There are very few new ideas in the world of high performance. But with modern technology, we can often revisit a clumsy, old idea and make it more efficient. Such is the case with compressed-air supercharging. The idea is simple enough. Compress and store a large volume of air into a high-pressure tank. Use a pressure regulator to control the air coming out of the tank, and step it down to a traditional boost pressure. Introduce the air on demand, and you have a killer supercharger that doesn’t create parasitic losses because the engine is not using power to drive it. Sounds simple enough, so what’s the catch?
Dale Vaznaian and Karl Staggemeir have been working to perfect the concept of compressed-air supercharging to make ridiculous amounts of horsepower andmake it practical for use on the dragstrip or even on the street. This concept, like most good ideas, is simple and rooted in basic physics. If we use a separate device like a scuba-tank shop’s air compressor to squeeze 3,300 psi worth of air into an air tank and then release this pressurized air into an engine, the released air will be much colder. And we all know that cold air is more dense and makes more horsepower than hot air. Any hot rodder who has ever operated an air compressor to drive a high-speed die grinder knows that compressing air heats it up, because the air in the tank is generally pretty hot. But the air exiting the gun’s discharge port is very cold.
So take that idea and now consider we are releasing air that has been compressed to 3,300 psi. To say that this discharge air will be cold would be a gross understatement. Staggemeir tells us the air leaving the bottle valve exits theoretically at around –200 degrees Fahrenheit, and they have actually measured it at –140 degrees! Since we know cold air is denser than hot air, you begin to see the potential here. Add pressure (boost) to this equation, and we have a phenomenal case for making really big horsepower. That’s exactly what Compressed Air Superchargers (CAS) set out to produce. Staggemeir and Vaznaian began their quest more than 10 years ago to create this system. Along the way, they had to design and build nearly all the components because the parts needed didn’t exist.
Let’s run through how the CAS system works and then we’ll show you what our testing at Westech revealed with this system on a 420hp small-block Chevy. Be prepared to be amazed.
Compressed-Air SuperchargerWe’ll start with the bottle, which is a large, 30-pound aluminum container that looks like a scuba tank. Each bottle is fitted with a CAS-specific 5⁄8-inch-id gate valve, with a 1,000-cfm flow potential. The bottle valve is connected to a -20 AN hose and fittings, which is the largest practical hose diameter the company can use. The fittings are designed to maximize flow and minimize pressure loss. Remember, the engine is going to be breathing only air from the tank, so minimizing flow loss is important. The hose is connected to a sizable pressure regulator located near the tank. This mechanical pressure regulator operates like a typical fuel-pressure regulator in that it reduces the tank pressure down to a working pressure selected for the system.
The next component in line is the electronic safety valve. The -20 AN line enters this electronic shut-off valve introducing pressure into the system. Just past this shut-off valve is a 40mm Bosch electronic throttle-body that performs the ramping function that’s a crucial part of the system. This means the CAS is fully electronically programmable to ramp the power in as a function of time or other user-designated functions such as rpm or vehicle speed. It allows the user to produce a sophisticated linear power curve as opposed to a simplistic on/off switch. The safety valve and Bosch throttle-body direct the pressurized air into what Staggemeir calls the “ejector valve.” This is a larger valve located inline with the normally aspirated inlet air tract. Inside this duct is a 3.5-inch valve that closes when boost is applied. This is necessary because without this valve, the boost would be lost to the atmosphere. When this large valve closes, all the pressurized air from the tank is ducted directly to the engine.
This is a very rudimentary explanation of how the Compressed Air Supercharging system functions. If you study the accompanying photos, this will become less confusing. The best part is the CAS system puts down some serious power.
The TestWe decided that using a basic fuel-injected small-block Chevy would help make this entire program easier to digest. Vaznaian had the 355ci small-block built by DNE Motorsports with a Dart iron block, a forged-steel Eagle crank, Eagle 5.7 inch rods, 0.030-over JE forged pistons, and a Milodon oil pump and pan for lubrication. The heads are a set of Racing Head Service 180cc intake-port aluminum castings with 2.02/1.60-inch valves and a 64cc combustion chamber. The static compression ratio came out to 9.2:1. For a camshaft, Vaznaian chose a Comp Cams hydraulic-roller camshaft with 236/248 degrees of duration at 0.050 with 0.520/0.540 inch valve lift with 1.5:1 roller rockers. The cam also has a slightly wider 113-degree lobe-separation angle (LSA) to help manage the boost so the pressure doesn’t blow out the exhaust during overlap. On top, Dale chose an Edelbrock Pro Flo multi-point EFI system to manage fuel flow. The Edelbrock single-plane intake uses a standard 4-bbl style throttle-body feeding air to eight 44-lb/hr injectors. Supplying the fuel pressure was an Aeromotive fuel pump and a boost-referenced fuel pressure regulator that added 1 psi of fuel pressure for every 1 psi of boost pressure. By jacking the fuel pressure to 60 psi, they created enough fuel flow to feed the engine at peak power. The size of the injectors limited the amount of power they could safely produce. With larger injectors, they could theoretically move even more power.
Mickey Thomson Tried ItThis is not the first time someone has attempted using compressed air to make more power in drag racing. In 1971, Mickey Thompson experimented with a somewhat complex mechanically controlled system on one of his Funny Cars and other racers also tried these systems that appear to have been the work of an engineer named Bob Keane, who owned Keane Engineering. HOT ROD’s story appeared in the Dec. ’71 issue with the title “Mickey’s Bottle Baby.”
The Basics of Charge DensityThis is the key to the CAS system. The basic concept that has been around for decades is that if you lower the inlet air temperature by 10 degrees, this is worth 1 percent power. Classic supercharger applications show that if our boosted engine is making 600 hp and we lower the inlet air temperature with an intercooler from 200 to 140 degrees, the 60-degree temperature change should be worth 6 percent power. At 600 hp before the reduction, our engine should now make 636 hp, which is a small gain. Using compressed air, because this system radically reduces the inlet air temperature to 0 degrees, the formula tells us we should make an enormous gain. Taking the above example, reducing the inlet air temperature to 0 degrees, that’s a massive 200-degree change, which would mean the engine gains 20 percent power. That’s equivalent to gaining 120 hp with an overall peak number of 720 hp.
Charge Density ChartThe following chart indicates the increase in manifold air density in several different configurations. The first column indicates the boost pressure that would be indicated on the gauge (psi gauge) with no aftercooling. These numbers are calculated based on a compressor adiabatic efficiency of 70 percent, which is a good average number for a centrifugal or turbocharger. Roots blowers are generally lower. Higher boost levels also generally create lower numbers. The essential message here is that the compressed-air supercharger concept can deliver far greater density numbers. This creates much higher cylinder-pressure numbers and therefore more horsepower and torque because the increased density delivers cooler air, which equates to more oxygen in the cylinders.
|Boost Level||No Aftercooling||Cooled to 110 Degrees||Compressed Air at 0 Degree|
BaselineRight out of the box, the little 355ci V8 managed an honest 422 normally aspirated horsepower at 6,100 rpm. This is decent power within reason for a mild small-block. The only thing a touch out of the ordinary was that it required 42 degrees of total ignition timing to achieve this horsepower. With the baseline complete, we didn’t change anything on the small-block except hook up the discharge tube from the CAS system and add Rockett Racing Brand 114-octane race gas, just to keep the 9.2:1 engine free from the possibility of detonation. Staggemeir tried a couple of runs with low boost of 5 psi. The test procedure was much like the way we test with nitrous oxide. We stabilized the engine at peak horsepower at 6,100 rpm and then hit the button on the compressed-air supercharger and allowed the dyno to stabilize while we captured the numbers. Then we recorded the best number under boost and compared that with the number we obtained from the best normally aspirated test. This first run under 5 psi of boost produced 655 corrected horsepower compared to the 422hp baseline at 6,100 rpm. That’s an increase of 232 hp—or nearly a 55 percent power increase. Remember, only 5 psi of boost pressure is already delivering more than a 55 percent power increase.
After some minor tuning, we upped the air pressure to 8 psi for our final test. Westech’s Steve Brulé ran the engine up to 6,100 rpm, Staggemeir hit the button, and the engine immediately responded to the 8 psi of boost with 836 hp at 6,100 rpm. That’s an impressive 414hp gain—a 98 percent power increase—and this was with the CAS system operating at 1,000 cfm.
What We LearnedTo no one’s surprise, the combination of below-freezing inlet air with a conservative amount of boost equals major horsepower. Part of the explanation is that the engine isn’t using power to drive a supercharger. Even a small blower can demand 40 to 50 hp to make 8 psi of boost, and we were essentially getting the boost for free with the CAS system.
Our testing also revealed we didn’t need to retard the ignition timing to make 836 hp. In fact, we tried retarding the timing from 42 to 36 degrees, but this resulted in losing 50 hp. It’s entirely possible that additional timing might have resulted in a power increase. We talked with Rockett Racing Brand’s Tim Wusz, and he said one possible explanation for the timing was that extremely dense, cold air will tend to reduce the fuel’s capacity to vaporize. This means it might require more ignition timing to give the fuel in the chamber additional time to vaporize and burn completely. Another potential benefit to the lower inlet air temperature is that octane may not be as critical a factor as it is with heated air from a supercharger.
It’s also important to note this was a near-production system, but CAS still has more work to do before a complete kit is ready for installation in a car. The photos make the system look cumbersome, but the system’s control portion located near the engine could be easily packaged in a box on the inner fenderwell of most muscle cars. The only fabrication would be mating the CAS 3-inch inlet duct to a fresh-air inlet tube. Of course, your engine will need a fully-boost-capable fuel-delivery system and preferably multi-point EFI with big injectors to flow the necessary fuel.
Vaznaian and Staggemeir are working on a tubbed ’68 Camaro with both the small-block and a CAS system so we can return in a few months to report on testing the car and system on the dragstrip. One question running this system in the car should answer is whether one bottle will support a quarter-mile pass. Staggemeir says a carbon-fiber bottle has enough capacity to feed 500 hp worth of air for about 13 seconds, or 1,000 hp worth of air for 6.5 seconds.
So how much will all of this cost? Vaznaian and Staggemeir don’t have a retail price as of yet, but they expect to see an 800hp system complete with a single bottle sell for around $6,000. CAS expects to have a complete production system ready for market by Winter 2014. Expect to hear much more about compressed-air supercharging in the coming year.
Why is the Air So Cold?Here’s where basic physics will explain why compressed air makes more power for the same amount of boost. Hang tight with this, and we promise no math. Let’s start by stating some obvious points. An important rule of thermodynamics is that energy cannot be created or destroyed—it can only be converted into something else. Normally, in the process of doing work, this generates heat. More pressure generates more heat in the air. You can imagine how hot the air and tank becomes when your local scuba shop squeezes the air to 3,300 psi. This process uses an external device (the pump) to put energy (work) into the air. Once the bottle is filled, we allow the bottle to cool to ambient air temperature. This means the heat put into the air has now dissipated, but we will have kinetic or stored energy because we have a bottle with 3,300 psi.
Now, when the air in the bottle is released, the energy put into the bottle is also released. Because the air has cooled, but energy cannot be created or destroyed, the air now will pull heat out of its surroundings. This is why the discharge temperature is so low, because it is pulling heat from its surroundings in an attempt to balance the amount of energy put into the air when it was compressed. As we mentioned, Staggemeir says they have measured the discharge temperature of the air at the bottle at –140 degrees, but by the time the air travels through the –20 AN line and all the fittings, valves, and ducting into the engine, the air has heated to roughly 0 degrees. This still is very dense air, which is why the engine responds with such a huge power increase. As the pressure in the bottle drops, the effect diminishes at the discharge point, but at the same time, the air inside the bottle is cooling, which tends to help in maintaining a very cool discharge temperature. One net effect of the low-temperature air moving through the system is that over a short period of time, the temperature of the valves and hose drops, so the inlet air temperature into the engine begins to decrease since the system is beginning to stabilize. All this happens very quickly and is very transient, yet all of these actions combine to create the power increase that we saw in the testing.