This is the age of the stroker motor, and when it comes to cubes, it's pretty much a case of bigger is better. Nevertheless, just how much better is highly dependant on the utilization of those cubes. In essence, there is low-tech cube utilization, which delivers so-so results, and there is high-tech cube utilization, which as we'll see here, delivers dynamite results. Moreover, the cost difference between one and the other may only be marginal. Read on to find out why.
Laz Mesa (the boss at Mesa Balancing in Hialeah, Florida) and I have one thing in common-we both like big-inch motors. A few years ago, we did a successful project on a stroker 351 Windsor, and since then we have shared test data to fine-tune Windsor stroker combinations. This all came to a head when I got a call from Laz telling me that Pro Power had a new budget stroker kit good for street/strip power levels up to 650 hp. I had successfully used a Pro Power budget stroker kit in the past to good effect, but the latest iteration had an upgrade on the rods, and more importantly, the pistons. In addition, Laz had sonic tested a 351 block that was good for .060 over. This, with the 4.10-inch stroke of the Pro Power stroker crank, would give us 425 inches. That's a whole 21 percent increase over a stock 351 Windsor.
Cubes & Efficiency The Pro Power stroker kit used here (including bearings and rings) can be had complete with a damper (tuned to the crank) for $1,399, and for $250 extra, the whole lot can be balanced. But buying the cube-generating parts and installing it all in the block is the easy part. To capitalize on the extra cubes, two factors become super critical. These fall under the heading of volumetric (breathing) efficiency, and combustion efficiency. Maximizing volumetric efficiency means maximizing the combination of airflow capability, and velocity of the carb, intake manifold, heads, and exhaust, such that with the right cam, the maximum amount of air can be passed through the engine. Achieving good combustion efficiency starts with a carb that delivers a mixture with just the right amount of fuel atomization, and assuring that the quality of the mixture does not deteriorate too much by the time it has arrived in the cylinder. Along with this, we need an ignition system that has not only high spark power, but also the right advance characteristics. All this means a substantial number of parts working together in a well-orchestrated fashion. It did not happen overnight, but the final spec of our engine, which came together in total over a period of some two years, was just that, so let's look at the key issues involved.
Cylinder Heads We have lots of cubes to feed, and if any sort of real power is to be had, the heads must be able to feed those cubes. To do so requires good airflow, but that alone is not the answer. If we are looking for high torque over a very wide rpm range, then port velocity becomes a real factor. Not only that, but the wet flow characteristics must also be such as to promote good combustion. We realized that all this is a lot to deal with, so we started with a set of heads with proven performance-namely a set of 200cc intake port RHS heads. The goals here were to increase both flow and velocity. On top of this, we wanted to increase swirl, and refine the wet-flow characteristics.
Pro Power's new budget stroker...
Pro Power's new budget stroker kit for the 351 Windsor is the basis of our stroker, and is good for up to 650 hp. With the 4.10-inch stroke of the Pro Power stroker crank and our .060-over block, it would give us 425 inches. This kit includes bearings and rings, and can be had complete with a damper for $1,399. For $250 extra, the whole lot can be balanced.
Made from cast steel, the...
Made from cast steel, the Pro Power crank is about 20 percent stronger than the alloy Ford uses, and has about twice the ductility.
Mesa Balancing used a selected...
Mesa Balancing used a selected block for our build. Normally, a .030-inch overbore would put displacement at 418 inches, but ours was good for .060 over, which allowed us to go to 425 inches.