block. They also said they prefer the aftermarket blocks because they come with taller decks and bigger bores, suitable for building monster big-block engines for their customers. The old adage, “bigger is always better,” certainly rings true for racing applications. Aftermarket blocks have been redesigned with better options than the Mark IV, including priority main oiling systems, blind-tapped head bolt bosses, standard four-bolt mains (minimum of Nodular iron caps), enlarged water jackets, thicker wall castings, intake valley head bolt bosses, etc. Most of the aftermarket blocks also accommodate all stock components such as starters, mechanical fuel pumps, oil filters, etc.
Main Cap Conversion
You may consider upgrading the main caps of your two-bolt main block if you are going to build your big-block to put out over 550 hp or the engine will have a redline over 6,000 rpm. Even the factory fourbolt blocks with cast main caps could benefit from upgrading to highstrength ductile aftermarket caps. Milodon and a few other companies offer conversion kits that replace the three center main caps. You typically replace the three caps and not the front or rear main caps because most of the flex in the crank happens in the middle of it. You can purchase the other caps separately if you feel the need to replace them.
Even though the rotating engine parts (the cam, connecting rods, and crankshaft) ride on the oil between the component and bearing surface, that doesn’t mean you shouldn’t use high-quality bearings. There are different quality bearings available. The most recognized bearing manufacturer in OEM and the aftermarket is MAHLE Clevite Inc. When purchasing your bearings, you should be aware that there are different bearings for different applications. The Clevite 77 P-Series (rod bearing CB743P) nonchamfered bearing is more suited for stock and lower revving engines. If you are building a high-performance engine, you should use Clevite 77 HSeries (rod bearing CB743H) bearings because they have enlarged chamfered sides for crankshafts with larger radius bearing surfaces and are made with a hardened steel backing for higher loads and increased revs. Running P-Series bearings on a performance radius crank spells disaster because the larger radius interferes with the side of the bearing and this causes bearing failure, so consult your machinist and/or the manufacturer of your crankshaft. There is also an M-Series bearing offered, but that’s for some specific applications. The most common Clevite 77 bearings are the P- or H-Series. Talk to your engine machinist for professional advice for your application.
Coating technology companies offer pre-coated bearings or you can send your bearings to an experienced coater. Engine builder and racer Paul Caselas says, “Get the coated bearings. It’s cheap insurance!” Clevite offers their TriArmor coating on their HSeries bearing line. Its coating is a lowfriction PTFE/polymer moly/graphite treatment that adds extra protection and lubricity on the surface of the bearing. It’s extra protection for your engine at startup and if it ever experiences momentary oil starvation.
Cast and forged-steel are the two types of crankshafts available. Of those two types, the forged crankshaft is the stronger of the two. There are stock and performance crankshafts available for both types. Chevy installed forged crankshafts in their performance engines; all other engines received the standard cast crankshafts. Aftermarket companies rate their cast crankshafts from 500 to 700 hp and their forged cranks to upwards of 1,500 hp.
Among the factory and aftermarket crankshafts, there are internal and external balance units. History shows that the Chevy 366 to 427 bigblocks were internally balanced, so they use zero-balance flywheels and harmonic balancers. The 454 and 502 engines are externally balanced, so it’s necessary to use a special counterweighted flywheel and harmonic balancer. Machinists and builders have expressed their dislike of the external balance design. Most said if given the choice in high-performance applications, they would spend the extra money to convert from an external balance crank to an internally balanced unit. Otherwise, they would buy a performance crank, like the ones offered by Eagle Specialty Products, which is initially cast or forged as an internally balanced unit. The process of changing external to internal balance is accomplished by drilling out the counterweight, welding heavy Mallory- metal into those holes, and typically costs a few hundred dollars.
Chevy changed the design of the rear main seal in 1991, from the trusty two-piece to the one-piece. With this change came a newly designed rear section of the crankshaft, which is easily identified. The flywheel mounting face on the one-piece rear main seal crankshaft is a perfectly machined circular hub, and the same surface on the two-piece main seal crank is a notched and misshaped flange. If you have a block utilizing aonepiece rear main seal, but you want to run a two-piece seal-style crankshaft, a few companies offer adapter ring kits. After talking with crankshaft and seal manufacturers, along with a couple of engine builders, I got mixed feedback on whether the oneor two-piece seal was a better design. The majority opinion was that both were good, but the one-piece design was better.
The aftermarket crankshaft companies have made some changes to crankshaft design, which further convolute your crankshaft choices. Did you notice I didn’t report that they made “improvements?” They changed the oiling design in the crankshaft. The new design is referred to as “cross-drilled oiling” and the original design is still referred to as “standard oiling,” There have been some half-truths circulating around the engine building industry on crossdrilled crankshafts. Some builders don’t use them because it’s been printed that this design siphons the oil from the system at high RPM. World-renowned racecar engine building company Reher-Morrison did tests years ago that proved siphoning occurred above 10,000 rpm. If you were building a big-block Chevy that will be revved that high, you probably wouldn’t be reading this book. For all intents and purposes, cross-drilled crankshafts should be considered for all applications destined to turn less than 10,000 rpm.
The engine’s displacement (cubic inch size) is determined by your bore and stroke. Displacement formula:
.7854 x Bore x Bore x Stroke x 8 (number of cylinders) = CID
Unlike in the old days, there are numerous cubic inch displacement (CID) options available with the introduction aftermarket blocks, stroker cranks, and pistons. Now the sizes range from 366 to infinity and beyond…well, at least 632 ci, and they keep getting bigger. You can change your displacement on an engine by putting a different-sized stroke crank in it. You can take a 396 or 402 block (that came with a 3.76-inch stroke crank) and put a 454 4-inch-stroke crank in it, but it’s not easy. Your machine shop will have to clearance the block to make it fit, and you will need some special stroker pistons and possibly a stroker- relieved oil pan. You may decide a more cost-effective way would be to just get a 454 block and put all that extra cash into a set of heads or something else. Although… stroker big-block Chevy engines make unreal torque numbers on the dyno.
The better you arm yourself with knowledge about the differences of available crankshafts, the easier it will be for you to make an educated decision for your application. Before making your decision on a crankshaft for your engine, don’t forget to take your plan for the vehicle into consideration. If it’s a stock rebuild, the cast crank is more than adequate. If you plan on driving the car like you just stole it, you should opt for a forged crank. Even though companies list their crank ratings in HP numbers, RPM and load ratings should also be considered. When it comes to the crank, rods, and pistons, it’s a good general rule to overbuild rather than undercut the foundation of your engine. You wouldn’t build a skyscraper on a wooden foundation. The stock 3/8- inch bolt-equipped connecting rods and stock cast crankshaft is good up to 500 hp, as long as you keep the RPM under 6,000. Any level over that, and you should seriously consider upgrading to an aftermarket crankshaft and rods.
Connecting rods are the important link between the crankshaft and piston. If you are doing a stock rebuild and the stock rods are in good shape, they will be fine for your application. If your engine is going to be used for anything other than basic street driving, you should upgrade the rod bolts to some aftermarket bolts, such as ARP. You’ll need to get the rods resized after replacing the rod bolts, but it’s worth it because half of the time (during the rebuild process) you’ll have to get the rods resized anyway.
Stock connecting rods come in two versions: standard duty, and high-performance. The 3/8-inch rod bolts easily distinguish standardduty connecting rods, while 7/16- inch rod bolts identify the high-performance rods. The performance rods are also beefier on the larger journal end.
In the old days, if you wanted to replace your rods with better ones you would have to scour the swap meets for good factory rods or spend a fortune to buy some performance rods. Now there are enough performance companies producing different levels of performance rods that you can find a good set to fit any budget.
Aftermarket rods come in two different configurations: I-Beam, and H-Beam. Depending on the manufacturer and the materials they use on their rods, the strength/horsepower ratings vary. The I-Beam version resembles the stock rod, but it is beefier around the journal area and along the beam. The H-Beam rod is significantly different. The most obvious difference is the beam shape. Besides design improvements, both types of aftermarket rods gain extra strength by utilizing heavyduty (typically ARP) rod bolts. For instance, Eagle’s ratings for its H-Beam rod jumps from 850 to a 1,200-hp rating just by changing the rod bolts. There are also aluminum connecting rods on the market but they are for full-tilt drag racing applications and should not be used for any other application.
Caution: You need to consider what type of heads you will use before purchasing pistons. Pistons for open-chamber and closed-chamber cylinder heads have differently shaped domes and can lead to major interference when used with the wrong head. Check for footnotes and specifications before making any purchases, especially when working with pistons for compression ratios greater than 10.5:1.
In the history of big-blocks, GM has equipped its engines with hypereutectic or cast-aluminum pistons on light-duty applications (starting in the early 1990s), and forged pistons on its high-performance engines. Any of these three types will do fine in a stock application. A step toward performance would be hypereutectic pistons. They feature high-silicon content, which reduces thermal expansion from heat. This allows for tighter clearance to the cylinder wall for reduced emissions as well as increased economy and power. The factory hypereutectic pistons don’t generally survive under the pressures of nitrous-oxide assisted, supercharged, or turbocharged applications, but with advancing technologies the aftermarket piston manufacturers have been improving upon them. The best piston for all performance, especially at power levels over 400 hp, has always been the forged piston.
Damper and Flywheel
The first and most important item to address about harmonic dampers is that there are two different dampers on the big-block Chevy. If you get the wrong damper on an engine, you can damage the bearings real fast. The two types are: a zerobalance version for the internally balanced big-block, and a counterweighted version for the externally balanced big-block.
For factory applications and GM crate engines (Gen IV, V, and VI), the 366, 396, 402, 427, and 572 engines are internally balanced. The 454 and 502 engines (both use the factory 4.00-inch-stroke crank) are externally balanced. With the introduction of internally balanced 4.00-inch-stroke aftermarket crankshafts you could potentially have or build an internally balanced 454 or 502. From the outside of the engine, if the engine doesn’t have a flywheel or damper attached, it is virtually impossible to distinguish between the internally or externally balanced big-block without researching the block casting numbers. The externally balanced damper and flywheel have extra counterweights on them and these are easy to identify from under the vehicle. The easiest part to identify is the extra weight on the backside of the harmonic balancer.
If during your rebuild you switch from an external to an internal balance crankshaft, or vice versa, make sure you get the correct flywheel and damper to go with it. This is very important: Using the incorrect flywheel and/or damper on the wrong crankshaft can cause severe engine vibration and destroy the bearings in a short time.
There are a few different types of harmonic dampers on the market. A stock engine works great with a stock replacement damper, which is made of a cast-iron hub and cast-iron outer inertia ringer separated by an elastomer band. The cast-iron ring can fatigue and fly apart if it’s used in high-stress and high-revving conditions. If you plan on racing your car on a regular basis, you should purchase an SFI-approved damper. The SFI unit is made from a machined, billet-steel hub and external ring separated by an elastomer ring for increased strength. The SFI rating is a racing specification for durability and strength standards required by racing associations.
The flywheel or flexplate for your application should also be considered. The SFI rating required on dampers is also required on flywheels and flexplates. For clarification, a flywheel is what you would have your clutch bolted to in a manual transmission application and a flexplate is what you would have a torque converter bolted to in an automatic transmission application. If you are building a mild daily driver engine, you need a standard-duty flexplate or flywheel. When you step up and start building your engine to pound out more than 400 hp, you should invest in heavier-duty equipment. The SFI-rated units are built from stronger materials and are designed to take more abuse without flying apart when they are put to the test in high-performance applications. The last thing you need is a chunk of your flywheel flying off your engine at 6,000 rpm and tearing your foot off. This is one of those areas of your build where it’s a good idea to over build your engine for your intended application.
This is an area where your engine plan is really going to be necessary. If you get an intake manifold that doesn’t work with your heads, you’re going to run into big problems.
Chevy made two intake manifold and head configurations: ovalport, and rectangle-port. You can’t mix rectangle-port heads with a set of oval-port heads or vice versa.
The oval-port intake and head design makes more power at a lower RPM range than the rectangle port versions. The oval-port design is found on most truck and passenger car applications producing less than 375 hp from the factory. The rectangle-port design was used on high-performance factory application engines, typically producing 375 hp or more.
Your choice of an intake manifold is completely decided by your plan, addressed in the beginning of this chapter. The first thing you have to take into consideration is the height of the manifold. If you are installing your big-block in a car with a stock or flat hood, you are limited to a few select low-rise intake manifolds. If you are willing to modify your hood or install a scooped hood, you can opt for a high-rise manifold. In some cases you may be stuck with a factory intake manifold.
Each intake manifold has an operating RPM range. If you fail to match the intake with the range of the camshaft and your application, you will be disappointed with the end result of all the time and money you spent to get there.
Even the factory cast-iron intake manifolds have an operating range, albeit very low-performance. The typical low-rise factory cast-iron intakes provide an operating range from idle to 5,500 rpm, but they take a long time to get there. Chevy also produced some high-rise cast-iron intake manifolds back in the day. Except for the fact that their heavy weight robbed power, they were decent performers. Chevrolet also produced high-rise aluminum intake manifolds for their high-performance engines.
Cast-iron intake manifolds retain heat, and as they get heat soaked, they heat up the air and fuel going into the engine. Colder air-fuel mixture getting into the combustion chamber makes more power because the lower temperature allows the mixture to be denser and burn better. Aluminum intake manifolds don’t soak up and retain the heat like castiron, so they are better for performance and they are about half the weight. Losing 35 lbs off the weight of your car is worth extra power.
Aftermarket intake manifolds are readily available from many manufacturers, such as Edelbrock, Holley, and Weiand. These are available with operating ranges of: idle–5,500, 1,500–6,500, 2,500–6,500, 3,500–7,500, and 3,500–8,500 rpm. The first two RPM ranges are probably best suited for your everyday or typical streetdriven carbureted cars. Switching to electronic fuel injection (EFI) changes the drivability of the specific design of an intake manifold because of fuel injector placement and computercontrolled fuel distribution. (That’s an entirely different book.)
Intake manifolds come in two different types. A divider running down the center of the carb breaks the dual-plane intake manifold into two sections. Its design forces the left half of the carb to feed four cylinders while the right half of the carb feeds the other four cylinders. The dualplane intake manifold is closer to the factory-designed intake and is better suited for stock to moderate performance levels because its design allows for more low-end performance and efficiency.
A single-plane intake manifold is completely open under the carb, which allows the fuel to feed all eight cylinders at the same time. High velocity is required to produce optimal power. These are better suited for higher RPM applications because they don’t get into their power range until 2,500 rpm or higher. Those numbers don’t work great on daily drivers, tow vehicles, or four-wheel-drive applications.
Chevy has produced a lot of different configurations of heads for different applications. Along with oval or rectangle port heads, there are also the open- and closed-chamber head designs. Open or closed refers to the combustion chamber configuration. Closed-chamber means the head has a small combustion chamber and openchamber means the combustion chamber is larger, as seen on page 12. Be careful when changing heads or pistons when rebuilding your engine. You can’t always mix pop-up pistons on closed-chamber heads.
Combustion chambers are all different sizes. They are measured in cubic centimeters (cc), which is the physical amount of volume of chamber. The size of your combustion chamber and the face configuration of your piston determine the compression ratio of your engine. Not all open-chamber heads have the same size combustion chamber.
If you are building your engine on a budget, the factory cast-iron heads work well for most applications. There are many heads to choose from, including open- and closed-chamber heads and oval- and rectangle-port configurations. The best factory head for your build-up depends on your application. If you are building a truck for towing, you are better off using oval-port heads. If you are building a street car with performance in mind, you may be better off with some early to mid 70sopenchamber “smog” oval-port heads because these provide better breathing and good low-end RPM power. For high-performance applications, stay away from “truck” heads. Truck heads have the smallest intake ports that are so small they are more round than oval and are matched with small valves. These heads are only good for low-RPM towing applications. If you are building a high-performance drag strip warrior, you might be better off using a pair of open-chamber rectangle-port heads. The factory also produced some aluminum rectangle-port heads back in the 60s and 70s for muscle cars.
All factory heads can be improved upon. If you want some extra performance from your heads, you can unshroud the valves to increase airflow around the entire valve instead of just one side as the factory left them. For more power, you can increase the size of the intake valve only. You can also upsize the exhaust. These performance upgrades can add up in the machine shop, so get an estimate first and check to make sure it doesn’t make sense for you to simply purchase a new set of aftermarket heads.
There is also power to be had in factory cast-iron heads by porting and polishing them. Read up on the procedures of porting your own heads. There are books on the market that get into detail on the right and wrong way to do these upgrades to your heads in your own garage. If you don’t do your homework ahead of time, you can make some serious mistakes in a hurry. If you have reservations, most machine shops offer good porting services or can point you in the direction of a good shop that can.
Since the mid 1990s, market demand and advances in casting technologies have created a skyrocketing increase in the aftermarket head offerings. Before that, it was hard to find a good assortment of aftermarket oval-port closed-chamber heads with oversized valves. The belief was that if you were buying aftermarket heads, you should buy 119-cc rectangle-port heads or probably just stick to factory heads. As mentioned earlier in this section, make sure you are buying heads that work well with your pistons. If you have pop-up piston domes, you can’t run closed-chamber heads. The piston can destroy the head and/or valves. Check the cc of the head and make sure you don’t make a serious mistake. For instance, if you have flat-top pistons pumping 10.0:1 with 96.4-cc heads, buy the best heads you can. However, if you install a 124-cc head rather than a 96.4-cc head, you may think you increased power but, instead, you just dropped your compression ratio to less than 8.5:1. Remember what I said about planning? You have to do your homework. If you have doubts or questions, ask a professional.
Even though more companies are casting aluminum heads, there is still a large market for cast-iron bigblock Chevy heads. World and RHS list their cast-iron heads as their entry-level performance heads and their aluminum heads are the next step in performance. The cast-iron heads are no slouches when it comes to performance gains. You can purchase cast-iron heads from a few different manufacturers such as RHS, World, and Dart.
With technological advances in aluminum casting, there are a lot of aluminum heads available in the aftermarket. With Edelbrock, AFR, World, RHS, Dart, Brodix, and others offering the full range of performance levels and configurations of heads, you can find a head that best suits your application. If you can’t find a head you aren’t looking hard enough. If you install cast-iron and aluminum heads of the same compression ratio, the cast-iron heads will make more power because they retain heat. Aluminum heads allow you to run more compression than cast-iron ones because the aluminum dissipates heat faster than iron heads, which lowers the chance of detonation. Along with increasable compression, the aluminum heads weigh 680 lbs less than the cast-iron heads. This provides more power to move your car.
Edelbrock has been known for years as a street head manufacturer and has head offerings ranging from street to high-end Big Chief racing heads for 1,500-plus-hp Top Sportsman racing. If you buy bare heads, beware of valve stem size. For instance, some heads, including stock heads, come with 3/8-inchdiameter stems. Some manufacturers choose to use 11/32-inch-diameter stems to promote flow and reduce valve weight. If you mix 11/32-inch valves with 3/8-inch retainers and locks, the first ignition of your engine will be a disaster.
Mark IV heads are a direct bolton for big-blocks built before the 1991 model year. In the 1991 model year, GM started producing the Gen V Big Block, which had a redesigned coolant system called a “parallel flow” design. This new cooling system changed the block and head castings so that the block and heads cannot be interchanged. The Gen VI block was redesigned so that the Mark IV heads could be bolted on with the right head gaskets. The part numbers have changed because of design changes, so it’s best to contact your parts store to get the latest design. The Gen VI block can be easily identified by its six-bolt plasticfront timing cover. The later “Gen” heads don’t work on the Mark IV block. In the past, a few companies have offered adapter bushings and gaskets to allow interchangeability, but none have stood the test of time. Big problems arise because the coolant passages can easily leak into the lifter valley.
There are entire books to educate you on valvetrain and camshaft selection so I will not provide exhaustive explanation in this section.
The valvetrain is made up of all the parts that operate the movement of the valves. The order of parts is: timing chain, camshaft, lifters, pushrods, rocker arms, and valves, which are controlled by the springs, retainers, and locks. All these parts work in unison to keep the piston and valve from having a fight, in which nobody wins. The strength of these parts should not be taken lightly in high-performance applications.
Upgrading one part sometimes shows the weakness of other parts. If you upgrade the springs for a slightly modified or high-performance engine, you may be asking too much of the retainers and locks, and they may fail. Take all parts into consideration when building a performance engine because one set of components must be compatible with another, otherwise you may suffer an engine failure. Consult your machine shop or speed shop if you have questions about what parts you should upgrade. At the same time, consider spending your hardearned money on parts that fit your application and budget.
A unique oil system design was made for 1965–1966 big-blocks. This oil system feeds the lifters by traveling up through a groove in the rear cam bearing and in the rear camshaft journal. If the camshaft and cam bearings are grooved, this is a 1965–1966 system, and you better make sure you get new cam bearings. The oil was fed through three holes in the rear cam bearing. The 1967 and later blocks only require a single hole in the rear cam bearing. While finding a cam for your 1965–1966 engine may be difficult, a machine shop can cut a 3/16- inch groove that’s 7/64-inch deep around the center of the rear cam journal. The groove in the bearing doesn’t provide enough of a passage to allow for proper oil supply to the lifters, so the groove in the cam is necessary.
Selecting a camshaft can be a daunting task if you’re trying to pick one on your own. The cam companies have included detailed descriptions of camshafts in their catalogs and on their websites to make the process easier. Some companies have cam and lifter kits designed for use with intake manifolds and engines of a specific power range. If you’re searching for a camshaft tailored to your driving style and the sum of the parts on your engine, you can either consult professionals at your local speed shop or call the cam company. The cam manufacturers have experienced tech personnel who can help you choose a cam that suits your gear ratio, transmission type, intake, carb, heads, compression ratio, and a bunch of other factors. They’ll be able to give you qualified professional advice on running a hydraulic or solid flat tappet cam or a hydraulic or solid roller cam to best suit your application. Their job is to help you be pleased with your engine build.
The choice between flat tappet and roller cams is completely up to your application and your pocketbook. Flat tappet cams have been working fine in stock big-blocks since 1965. Roller cams are more exotic and well suited for any performance, but especially ones that rev to more than 5,500 rpm. The roller hydraulic cams have been used in Chevy production engines for many years, providing great performance and reliability. The roller tip allows some stock engines to run trouble-free up to a few hundred thousand miles, while the friction from most flat tappet cams causes signs of serious wear after 100,000 miles. Flat tappet cams are more than enough for most applications, so spend your money wisely.
Your choice of lifters should be determined by your camshaft selection. There are hydraulic and solid flat tappets and roller versions of both. You can’t run a flat tappet on a roller cam or vice versa. Solid flat tappets can’t be used on hydraulic flat tappet camshafts or vice versa because of the incompatibility of design and materials used. I’ve heard of using solid roller lifters on hydraulic roller cams, but it’s not suggested due to aggressive cam-lobe profiles.
Lifter technology has advanced a lot in the last 30 years. The roller lifter is at the forefront of those advances. Roller lifters have received much needed attention in the effort to reduce power-robbing friction and increase valvetrain life. The introduction of hydraulic roller lifters has changed the way people look at a roller valvetrain.
For so many years enthusiasts have avoided using solid roller or flat tappet cams on the street because they think it necessitates adjusting their valves all the time. Times have changed and so have valvetrain accessories. In the past, solid lifters would get out of adjustment because of the absence of stud girdles and locking rocker arm adjustment nuts. Valvetrain materials in general were not as good as they are today. Solid lifters still need to be adjusted but a lot less frequently than the myth suggests. The bigger drawback of solid lifters is that they produce more valvetrain noise than hydraulics do.
Standard duty big-blocks have been equipped with 5/16-inch- and 3/8-inch-diameter pushrods, depending on year and application. GM only installed the huge 7/16-inchdiameter pushrods on their performance engines.
Replace any 5/16-inch pushrods with 3/8-inch pushrods when rebuilding a big-block that’s going to be exposed to performance driving with RPM reaching near 6,000. Only severe-duty high-output big-blocks should consider the tree-trunk-like 7/16-inch pushrods.
Pushrods must be made of hardened steel because the canted valve orientation of big-blocks requires pushrod guide plates. Any nonhardened pushrods are too soft and get chewed up by the guide plates.
Aftermarket companies sell specific pushrod lengths for the bigblock. In a perfect world of engine building, you could use exactly what the catalog calls for. Unfortunately, the world is not perfect. Pushrod length changes if the block has been decked, the heads have been shaved, or you are installing all new aftermarket parts. Purchasing pushrods at the start of the build is just asking for trouble. It would be great to have them on your workbench when you get to that step, but you may have to return them for a different-length set. There are two tools on the market to assist you in checking for correct pushrod length: a pushrod length checker, and a pair of adjustable pushrods (the intake pushrod is shorter than the exhaust and requires two different tools). To be precise, you should take your measurements after installing the cam and lifters in the block with assembled heads bolted on the block with the head gaskets in place. This will ensure the proper length measurement.
For stock applications, you can use stock rocker arms. As soon as you increase the lift on your camshaft, the rocker arms should be upgraded. A stock rocker has a slot at the base that allows it to pivot on the rocker stud by using its fulcrum ball. Increased valve lift tries to pivot the rocker more than the slot is cut for. There are just as many pounds of leverage at the rocker arm as at the valve spring (447 lbs for the 496 project engine). When there’s binding, a stock-sized slot in the rocker (the weakest part) fails. Either the stud snaps off in the head or the rocker arm snaps at the base around the slot.
Long-Slot Rocker Arms
To use larger lift cams and stockstyle stamped steel rocker arms, many companies offer rocker arms called long-slot rocker arms. The slot in the base is longer to eliminate bind when used on higher lift camshafts, hence the term “long slot.” Crane suggests using long-slot rockers for camshafts ranging from stock lift to .560 inch and their extra-long-slot rocker arms for applications over that.
Roller-Tip Rocker Arms
Typically, performance enthusiasts upgrade to a roller-tipped stamped-steel rocker arm from the long-slot stamped rocker arm. These roller-tipped rockers have a longer slot already designed into the body. The roller on the tip reduces friction by rolling on the tip of the valve stem. This reduced friction is usually good for a good gain of a few horsepower.
True Roller Rockers
The next upgrade in rocker arms is the true or full-roller rocker. It has a roller at the tip like the previously mentioned rocker arm, but is not hampered by the design of the stock fulcrum it has to pivot on. The true roller rocker has a body that rides on needle bearings that reduce friction over stock-style fulcrum. The rocker’s rollerized pivot points offer greater reduction in side-loading the valve into the valve guide, for less guide wear and increased power.
If you are building a brutal, highperformance big-block and cost is not an issue, you can’t do better than shaft-mounted rockers because the location of the shaft fully maximizes rocker geometry. Crane Cam’s shaftmounted rocker arms use a unique “Quick Lift” geometry by placing the pushrod seat location lower in the rocker body than other brands and increase the advertised rocker ratio a full .1 higher during initial opening. So a rocker advertised at 1.7:1 rocker ratio will act as a 1.8:1 ratio for the first .300 inch of valve opening, then reduce to the advertised 1.7:1 until the valve returns to within .300 inch of the seat when the ratio increases again. This Quick-Lift increases power by allowing flow into the combustion chamber sooner to maximize cylinder pressure. The design also works on the exhaust valves, allowing spent gases to exit from the chamber faster. This geometry is much like changing to a more aggressive camshaft profile without changing the operational cam duration. Crane’s shaft-mounted rockers also utilize a unique low-friction polymer-matrix bearing on a specially treated oversized 5/8-inch shaft for reduced friction and increased durability.
The valvesprings should be replaced during the course of every rebuild, unless your springs have less than 10,000 miles on them, even if it’s a stock rebuild. I only state that because stock replacement springs do not cost much and they are cheap insurance. Valvesprings take serious abuse and weaken from harmonics and heat produced in the valvetrain. A broken spring will lead to a cam failure in a hurry.
All aftermarket camshafts have suggested valvesprings to use in conjunction with them. If you are upgrading your camshaft for a performance application, you need to read the information that comes with it. It’s possible to use some power-upgrade camshafts with stockheight valve springs. A camshaft with higher lift than stock requires a valvespring with the proper compressed height. If you run a stock spring on a high-lift camshaft, the spring could bind before the cam is at full lift. If this happens, the valvetrain will destroy itself in an instant.
Spring pressures and rates are important, too. You can wipe out the cam if your chosen cam and lifter combination is incompatible, and if the combination is installed with too much spring pressure and increased friction load. If the spring pressure is not high enough, the engine can experience valve float before peak RPM. Spring pressures are measured as seat pressure (uncompressed) and open pressure (compressed). The spring rate is determined by the amount of pressure required to compress it. Conventional valve springs have the same outside diameter from top to bottom and are rated linearly. For instance, a linear rated spring of 400 in-lb would take 400 pounds to compress it 1 inch and 200 pounds to compress it 1/2 inch. Beehive valvesprings have a progressive rate; a 400 in-lb beehive spring would take 400 pounds to compress it 1 inch, but it may only take 165 pounds to compress it 1/2 inch. Because the beehive spring diameter is smaller at the retainer end, the retainer and keeper is smaller, which reduces valvetrain weight. Also, they are not subject to the same damaging harmonics as conventional springs. With those benefits, the beehive spring is great in some, but not all, applications due to its progressive spring rate.
If you have questions about your application that can’t be answered by the catalog or website, call the tech line at the camshaft manufacturer. They are always willing to get you what you need to have a good experience with their products. Before calling, make sure you have the specs on your camshaft and engine readily available.
Retainers and Locks
Don’t skimp on retainers and locks. Stock retainers and locks are not designed for performance use. The piston and the valve get acquainted really fast when these parts fail. If you’re building a stock engine, inspect your current retainers and locks for signs of wear. Consider replacing them with new stock replacements, if possible. If you’re building an engine with more than 375 hp, you should be upgrading these valvetrain parts. Purchase the best ones your application requires.
Depending on what year bigblock Chevy you are working on, your engine could have 5/16-, 3/8-, or 7/16-inch pushrods and sizecorresponding guide plates. Unless you are going to install shaft rockers on your big-block, you’re going to need guide plates. There’s a good chance you’re working on an engine with perfectly good guide plates. There are only three reasons for replacing your guide plates: you are building a new engine; you are rebuilding an engine with damaged/ worn-out ones; or, you are upgrading the size of your pushrods. Just about every valvetrain manufacturer sells new guide plates, but most only offer 3/8-inch and 7/16-inch versions.
Timing Chain or Gear Drive
Some older low performance bigblocks had single-row chains mixed with gears with nylon teeth. In the past, some racers have found success with using standard single-row factory timing sets. Nowadays the most-common timing chain upgrade is to install a double-roller setup. If you are going to spend time to dial-in your cam for extra power, you might as well buy a true double-roller timing set with multiple crankshaft keyways. Timing sets are available with hard-set timing and some have an adjustable cam sprocket. These timing sets, such as the Hex-A-Just chain set from Edelbrock, allow timing adjustments of plus or minus six degrees without removing the lower sprocket from the crank for adjustment. The adjustment is in the adjustable offset bushing on the cam sprocket.
Gear drives are an option if you want to do away with the timing chain and have the most precise timing without the possibility of chain stretch. They come in two types. There is a fixed-idler type with a single idler attached to the timing cover (like the Milodon gear drive) or a non-fixed idler that has two idlers connected by two bars that float between the cam and crank sprockets. Milodon’sfixedidler system can be set up as quiet or noisy while being installed. The nonfixed type can usually be purchased as noisy or quiet systems, but if you don’t like the noise of a jet engine running without oil, you should buy a quiet gear drive. Some non-fixed gear drives require a little machine work to install them and some drop right in, so check with the manufacturer before purchasing. The drawback to gear drive, especially the noisy ones, is their interference with knock sensors on computer-controlled engines.
Your moving parts don’t ride on bearing surfaces; they ride on a thin layer of oil. Getting oil from the pan to the bearing surfaces is priority one. Oil pumps should be purchased for your engine according to the application. Bearing clearance set by your machine shop and planned operating RPM should be the deciding factors. Tighter bearing clearances on stock engines don’t require as much volume to keep the pressure high. Due to increased bearing loads and heat, high-performance engines have higher operating-bearing clearance. Increased clearance means that it takes more volume to keep the same pressure in the engine because more oil is escaping out of the larger clearance. The higher projected RPM will demand more volume to keep the pressure up since the rod journal travels on a circle around the cranks axis. The higher the RPM, the more centrifugal force pulls oil out of the rod journal. Consider that, compared to the center of the crankshaft, the outside edge of the cranks rod journal is spinning about 15-mph faster at 1,000 rpm and by 6,500 rpm the journal is reaching speeds of 100-mph faster. That force pulls a lot of oil out of the system. If you are building a high-performance big-block, you should be installing a high-volume oil pump. If you are building a stock engine, you should consider replacing your oil pump with a stock replacement pump.
The camshaft indirectly drives the oil pump. The camshaft drives the distributor, which turns the oil pump shaft. The stock oil pump driveshaft has a nylon collar that centers the shaft on the top of the oil pump. The nylon collar can become brittle with age. For extra insurance, especially on high-performance applications, most engine builders ditch the stock shaft and collar. They suggest replacing the stock setup with a heavy-duty shaft with a steel collar because they hold up better when subjected to the stresses from moving more volume and heavier oils than the factory intended.
The oil pan is a seriously overlooked part. It’s very common to not consider the oil pan when building an engine. The stock oil pan will work for stock, moderate street/ racing/off-road, and mild open-track driving. Higher levels require more specific oil control and purpose-built pans. More acceleration, deceleration, and cornering g-forces move the oil away from the oil pump pickup. Don’t allow the oil pump to starve, or your bearings will be very upset. Manufacturers like Milodon have a full line of oil pans that cover your street, drag race, circle track, road race, and off-road applications. Many Milodon pans are notched for 454s being stroked with a 4.250-inch crankshaft and they are zinc plated for protection against the elements.
Uncontrolled oil flow in the oil pan can rob power from the engine. Milodon has tested their windage trays on 400-hp engines, and its louvered windage trays have been shown to add about 12 hp while its Diamond Stripper can add up to 25 hp. Installing a windage tray helps control oil in the pan during hard braking, acceleration, and cornering. Milodon’s Diamond Stripper has a specially angled mesh screen. Oil flying off the crank (outer crankshaft counterweight speed can reach approximately 240 mph at 6500 rpm) passes through the screen, and it also controls the oil from splashing back up into the crankshaft.
Technology has come a long way since the big-block first rolled off the assembly line. Some gaskets on the market for Mark IV engines have been made with little change since the 1960s. For instance, you can still purchase cork oil pan gaskets with rubber end seals. I will admit that the cork composition has changed to improve its sealing abilities since then, but you can upgrade to Fel-Pro late-model one-piece silicone-rubber oil pan gaskets with a solid steel core, crush-proof bolt shims, and anti-stick treatment for easy removal. These gaskets just make sense.
Make sure you get the right gaskets for your application. Each version (Mark IV and Gen V, VI, and VII) of the big-block requires different gaskets. The timing cover, oil pan, and intake gaskets are easy to identify as being wrong when you get ready to install them. The head gaskets are not easy to identify as wrong and will cause you a lot of overheating problems if you install the wrong ones for your application.
There are two different types of big-block coolant flow systems: series and parallel. The water in the “series flow” system is designed to flow from the water pumped into the front of the block, around the cylinders, and to the back of the block. At this point, it flows up through two large holes in the head gasket into the two corresponding holes in the head. Then, the hot coolant flows to the front of the head where it’s forced up into the intake manifold and thermostat.
The water in the “parallel flow” system gets pumped into the front of the block and around the cylinders and ports in the head gasket between each cylinder. This allows coolant to flow up into the head as well as one small port in the back of the block. In other words, the parallel flow system flows coolant evenly up into the head from the entire deck surface, from front to rear. All the coolant travels to the front of the head where it flows into the intake manifold and thermostat.
Don’t make the mistake of installing a Gen V, VI, or VII head gasket with a small rear port on an early Mark IV block. The Mark IV’s (depending on the year) deck surface doesn’t have the ports between the cylinders, and it relies on the two large rear passages for all of its flow. The late-model gasket with one small rear port seriously restricts the coolant flow and causes overheating problems that will plague your engine until the gasket is replaced.
Both the series flow and parallel flow cooling systems work well. Some engine builders have found a slight advantage to the parallel because it cools the engine a little more evenly than the series flow does, but it’s not worth the trouble of trying to convert a series flow to a parallel flow.
You will face cooling problems from installing the wrong head gasket, but you can have a few other problems as well. The gasket could be the wrong material for your application. For instance, steel shim gaskets are almost always used only on castiron- headed applications while composite-type head gaskets can be used with cast-iron and aluminum heads. Solid copper head gaskets are supposed to be used in conjunction with stainless steel O-rings, which require machining O-ring grooves in the block, and are not suggested for street use. Proper cylinder bore size and gasket thickness is also important when picking your new head gaskets. Fel-Pro also has a full line of head gaskets for your big-block. Check with your machine shop for the best head gasket for your application.
Using the correct bolts and nuts to assemble your engine is as important as adding oil to your engine before start-up. I’ve seen engines with cylinder heads held on by Grade 5 hardware store bolts. There are plenty of different levels of quality bolts available on the market for your engine.
If you are building a stock engine, you can get away with reusing most of the original bolts. However, since you are spending the time to rebuild your engine, you may want to consider replacing critical bolts like rod bolts, main bolts, and head bolts. Victor Reinz and Fel-Pro sell stock replacement bolts if you don’t want to upgrade to aftermarket bolts.
Because you are going to spend some good money to rebuild your engine, you should consider replacing your critical bolts with aftermarket bolts to protect your investment. There are different levels of aftermarket bolts available. If you are on a budget, you can find great aftermarket bolts available from companies such as Mr. Gasket and Milodon. Both companies offer bolts for just about every need on your engine. ARP fasteners cost more than stock, but this brand is chosen by more engine builders than any other available fastener.
There are different types of bolts available for most applications. The most common bolts are hex-head bolts, which are identified by their 6 points. Although less common, 12 point bolts are the choice of some engine builders because, in tight spaces, you can reposition a 12-point combination wrench on the head with a smaller turn of the wrench.
Studs vs. Bolts
Which is better, studs or bolts? Studs are the best way to go, whenever possible. When you torque a bolt, it twists into the threaded hole, which causes two different forces (twisting and clamping) to get to the proper torque. A stud is installed in relaxed mode, only threaded finger tight. When you torque a nut on a stud, all the clamping force is on a single axis for a better and more precise torque. This also saves the threads in the block by only pulling in one direction when the threads are fully engaged. It’s recommended to use main studs because they reduce cap walk and fretting, which can spell disaster for bearings, especially on high-performance applications. If you’re going to use studs in critical places such as the mains and heads, you need to purchase them before machining is done. As you just read, the clamping force is different between studs and bolts. The studs change the way the main caps fit the block, so the main alignment should be checked with the studs installed. Head studs are much better than head bolts, but sometimes they make extra work because they don’t allow for removal of the head (while the engine is installed in the car) without removing the studs first. Cooling System Don’t overlook your cooling system during the course of your engine rebuild. The wearing parts of a cooling system consist of the water pump and thermostat. Don’t overlook the hoses. They should be checked for swelling and/or surface cracks and possibly replaced before installing your newly rebuilt engine. You should take the vehicle’s radiator to be checked and flushed while the engine is out of the car, so you can start with a completely fresh cooling system.
During tear down you identified your water pump as good or bad. If it was bad, you should replace it. If you plan on upgrading the performance output of your big-block, you should look into installing an aftermarket high-flow water pump. Aftermarket performance pumps are available in cast iron and aluminum. Aluminum pumps are higher priced, but they don’t retain as much heat and they weigh less. As I mention throughout this book, you get what you pay for.
As a cheap insurance policy, you should think about replacing your thermostat. You could go through the trouble of sticking your original thermostat in a beaker of water while using a thermometer to make sure it is opening at the proper temp (typically stamped in the housing) and that it closes when it’s cold. Or, you could just save yourself the hassle and buy a new Mr. Gasket or Stant unit. Thermostats come rated for specific temperatures. The most common are rated 160, 180, and 190 degrees. A general rule is to use a 180-degree unit. In drag racing applications, some guys leave the thermostat out or install restrictor plates in place of the thermostat. Drag racing has short bursts of intense power and heat, so they can get away without using a thermostat. Run a thermostat if your car will be driven more than a quarter mile at a time. Without a thermostat, your car will take much longer to warm up on the street. A colder operating temperature increases the wear of parts like piston rings and cylinder walls. Wear decreases substantially when the operating temp is higher than 140 degrees. A good operating range for performance and drivability is between 180 and 195 degrees.
Cooling System Accessories
Don’t overlook replacing old, corroded, and possibly failing coolant plugs, fittings, and the thermostat housing. You must run fresh coolant through the system at all times or else parts start to deteriorate from exposure to the elements. Thermostat housings deteriorate and cause pinholes in the casting, or they can be over-torqued and start to leak. Consider replacing them with new parts so you know these parts won’t cause an unforeseen overheating problem down the road. These fittings and housings come in many forms. The most cost-effective ones you can buy are available from Mr. Gasket. These are typically chrome-plated steel and can survive the elements better than some other brands. If you want plugs or fittings (factory style or aftermarket) that will never give you a hassle or rust (internally or externally), you should look into stainlesssteel fittings from Performance Stainless Steel. They also offer stainless- steel thermostat housings that stand up to the harsh elements like no other housings on the market.
You’ve got to have fuel if you want fire. Getting the right amount of fuel is the most important part. Too much fuel can wash past the piston rings and contaminate the oil, which, in extreme conditions, can cause bearing failure. Too little fuel can cause catastrophic meltdown of your pistons under the right conditions. Pick your fuel system with care.
The stock mechanical pump bolts to the mounting pad on the passenger side of the engine on carburetorequipped Gen IV (and limited numbers of V and VI) blocks. Fuel pumps are different for each application due to space constraints, along with fuel and smog requirements. The standard performance stock engine doesn’t require high volumes of fuel to be supplied to the carburetor. When you step up the performance level or you are working on a high-output big-block, you will need a higher-output pump. Companies such as Edelbrock offer mechanical fuel pumps for power levels up to 550 hp that pump 110 gph (gallons per hour) and operate at a pressure suitable for a carburetor without a separate regulator. For racers who continue using a mechanical pump beyond the 550-hp rating, Edelbrock sells a Victor-series pump that feeds 130 gph at 13 to 14 psi. However, this is too much pressure for the needle and seat of a carburetor, so this pump requires a separate fuel-pressure regulator to limit the pressure being fed to the carb until the demand increases.
There are reasons to run electric fuel pumps: You may be running fuel injection, or you may simply prefer to not have your engine pumping its own fuel. Whatever your reason, make sure you are getting sufficient fuel. Electric fuel pump manufacturers require installing the fuel pump as close (within 12 inches, typically) to the tank as possible. A fuel line up to the carb on every big-block should be at least 3/8 inch in diameter, or as big as 5/8 inch, depending on the power output. If you don’t get enough fuel to the engine you’ll run the risk of running lean enough to cause piston damage.
The stock fuel pump pushrod is a solid piece of steel actuated by a lobe on the camshaft. At high RPM, the weight of the pushrod can cause the pump arm to stay compressed and the engine will run out of fuel. If you still want to run a mechanical fuel pump pushrod you can get a lightweight version from many manufacturers. It is typically a hollow rod with hardened ends. Note: A fuel pump pushrod will wipe out a roller cam due to material incompatibility.
Written by Tony Huntimer and Posted with Permission of CarTechBooks