The integrity of a concrete slab that forms the foundation of a skyscraper is critical for the long life and stability of the structure. In similar fashion the shortblock of any engine is the platform that both helps harness the power released in combustion and transmits it to the transmission. The shortblock consists of the cylinder block, pistons, connecting rods, bearings, piston rings, and oiling system. The careful selection and preparation of components in the shortblock are fundamental to building an efficient and reliable high-performance engine.
Whether the engine you have in mind will power a street driven vehicle or accelerate a hotrod through the quarter-mile, how much power you require the engine to produce must become the guideline for the selection of all engine components. So even before putting the pieces together, a lot can be said about how the final assembly will perform. If the engine will power a street machine, it is practical to aim for excellent power, but bear in mind the possible trade-offs of targeting too high. Remember you can not have it all. If you are smart, you will shoot for a practical power level carefully based on the intended usage, and your available budget.
To a certain extent selecting the optimum size motor for your vehicle is an easy choice. If your looking for maximum performance, the old racing adage "There is no substitute for cubic inches (c.i.)" holds as true today as in the past. In other words the larger the motor the easier and cheaper it is to build horsepower. If your are starting out with a Chevy 302 smallblock, a little investigating will reveal that 350 block and crank cores are quite inexpensive and that it usually makes sense to forget the 302 and build up a 350. The cost of building a shortblock is virtually the same, but you are ahead by 50 c.i. and that can easily add 50 or more horsepower (hp.). On the other hand, if you take a 454 ci. bigblock, stretching it to 500 ci. can be quite expensive. The cost of finding the extra 50 c.i. or so in this case could be ten times that of the smallblock.
By reducing vehicle weight, more performance can be obtained while actually increasing mechanical reliability ("reliability" here means both avoiding component failure and extending engine life). This is possible because as vehicle weight is reduced, the engine is required to work less hard in all but full-throttle situations; and in full throttle, reliability will increase since the vehicle will accelerate faster requiring the engine to produce maximum power for less time. A reduction of 200 to 300 pounds can improve ¼ mile acceleration times between ¼ and ½ second, and this is typically equivalent to 30 to 50 extra hp. from the engine.
The most important aspect of block is the makeup of the cylinder bores. Each cylinder bore must provide a lubrication-carrying surface for the pistons and rings to ride against, and it must remain perfectly round while being subjected to thousands of pounds of load and surface temperatures of over a thousand degrees. The techniques of preparing the cylinder bores by precision machining, and even more basically the selection of block with structurally sound bores in the first place, are critically important to obtaining optimum power and reliability.
Crank selection is also very critical as this also pertains to the cubic inch displacement of the motor and to the over all strength and reliability of the short block assembly. For example; a crank from a 400 ci. engine properly installed into a 350 ci. block will raise cubic inch displacement (c.i.d.) to 383 ci. The strength of the crank is very important. Every time cylinder combustion happens (this is when the air-fuel mixture in the cylinder is ignited by the spark plug) the pressure from the down force
is directly put on the crank making crank strength very critical.Deciding on what compression ratio to have directly effects on whether the vehicle will be a practical street machine or more of a racecar. Compressions ratio is a comparison of the volume of air fuel mixture that exists in the cylinder when the piston is located at the bottom of the stroke to the "compressed" volume when the piston reaches the top of the stroke. A 14 to 1 compression ratio means, you are taking 14 cubic inches of air fuel mixture and compressing it in to 1 cubic inch. The higher the compression ratio, the less fuel the engine will use to produce the same horsepower.
The cylinder-head design and preparation is one of the most important ways of developing horsepower and efficiency. The shape of the ports, the size and design of the valves the shape and thickness of the combustion chambers, the rigidity of the overall casting, and many other factors have both important and subtle effects on the horsepower output of the engine. On the surface, it may look like a simple assembly, but in reality most successful race-engine builders put forth a special effort to understand and optimize what happens on the combustion’s chambers and parts of the cylinder-head casting. This is one place to spend as much money as your budget will allow.
The selection of a camshaft at first appears to be relatively simple. Finding and installing an optimum camshaft for your particular application can be very difficult. Selecting a performance camshaft should begin by making two important decisions: 1) what is the over all-purpose of the vehicle and 2) determine the main operating power range of the engine. The camshaft, more so than any other engine component, critically influences the selection and function of virtually every other engine system. Consider: The camshaft directly affects the carburation, induction, and the exhaust systems; but it also greatly influences the design of the valvetrain, the optimum compression ratio, and to a lesser degree, even the chassis and driveline must be "built around" the camshaft. Put simply, camshaft design dominates part throttle and full throttle horsepower output, and selecting this component is one of the most important decisions that an engine builder can make.
The induction system includes everything that delivers the correct air-fuel mixture to the combustion chambers. Induction system is defined as the intake manifold, carburetor. These components are the main supplier of air and atomized fuel; they have – to a great extent – a predictable effect on horsepower. Intake manifolds are designed to operate within specific engine-speed ranges. Select the intake manifold as part of a coordinated "package" – including the camshaft, exhaust system, and other components. When selecting a carburetor remember that this is the basic source for all horsepower. Sense maximizing horsepower is a primary goal here; you must choose a carburetor that has as much air flow capacity as possible consistent with producing effective part-throttle and low-rpm (revolutions per minute) performance.
When choosing an ignition system you will want to buy the best that your budget will allow. No matter what kind of engine you will be building, a good ignition system will work with any motor combinations that you will want to build now or in the future. So spend the money on a good ignition system in the beginning so you will not have to buy a better one in the end.
This is a very broad how to on what is involved in building a motor for any kind of horsepower level you would like to build.