Frank H. Cicerale
January 1, 2008
Here is our stroker ace completed. We cruised to JDM Engineering to get the 4-1-1 from the crew on the new Three-Valve stroker engines, and they allowed us to help assemble one. Talk about crazy!

When it comes to making power, the old saying that there's no replacement for displacement has been replaced, in a sense, with the sick, power-producing properties of a turbocharger, centrifugal, or positive-displacement supercharger. Even a small hit of the sauce can bring about an on-demand supply of extra ponies. So are extra cubes really necessary?

While the dollar-per-horsepower number of a blower, turbo, or laughing gas may outweigh the cost of building a thundering naturally aspirated combination, there's still the allure of a modular engine sporting a larger-than-normal cubic-inch figure. In a sense, while power adders are good, utilizing them in conjunction with a supersized stroker motor is even better.

Building a stroker motor is nothing new in terms of the venerable 5.0 pushrod motors, but for the modular crowd, especially those with the newer Three-Valve 4.6 engine, strokers are becoming an accepted and easy way to make more power. With the bore spacing for the 4.6 block being extraordinarily close when compared to the spacing in the 5.0 pushrod engines, the easiest way to add inches without compromising the block's cylinder sleeve structure is to drop in a longer-stroke crank.

The goods themselves can be seen here. The rotating assembly is all forged components for the utmost in strength and reliability.

One of the leading performance shops pumping out stroker Three-Valve mod mills is JDM Engineering in Freehold, New Jersey. JDM and company spearhead Jim D'Amore have long been associated with muscular Mustangs and fast Fords, and they were kind enough to allow us to tag along as they built a brand-new Three-Valve stroker engine.

The main focus of the stroker engine is, obviously, the components to the rotating assembly, specifically the crank. JDM uses a forged-steel stroker crank, forged Manley H-beam 4340 connecting rods, and a set of forged Manley pistons, all of which were manufactured to JDM specifications. The 3.750-inch stroke of the crank, when combined with the standard 3.555 bore of the 4.6's cylinders, brings the cubic-inch displacement to 298-17 ci more than the factory offering of 281. D'Amore points out, though, that while the cubic-inch increase may be small in number, it's more profound when looking at it in terms of engine percentage increase.

The interesting thing is why JDM went with a crank that creates 298 cubes as opposed to the more common 302 offering. "I wanted to be able to turn higher rpm in this motor, so I went with the 3.750-inch crank to gain the right rod angle," D'Amore says. "With this crank, there should be no problems with the engine both on the track and on the street for an extended period of time. With the longer crank, there would be an increase of side load on the piston skirts, which would lead to a shorter lifespan for the engine."

In addition, JDM currently offers two versions of its Three-Valve stroker package. One is made specifically for naturally aspirated combinations, while the other is geared exclusively for super-charged applications. "The major differences between the naturally aspirated and supercharged stroker engines lies in the pistons, the compres-sion ratio, and the ring gaps," D'Amore says. "In the naturally aspirated motors, we use a flat-top piston and run a 10.8:1 compression ratio. The supercharged motors are obviously different because you don't want to run into any detona-tion. For those motors, we put in a set of dished pistons, lower the compression ratio to 9.8:1, and run a tighter end gap on the piston rings."

The rotating assembly is dropped into an aluminum Three-Valve 4.6 block that is common to the new S197 cars. According to D'Amore, there is no special machining of the block to accommodate the increased stroke of the crank. Also, JDM has the bottom end of each stroker put together exclusively by Anthony DiSomma of M2 Race Systems. While the clearance specs for the engine are proprietary, D'Amore made sure to mention how extra attention is paid to that part of the build throughout the assembly, with the Three-Valve modular engines being especially reliant on proper oil control. "The reason why oil pressure and control are so important on these motors is because the cam phasers in the Three-Valves rely heavily on oil pressure, especially at idle," he says. "Having too much clearance is bad for the cam phasers."

While the stroker crank is the main bit of attraction for this engine, with the extra cubic inches, a good set of cylinder heads need to be bolted on to get more air to flow into the cylinders. The heads are stock Three-Valve heads, though they've been massaged by DiSomma for maximum flow. "The heads get a full CNC port job, as well as a valve job," D'Amore says. "The heads are then equipped with 1mm oversized valves, heavy-duty valvesprings, and titanium retainers."

The cylinder heads are factory castings that have been worked over by DiSomma.

Another note of interest was D'Amore's usage of the stock camshafts. While a set of aftermarket cams will unquestionably make more power over the stock cams at certain points on the dyno graph, D'Amore likes using the stock cams because they allow him to tune the torque curve of the engine easier. "The reason we use the stock camshafts is because they allow me to tune how I want in terms of the retard to the cams themselves," D'Amore says. "I do this with the cams to broaden the torque band, and the stock cams make doing it so much easier. So far, we've been able to get a new Mustang GT into the 11s with the stock cams and a stock torque converter in an automatic [naturally aspirated-Ed.]. This is great for everyday driveability. You can make as much power as you want, but if the car isn't driveable, then it's useless to customers. As we progress, we'll be testing cams and looking to produce 400 hp at the wheels on motor and much more with a blower or turbo."

So how much power is the JDM naturally aspirated stroker engine worth? Let's look at one of the in-house cars at JDM. This particular '07 S197 started out as a stock GT with bolt-on parts such as an exhaust, cold-air kit, underdrive pulleys, and a custom tune making 306 rwhp (see dyno graph). After putting in a 298-inch naturally aspirated stroker motor with the identical aforementioned bolt-on modifications, the same car pounded out 352 rwhp. In addition, the torque numbers at the rear wheel increased from 323 to 362.