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E-Turbo Revolution: Electric Turbos Get Real!

HOT ROD logo HOT ROD 9/23/2020 Marlan Davis,Dr. Charles Jenckes
100B-MERCEDES-AMG-PETRONAS-F1-Hybrid-Power-Unit-MGU-H © Hot Rod Network Staff 100B-MERCEDES-AMG-PETRONAS-F1-Hybrid-Power-Unit-MGU-H

Written by Dr. Charles Jenckes

No Lag, Instant Throttle Response, Big Power Gains, and Energy Recuperation: Perfected in Formula 1, MGU-H Electric-Assist Turbocharger Technology Will Soon Hit the Street

"Matching the turbo to the engine has always been a tradeoff. A bigger turbo might make more power, but it takes longer to spool it up, so you'd have to compromise to find the right balance. With an electric motor both eliminating lag and controlling boost [on an e-turbo], we can make much more power." —Craig Balis, Garrett Motion Senior VP and Chief Technology Officer

We've all seen those scam advertisements for the so-called "electric turbo." These inexpensive devices are claimed to function as turbochargers, but they are really just simple ducted fans or blowers, at best good only for blowing smoke. If you think there's anything to them, there's a bridge in Brooklyn I wanna sell you. This is not that article. So, stop laughing, and forget about all that scammer BS. What you're about to read about here is not your gardener's leaf-blower or a phony low-cost electric turbo. Instead, we are going to look at the cutting edge of what you might call electrically assisted turbocharger technology. We're going to tell you about the revolutionary "e-turbos" perfected on Formula 1 (F1) racing's V6 MGU-H powerplants and how this now-mature turbo revolution will be coming to production cars at your local dealership within the next few years. It's about the next wave in power-making technology, further fuel economy improvements, and making ever-smaller engines perform as well or even better than the larger engines they replace. It might be the key for allowing the internal combustion engine to stick around for another generation; and someday, sooner than you think, making big unlimited, unrestricted racing engines churn out even more power than they ever had with conventional turbochargers.

a close up of a truck © Hot Rod Network Staff

If it's Ferrari red—well, it's gotta be Ferrari. Here, Ferrari's F1 car cuts a corner at the 2020 Styrian Grand Prix. The electric turbo augmentation in current F1 cars means instant boost at throttle tip-in and adds 150 to 200 hp to the otherwise 850hp F1 engines.

Photo: @Scuderia Ferrari

Boost, the Replacement for Displacement

Before we get into why an electrically assisted turbocharger changes everything, let's take a quick look back on superchargers and turbocharger evolution and the advantages and disadvantages of each. We've all heard—I've said it myself many a time: "There's no replacement for displacement." But actually, there is: add boost via forced induction. Engines make more power with forced induction because it increases the density of air entering the engine by pressurizing or "boosting" it above atmospheric pressure with a supercharger or exhaust-driven turbocharger. The more boost—as measured in psi in the U.S. system or Bars in the ISO system—the more the engine's power potential. A small engine acts like a bigger engine. And an already large engine acts like, well, a monster. (See for example, "The Nuclear Option" and "World's Fastest—Again!".)

a close up of an engine © Hot Rod Network Staff

A traditional supercharger like this old classic GMC-pattern, Roots-type, supercharger boosting an old Don Hardy small-block Chevy-powered Vega is an air-moving device driven by a belt off the engine's crankshaft. Instant boost, but this ancient technology is relatively inefficient.

Photo: HOT ROD Archives

Superchargers and turbochargers are both air-moving devices. The difference is a supercharger is traditionally driven by the engine crankshaft and the turbocharger by the engine's exhaust gases. The turbocharger uses exhaust heat and converts it to useful work, spinning a shaft that drives a turbine on the inlet side. The basic technologies go back over a century: A supercharger for forced induction was first patented for automotive engines by Gottlieb Daimler in 1885. The first turbochargers were developed by General Electric between 1905 and 1916 for early aircraft engines. They've gotten immeasurably better and more efficient as technology advanced, especially within the last 20 years, as CNC blade-machining technology, variable geometry turbines (VGT), computer modeling, and electronic engine management has gone mainstream, but there was still room for improvement.

a close up of a motorcycle © Hot Rod Network Staff

A conventional turbocharger has a compressor section and a turbine section. Driven by exhaust gas, the turbine spins up the compressor, which moves air under boost into the engine. With its variable geometry turbine, this BorgWarner unit is as efficient as a pure exhaust-gas-driven turbo can be without electrification.

Photo: BorgWarner

Turbos Lag Behind

As it's directly connected to the crankshaft, the traditional benefit of a belt-driven supercharger is that it creates instant response when you slam the throttle. On the other hand, it takes a large amount of power to drive a big supercharger. In drag racing, driving a Top Fuel dragster's 14-71 Roots blower consumes 900 to 1,000 crankshaft hp at 65 psi of boost. An efficiently designed turbocharger exhaust system consumes much less power at an equivalent performance level, mainly through exhaust path restrictions. However, the main problem with turbochargers is the time delay between when the throttle is opened, and when the exhaust gas can "spin-up" the turbo—what engineers and racers call "turbo lag" or "transient response time." The bigger the turbo, the greater the lag. A small turbo can reduce lag, but this compromises top-end power. A turbine with VGT—which broadens the turbine's low- and high-end efficiency envelope—is still only a compromise. Another solution is to use multiple, smaller turbos in parallel or even several turbos mounted in series. This adds to cost and complexity.

a screenshot of a cell phone © Hot Rod Network Staff

VW's "Twincharger" was a combination of an exhaust-driven turbocharger and an engine-driven supercharger, each mitigating the other's weakness. It developed instant throttle response and—with no turbo "throttle lag"—allowed using a larger turbo for better-top-end power.

Photo: Ryan Lugo

Volkswagen even produced a 1.4L (85ci) engine with both a turbocharger and a belt-driven supercharger that supplied instant response from the supercharger and top-end power from the turbocharger. Known as the VW "Twincharger," this engine produced more torque than a 2.3L naturally aspirated engine using 20 percent less fuel. The Twincharger engine was crowned "Engine of the Year" in both 2009 and 2010 by an international panel of automotive journalists. Unfortunately, with both a turbo and a supercharger, the engine was expensive to produce. VW eventually replaced it with a less costly single turbocharger even though overall performance slightly declined.

Electric Supercharger

a close up of a map © Hot Rod Network Staff

In addition to supplying instant boost, the BorgWarner eBooster can work as a compound compressor. Because the supercharger and turbocharger are connected in series, the pressures of the two charging units are multiplied, providing even more boost and engine power!

Photo: BorgWarner

The next evolution in fighting turbo lag is replacing the auxiliary belt-driven supercharger with a small electrically driven supercharger used in conjunction with a turbocharger. One example is BorgWarner's eBooster system, which eliminates turbo lag and allows sizing the turbo for peak power. The first commercially available application for the eBooster will be the 2021 Mercedes Benz 3L S-class engine. The supercharger is driven by an advanced brushless DC ultra-high speed electric motor.

a close up of a map © Hot Rod Network Staff

Compared to a conventional standalone turbocharger, a BorgWarner eBooster demonstration project took only 2.5 seconds to reach peak torque and added 50 percent more torque under the curve.

Photo: Marlan Davis

An effective interim solution, an "extra" supercharger—be it belt- or electric-driven—still takes up a lot of packaging space integrating the additional hardware into the existing powertrain; two devices are heavier, bulkier, and more expensive than one. There's still no power regeneration capability, the electrical power demands are still high, and it doesn't address the power of "wasted" potential energy bypassed by the wastegate out the exhaust.

Exhaust Waste Heat is Lost Potential Energy

a close up of an engine © Hot Rod Network Staff

One of two big electronically controlled Precision Turbo wastegates on a Ken Duttweiler Bonneville record-holding small-block Chevy.

Photo: Wes Allison

On a turbocharger, you use a "waste gate" to control the amount of boost. A wastegate is a valve that opens upstream of the turbocharger to bypass heat energy around the turbo directly to the exhaust. This prevents the turbo from either making too much boost or losing efficiency by going into "overspeed" (there's a critical blade speed depending on the blade's rotating mass and size). Notice the word here:wastegate. That's right. When a wastegate opens, potential heat energy is "wasted," or lost out the exhaust. That's inefficient. Engineers hate inefficiency, but "waste heat" was just something you took for granted on an internal combustion (IC) engine. Remember this concept: Heat—whether lost through the engine's cooling jacket into the radiator or bypassed around a turbo's turbine section—is theoretically lost energy. If there is a way to put some of that "lost" heat back to work, an engine could be made more efficient (and from a performance point of view) see a significant power gain.

a screenshot of a cell phone © Hot Rod Network Staff

A wastegate bypasses some exhaust flow around a turbocharger's turbine section to control shaft speed or boost. A spring inside the actuator canister holds the wastegate valve shut. When preset pressure limits are exceeded, the actuator progressively opens the wastegate, allowing exhaust flow to bypass the turbine.

Photo: Dr. Charles Jenckes

Origins of the E-Turbo

What if you could "boost" initial turbine speed to overcome lag not by an auxiliary supercharger, but by instantly spinning up a turbocharger's turbine section with a relatively small, yet extremely powerful, electric motor? What if you could take that exhaust waste heat and essentially use it recharge the electrical system that expended all that electric power initially getting the shaft up to speed in the first place? Turbo industry leaders like Garrett Motion, BorgWarner, Mitsubishi, and others have been playing with the idea of e-turbos for years. Turbodyne in collaboration with then Honeywell International developed and patented electrically-assisted turbos as early as 1995, primarily to address Detroit Diesel two-stroke emissions in Greyhound buses. But it wasn't until the early years of the 21st century when turbochargers gained popularity across a broad model spectrum (not just high-end models) that the industry really got interested in e-turbos when worldwide gasoline prices—particularly in Europe—started going through the roof. But it took new developments in electric motors and high-tech battery technology, plus a big "push" from the Formula 1 open-wheel road race series, to really kick-start the concept into high gear. Garrett Motion, for instance, partnered up with Scuderia Ferrari, combining its 65 years of turbocharging experience and electric turbo assist experiments with Ferrari's F1 engine and chassis expertise.

F1 Leads the Way

"F1 has served as a real-world laboratory for our e-turbo development." —Garrett Motion
a motorcycle parked on the side of a road © Hot Rod Network Staff

All F1 competitors have been using electrically augmented turbos and energy recuperation since 2014. Mercedes-AMG has been dominating F1 since the current rules went into effect in 2014. Mercedes builds its own F1 engines and e-turbos.

Photo: Morio via Wikipedia / Lic. CC4

If you think that NASCAR, Top Fuel dragsters, and even Bonneville LSR cars are the last word in piston-engine performance, you've been missing the boat when it comes to pure engine efficiency. Formula One (F1) is the World's most technically advanced racing series, and their engines have long been among the most powerful and efficient for their size. In 2014, F1 engine rules were considerably revised to start the process of moving away from hydrocarbon-based fuels, and they're still pretty much unchanged as of late 2020. The current F1 1.6L (97.6 ci) V6s are limited to a single turbocharger. The engines can use just 110 kg/hr of gasoline (242 lb/hr or about 40 U.S. gallons)—enough fuel for about two hours of racing. Nevertheless, these motors make about 850 hp at the flywheel on gasoline, as measured by the SAE "net" horsepower spec J1349 (about 4 percent lower than the J607 standard we hot rodders typically use). Pretty impressive by itself, but currently the engines are generating another 150 to 160 hp with a sophisticated energy recovery system (ERS) that puts otherwise lost heat energy generated by the braking system and "wasted" exhaust gases back to work. The result is a combined 1,000 hp, or 10.2 hp/ci—on gasoline!

© Hot Rod Network Staff

The tiny DOHC 1.6L V6 F1 MGU-H power units are the World's highest efficiency gasoline-fueled racing engines. Part of the secret is the electrically augmented turbo that works in conjunction with a sophisticated 800-volt powerpack and controller—the gas tank-like object to the right of the engine in this photo. Total weight of the engine, turbo, and the electrical augmentation unit is just 149 kg (319 lbs).

Photo: Daimler AG

Electric-Assist Yields a Turbo with No Lag!

Here, we're primarily interested in how the MGU-H and its electrically augmented turbo system ends turbocharger lag (though they also improve braking performance). F1 refers to its hybrid, turbo'd, power plants as a "Motor Generator Unit-Heat" (MGU-H). This is a true hybrid turbocharger (often called an "e-turbo") that combines the traditional turbocharger with a high-speed electric motor that spins the turbo up to speed, creating boost the instant you open the throttle—exactly as a supercharger does, but without the parasitic drag of a belt, pulleys, or supercharger rotor friction. Turbocharger shaft speed is now regulated by an electric motor and is no longer strictly dependent on increasing exhaust gas pressure as it is in the traditional turbo's turbine-compressor feedback loop. Bottom line: No more turbo lag, period, and without the "crutch" of multiple turbos or an auxiliary supercharger.

Solving the lag issue provides yet another critical advantage for an electrically-assisted turbocharger: An e-turbo can be sized to develop the best power and boost curve for a given engine/driveline combination without worrying about transient response or turbo lag. This applies to both racing and any potential street use. When it comes to turbos, bigger is now actually better.

Waste Not Want Not: Heat Energy Recovery

a close up of a device © Hot Rod Network Staff

Garrett's vision of a fully realized E-turbo system in more "streetified" trim. The Garrett E-turbo system works in both directions, allowing a down-spooling turbocharger to send power back to the battery.

Photo: Garrett Motion

The electric turbo's motor also functions as a generator to slow down the turbo to control boost by reversing torque. The excess energy formerly wasted when the wastegate opens instead recharges the battery. Alternatively, the "recovered" energy stored in the battery can be "recuperated" to add power to the driveline through a separate electric motor. Whether in racing or on the street, such "hybridization" not only adds power, it also saves gas—a truly efficient perpetual feedback loop (until you run out of fuel, of course—still no such thing as perpetual motion).

Revolution in Electric Motors

"Now that you have more hybridized powertrains and the vehicle infrastructure coming into place to support them, an e-turbo is a natural fit, opening up additional ways to further optimize vehicle efficiency as well as performance. "—Garrett Motion

An e-turbo becomes workable (and now mature) technology thanks to vast improvements in brushless electric motor technology and new hybrid street vehicle high-power electrical systems. A lot of this tech was originally developed for aerospace applications where cost is no object, so to make this all viable in mainstream automotive use (not just similarly cost-is-no-object F1), part of the deal is figuring out how to commercialize this tech at a reasonable price for mass consumer use. Looking at motors first, Garrett explains, "An electric motor should be as compact as possible to have rotor dynamics under control. You are really targeting high power density. So, it is a must to get as much power as possible from a small motor to allow the turbo to have the same speed range," in some cases as high as 250,000 rpm on the smaller e-turbos. "Rare earth materials and high switching frequencies are types of considerations for increasing maximum power density within limited dimensions. Controllers continue to mature. Garrett is focused on moving this need from Aerospace applications (high cost) to industrialization applications that are acceptable in automotive. You need insane power density under a 12V system—and there is just no cost/value justification for doing so in this scenario. Garrett did develop a 12-volt E-turbo system, but there was no market for it. By moving to a 48V or higher electrical system, this enables a better value proposition enabling effective power output."

Revolution in Electrical Output

48 volts: That's only a starting point. For high power, you need high voltage. F1 cars are supposedly running 800-volt(!) electrical systems to achieve the necessary electrical motor power in their compact, ultra lightweight chassis. Remember that we define power as the amount of energy transferred per unit of time. For a combustion engine, power is chemical energy from the fuel converted to mechanical energy per unit time (expressed in the U.S. as "horsepower" or hp). For an electric motor, power is electrical energy converted into mechanical energy per unit of time, expressed in the ISO system as "Watts" (W)—which is also the traditional metric expression of "horsepower". The correlation is 1 W = 0.00134102 hp. To find electrical power in Watts (W) you multiply voltage (V) by amperage (A): W = V x A.

Watt it Means for Electrical Efficiency

The math shows us that if you increase system volts, then the amperage (current) needed to maintain the same power output in Watts decreases. Lowering current reduces the size, weight, and cost of the cables that carry the electric current. For you old timers around when the OE's switched from 6- to 12-volt car electric systems back in the mid-1950s, you'll remember that wire gauge size was halved after the conversion. Think how much weight it would save merely by moving from 12 volts to 48 volts—wires could be one-fourth the size they are now. The only limitation on size reduction would be the physical strength of extremely thin wires, not their current-carrying ability.

Going to a higher voltage electrical system also means that to produce the same electrical power (watts), an electrical motor operating at 48 volts is much smaller and more efficient than it would be for a 12-volt motor of equivalent output—assuming it was even possible in the real-world to do so: A theoretical 12-volt motor would end up at least as large, if not larger, than the engine itself!

Still don't believe it? Wrap your head around this: Many current (pun intended) 12-volt automotive systems (about 14.5 volts as regulated) have a 200-amp alternator. So, working at peak output, they potentially produce about 2,900 watts (14.5 V x 200 A = 2,900 W). A hypothetical 48-volt alternator would need only about 60.4 amps to develop the same wattage—and much of the alternator's traditional job could be handled off to a fully-realized hybrid system's energy recuperation loop.

48-Volt (or Higher) Electrical Systems Soon to Go Mainstream

As for actual numbers, BorgWarner's first e-turbo system uses 17 kW at peak power. 1 kW (kilowatt) equals 1,000 watts, so 17 kW equates to 17,000 W or about 22.8 hp. Further down the road, BorgWarner is playing with a 400/800-volt e-turbo which produces 6 to 34 kW (about 8 to 45.6 hp) at peak power. That's approaching F1 efficiencies—on the street. With 48-volt systems now ready for mainstreaming and high-output 400-volt set-ups already used in some plug-in hybrids, electrically assisted turbochargers become a practical option that won't require further vehicle redesign. But never forget: It took the forced-push in F1 racing to perfect e-turbos, much as the 1960s push to be first on the Moon catapulted material science and computer technology across many diverse, seemingly unrelated fields of technology. Who says racing doesn't improve the breed?

Street Implications of Electric Turbos

"On the same engine, compared to a conventional turbo, an e-turbo can move you from 110 to 160-170 kW/L (2.417 to 3.516 hp/ci). This is the effect of right-sizing the turbo and using the electrification for transient response." —Garrett Motion

Thanks to the F1 "proof of concept," we can begin to see the implications of e-turbo technology for near-future production street cars. Small engines can act like big engines when you need power; but when you don't the engine can sip fuel; drivers would think they're driving a big-displacement engine except when they cruise by the gas pumps. Using less fuel also reduces carbon-dioxide emissions, which some scientists hypothesize as a source of man-made climate change. Garrett Motion claims up to a 15 percent reduction in carbon dioxide with an e-turbo. On the street, e-turbo technology can also improve emission system durability by better controlling EGR and downstream exhaust temperatures. "Using electrical power to help launch the vehicle is a great benefit. And optimizing the size of the turbo helps with overall engine efficiency as well by supporting down-sizing and down-speeding," Garrett explains.

With transient response and boost electrically regulated, and everything tied into the engine and drivetrain computer, Garrett says it's possible to tightly regulate combustion response. "We will be able to maintain stoichiometric Lambda under full-load conditions for a more efficient engine using a larger turbo when we don't have to worry about lag. Today we still run rich under load, now we can start changing combustion strategy." With turbo right-sizing, variable-geometry turbos, and now electrically assisted turbos, engineers are on the verge of achieving "Millerization," the holy grail of perfect combustion, under all operating conditions.

Initial "Street"-Car Implementation

a silver car © Hot Rod Network Staff

Photo: Anadolu Agency / Getty Images

a car parked on a city street © Hot Rod Network Staff

Photo: Mercedes-Benz USA

Based on Mercedes and Garrett's F1 power-unit technology, the limited production, 200-mph, street-legal 2021 Mercedes-AMG Project ONE should be hitting the streets in 2021. $2.72 million each, but don't fret—all 275 have already been presold.

a close up of an engine © Hot Rod Network Staff

Like the F1 power units it's based on, the Mercedes-AMG ONE will use a DOHC 1.6L V6 MGU-H power unit with electric exhaust gas Garrett e-turbo technology plus four electric motors.

Photo: Mercedes-Benz Cars and Vans

"The two-seater Mercedes-AMG Project ONE will transfer the latest and most efficient Formula 1 hybrid technology almost one to one from the track to the street for the first time." —Mercedes-AMG

Now working with major F1 competitor Mercedes-Benz, it looks like Garrett Motion will be the first to have an e-turbo system up and running in a streetable vehicle. "Our F1 experience—system integration, thermal management, high-speed motors in support of an electrical architecture—has provided our engineers with a tremendous opportunity," Garrett explains. "Coupled with our 65-year legacy of turbo innovations we have been able to bring [e-turbo] technology forward for use in passenger vehicles first."

That is, if you can call an exotic foreign two-seat supercar a "streetable passenger vehicle." (We can, and we will.) The Mercedes-AMG Project ONE produces over 1,000 hp at a maximum speed of over 350 kph (217 mph). It's the closest you can get to driving an F1 engine on the street. Forget about 0-60 mph time. How about 0-200 km/h times of less than 6 seconds (that's 0-124 mph for those of us who don't speak ISO). Mercedes will only build 275 Project Ones, at a unit price of US $2.72 million apiece. Don't get in line—the entire run is already presold, and Mercedes has supposedly written into the sales contract that the owner can't "flip" the car to make a quick profit. Cannonball Race, anyone?

a close up of an engine © Hot Rod Network Staff © Hot Rod Network Staff

Using Garrett components, Mercedes-AMG is the first to implement F1-based electric exhaust gas turbo tech into the upcoming AMG ONE street supercar. Note that a residual wastegate is still present with most e-turbos, but it only functions when the driver suddenly backs off the throttle momentarily, "burping" open to relieve sudden gas pressures that result in shaft speed irregularity (overspeed, hah).

Photo: Mercedes-Benz Cars and Vans

Garrett Motion Case Study

In a more real-world car, a Garrett demonstrator showed considerable improvement switching from a conventional turbo to an e-turbo. At low, 1,500-rpm engine speeds, target torque was reached in 1 second versus 4.5 seconds in the current production model. Rated power increased 16 percent, torque increased 10.5 percent, and 60 to 100 kph (37 to 62 mph) acceleration time dropped from 11 seconds to 8.8 seconds, a 25 percent improvement. Garrett believes it has an advantage over competitors because of its tight integration of boost control algorithms in existing Engine Control Modules (ECMs) as well as real-time monitoring of the entire vehicle "air loop" in real time.

Case Study: BorgWarner E-Turbo

a car parked in a parking lot © Hot Rod Network Staff

A Porsche 718S Boxster e-turbo demonstration car had its conventional turbo swapped out for a BorgWarner e-turbo.

Photo: BorgWarner

a close up of a motorcycle mirror © Hot Rod Network Staff a close up of an engine © Hot Rod Network Staff

Typical BorgWarner e-turbo showing compressor section (A), turbine section (B), electronic wastegate actuator (C), and the electric motor (D) packaged with the bearing assembly center section (E).

Photo: BorgWarner

BorgWarner tested e-turbo technology on a converted 2017 Porsche Boxster 718S originally equipped with the standard production VGT turbocharger on its 2.5L 4-cylinder engine. Like F1, the e-turbo spins up the turbine shaft to supply instant boost, while also acting as a generator to convert heat energy into electricity and charge a storage battery. The battery can then power another electric motor connected to the final drive to add torque and power to the vehicle. The e-turbo is larger than the standard conventional turbo it replaced because there's no lag, which increased power not just at the top-end, but throughout the entire engine operating range.

BORGWARNER PORSCHE 718 S

STANDARD TURBO VS. E-TURBO SPECIFICATIONS

Parameter 718 S Factory 718 S E-Turbo
Turbocharger Type VGT + WG WG
Turbine Wheel 55 mm 61 mm
Compressor Wheel 64 mm 71 mm
Max Boost Pressure 1.0 Bar 1.5 Bar

Post-conversion, the performance with the e-turbo equipped Boxster was stunning: Would you believe a 105 percent torque improvement at 1,500 rpm even before it started to accelerate? The car's time to reach 300 lb-ft of torque from 1,500 rpm in fourth gear dropped by 3.36 seconds or 720 percent, providing an incredible driving experience—truly big engine performance from a small engine. Granted, the e-turbo was running 0.5 Bar (7.25 psi) more boost than the base car, which accounts for some of the power and torque gains—but a large turbo which would have matched the e-turbo in boost level would have had even more lag. The most important aspect of the e-turbo technology is that it allows the use of a big turbo with no lag.

© Hot Rod Network Staff

After replacing the standard turbo on the Porsche Boxster's 2.5L 4-cylinder engine with BorgWarner's e-turbo the performance improvement almost matched a Porsche 911's 3.8L 6-cylinder normally-aspirated engine.

Photo: BorgWarner

a close up of a motorcycle © Hot Rod Network Staff

The powerpack for the BorgWarner e-turbo includes a 48-volt motor controller, DC-DC converter, controller cooling system, A123 8-amp-hr battery, and safety interrupts.

Photo: BorgWarner

a close up of a car © Hot Rod Network Staff

BorgWarner installed the powerpack in the Boxster's trunk. Not much space consumed compared to the great performance gain!

Photo: BorgWarner

In sum, the e-turbo conversion produced:

  • 400 rear-wheel hp (an 11-percent improvement over the conventional turbo)
  • 450 lb-ft of rear-wheel torque (a 36-percent improvement)
  • Time to torque in less than 0.5 seconds at any engine speed (a 200 to 700-percent improvement)
  • 39 mpg highway (test) and 32 to 33 mpg observed overall (a 5-percent improvement), better than the 911's six-cylinder 3.8L engine.
  • 33 kph to 80 kph (20.5 mph to 50 mph) acceleration was about 0.5 seconds quicker.

a close up of a map © Hot Rod Network Staff

Rear-wheel torque and horsepower comparison of BorgWarner E-turbo with original OEM VGT turbo on Porsche Boxster S 2.5L 4-cylinder engine.

Everyday E-Turbo Production Cars—When?

When will this technology be in production for daily drivers? Turbo manufacturers are playing it close to the vest, but rumors keep leaking out like that old faucet you never quite got around to fixing. BorgWarner sees the market entry point for e-turbos in the 1.5-4L gasoline engine market with performance customers leading the way with highly boosted engines replacing larger displacement engines with more cylinders. It says the first vehicle with its e-turbo technology is scheduled for release in 2023 model-year vehicles.

Further out, BorgWarner is working on e-turbo configurations which produce as much as 125 kW (67 hp) peak and 80 kW (107 hp) continuous for unique applications. The power numbers refer to how much electrical power the e-turbo electric motors can add over a "normal" turbo. As previously noted, when not used to spin up the e-turbo, under non-boosted conditions the surplus electrical power can be recuperated back into the driveline and/or effectively serve as a generator to recharge the battery. BorgWarner says we may have this full recuperation ability in the medium to heavy-duty truck market by 2027.

Meanwhile, Garrett has about a dozen projects underway with global manufacturers in various stages of development. Garrett says these applications "range from 1.2L to 4.0L gasoline and diesel engines, with the 4.0L project actually being a twin e-turbo application. We have something capable as a single turbo for up to 3L gas. We also have commercial vehicle turbo projects focused on recuperation for up to 10.0L engines." Besides the AMG in 2021, "we expect other systems coming into the market in the next 2 to 3 years."

But What Does It Cost?

"An e-turbo will increase the on-boarding cost, but not exponentially. E-turbos are likely to be three- to four-digit costs depending on specifications by application. This is considerably less than full electric-battery systems, and with no performance loss in driveability for the customer. No change in vehicle interaction." —Garrett Motion

As electric turbo technology rolls out, initially it will be available first on performance or premium vehicles before trickling down to everyday drivers. As with anything brand-new, there will be a cost increase but with measurable performance gains to go along with it. While no cost data is available at this time it is likely to be on the order of any performance engine version compared to a standard engine for the OEM. You always pay for performance. On the other hand, there are potential cost "recuperation" offsets (pun intended): "Turbos are traditionally a technology with an on-boarding cost most often measured in hundreds of dollars—but often it comes with financial offsets as engines downsize from 6 cylinders to 4 as an example," Garrett explains.

E-Turbo Tech on Hot Rods—When?

"We will flow technology to the aftermarket as it becomes more mature." —Garrett Motion

The latest electric supercharger and electric turbocharger may not be available in the performance aftermarket yet, but it won't be long before the SEMA crowd is all over this new technology. But impatient hot rodders likely won't wait for the performance aftermarket. As soon as 2021 S-Class Mercedes wrecks show up in the salvage yard, some enterprising hot rodder will try adapting its eBooster system to their projects.

How could this work? The electric eBooster supercharger is small; it could mount anywhere as it needs no direct engine connection to drive it. The only connection to the engine would be a pipe or hose duct to the throttle to supply the air. The battery and controller could mount remotely as well. It is always best to keep the high current power lines that feed the eBooster as short as possible, though.

To make power, more fuel will be needed to go with the air, but there are many aftermarket solutions already for this problem. On a carbureted engine, use a sealed airbox or hat on a blow through application. On older fuel injected cars with a pressure regulator and a return line, a boost referenced pressure regulator could add more fuel by increasing the pressure to the injectors under boost.

Do you remember RoadKill's leaf blower supercharger test? Put an eBooster, battery, and controller in the trunk; get a long piece of flexible hose and run it from the trunk to the intake. Add some duct tape to hold everything in place and you could be in the finals of the next "rental car drag race nationals".

While some adventurous and tech savvy Hot Rodder will likely have a junkyard small e-turbo running as soon as one shows up, for a pure e-turbo street retrofit system, we might have to wait until the performance aftermarket steps up with a retrofit turbo sized for our big V-8. There's also the high-end electrical control system and engineering integration challenges. Explains Garrett, "Because of the complexity of the e-turbo (heat source and electrical source) there are a number of controls that would be needed for use in the aftermarket. A great deal of education will be required to meet objectives. There is a systems approach that cannot be underestimated."

But when this technology does become available for retrofit, the reward will be the instant boost of a supercharger with the power of a larger turbo. Crazy performance! Imagine a 1969 Camaro resto-mod style with an e-turbo equipped LS. A 160-hp brushless DC electric motor could be connected to the back of the transmission to serve as an additional power-adder. This motor could supply 160 hp under acceleration and charge the battery under deceleration or braking. The battery could also be charged from the e-turbo with the heat from the exhaust. Imagine the possibilities.

But we can't wait! Well, try this one on: For short-term drag-racing use only, conceivably you could fill the trunk with four 12-volt batteries wired in series to make 48 volts (for the basic voltage-multiplying concept, see "Wire Two 12-Volt Batteries in Series to Make 24 Volts"), then drive the turbo's electric motor 1/4-mile at a time, recharging it externally back in the pits between runs. That would certainly solve the "getting boost instantly off-the-line" problem that has plagued turbos in drag racing. (And four batteries in the trunk sure won't hurt traction!) Garrett sources say a scheme like this "really is possible; in fact, we had some tests where we did this for convenience. It's a fun project, but [of course] not optimal for energy optimization."

The missing ingredient at present is large e-turbos suitable for use on our big V-8s. Likely, the first practical candidates will be based on the big e-turbos for heavy-duty trucks said to be under development. Don't sneer: Back in the day, that's where the first big racing conventional turbos came from.

"They" keep trying to exterminate the internal-combustion engine. But like those roaches you just never seem to get rid of, it just adapts and thrives.

Electric-Assisted Turbos are Real

  • Traditional exhaust-driven turbocharger potential is compromised by the need to overcome lag, or the transient delay between going to full-throttle and the turbo's turbine spooling up to shaft speeds capable of generating boost in the compressor section.
  • The larger the turbo, the greater the tip-in lag—so minimizing transient-induced lag usually requires selecting a smaller turbocharger than what's best for making the most top-end power in an engine.
  • About 58 to 62 percent of an internal combustion engine's potential energy is "wasted" out the exhaust and cooling system.
  • Recovering "wasted" exhaust heat and eliminating turbine spool-up lag could greatly improve engine power, efficiency, and gas mileage.
  • A VGT (variable-geometry turbine) helps broaden a turbocharger's efficiency curve, but still doesn't entirely do away with lag.
  • Other lag-overcoming approaches include multiple small turbos, a small belt-driven supercharger that drives the turbocharger (VW's "Twinbooster"), or an electrically-driven small supercharger that "fills in" for the turbo downstairs and then acts as a compounding device upstairs (BorgWarner's "eBooster"). These work but take up a lot of room, are costly, and still don't address exhaust heat recuperation.
  • The Formula 1 race series' 1.6L V-6 "motor-generator unit" (MGU-H) has perfected the "e-turbo"—a high-tech "electric" turbo with an electrical motor attached to the center section that instantly spins-up the turbo's turbine section at full-throttle, thereby eliminating all throttle-lag and adding about 150 to 160 hp to the already 850-hp engines, as well as broadening the torque curve.
  • The e-turbo's electric motor and its computer controller precisely control boost levels by regulating shaft speed, eliminating the primary function of a traditional wastegate, which now is only used to "burb" the engine and prevent momentary shaft overspeed upon sudden throttle closure.
  • After the e-turbo's turbine side has reached full speed, or when the throttle is backed off, the e-turbo electric motor "recycles" previously wasted exhaust gas to recharge the battery and/or flow electric current back into the driveline downstream for additional power as desired. Previously wasted exhaust heat energy is thereby recuperated to perform useful work.
  • With turbo lag eliminated, turbos can be "right-sized" to generate the most top-end power for the application and intended use.
  • 12 volts won't cut it on an electric turbo. The new electric motors need truly high-voltage electric systems—48 volts minimum, but at the extremes Formula 1 electric turbo tech is based on an 800-volt electrical system.
  • Practical, compact, and lightweight direct-current, high-voltage systems are made possible by advances in brushless electric motor technology as well as in battery and charging systems.
  • Truly extreme-voltage systems were initially developed for cost-is-no-object aerospace applications, so they're fine in cost-is-no-object Formula 1; the trick is mass-producing them at a reasonable cost for consumer use. The needs of consumer hybrids and all-electric cars will help drive commercialization, costs, and availability.
  • Mercedes-AMG Project ONE is a 2021 model-year, $2.7 million (U.S.) limited-production, 1,000hp, 215-mph street-legal supercar using Garrett e-turbo technology and a 1.6L DOHC V6 engine derived from Mercedes' F1 racing experience.
  • Expect e-turbos to appear in more mainstream production cars within the next few years as mileage and emissions standards continue to tighten. Garrett Motion and BorgWarner are among the leaders and have demonstrators running around right now that develop incredible power, torque, and gas mileage from their tiny engines.
  • Performance aftermarket retrofit pure e-turbo systems for street-driven hot rods are a way off due to their complexity, but soon you could at least go drag-racing by packing the trunk with four 12-volt batteries wired in series to produce 48 volts, and recharging in the pits between rounds.

Sources

BorgWarner Turbo Systems; Asheville, NC; 800.787.6464 or 828.684.4027; BorgWarnerBoosted.com

Ferrari S.p.A.; Maranello, Italy; 877.933.7727 (U.S. ); Ferrari.com

Garrett Motion Inc.; Torrance, CA; 310.512.5424; GarrettMotion.com/racing-and-performance

Mercedes AMG High Performance Powertrains; Brixworth, Northamptonshire, UK; +44 (0)1604 880100; Mercedes-AMG-HPP.com

Mercedes-AMG GmbH; Affalterbach, Germany; Mercedes-AMG.com

Mercedes-Benz USA LLC; Sandy Springs, GA; 800.367.6372 (U.S. customer care); MBusa.com/en/future-vehicles/mercedes-amg-one

Mitsubishi Turbocharger Aftermarket; Addison, IL; 630.268.0750; Mitsubishi-Turbo.com

Porsche Cars North America Inc.; Atlanta, GA; 800.PORSCHE (customer service); Porsche.com/usa

Volkswagen of America Inc.; Auburn Hills, MI; 800.822.8987 (customer service); VW.com

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