If Thomas Knight Turbos has its way, being "on the juice" will soon have a whole new meaning. TKT has certainly performed the proper due diligence on this one and the ESC-400 has the look of a viable solution to those enthusiasts on the wrong side of the forced-induction fence. Time will tell if this technology catches on.
Pros
Belt-driven superchargers require the engine to power the unit. This parasitic loss can be substantial, especially at higher boost levels.
Turbos are not free power, as some will claim. A turbo is a turbine-driven supercharger and to drive something requires horsepower. The turbine needs velocity, volume, heat and pressure to operate. The first three won't make any boost. It's pressure that makes boost. The first three help with greater efficiency. The pressure in a turbo is measured by the difference in intake manifold pressure and exhaust manifold pressure. This is referred to as the exhaust-to-intake pressure ratio. Most turbos operate at a 2:1-to-3:1 ratio, meaning that if 10 psi is in the intake manifold, the exhaust manifold will see 20 to 30 psi. (The GN operated on a 2.5:1 ratio and the 300ZXTT had a 2.7:1 ratio). Some racecars make PR better than 1:1, but they're still making backpressure. Backpressure is a restriction, and a restriction is not free power.
Cons
Battery technology and weight are the classic detractors. However, battery technology has advanced significantly in recent years and the lightweight batteries that are available already will become lighter as the technology evolves.
The system lacks an electronic boost control strategy. This will be available soon.
Low-output alternators, which can't recharge the batteries quickly enough, can limit ESC running time.
Wiring must be properly installed. This is key in the overall performance of the unit.
ESC Q&A
Turbo: Why did you build an electric supercharger?
Thomas Knight: The idea of a serious electric supercharger has always intrigued me. There are no parasitic losses, the unit can be mounted anywhere in the car and it can be run in any car; it's not application specific.
T: When did you start on your design?
TK: I built my first electric supercharger in 1978. I was working at Turbo Tech in Miami and used an Airesearch T11 airplane turbo combined with an automotive starter. I ground the turbine wheel blades off and fit a small multi-groove V-belt pulley on the shaft with some ball bearings. It worked great on my VW beetle. I mounted it where the back seat was and ran a duct through the firewall to the carb top. An extra car battery in series with the stock battery (24v) made 6 to 7 psi at low rpm, then tapered to 3.5 psi at high rpm. I threw V-belts every 30 seconds or so.
T: Have you designed different types of electric superchargers?
TK: I've built more than 100 different designs with varying success, but the same problem always occurred-not enough boost to make me happy. Four psi is better than nothing, but my goal was 15 psi.
T: When did you develop the idea of using three motors?
TK: About 10 years ago I developed a program to determine the horsepower requirements for electric compressors. It was a very difficult program and it took me a long time to get the parameters correct. I found that flowing 780cfm at 15 psi required 80 to 100 hp. I went smaller on engine size and lowered boost requirements until I reached 450cfm at 8 psi, which required 18 to 22 hp, so I looked for a 20-hp dc motor. All I found were 50-plus-pound motors, which were too large to use in my intended application. Three years ago I realized if I used multiple motors, I could get to the 20-hp mark.
T: Why a Roots-type supercharger?
TK: I designed many different models and applied for the patents. I also have patents pending on screw, roots, centrifugal and sliding vane-type electric superchargers. The centrifugal design is in the works, and the screw is simply too expensive to use. The sliding vane is great but quite large, so the Roots is cost effective, reliable, simple, durable, and provides the quickest boost response.
T: How does your system operate?
TK: The ESC-400 is somewhat like nitrous, as the batteries must be recharged after awhile. Nitrous is great but is quite expensive and filling the bottle is time-consuming. Recharging batteries costs pennies a day. Think of the batteries as the same as a nitrous tank.