Superchargers are magical devices. They increase the oxygen supply to the engine by compressing the air, thus increasing its density. Accordingly, the engine burns more air-fuel mixture and produces more power.
In a centrifugal supercharger, the air is propelled through the compressor wheel and compressed in the diffuser—the thin passage formed between the compressor cover and the bearing housing—and in the volute, or scroll, where its kinetic energy is converted to pressure. All of the dimensions, including the diameter of the diffuser, diffuser gap distance, and size and diameter of the volute contribute to the degree of compression.
In a turbocharger—exhaust-driven forced induction—the compressor wheel is powered by exhaust flow, but in the supercharger the compressor wheel is driven via a gearbox that takes its power from a crankshaft pulley by way of a drivebelt. The gearbox accelerates the compressor wheel from engine speed to a point where the compressor operates efficiently.
Typically, maximum efficiency is reached when the compressor wheel spins at 70,000 rpm and beyond. But it is not the compressor wheel’s ultimate revolutions on which the engineers focus; instead it is the tip speed of the wheel’s outer diameter. Tip speed is calculated in meters-per-second and it is this velocity that determines the supercharger’s efficiency.
Notably, splitter blades on the compressor wheel increase the efficiency of the compressor. Traditionally, the compressor wheel comprises 16 blades, 8 of which are splitter blades. Placed alternately, these splitter blades extend up the tapered hub toward the inlet but their height is curtailed, otherwise they would become too restrictive at the top.
The greatest attribute of the TorqStorm supercharger probably lies in low-end torque. In this area, it has taken its most substantial leap forward. You don’t actually need more than 1,850 rpm on the clock before it will summon up much of the torque it possesses and it will continue to generate it all the way to 6,500 rpm.
More commonly, the boost range of traditional centrifugal superchargers is initiated between 3,000-5,200 rpm. Tellingly, the TorqStorm’s increased range of operating efficiency, kicking in at 1,850 rpm, is accomplished mostly by a revised configuration of the compressor wheel.
“We’re CNC machinists by trade,” explains TorqStorm’s co-founder Chris Brooker, “and we were approached by a company several years ago to assist them in the redesign of an obsolete supercharger. It was a compelling challenge because several of us at the shop are avid hot rodders. For the most part, we applied proven technology already developed. But as the design entered its final phase, the company that initiated it unexpectedly abandoned the project. As you can imagine, we had devoted endless hours of R&D time in creating the prototype. When aborted, it seemed wasteful to let the project languish on the shelf.”
The design distinguishes itself in several important ways, not the least of which is by its use of a billet gearcase, in contrast to the traditional cast case. “This significantly reduced bearing deflection and improved sealing,” says Brooker. “We also introduced a self-contained oil supply, which further simplified the installation by eliminating oil feed lines. So, given our tool and die background, where everything has to be so precise, and knowing that we had a competent product, we decided to market it ourselves.”
One common deficiency about some supercharger installations is that the parts don’t always line up. “We resolved this,” explains Brooker, “by including a 3/4-inch-thick billet mounting bracket that eliminates any fitment concerns. It also improves belt alignment and ends deflection—and the violent act of belt throwing.
Today, TorqStorm’s broad array of kits cater to virtually every Chevrolet variation, whether big-block, small-block, or LS. The LS units include single or twin superchargers—fuelled by either EFI or carburetor.
For small-blocks and big-blocks, right- or left-hand mountings are accommodated as well as long- or short-reach water pumps, and all of these superchargers work in conjunction with the stock power steering from 1969 onward. By design, the supercharger is positioned in front of all factory accessory drives.
According to TorqStorm, their single supercharger kits add between 120 and 150 hp at 6-9 psi to any small- or big-block Chevrolet. But during recent supercharger comparison tests these numbers were found to be surprisingly modest.
Pace Performance, the Boardman, Ohio, engine suppliers, had plans to engage TorqStorm as their supercharger supplier, but a comprehensive testing was first required. To initiate the program, Pace hastened a 383ci small-block Chevrolet to the premises of Lamar Walden Automotive in Doraville, Georgia.
BluePrint Engines has long been a Pace engine supplier and they provided PN BP38316CT1—an engine specifically designed for power-adders.
Back at Lamar Walden’s, the 383 with a Demon blow-through carburetor was attached to the dyno. Then the crankshaft drive pulley and spacer were attached to the harmonic damper. Next, the 3/4-inch-thick billet bracket is installed on the left cylinder head with three spacers and a backing plate. The supercharger is then secured to its mounting bracket by seven head bolts.
Now, the eight-rib serpentine belt is installed and adjusted. All that remains is to fit the hat on the carburetor and to connect it to the supercharger with the two large-bore discharge tubes supplied with the kit. Positioned between the discharge tubes is an inline blow-off valve. A small-bore hose is connected between the boost-reference port on the blow-off valve and the carburetor. Tightening the four stainless steel hose clamps completes the arrangement.
Aligning the supercharger with the discharge tubes is made convenient by the introduction of a V-band clamp that allows the charger to be rotated to the correct position. The bonnet is a universal device that serves either blow-through carburetors or EFI systems that feature a traditional 4150-style air-cleaner mounting flange.
In the dyno room, Rob Walden, who has been scrutinizing and testing high-performance and competition engines and engine parts for 25 years, supervised the comparison tests. The process involved baseline testing power output of the naturally aspirated BluePrint 383 engine, installing and dyno-testing with the TorqStorm supercharger, and then repeating the process with a supercharger from a leading manufacturer.
In his private thinking, Walden separates the needs of a supercharged engine from a naturally aspirated variant by ensuring there is sufficient fuel available for the thirstier boost condition. “Idle and cruise conditions don’t alter fuel consumption appreciably,” he says, “but boost conditions do. Also, it’s important the spark plugs operate in the correct heat range.”
Compared to a naturally aspirated engine, a supercharged counterpart generates higher combustion temperatures and therefore runs spark plugs that are one or two steps colder to deter detonation—depending upon the amount of boost employed.
The dyno preparations for the tests were routine: crank up the engine and allow it to reach normal operating temperatures—coolant around 180 degrees, lubricating oil over 100 degrees, and ignition timing checked, which was 32 degree total.
The dyno tests began by revealing what was already expected: the BluePrint small-block made 436 hp and 460 lb-ft of torque at 5,700 and 4,300 rpm, respectively. When the TorqStorm was added it generated 627 hp—an improvement of 191 hp—with 566 lb-ft of torque at 5,800 rpm.
But the best part was its 400 lb-ft of torque at 2,000 rpm; its rival reached 400 lb-ft at 2,500 rpm. At 3,000 rpm, the ’Storm generated 484 lb-ft, compared to 436, and as engine speeds increased the deficits slowly diminished to around 10 lb-ft at 5,800 rpm.
Returning to the blow-off valve for a moment, this is a vacuum-controlled device that serves a dual purpose. First, it allows boost to occur only above light throttle, when vacuum drops to a preset point. Second, it releases excessive boost to prevent damage to the system if the throttle suddenly closes on deceleration.
And why is this so important? Well, those adept in the ways of centripetal force—the principle at play in a centrifugal supercharger—contend that if you have an abundance of high-speed air in the tubing and you close the throttle, the inertia must be able to escape. If not, high boost spikes could cause damage, including blowing a hose off or splitting the tubing. It can also damage the throttle body butterfly or shaft.
Although it’s common to hear boost expressed in pounds per square inch (psi)—it is much more useful to consider it as a pressure ratio, which is the pressure exiting the compressor divided by the pressure entering the compressor. In so doing, this allows us to correct for differences in atmospheric pressure. Since atmospheric pressure at sea level is about 14.7 psi, and if your boost gauge is reading 7 psi, your formula is as follows: 14.7+7/14.7, which gives us a pressure ratio of 1.47:1.
Finally, when you learn of TorqStorm’s limited lifetime warranty and its modest cost, $2,800 depending upon its finish (natural alloy, black anodized, or micropolished), you wonder how so. Chris Brooker responds: “We machine everything ourselves in Michigan—including the supercharger gearcase, the compressor wheel, brackets, pulleys, tensioner—and we’ve found that this tightly controlled formula is the key to suppressing costs.”