Builders of high-boost 4-cylinder engines are always looking for more ways to increase cylinder pressure, which in turn, hammers the life out of a production crankshaft. So it’s no wonder that more off-the-shelf billet cranks are available for the popular inline-fours from Mitsubishi and Honda as well as the Boxer-configured 4-banger from Subaru.

“When new opportunities arise, and there is a demand, we do our best to meet those needs,” says Justin Whitman, a tech rep from Callies Performance Products shedding light on the company’s new Compstar Sport series line of sport-compact billet and forged crankshafts.

Billet crankshafts were once available only through custom ordering. Aside from excellent strength properties, billet crankshafts are easily configured to an engine builder’s exact specifications. Customers can order dimensions, oiling strategy or counterweight profiles that normally could not be machined on the base forging for a specific application. Since the tooling required to produce new forgings is quite expensive, crankshaft suppliers developed quicker and more efficient billet programs to serve engine builders requiring custom cranks.

Callies leveraged its considerable experience in building custom billet cranks in the popular V8 markets to develop the Sport series crankshafts that are less expensive than custom models but offer many of the same features. Here’s a quick look at the current applications of billet crankshafts with all strokes listed in millimeters (mm):

• Mitsubishi 4G63 7-bolt: 88, 94, 100, 102
• Mitsubishi 4B11T: 94, 96, 98
• Honda B18: 92, 95
• Subaru EJ20/EJ25: 75, 79, 83

“The Mitsubishi 4G63 are 7-bolt versions. We’re also working on 6-bolt 4G63 cranks,” promises Whitman. “Also, for the Honda, we have a lightweight knife-edged version as well as a full counterweight version.”

Another classic sport-compact engine joining the Callies Sport billet series will be the Toyota 2JZ in strokes of 86, 91, and 94 mm. For 2018, expect to see Sport series billet crankshafts available for the Honda K-series, Honda F-series, and Nissan VG30DETT.

“We are a production shop, so it is much easier to launch new products when there are larger quantities to justify manufacturing, engineering, and tooling costs,” adds Whitman.

Callies also offers Compstar 4340 forged versions of the Mitsubishi 4G63 7-bolt 88mm and 100mm cranks. The semi-finished forgings are imported with Callies handling the finishing (including sizing and polishing), inspection, heat-treating and nitriding in-house at the company’s Ohio manufacturing facility.

“All critical dimensions are the same,” says Whitman, comparing the forged version to the billet. “The billet has more material deployed in specific areas to enhance stiffness and resistance to fatigue.”

The Sport series crankshafts start out as a 170-pound chunk of 4340 billet steel, and after eight to ten weeks of production work end up as a 34-pound crankshaft. The preliminary machining is performed at the sourcing plant overseas; then Callies handles all the finish machining and nitriding in Ohio.

“That time includes numerous heat treatments and a 30-hour nitride cycle,” adds Whitman, noting that all the machining is performed on CNC machines. “There is a vast variety of specialized equipment to do this work. There are many steps, and there is no ‘off the shelf’ equipment used.”

Developing an inline-4-cylinder crankshaft requires attention to some issues not associated with V8 crankshafts.

“Second-order vibrations in 4-cylinder engines are noticeable while basic load-bearing characteristics are similar for all crankshafts,” says Whitman, noting there is an exception with the 180-degree cylinder layout of the Subaru engine. “It’s a smoother engine that does not have second-order vibrations.”

Second-order vibrations, which occur twice per revolution, develop in an inline 4-cylinder due to crankshaft configuration, rod angle and piston speed. Picture a cross-section cutaway of a conventional 4-banger engine. The two inner pistons are 180-degrees opposed to the two outer pistons. Remember, most inline 4-cylinder engines utilize a crankshaft where the connecting-rod pins are arranged in an up-down-down-up order. When the pistons are at TDC-BDC-BDC-TDC, it appears that the connecting rods are perfectly vertical and balanced.

However, when the crankshaft is at mid-travel through the stroke, the pistons are not at mid travel within the cylinder due to rod angularity. The two pistons on the intake and combustion down strokes are at a slightly different position than the two pistons on the compression and exhaust upstrokes. Another way to look at this dynamic is that the pistons starting from TDC will reach their maximum speed before half-stroke. Consequently, those coming up from BDC will be past the same point before they stop accelerating. Basically, the acceleration of the piston is greater at TDC than at BDC, so forces do not completely cancel each other out, and the combination of all these factors lead to second-order vibrations.

With a Boxer or 180-degree configuration, each bank of cylinders is an exact mirror to the opposite. Regardless of the crank rotation, rod angle or piston speed, the forces on each side cancel out the other side because they’re exactly the same and occur at the same time. In other words, the rotational and reciprocal forces are balanced. Also, the firing forces are balanced since firing events occur every 180 degrees. Callies takes these factors and many others into consideration when designing new crankshafts for performance engines. Also, lessons learned on the V8 often apply, such as understanding the benefits of journal overlap.

“First, we take our design queues from what is already out with the OEMs and address any shortcomings in what we see in those designs,” explains Whitman. “Everything is tested in virtual world. We use FEA to find hot spots with the complexity of torsional and bending loads. Laboratory testing is very difficult and not always representative to what applies to it in an engine. And, yes, overlap is always 100 percent in consideration when judging strength.”

Finally, unlike custom billet orders, the Sport series doesn’t offer options like reduced journal diameters. Also, as with any other stroker crankshaft, the engine builder will have to be aware of clearance issues.

“Reduced journal diameters are desirable up to the point that they don’t sacrifice durability. Certain applications are good for having reduced size journal, while other applications are not, such as high boost or nitrous,” explains Whitman. “Certain applications will require clearancing of blocks depending on stroke, and rod combination.”