Muscle Mustangs & Fast Fords
617HP Paxton Street Stroker
The only thing better than a stroker motor or boost is a stroker motor and boost!
Why are stroker Ford combinations so popular? The answers are many, but mainly, when it comes to building a performance powerplant, bigger is always better. That is to say it is always easier to produce a given amount of power with increased displacement. Where a 500hp normally aspirated 302 might be a tad on the grumpy side for daily street driving, a 500hp 408 would be much more manageable. Thus, the extra cubes make it not only easier to achieve the desired power output, but it can do so while simultaneously improving drivability.
After all, every build is not an all-out race motor. The vast majority of engine combinations go in daily drivers, or at least something that needs to offer sufficient street manners. A high-compression motor with wild cam timing that has a tendency to overheat in stop-and-go traffic is not going to bring many smiles, no matter how fast it is when you finally bring it up on the cam.
The only thing better than big power from a big motor is even bigger power from a boosted big motor. With that, let’s take a closer look at the benefits of a stroker motor before adding the Paxton supercharger to this 331 combo.
As indicated, the greatest benefit of a stroker is the sizable jump in power, but the gains come in at more than just peak rpm. An example works well here. Suppose we build a 5.0L 302 that puts out 302 hp. Given the available performance components, achieving 1 hp per cubic inch is pretty simple. If we produce the same efficiency (by applying the same performance components) on a larger 331 stroker, our motor should produce 331 hp. While an extra 29 hp is always welcome, the real benefit of the stroker can be found at engine speeds well below the power peak. The stroker adds a hefty chunk of torque, and not just at the torque peak, but everywhere along the curve. This extra torque greatly improves part-throttle acceleration, drivability, and it can eliminate the need to downshift when passing. In short, the extra power offered by the stroker adds fun any time you stomp on the loud pedal.
To illustrate the power offered by a streetable stroker, we decided to build one and run it on the dyno. Working with Probe Racing, L&R Automotive, and Procomp Electronics, we chose a 331 stroker in lieu of the larger 347. The stroker kit included a 3.25-inch forged-steel stroker crank. The 4340 forged steel crank was probably overkill for this street application, as the limiting factor in terms of power was certainly the strength of the production 5.0L block. In reality, a cast crank would work just as well on this application. We have run cast cranks in excess of 600 hp, so fear not if you choose a cast version to save some money.
Since we planned on keeping boost, engine speed, and eventual power output to reasonable limits, the components we picked were less about maximizing power as they were about building a combination for performance and drivability. The 3.25-inch crank was combined with forged I-beam connecting rods (from Procomp Electronics) and forged pistons from Probe Industries. The I-beam connecting rods were 5.4 inches in length, thus improving the rod-to-stroke ratio over a standard 302-length (5.09) connecting rod. The use of the 5.4-inch rod improved the rod-to-stroke ratio from 1.566:1 (with the 5.09-inch stock rod) to 1.66:1. The Probe dished pistons featured dual intake valve reliefs to allows use with either the standard inline valve locations of most 5.0L heads, or the offset locations featured on the Trick Flow Specialties Twisted Wedge heads. This came in handy as we planned on topping the stroker with a set of aluminum TFS Twisted Wedge heads.
Once assembled by Ford Performance Solutions, the 331 was treated to a mild Comp Cams Xtreme Energy (PN XE266HR) hydraulic roller cam, lifters and double-roller timing chain. The dual-pattern XE cam offered 0.544 intake lift and 0.555 exhaust lift. The duration was likewise skewed in favor of the exhaust, with 216 degrees of intake duration and 224 degrees of exhaust duration.