All images from Porsche.
“Hybrid is the devil!” Waterboy voice. “Not so fast my friends!” Lee Corso voice. I think most people associate the concept of a hybrid car with the Prius; i.e. the antithesis of a performance car. So, when Porsche announced the 992.2 generation of the 911 would have a hybrid variant, many people immediately had a negative reaction. However, the T-hybrid system from Porsche is what I consider to be the first implementation of the current Formula 1 powertrain technology in a street car: a high-voltage system for a high-power e-turbo and electric drive motor. The result is the ultimate in turbocharged engine powertrain response with a reduction in emissions and fuel consumption.
New European emissions regulations drove the push for Porsche to make the T-hybrid system come into existence. As it turns out, this cleaner emissions push drove Porsche to implement e-turbo which I consider the holy grail in ultimate response turbocharger technology. E-turbo is a critical enabler for reduced emissions by allowing the engine to operate at Lambda = 1 across the entire engine operating load range while still have good response. Or as it has turned out, the best response of any turbocharger setup to hit the street.
Lambda is a term for air:fuel ratio. When lambda = 1, there is exactly enough mass of oxygen to burn the mass of fuel. In the perfect combustion of a hydrocarbon fuel at stoichiometric air:fuel ratio, your products are CO2, H2O, and N2. There is never perfect combustion which is why we have 3-way catalysts. You end up with unburnt hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). The nitrogen comes from air which is about 78% nitrogen and 21% oxygen. If lambda = 1, then the 3-way catalyst is highly efficient at converting HC, CO, and NOx into CO2, H2O, and N2. If there is excess fuel due to fuel enrichment, so lambda is less than 1, you don’t have enough oxygen to burn all the fuel. You end up with high levels of HC and CO. Up until now, fuel enrichment was used to make maximum power. If you have excess air, lambda is greater than 1, there is extra nitrogen that ends up in NOx.
If you want to avoid fuel enrichment, you have to keep the engine load down. In other words, you need to keep the Brake Mean Effective Pressure of the engine down. Porsche isn’t going to have a newer generation car be less powerful or slower than the previous generation, so Porsche had to go to a larger displacement engine. The bigger 3.6L engine can operate at a lower BMEP than the old 3.0L engine and make similar power. On turbocharged engines, in order to make maximum power for a given BMEP, you also need a big free-flowing turbine which usually means poor response. On top of that, the new setup has a single really big turbo; the old setup uses a pair of small turbos which have significantly less inertia for better response.
The modern solution to improving turbocharger response is electrification as has been proved out in Formula 1 for the last decade. To be fair, Garrett launched the first e-turbo in a street car application on a Mercedes AMG. However, I don’t consider that the full Formula 1 implementation as that system is lower voltage and both the turbo and electric drive motor in the Mercedes are much less powerful. Also, the Garrett e-turbo in that application still has an internal wastegate. The Porsche T-hybrid system uses a big e-turbo from Borg Warner on the 992.2 GTS. As you can see, the turbine housing is integrated with the exhaust manifold for one side of the flat-6 engine. The result will be a bit of old-school Subaru EJ25 unevenness, but modern cars have fake noises pumped into the cabin through speakers anyways. The other feature that makes this T-hybrid setup like Formula 1 is the lack of a wastegate. To prevent the turbo from spinning too quickly, which is the function of the wastegate, the e-turbo uses the motor as a generator which can recoup up to 11kW of power. Previously, the power in the wastegate flow was lost, but now this e-turbo is able to recoup that power; that power can then recharge the battery or go into the electric motor in the transmission to boost the total power to the wheels. I should add that Porsche has recovered the power in the wastegate flow before. On their 919 racecar with the Garrett DualBoost turbocharger, there was also a Garrett turbine and electric generator in the wastegate flowpath. From what I can tell from having seen pictures of the actual turbo, the center housing is water-cooled. In this 3d model representation that is not 100% accurate, it does show part of the water jacket in the center housing.
Here is some data from Porsche showing how quickly the new e-turbo spools up. 20kW of power has a way of doing that. The gear and engine speed are not highlighted, but there is ‘5G’ in the file names, so potentially going full throttle at low engine speed in 5th gear. The new T-hybrid e-turbo setup gets to full boost in about 1 second whereas the old engine and twin-turbo setup took about 3.5 seconds. Looking at the charge pressure line for the new T-hybrid setup, my guess is it’s taking all 20kW of power to get to that initial mid-level boost. Then it takes a bit of time for the engine to flow enough exhaust gas to spin the turbo up the rest of the way.
The T-hybrid layout places a 400V, 1.9kWh li-ion battery up front where the old 12V battery typically lives. High voltage cables run down the middle of the car to the power electronics and motors at the rear. It’s hard to see, but there is a big single intercooler going across the rear of the car.
18 comments
This technology only reduces turbo lag. Normal aspiration eliminates it. Plus hybrid setups add weight (hurting performance, reducing efficiency, reducing safety), add complexity, add to the upfront costs, and create environmental costs (rare earth elements, non-recyclable batteries, etc.) that are always glossed over or ignored.
The same EU bureaucrats that pushed diesel as a green solution are now pushing lambda 24/7, EV’s, hybrids, and “CO2 is poison”. They were wrong then and they are wrong now.
High output NA engines have lag too!
You’re not going to find any NA engine that comes close to the torque and power output of this powertrain in the 992.2 GTS normalized for displacement. I’ll take that trade of milliseconds of lag for much greater torque and power. At max engine power for max engine power, the 992.2 3.6L will have lower emissions and fuel consumption than the 3.0L in the 992.1 because the 992.2 does not do fuel enrichment. Of course, the 992.2 has the electric drive motor to add more power which more than makes up for the weight increase. Hybrids do add weight, but your statement of reduced efficiency and safety are not remotely correct. For the environmental costs, battery recycling capacity is increasing. Usage of rare earth metals are being reduced. LFP battery chemistry eliminates the cobalt used in NCM. BMW uses electric motors that do not use permanent magnets. Don’t forget that catalytic converters for gas engines require platinum, palladium, and rhodium. There’s the whole issue of harmful emissions too with gas engines that lead to respiratory health issues. Or death as has been the case when people forgot to turn off their Prius in the garage and died of carbon monoxide poisoning. There’s the whole issue with oil being a finite resource too. Look up the various lists of proven known oil reserves by country. I can tell you that no matter which list you look at, countries in North America and Europe are not at the top of any of them. In the US, fracking is common because it’s getting harder to pull oil out of the ground and fracking has numerous environmental and health issues associated with the process.
It’s funny how media can be circular and just feeds itself, especially if it doesn’t acknowledge outside criticism.
F1 – “these new hybrid turbo powertrains are in the spirit of innovation that F1 has always had.” Except the innovation of the past came from teams looking for loopholes like turbocharging, not top down regulation forcing use of certain technology. Which killed historic teams like Williams and Sauber and removed independent manufacturers like Cosworth from the mix. Not even mentioning fan reaction to the current regs.
Which trickles down to reviews like this – This car is cool because it’s like F1 tech. Not acknowledging that the current engine regs have been a failure for the sport and fans. The amount of car reviews and magazine articles I’ve read preaching the benefits of lightweight cars and how it improves every aspect are now replaced with “zero lag” and 0-60 numbers while the cars munch tires and brakes under their weight.
Which gets down to the enthusiast. We like our cars, we like to maintain our cars, we like to modify our cars. When I see an article like this on motoiq; about a car that will be stupid expensive to buy, maintain, modify, and is based on tech that’s killed a segment of motorsport, I feel like you’ve lost the plot a little. I can appreciate the tech, but is there not room for even one paragraph about how this car is antithetical to what most enthusiasts want?
I take it you’ve read my prior articles; as an engineer, I focus on the tech. Once in a blue moon, Mike will write a little editorial type opinion piece. But for the most part, I’d say Jalopnik fills that niche.
From an engineering perspective, what modern Formula 1 has achieved has been astounding. The problem statement was basically this: go as fast as before, go as far as before, use half the fuel. That’s a tremendous engineering challenge. Then there’s the engineering complexity at component levels and system controls level. And then making it all work together reliably in the toughest environment possible. If you remember, the very first practice session of the modern F1 powertrain, most of the cars didn’t even make it around one lap.
Integrating high power electronics into a very high-speed rotating and very hot turbocharger is not trivial. Then someone figured out the wastegate could be eliminated: “You’re telling, I can get rid of the wastegate which reduces parts and complexity AND get more power and efficiency out of it?!” Also, “zero lag” has always been the goal since turbos started popping up on cars about half a century ago. Nissan tried ceramic turbine wheels in the 90s, but the wheels would shatter. The FD RX7 and MKIV Supra had complex sequential twin turbo systems. Twin-scroll turbos became common in the 2000s. TiAl turbine wheels have taken about 15 years to become reliable, relatively speaking. On the diesels in Europe, complex twin-turbo compound systems were developed. More recently, Porsche developed a clever controls scheme enabled by electronic throttle plates to do their ‘dynamic boost’ system. From what I can tell, GM basically copied it on the new LT7 twin-turbo V8 in the ZR1.
To hit the power and efficiency targets of modern Formula 1, they have gone over 50% brake thermal efficiency. Up until the modern F1 era, they were hovering roughly around 25% BTE for decades with little advancement. Combustion technology has come a long way in the last decade. Trickle down, you can now go buy a Honda Civic that gets well over 40mpg on the highway while knocking off a 0-60 in 7.3 seconds while having lower emissions than my sister’s old 1991 Civic that took about 11 seconds to get to 60, had lower mpg, and higher emissions.
High-power battery tech developed in F1 also trickles down to our everyday cars. The thermal management is critical and cell chemistry development trickles down to both PHEV and EVs as everyone wants faster charging. F1, and motorsport in general, is a rolling accelerated development lab.
Now, in my article, I didn’t talk about the 992.2 as a car as a whole because I focused on the technology of the powertrain. If you want my OPINION, the 992 generation is too big, too heavy, and rear engine was always a negative which means I think the 911 has never been the optimum platform. Which is why I bought my mid-engine 718 with a manual.
Its an interesting solution to increasingly strict regulations. When comparing the response of this e-turbo to the previous turbo technology, especially in the data plotted in the article, I think its important to distinguish between lag and boost threshold. This data shows how the e-turbo helps improve the response by lowering the boost threshold with help from the electric motor. The biggest impact to the driver is improved low speed acceleration resulting in more favorable drive-ability. Its hard to say from the data, but I wonder if there are any improvements to actual turbo lag with this new technology. Will the driver experience any benefits during high performance driving? or is this just an improvement for around town driving?
Electric motors have a response time of milliseconds to torque demand changes. I think the stat for full forward torque to full reverse is 10 milliseconds. The transient response for a ball bearing turbo is more in the hundred millisecond magnitude range assuming the engine is already at higher engine speeds. The regular turbo has to wait for the throttle to open more, more fuel to be injected, and a few power strokes to get more exhaust flow to spin up the turbo faster. With e-turbo, it just sends more current in milliseconds to the turbo to spin it up faster.
The W206 C 63 AMG weeps reading the intro.
I had to look it up. I’ll agree the base components are basically the same, but with different architecture and control schemes. It has a 3x larger battery pack and bigger and more powerful electric motor because it’s a plug-in hybrid. I would think the turbo on the 2.0L engine is the same Garrett e-turbo with wastegate as is on the other AMG model.
Well, we are still going to have to wait for the manual version. If they develop a manual for this like the CR-Z hybrid then it would certainly be the ultimate drive train. As always, the best 911 is the next 911.
I find it unlikely Porsche will pair the hybrid system with a manual for three reasons.
If you split the Porsche customer demographic into two camps, it would be ‘purist’ manual crowd and ‘grand touring’ PDK crowd. That’s ignoring the go as fast as possible at all cost GT-RS track day crowd or the straight-line crowd which requires the faster shifting and higher torque capacity of the PDK. The purist manual crowd wants minimum weight and complexity, so no hybrid for them.
From a driveability perspective, a lot stronger clutch would be required with the hybrid system to handle the torque. So that could negatively impact the manual driving experience.
Lastly, I think it would be a costly development for a product configuration with low take-rate resulting in financial losses. Ferrari and Lamborghini ditched manuals a long time ago for this reason.
If anything, I could see Porsche going hybrid with a simulated manual gearbox such as Koenigsegg has developed. IMO that’s the only way forward while maintaining any decent driving experience
How long does the charge last? Can you run out of charge with super aggressive driving? I know it does regen during braking, but its not that efficient conversion. How many spool up cycles can it do?
The braking regen will put back into the battery as much power as the battery can handle. The e-turbo only uses power for a split-second during initial spool-up. Then it turns into a generator and can charge the battery or power the electric motor in the transmission. I did some quick numbers in my head and if the battery is full, the car could run about 2 minutes straight at full power. There are only two places in the world off the top of my head to do that and that’s the super huge ovals at GM proving grounds and one in Italy where OEMs can do top speed testing. The GM oval is 3.8 miles long and the Nardo Ring in Italy is 7.8 miles long. I’m actually not sure the cars can go full speed in the turns at the GM oval. That all said, I find it highly unlikely the battery would get fully discharged. The GM Corvette E-Ray hybrid has two drive modes: one is full track attack max power mode and one is sustained use mode. In the max power mode, the battery will run out after a couple laps. The sustained use mode has reduced peak power so that the battery will not run out. The main difference compared to Porsche’s T-hybrid setup is that the Corvetter E-Ray only has braking regen to recharge the battery whereas the 992 GTS has the e-turbo to act as a generator when it’s ‘wastegating’ in addition to braking regen. Also, you don’t see F1 cars run out of batteries right?
The turbo is not the only consumer of the charge. The 40kw PDK motor uses it as well, I guess they can limit how much the PDK motor uses and always leave power to spool turbos and regain power when the turbo is acting like a generator. It won’t be consistent though. I am sure the PDK motor could use the charge pretty quickly.
Battery is 1.9kWh capacity. The PDK motor is 40kW. The turbo can generate 11kW, so that’s a net drain of 29kW. I was actually a bit off on my math; the car going full power would take about 3.9 minutes to drain the battery.
I just read about Porsche building their prototype e-turbo system on a 718 Boxster. While, I am certain this will never be available in the market, it is a drive train modification to drool over.
https://www.motortrend.com/how-to/e-turbo-electric-assist-turbocharger/
Consuming excess turbine power to charge a battery, rather than wastegating excess, will noticeably increase exhaust hackpressure… right?
How big of a concern is that? I thought exhaust backpressure and negative engine deltaP (intake vs exhaust manifold pressures) could among other things drive knock.
Seems a little bold to me especially running lambda 1 and relatively high (10.5:1) compression but I’m not an engine expert.