"Ford Motor Company knows how to build engines with lots of power, but they don't build short-deck big cube engines. That's because there is always a compromise, like when you stuff a long stroke crank in a short deck block. It's usually the ring seal that is compromised because the piston is pushed upward with the connecting rod being on such an extreme angle. This can cock the piston, and when that happens you can lose ring seal. And when you trade ring seal for cubic inches the longevity of the engine suffers and the manufacturers can have that," explained Tom Naegele of DSS. "That's why Ford created the taller 9.48- and 9.50-inch deck height blocks when they wanted to go to 351 cubic inches," he added.
In contrast, many builders believe the 347 (with a 3.4-inch stroke) is fine in a 8.2 block. That is, as long as the engine isn't revved past 7000 rpm on a consistent basis. We've seen many 347s make great power both on the street and on the track.
You should also know that increasing stroke also increases piston speed (which is different from engine rpm). And this is something you must consider if you plan on turning your stroker past 7000 rpm. When the stroke is increased, the piston must cover the distance between TDC and BDC in a shorter amount of time (as compared to a stock stroke). Since the pistons have to start and stop quicker, the load on the internal components is increased. This includes the main webbing in the block, the main caps, wrist pins pistons and connecting rods.
Knowing this, I recommend using the strongest and lightest pistons and rods when building a high-rpm stroker. One example is the Probe forged pistons found in the Coast High Performance 347 engine kit. These pistons weigh about 410 grams as compared to a stock 5.0 piston that weighs about 700 grams.
Blocks
The foundation for any stroker engine buildup is the engine block. When it comes to Ford small-block engines there is no black magic. There are only so many choices, some stock and some not. It's likely that the block you select will be based on cost, but we recommend using the best block you can afford (sometimes).
The stock 5.0 roller blocks are the most common and are great for applications up to (about) 500 horsepower. Naturally, you've seen them make more, way more in some cases, but they are not designed for 600-700 horsepower use and if you make that much you'll be taking your chances.
A better choice for an all-out race engine is a Boss block or the Ford Racing A4 or R-302 blocks. The Boss and the Ford Racing blocks feature 4-bolt main caps, they are beefier and are designed to make well over 850 horsepower. Note: Avoid using a 289 block for any serious stroker because they have shorter cylinder bores (compared to the 302) which will allow the piston to stick out of the block at BDC, creating a stability problem.
If you're using a stock block, we recommend sticking with a .030-inch over bore. The stock block is certainly an economical choice, but you can expect to swap blocks after a season or two if you make over 500 horsepower.
If you are building a 351 stroker, you can select between the many choices in the Ford Racing catalog. You'll find both 9.2 and 9.5 deck height casts that can be used for all types of racing. Whether you use a stock block or a race block we recommend that you have the block Magnufluxed (checked for cracks) and sonic tested if you plan to increase the bore above .040-inch.
No matter which stroke length you select, it will be necessary to notch the bottom of the cylinder bores to add clearance for the rod bolts.
Crankshaft
The crankshaft is the heart of any stroker kit. It takes the energy from the power stroke and converts it to torque that's used to drive the car. Each Ford small-block crankshaft has five main journals on the crank centerline. Those journals secure the crank to the engine block, but also allow it to spin freely. The crank also has offset journals (four of them in a V8) for the connecting rods, and counter weights opposite the connecting rod journals that offset the weight of the pistons, wrist pins and the rods.