Steve Baur
Former Editor, Modified Mustangs & Fords
July 1, 2007
Before final assembly, all D.S.S. Racing short-blocks are balanced on a Hines Eliminator computerized spin balancer. The crankshaft is spun at 500 rpm with adjustable bob weights. The bob weights are then made to be the same weight as the specific pistons, rods, rings, and rod bearings for each rotating assembly. The computer senses the heavy and light part of the crankshaft and tells you where to drill or add material to make it balanced. Not only does it tell you in degrees where to remove, but also how deep to drill. There is no guesswork. A final check spin indicates you are balanced to spec and ready to go.

Last Month, we gave you an intimate look at the new Boss 302 engine block from Ford Racing Performance Parts ("Major Management Muscle"), and briefly talked about our plans for the rotating assembly that would eventually propel our proud project car, Stolen Goods. This month, the D.S.S. staff screws together our Super Boss Bullet, and we'll show you exactly what's going in our big-bore 347ci powerplant.

Having set a goal of 400-425 flywheel horsepower, and choosing to go with a 3.250-inch stroke, a 5.315-inch connecting rod, and a 4.125-inch piston, our Boss 347 presented a couple of challenges when it came time to assemble it. While FRPP has 100 or so of these blocks out in the hands of various engine builders, ours was the first that D.S.S. Racing had seen come through its doors, so the machining process would be slow and precise. The big-bore combination has been done before, but since the hunk of iron is an all-new casting with its own characteristics and traits, it would require an entirely new CNC milling program.

Machining the cylinder bores and crankshaft centerline is fairly easy, as the mathematics involved are mostly the same for all engines. However, machining the lifter bores was a task that Tom Naegele at D.S.S. Racing was a bit tentative to complete.

The Boss 302's new casting features big, beefy lifter bores that allow you to run extra-large lifters or offset lifters. Offset lifters allow more radical port designs so you can straighten the ports and drastically increase port volume without a pushrod tube intruding into the port. Larger-diameter lifters are common in circle track, flat-tappet cam designs, as they allow for more radical flat-tappet cam profiles.

As our engine will be using a hydraulic roller camshaft setup, we needed to make sure the lifter retaining cage would apply the proper amount of pressure to the lifters. After mocking up the cage and lifters, Naegele wasn't happy with the tension that he was seeing, so the lifter bosses needed to be machined down for a better fit.

"Usually we obtain a junk block to fine-tune our CNC program on, so I was a little concerned about using this production piece," Naegele says. Though our block was a production piece, they were a bit hard to come by at the time we wrote this, and with deadlines hanging in the balance, we couldn't afford to mess it up. Naegele and the D.S.S. crew handled the job superbly, though-no doubt a result of their vast experience in building engines of all sorts. Keep in mind that this process is not necessary for link bar-style lifters or flat-tappet lifters, just the OEM hydraulic-roller hardware.

One of the other procedures that D.S.S. performs to all of its blocks is torque-plate honing. Head-bolt torque can distort the cylinder bore, hindering ring seal in the process. Proper use of torque plates prestresses the cylinders so that when the head is torqued on, the cylinders will be exceptionally straight and round. "The D.S.S. Level 10 and 20, which feature this process, have been dyno-proven numerous times to be worth 30-40 hp over commonly used performance rebuilding practices," Naegele says. "Attention to detail, not how fast you can get it done, is the key to power and longevity."

The piston-ring package on a small-block Ford stroker engine is extremely important, not only for making power, but for engine longevity as well. On our build, D.S.S. used Speed-Pro severe-duty ductile iron, plasma-moly rings. The rings' end gaps are adjusted to match the intended application, with wider gaps for boosted or nitrous-fed applications and a tighter gap on naturally aspirated combinations. Piston-ring design and choice is directly dependent on piston design, and these again are important to the architecture of a small-block Ford stroker engine.

Short-stroke, big-bore pistons have a thicker ring land on the piston to provide more space between rings. This additional space is good for strength and power, as rings need volume between them to work properly. It also acts as a reservoir so pressure does not build up between rings, which can result in ring flutter. Ring flutter is when ring seal is compromised because the ring is unseated from the bottom of the ring groove. The ring is pushed against the cylinder and sealed by compression or combustion pressure getting on top and behind the ring, not underneath. With the big-bore, 347 pistons, there is an additional groove between top and second, offering more volume. There's simply not enough room on the piston for that groove on the conventional 347.

"Almost all aftermarket cylinder heads measure 4.100 inches across the chamber," Naegele says. "Most gasket bores measure 4.100, and a standard 302 bore is 4.00. A decent rebuild is 4.030. You can see in the illustration that you end up with a lip at the top of the cylinder that really causes havoc with flow. The shrouding effect of the cylinder and disruption of smooth flow into the cylinder is detrimental to power. If you want to maximize your investment in high-flow cylinder heads, put them on a big bore or use a Level 20 block with the elliptical chamfer."

A big-bore 347ci combination offers a better rod ratio than with a conventionally designed 347 (1.63 compared to 1.58). This improved rod ratio combined with more efficient piston design means better ring seal, less friction rubbing the cylinder wall, reduced piston rock, better cylinder-head breathing, and improved longevity. All D.S.S. pistons feature forced pin oiling, from the Pro-X series pieces we'll be using down to the $349 economy pistons.

"Many competitors' pistons use the OEM method of splash oiling and forged-in oil-return windows," Naegele says. "This method is OK on low-horsepower applications, but it does not support big power or power adders." D.S.S.' Pro-X pistons are aluminum forgings that are CNC-lightened to remove weight in areas where material is not required for strength.

"Most piston companies are mainly concerned with how many pistons per day they can produce," Naegele says. "We feel the extra time spent on details like CNC-lightening, drilled oil returns, full CNC valve reliefs and profile, and forced-pin oiling set our pistons apart and ultimately benefits our customers and our reputation in this business."

The D.S.S. Pro-X forged pistons can take whatever you want to throw at them: blower, turbo, nitrous, or a combination of these induction modifiers. These pistons are also light too, as a single D.S.S. 302 forged piston (PN 4000) is about 160 grams lighter than a stock piston, which translates into more power and higher rpm capability.

There are two designs available: a flat-top, single-fly-cut design (pushrod) that raises compression for naturally aspirated and nitrous cars. Optional is the D.S.S. Max Quench reverse-dome piston that lowers compression for boosted applications. All D.S.S. pistons feature tight piston-to-wall clearance for long-lasting performance, standard full-floating wristpins, and deep CNC-machined valve reliefs (pushrod applications) in the Pro-X series pieces to allow for even bigger valves and higher lift cams. With the cylinder heads we chose and a 0.040-inch gasket thickness, our Boss 347 should come in at a 10.5:1 compression ratio.

Making the connection between the pistons and the crankshaft are the D.S.S. H-beam connecting rods. Naegele specified the H-beam design for added strength, given our intended road-course use and extended amount of time at high rpm. The H-beams are made from 4340 forged steel and feature ARP 8740 cap screws.

The whole rotating assembly relies on the D.S.S. Pro-X Series big-bore rotator-a forged-steel crankshaft made from premium aircraft-quality steel using a vacuum-degassed forging process to ensure a clean and pure crankshaft. Each crankshaft is visually inspected, X-rayed, magna fluxed, ultrasonic-tested, and finished with a multistage heat-induction process hardened to HRC60 and micropolished for superior wear resistance. D.S.S. utilized Speed-Pro heavy-duty Tri metal bearings to support the crankshaft inside our Boss block.

Now that we have our short-block assembled, all of D.S.S.' hard work on our project comes to a close. We have to thank Tom Naegele and his team for getting our Boss 347 done in time to meet our deadlines-a feat not easily accomplished given that D.S.S. was in its busiest time of the year, when racers are banging down the doors and blowing up the phones trying to get their engines back and in their cars for the start of the racing season.

For Project Stolen Goods, it's time to button up the engine and get this Pony burning rubber and banging corners. Next month, we'll give you the skinny on our induction setup-which includes Anderson Ford Motorsport-modified Twisted Wedge cylinder heads, an AFM camshaft, and a Trick Flow intake manifold-and drop this bullet between the framerails.

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