Compressor efficiency

Supercharger manufacturers strive to achieve the most efficient compressor design possible. Although it’s possible to achieve inlet air temperatures as low as 60 degrees after a 1/4-mile run with ice-packed air-to-water intercoolers, supercharger efficiency is still critical to performance. According to Vortech, while it is true that certain charge cooling strategies may always be employed to reduce charge air temperatures, this in no way helps alleviate the parasitic load on the crankshaft. In other words, there are two performance benefits to efficient compressor design, and charge cooling addresses only one of them. Inefficient compressors will require even larger heat exchangers for removing this waste energy, which will always come with some pressure loss. “To design a state-of-the-art centrifugal compressor, you will need a talented and experienced designer with some very expensive software and a method of quantifying the resulting performance. It takes a lot of knowledge and work to get it right,” Jim opines. “When comparing two similar supercharger systems in vehicles with charge coolers that have the same inlet air temperature entering the engine, there will remain a larger disparity in performance between the two if one has a properly matched, efficient compressor and the other does not. On the inefficient car, much more horsepower was lost when used to produce the same pressure and flow, perhaps as much as 100-200 hp on the most extreme combinations. Cooling the charge back down does not recover this loss, and in fact, there are probably more losses in the cooling process due to pressure loss.”

Same boost, more power

Not all boost pressure is created equal. When switching from a less efficient to a more efficient supercharger, people sometimes report making more power with the same amount of boost. Elementary physics dictates that the process of compressing air adds heat, and keeping the amount of heat gain to a minimum is the key to optimizing supercharger efficiency. “A more efficient compressor absorbs less power off the crankshaft for any given air flow and boost pressure. Likewise, increasing compressor efficiency delivers lower charge air temperatures, and therefore a denser air charge,” Jim says. “Due to these factors, designing a more efficient compressor may make use of smaller, reduced-loss charge air cooling strategies, because the thermal loads are significantly reduced in the first place. All of these benefits result in improved overall power, and the charge cooling band-aid applied to an inefficient compressor only addresses one problem.”

Gears

As horsepower levels increase, the load imparted on a supercharger’s gearset increases dramatically. Granted that maximizing gearset durability is paramount to supercharger longevity; minimizing friction, heat, and parasitic power loss are top design priorities as well. To address these needs, Vortech started from scratch to design an all-new, state-of-the-art gearset for the V-20 supercharger. “We are very happy with our gear design, except for the price. For a high-power, high-speed gear system, the gear must be carefully designed,” says Jim. “When designing our gears, Vortech engineers actually took the load deflection into account when developing the tooth profile. We also employ an onerous, multi-step manufacturing process that ends with CNC precision grinding. Oil control is also an important aspect of gear design, and we utilize many proprietary techniques to ensure optimal lubrication.”

Cast or billet?

High-performance centrifugal superchargers are built from a combination of cast and billet components. While billet has a reputation of increased durability, manufacturing efficiency is often what dictates which supercharger components are cast and which are machined from billet. “The billet question is more about perception and in some ways it can be about cost. For large-scale production, cast parts are generally preferred and the cost of tooling makes them a more logical option,” Jim explains. “For custom and small production runs, it’s easier to machine parts from billet since it’s not cost-effective to develop the tooling. Billet parts are generally shiny and attractive. Whether they function better or not is largely based on a personal perspective, not necessarily the technical side of the equation.”

Impeller design

When designing a supercharger impeller, factors such as impeller diameter, pitch, angle, and number of vanes all affect compressor performance. While prying trade secrets out of manufacturers for cutting-edge race hardware like the V-20 is always a challenge, Vortech’s insight into impeller design is enlightening nonetheless. “Without touching too much on proprietary design strategies, let’s just say the basic impeller design for a given compressor stage is a key priority, and we invest considerable time and energy into attaining the most efficient designs possible. Impeller speed and diameter, and the flow and boost requirements for an engine combination are design ‘knobs’ that all play off of each other. It turns out there are, in fact, optimum combinations of these various design parameters, all of which we explore in the design space when approaching a clean-sheet product. Understandably, we cannot touch too much more on specifics and why we take one approach versus some alternative for any given product, but racers can rest assured that Vortech has invested tremendous R&D time to develop the most powerful impeller possible.”


“For Vortech’s V-20 series superchargers, only a rolling diaphragm blow-off valve is recommended. For racing, depending on the class and setup, we recommend using either one or two of our Maxflow BV57s.” – Jim Middlebrook


Tolerances

With impeller speeds that can exceed 80,000 rpm, substantial loads imparted by the crankshaft, and toasty underhood temperatures, superchargers must perform in a brutal environment where maintaining close tolerances are critical to durability. Not surprisingly, Vortech invests a tremendous amount of time and effort to ensure close control over these tolerances “There is probably enough information to publish a textbook on this topic alone. We believe the basics are probably well known, but there are many factors to consider,” explains Jim. “The first step is using premium, heat-treatable alloy steels to manufacture aerospace-class gearing and shafting. Both cast and billet casing components require precision, highly repeatable milling, and turning operations. In particular, the bearing bores and final shaft alignments are held to tenths of an inch, and these various critical components are hand selected and matched for final assembly. Furthermore, Vortech uses over a dozen large CNC lathes and mills, many with integrated measuring probes, robotic loading systems, and live tooling. We employ an inspection process that has been adopted from the aerospace industry. Finally, our quality control room is temperature controlled for measurement accuracy. It is fitted with an array of measuring devices including two Zeiss robotic coordinate measuring machines.”

Lubrication

Centrifugal superchargers utilize either engine oil or a separate, self-contained oil system to lubricate their gearsets. Vortech uses both styles of systems in its supercharger model line, but opted to lubricate its new V-20 race superchargers by tapping into the engine’s oil system. “The Vortech V-3 self-contained supercharger works well for most street applications. It is easy to install and runs quite cool for most uses,” says Jim. “In contrast, the Vortech V-2 and V-20 type supercharges use engine oil for lubrication. Although, this arrangement requires tapping into the engine’s oil system and are a little harder to install initially, they are maintenance free thereafter. Using engine oil for supercharger lubrication is generally preferred for continuous or racetrack use.”

Intercooling

Forced induction enthusiasts often debate the merits of air-to-air intercoolers versus air-to-water units. Although there are compelling arguments for both platforms in street applications, air-to-air intercoolers are very uncommon in 1,500-plus hp engines. As Vortech explains, the primary reason for charge cooling is to improve air density. However, it’s possible to actually have a net loss in density with a poor charge cooling system. While intercooling reduces inlet air temperature, it also reduces boost pressure in the process. If the pressure loss through the intercooling system is too great, the cooler air temps will not make up for the pressure loss and the result is a net loss in air density. “On an air-to-air system, the charge air takes a long path through a rather small channel in the cooler core while the cooling air from the grill of the car has a very large area to pass through. There are pressure losses associated with this and the ducting,” Jim explains. “With an air-to-water system, it is the water that takes the long path through the core, and the air to the engine that takes the short path, resulting in minimal pressure drop and a big increase in air density. An added performance-increasing feature is that ice can be added to the water for even greater gains. The benefits of this approach was not lost on competitors back in 2008 when Vortech first offered the Mondo Cooler, which is also referred to as the Igloo. Air-to-air systems simply cannot compete against air-to-water technology because of the benefits of maximum cooling with minimum pressure loss. Physical size is the primary limitation for such a heat exchanger, as the air-to-water designs can be much more compact with less pressure loss, and are well suited to the very short thermal loading cycles associated with drag racing.”

SOURCE
Vortech Superchargers
1650 Pacific Avenue
Oxnard
CA  93033
805-247-0226
http://www.vortechsuperchargers.
com/