Modified Mustangs & Fords
Engine Building Part 2 - Power Principles
Block Options and Machining Techniques
Fortunately, the aftermarket has provided us with a very nice selection of engine blocks for performance builds. For the Windsor crowd, there are blocks available from Ford Racing, Dart, and some others. Most of these blocks are available in either cast iron or aluminum, and offer excellent strength for big power builds, arriving with billet four-bolt-main caps and extra thick siamese cylinders. The 351W-based blocks are available with the Cleveland (2.750-inch) main bearing size. This brings the best of both worlds, the Windsor deck height (allows for big stroke) and the smaller main bearing size of the Cleveland.
The big-block guys aren't left out in the cold here either. For the 460 fans, Ford Racing has a couple of blocks available, with one being offered in a 4.600-inch bore size. With a 4.500-inch crankshaft, you can essentially squeak your way up to the 600-plus-cubic-inch- displacement range (4.625x4.500).
Genesis, Pond, and Shelby are your manufacturers for aftermarket FE blocks. Most of these are available with larger bore sizes as well, which allow displacements well into the 500ci region. Genesis and Robert Pond offer their blocks in either cast-iron or aluminum. You'll pay a higher premium for aftermarket blocks, but the up side is that you won't have to grit your teeth every time you step on the loud pedal. All of these blocks will hold a substantial amount of horsepower.
Once you've decided on the block requirements for your engine build, you will need to have it prepped and machined. If it's a factory block, then it would be beneficial to have the block checked out before you put a decent amount of money into machining it. Several key areas need to be examined first:
1. Obviously, the block needs to be inspected for apparent flaws: "windows" in the block, broken bellhousing bolt bosses, major cracks, and more.
2. The block bore needs to be measured. There's no use in taking a block to a machinist to have it bored if it's already been bored past the "comfort zone." For example, if you have a 351W block that's already at 0.060-inch overbore and it will need to be bored further to straighten the cylinders, then this would be a block that should be passed on. If you're concerned about how far you can go on a particular core, then the sonic test would be your best bet to get an accurate map.
3. Once you check those first two tasks off your list, then it's wise to have the block pressure tested and Magnafluxed. Pressure testing will ensure that there are no internal cracks or areas where the block can leak. Magnafluxing will take care of the areas that can crack but have no fluid pressure behind them (main caps, main journals, and so on).
After the block has passed all inspections, then it's time to have it machined. Let's go over what's deemed necessary for a "detailed" block machining process:
Bore & Hone: A block needs to be bored to get rid of any straightness issues in the bores, to get rid of any cylinder flaws, and to roughly prep the engine for the new pistons. I generally recommend to only bore the minimal amount needed. It's unnecessary to take 0.060-inch out of a cylinder wall, when a 0.020-inch cleanup would suffice. Adding bore doesn't add that much to the displacement of the engine. I've heard many guys boast that their engine block is "bored to capacity." This isn't really something to boast about, as they've only added 5-10 cubic inches and they've got extra thin cylinder walls now.
Following a bore, the cylinders have to be honed. Boring a block will not put the finish on a cylinder that is necessary for proper ring seal and wear. To hone a block, torque plates are bolted to the deck surface to simulate the clamping force of the cylinder heads and fasteners, and a series of honing stones are used to put a final size on the bore and to put a "cross-hatch" on the cylinders.