a detonation-prone combination.
The typical calculation for a normal 390 Ford with flat top pistons (rounded numbers) is:
Bore = 4.050
Stroke = 3.780
Cylinder volume = (calculates to 48.71 ci)
Chamber volume = 72 cc (converts to 4.39 ci)
Deck clearance = .030 (calculates to 0.39 ci)
Gasket volume = 10.2 cc (converts to 0.62 ci)
Piston dish volume = 6 cc (converts to 0.37 ci)
Total volume with the piston at the bottom of its stroke = 54.48 ci
Total volume with the piston at the top of its stroke = 5.77 ci
Compression ratio = 54.48 divided by 5.77 = 9.44:1
Deck Clearance
This clearance is the result of a stack up of component dimensions. It is the distance between the top of the piston at its uppermost travel and the head gasket deck surface of the block. These days we seem to prefer to get this as close to zero as we can without going positive. The currently accepted ideal range for best power and combustion is for the piston to be between .040 and .060 away from the cylinder head at top dead center. To achieve this with the common .040-thick head gasket, we need to have the piston somewhere between .000 and .020 below the block’s deck.
Add up one half of the crankshaft stroke, the center to center length of the connecting rod, and the compression distance of the piston. Compression distance is the measurement from the centerline of the piston’s pin hole to the upper flat surface of the piston.
Example (using a 390 Ford FE and rounding up for simplicity):
Block deck height from factory measured from main center to deck surface = 10.17
1/2 of the 3.78 stroke = 1.89
Connecting rod center to center 6.49
Piston compression distance 1.76
Total = 10.14
Block deck height minus the total of parts = .030 deck clearance
This means that a simple clean-up machining of .010 to the block’s deck will get you into the desired range.
Piston compression distance is a different dimension, and is determined when the piston is manufactured. This is measured from piston pin centerline to the top flat portion of the piston’s head. This may not be the highest point on a piston; a domed piston will have a portion protruding above this point. Your piston manufacturer will usually provide this dimension for you in the instructions or packaging. It can be difficult to accurately measure on your own.
Ford FE Specific Design Choices
With some of the basic concepts in the background, we can take a look at the stuff that makes an FE Ford engine build unique. This will involve a bit of history to provide context to the possibilities within the factory architecture and using factory parts. While several aftermarket stroker packages are available now, this book is focused more on rebuilding and upgrading popular factory-style engines.
The engine pictured here is a completely original 1969 390GT. It has on it about 11,000 miles. The owner installed the vintage Cal Custom valve covers shortly after purchasing the car new, and it had been in storage for decades before he decided to refresh it and put it back into service.
Despite changes over the years, the majority of parts will physically interchange from one FE engine to another. It’s a bit unusual to be referring to engine changes as “new versus old” when talking about an event that occurred 50 years ago, but that’s what we do. The camshaft thrust design was altered in the early 1960s. You don’t see many of them around, but the old engines can be easily converted to the newer configuration. The motor mounts changed in 1965; old ones used two bolts while the newer configuration has four bolts per side. The new-style blocks can be mounted into the old platform but the older ones need some adaptation to work in a post-1965 vehicle.
The most common Ford FE engines by far are the 352, 360, and 390. Used in hundreds of thousands of passenger cars and trucks, these are the engines you will most likely find in cars, barns, and salvage yards. Less likely although still possible are 391 and 361 medium-duty truck engines. It’s also possible to find 428 blocks since they were used in full-sized cars and Thunderbirds, as well as in irrigation and industrial applications. The odds are very much against finding a 427 or 406 engine anywhere outside of the performance and restoration marketplace. The acquisition cost of those engines pushes them to the outside of this book’s budget-oriented focus, but all the concepts and processes described still apply.
The 352 starts out life with a 4.00-inch bore and a 3.50-inch stroke. The 360 starts out with a 4.05-inch bore and the same 3.50-inch stroke. A 390 has a 4.05-inch bore and a 3.78-inch stroke. With that noted, I tend to turn any 352 or 360 into a 390 almost by default. The cost of a 390 crankshaft and rods is very low, and the gains from the additional 30 or 40 ci are significant. A true winner in that risk versus reward equation.
The 428 is a special case with a 4.13-inch bore and a 3.98-inch stroke. Despite what you may see on the Internet it is best to assume that you cannot overbore a 390 block to 428 dimensions. These are thin-wall castings, and odds are you will eventually split a cylinder even if you get it running. More 428 crankshafts seem to be available than there are blocks, likely a testament to the crank’s durability when other parts failed in racing efforts. The 390 block and 428 crankshaft combination will yield a 410-inch engine, a factory package used in a very few Mercury cars for a year or so. If you already own a 428 crank this is worth doing, but piston availability is limited and often pretty expensive, putting your build cost into the realm of a stroker kit.
The engine we are primarily concentrating on rebuilding for this book is a cool 428 CJ out of a 1969 Shelby GT500. The processes and machining are the same as we would find in rebuilding a more common 390 for a pickup truck or Galaxie, or any FE engine for that matter. I use other engine images where necessary to illustrate a particular process or concept.
I am going to make some assumptions here. The first is that you intend to build and assemble the engine yourself; hence the purchase of this book. The next is that, as part of this task, you will take the engine components to a machine shop at certain points in the build to get things done that are not possible in the average home shop.
Every engine-building project requires decision-making over a wide range of options. One very important series of decisions revolves around selecting the level of build quality. For some folks the decision is entirely based upon economics, and any way to save on costs is key. For others it’s always going to be around quality, with a focus on having and doing things in the best possible way regardless of expense. Throughout this book I present a few options in both product and labor that range from “must do
