after the engine has been installed and in service for a while than it is to move to forged pistons or change cam types.
Throughout the actual rebuild process, you will be faced with decisions about whether to reuse and rework the original parts or replace them with new items. Some of these are normal wear items and are assumed to be intuitive; you are going to acquire new piston rings, engine bearings, gaskets, timing set, and such. Some items are potentially reusable but should be replaced in the context of a true rebuild. In this book I am assuming a minimum of new pistons, new cam and lifters, and the complete machining and reconditioning of heads and block. On the cylinder heads in particular, consider the cost of reworking the originals against the price of new replacements.
As a quick reference, at the time of writing this book the cost of stock replacement–type parts and complete machining will easily approach $2,000. Even when doing all the disassembly, inspection, and assembly work yourself, I would keep a $3,000 or $4,000 minimum budget in mind for a proper rebuild. It’s very easy to double that (or more) when contracting some of the work or adding in upgraded or higher-performance parts.
Performance goals have a direct relationship to the budget process. Almost everything you do to improve performance will have an impact on the project’s cost. With that fact noted, quite a few performance improvements are possible for a modest cost increase. On the risk versus reward scale we can get a nice initial increase with very low risk/cost.
The first question when looking at performance goals will be the intended use of the engine. It might be fun to ask for 600 hp, 20 mpg, a smooth idle, and a low budget, but reality dictates that you are not going to get all of those at the same time. The right answer for a 4-speed Mustang is different from the proper package for a four-wheel-drive truck. It’s most common to ask for a certain amount of power and then try to fit that engine into your design and budget envelope. It is often a better idea to approach it from the opposite direction: Define the vehicle needs and budget first, then see what kind of power you can get within those boundaries.
From the factory, the non-high-performance Ford FE engines used in passenger cars and light trucks were good running, durable, and reliable. But they were not noteworthy for outright power. They were intentionally designed for low-RPM torque; smooth, responsive driving; good idle quality; tolerance for low octane fuels; and low maintenance. In today’s environment we have much better ignitions, more consistent (perhaps not better) fuel quality, and enthusiast owners who are much more involved in terms of tuning and more tolerant of high-performance characteristics such as idle quality, noise, and part throttle behavior.
A well-built stock or moderately upgraded 390 4-barrel engine should provide between 300 and 400 hp. A similar 428-based engine should deliver between 350 and 450 hp. While the 352 and 360 engines are worthy powerplants for street use, the reality is that you are far better off converting them to 390 cubes or more during the rebuild process. The upside gains in power and torque are dramatic, and the costs are nominal.
Limitations that should be considered included fuel tolerance. A compression ratio between 9.5:1 and 10.0:1 will usually work well with pump premium. Heavy vehicles with highway gearing should trend to the low side of that range, while a lightweight vehicle with steeper gears can go to or beyond the high side. This has more to do with the amount of load the engine sees going through the torque peak than with the absolute numbers. You also need to consider vacuum at idle if you are using power brakes. The bigger cams and larger carburetors associated with high power will reduce available vacuum, possibly below the minimum 10 or 11 inches desired at idle.
In this book we will restrict discussions to street performance applications within a range between 300 and 450 hp. We will primarily be covering builds based on 360, 390, and 428 engines. You can certainly make a lot more power using aftermarket or factory high-performance parts, and the comparatively rare 427 block, but that type of build falls outside the context of this volume.
A group of formulas and equations are employed in both stock and high-performance engine building. Some of these are used to determine the basic configuration of the engine, such as displacement or compression ratio. Others are used during assembly to verify measurements such as deck clearance or ring gaps.
These days most of the calculations are readily available on the Internet or as part of engine-building software packages. Instead of listing them all out in complete mathematical detail, I will describe the purpose of the most popular ones, give a simple overview of the math and the impact they have on the build, and provide a couple examples. I will cover the measurement and clearance numbers during the assembly chapters.
Displacement
This is the measurement of “how big” an engine is in terms of cylinder volume. Displacement is referenced in cubic inches (or cubic centimeters). It is a simple cylinder-volume calculation, multiplied by the number of cylinders in the engine. Neither the combustion chamber nor the piston shapes affect displacement.
To calculate this number we need only the diameter of the cylinder and the stroke of the crankshaft (the distance the piston moves up and down during each crankshaft rotation).
To calculate displacement, we take the cylinder bore’s radius squared (the bore diameter divided by 2 then multiplied by itself); multiply that value by PI (22 divided by 7); and then multiply the result by the stroke. You now have the displacement of one cylinder. An increase in bore diameter or stroke gives you more displacement.
This formula can be simplified and calculated as: bore × bore × stroke × 6.2832 inches.
An example for a .030 over 390 would be:
Compression Ratio
This is a comparison of the total volume in a single cylinder when the piston is at the bottom of its stroke versus when it is at the top. The combustion chamber and the piston have a great deal to do with this more complex calculation.
Compression ratio is expressed as a value over 1. We are comparing the total volume above the piston when it is at the bottom of its travel to the total volume above the piston when it is at the top of its travel. If we have 10 times more total volume at the bottom of the stroke than we do at the top of the stroke, we have an engine with a 10:1 compression ratio.
To perform this calculation we need the bore diameter, the combustion chamber volume, and the head gasket volume. You’ll also need the deck clearance volume (the distance from the top of the piston to the top of the block when that piston is at the uppermost end of its stroke travel). The last thing we need is the effective dome volume of the piston; add this if it’s a dish or subtract it if you have a dome.
Take the individual cylinder volume number calculated in the displacement discussion. Add in all the head gasket, combustion chamber, crevice, deck clearance (volume of that small space calculated as a cylinder), and dome volumes (some of those are usually given in cubic centimeters, which you’ll need to convert to cubic inches). The total number is “on top” of your ratio. Now take all those volumes except for the displacement and you have the bottom number in the ratio. On a street engine you should end up somewhere between 9 and 10 to 1. Higher compression ratios will deliver more power, but will not tolerate low-octane pump fuels. On the risk versus reward scale, an extra point in compression might get you another 30 hp but cost
