4 ms·

My first car crush was in high school: the 2002 Subaru WRX. It would be fine to get some souped-up monster, and high-end BMWs are always fast, but when I first

My first car crush was in high school: the 2002 Subaru WRX. It would be fine to get some souped-up monster, and high-end BMWs are always fast, but when I first saw those silly little bug eyes and the trademark blue color? God did I want one. It was weird to figure out that it only came with a 2 liter engine. Apparently turbos help a lot. It was even weirder when the 2005 STI came out with the same engine ... and a bigger turbo. And it was yet weirder when I looked at a 2014 BMW 3 series ... and they have twin turbos and tiny engines. To me, the last 15 years have been car manufacturers figuring out that with the right kind of engineering, you can get rid of turbo lag, and if you don't have lag or reliability problems, turbos make everything better. Smaller, faster, more fuel-efficient. My dad's sedan has a twin turbo these days. It gets 35 mpg. I get that it's only one piece of the puzzle, but it's been so fun to see that tech go from niche-y to ubiquitous.

semi-extrinsic 9y ago
In F1 they now have waste heat recovery systems, as I understand it (please, F1 engineers, correct me if I'm wrong) in the form of mechanically decoupled turbine and compressor wheels on the turbo. The (exhaust) turbine generates electricity which it can feed either to the battery or to the compressor wheel motor (acting like a regular turbo in the latter case). In this configuration, you can also electrically spool up the compressor wheel from the battery, giving exactly zero turbo lag, and they can also recover impressive amounts of energy that would otherwise be wasted - about 1 kWh in a 90 second lap. [For a longer while, we've had anti-lag systems on racecars that basically burn petrol in the manifold, always keeping the turbo spinning. These are horribly fuel-inefficient and destroy turbos etc. quickly.] I sincerely hope that electrically coupled turbo systems are adopted in road cars. The recent Audi/Bentley top-end (diesel!) SUVs with electric turbos are promising in this regard, but I don't think they do waste heat recovery per se.
- davewritescode 9y ago
  The coolest thing about current F1 engines is that they eliminate a major inefficiency of turbos. In a modern turbocharged, once the turbo hits maximum boost an electronically actuated wastegate opens to avoid over boosting the engine which wastes all the energy you worked to create. Coupling the turbine shaft to a generator allows you to recapture that energy normally lost to the wastegate.
- Too 9y ago
  Volvo has something similar in their latest engines, they call it power pulse. It's building up the turbo with an electric compressor and opposed to audi e-turbo the pressure is also stored in a pressure tank instead of constantly pumped by the compressor, which at least on paper sounds like it would reduce the lag even more. Anyone got more experience?
- hvidgaard 9y ago
  F1 nerd here. The turbo and compressor are still mechanically linked. Mercedes pioneered this eras engine with the exchaust side and intake side on opposite ends of the engine, and still managed to connect them with a shaft. If you know anything about turbos, think about this for a moment. They have mechanically connected two components with a shaft along the entirety of the engine block, rotating with 100.000 rpm. That is amazing. They have an electical motor on the same shaft that will either harvest or keep the turbo spinning. This beautiful arrangement means that they design the turbo to extract as much energy as posible, and control it with the motor, rather than rely exclusively on the wastegate. This as you state, means that they can recoupe quite a bit of extra energy. I would not be surprised if we see non turbo charged engines, with an exhaust energy recovery system for hybrid engines.
rsync 9y ago
"To me, the last 15 years have been car manufacturers figuring out that with the right kind of engineering, you can get rid of turbo lag, and if you don't have lag or reliability problems, turbos make everything better. Smaller, faster, more fuel-efficient. My dad's sedan has a twin turbo these days. It gets 35 mpg." I think this is a mistaken interpretation of what is going on. What I believe is happening is that ever-increasing emissions and fleet efficiency requirements have seriously clamped down on what carmakers can produce, with technology and feature creep continuing to add weight to the car. That is why we see cars going to smaller and smaller engines (basically the entire Volvo fleet is 4 cylinder now) with increased reliance on turbo/super charging to achieve necessary horsepower. But these things are not equal - smaller engines vibrate more, they are louder, they are most likely inline and therefore have badly balanced "secondary forces" and they are going to have trouble achieving displacement larger than 2.5L. I have no skin in this game since I don't care at all about ICE or ICE car culture and I want to transition to fully electric vehicles ASAP. But never forget, kids: there is no replacement for displacement.
- chadgeidel 9y ago
  Turbocharged cars (exhaust driven) are more efficient partially because they capture waste heat from the combustion process. A manufacturer can tune the engine and gearing to have a really good "sticker" EPA economy rating, but that generally doesn't translate to a good "actual" economy rating (because people are always gunning the engine to get that sweet boost). Unfortunately small turbo engines have higher emissions (forget the specific component, the other advancement of direct-injection has higher NOx emissions I believe) and manufacturers are now moving back to larger-displacement naturally aspirated engines because people don't drive like the EPA test works.
- justin66 9y ago
  > But never forget, kids: there is no replacement for displacement. Said no one who has ever compared this generation's Porsche Cayman/Boxster to the previous generation. trjordan's right, the engineering of the small-displacement turbocharged motors has become completely amazing. You could scale up (ooooh... put AWD in too, for some reason!) but the cars are already overpowered.
ehaliewicz2 9y ago
Turbos do not make anything more fuel efficient, they simply allow you to have the fuel efficiency of a small engine off boost, and match the power of a larger engine while on boost. It's still a tradeoff however, there's always some lag and delay to throttle response, extra piping and cooling hardware, and more backpressure in the exhaust means it loses efficiency compared to a naturally aspirated variant of the same engine.
stupidhn 9y ago
>To me, the last 15 years have been car manufacturers figuring out that with the right kind of engineering, you can get rid of turbo lag I own a Fiesta ST that comes with a 1.6L turbo-charged engine that produces about 200hp/210+ft-lb of torque...on 87 octane. If I drive the speed limit I can get well over 40mpg (~5L/100km). I can't recommend these cars enough (if the small stature suits you). The fit and finish isn't great, but it's a piece of machinery when it comes to performance. http://www.caranddriver.com/ford/fiesta-st http://www.caranddriver.com/ford/fiesta-st
hvidgaard 9y ago
> if you don't have lag or reliability problems, turbos make everything better. Smaller, faster, more fuel-efficient. No. Mazdas SkyActiv-G do the exact opposite, because, as Mazda states it: "When you add forced induction the combustion becomes harder to control, resulting in lower efficiency". Car companies collectively research EVs and high compression Atkinson style engines, because the real world efficiency are significantly better. But for driveability, a fast responding turbo makes sense, but a larger NA engine is better. Neither is good for efficiency. My EcoBoost Fiesta, driving 80kmph (50mph), gets around 4.0L/100km (around 59mpg), but 130kmph (80mph), is around 6.5L/100km (36mpg). This is expected due to how drag works, but the kicker is city driving. It's worse, and I can drive a Mazda 6, a significantly bigger car, with a bigger engine, in the same city, same driving, more efficiently.
- davewritescode 9y ago
  Mazda has a turbocharged SkyActive-G 2.5 these days they're using on the CX-9 and it's been pretty well recieved - https://insidemazda.mazdausa.com/press-release/mazdas-turbocharged-skyactiv-engine-wins-2017-wards-10-best-engines-award/ https://insidemazda.mazdausa.com/press-release/mazdas-turboc... It makes a ton of torque very low down low (300 ft/lbs) which makes it very suitable to push around a midsized CUV.
  - hvidgaard 9y ago
    According to their engineers it was a compromise because they needed a more powerful engine, and adding a turbo was simpler and faster, than design larger one in line with their SkyActive-G design philosophy.
driverdan 9y ago
> It was even weirder when the 2005 STI came out with the same engine The 2005 STi has a 2.5L engine, not the 2.0 found in the WRX. It's the same block as the Forester's 2.5L turbo.

semi-extrinsic 9y ago

In F1 they now have waste heat recovery systems, as I understand it (please, F1 engineers, correct me if I'm wrong) in the form of mechanically decoupled turbine and compressor wheels on the turbo. The (exhaust) turbine generates electricity which it can feed either to the battery or to the compressor wheel motor (acting like a regular turbo in the latter case). In this configuration, you can also electrically spool up the compressor wheel from the battery, giving exactly zero turbo lag, and they can also recover impressive amounts of energy that would otherwise be wasted - about 1 kWh in a 90 second lap. [For a longer while, we've had anti-lag systems on racecars that basically burn petrol in the manifold, always keeping the turbo spinning. These are horribly fuel-inefficient and destroy turbos etc. quickly.] I sincerely hope that electrically coupled turbo systems are adopted in road cars. The recent Audi/Bentley top-end (diesel!) SUVs with electric turbos are promising in this regard, but I don't think they do waste heat recovery per se.

davewritescode 9y ago
The coolest thing about current F1 engines is that they eliminate a major inefficiency of turbos. In a modern turbocharged, once the turbo hits maximum boost an electronically actuated wastegate opens to avoid over boosting the engine which wastes all the energy you worked to create. Coupling the turbine shaft to a generator allows you to recapture that energy normally lost to the wastegate.
Too 9y ago
Volvo has something similar in their latest engines, they call it power pulse. It's building up the turbo with an electric compressor and opposed to audi e-turbo the pressure is also stored in a pressure tank instead of constantly pumped by the compressor, which at least on paper sounds like it would reduce the lag even more. Anyone got more experience?
hvidgaard 9y ago
F1 nerd here. The turbo and compressor are still mechanically linked. Mercedes pioneered this eras engine with the exchaust side and intake side on opposite ends of the engine, and still managed to connect them with a shaft. If you know anything about turbos, think about this for a moment. They have mechanically connected two components with a shaft along the entirety of the engine block, rotating with 100.000 rpm. That is amazing. They have an electical motor on the same shaft that will either harvest or keep the turbo spinning. This beautiful arrangement means that they design the turbo to extract as much energy as posible, and control it with the motor, rather than rely exclusively on the wastegate. This as you state, means that they can recoupe quite a bit of extra energy. I would not be surprised if we see non turbo charged engines, with an exhaust energy recovery system for hybrid engines.

rsync 9y ago

"To me, the last 15 years have been car manufacturers figuring out that with the right kind of engineering, you can get rid of turbo lag, and if you don't have lag or reliability problems, turbos make everything better. Smaller, faster, more fuel-efficient. My dad's sedan has a twin turbo these days. It gets 35 mpg." I think this is a mistaken interpretation of what is going on. What I believe is happening is that ever-increasing emissions and fleet efficiency requirements have seriously clamped down on what carmakers can produce, with technology and feature creep continuing to add weight to the car. That is why we see cars going to smaller and smaller engines (basically the entire Volvo fleet is 4 cylinder now) with increased reliance on turbo/super charging to achieve necessary horsepower. But these things are not equal - smaller engines vibrate more, they are louder, they are most likely inline and therefore have badly balanced "secondary forces" and they are going to have trouble achieving displacement larger than 2.5L. I have no skin in this game since I don't care at all about ICE or ICE car culture and I want to transition to fully electric vehicles ASAP. But never forget, kids: there is no replacement for displacement.

chadgeidel 9y ago
Turbocharged cars (exhaust driven) are more efficient partially because they capture waste heat from the combustion process. A manufacturer can tune the engine and gearing to have a really good "sticker" EPA economy rating, but that generally doesn't translate to a good "actual" economy rating (because people are always gunning the engine to get that sweet boost). Unfortunately small turbo engines have higher emissions (forget the specific component, the other advancement of direct-injection has higher NOx emissions I believe) and manufacturers are now moving back to larger-displacement naturally aspirated engines because people don't drive like the EPA test works.
justin66 9y ago
> But never forget, kids: there is no replacement for displacement. Said no one who has ever compared this generation's Porsche Cayman/Boxster to the previous generation. trjordan's right, the engineering of the small-displacement turbocharged motors has become completely amazing. You could scale up (ooooh... put AWD in too, for some reason!) but the cars are already overpowered.

ehaliewicz2 9y ago

Turbos do not make anything more fuel efficient, they simply allow you to have the fuel efficiency of a small engine off boost, and match the power of a larger engine while on boost. It's still a tradeoff however, there's always some lag and delay to throttle response, extra piping and cooling hardware, and more backpressure in the exhaust means it loses efficiency compared to a naturally aspirated variant of the same engine.

stupidhn 9y ago

>To me, the last 15 years have been car manufacturers figuring out that with the right kind of engineering, you can get rid of turbo lag I own a Fiesta ST that comes with a 1.6L turbo-charged engine that produces about 200hp/210+ft-lb of torque...on 87 octane. If I drive the speed limit I can get well over 40mpg (~5L/100km). I can't recommend these cars enough (if the small stature suits you). The fit and finish isn't great, but it's a piece of machinery when it comes to performance. http://www.caranddriver.com/ford/fiesta-st http://www.caranddriver.com/ford/fiesta-st

hvidgaard 9y ago

> if you don't have lag or reliability problems, turbos make everything better. Smaller, faster, more fuel-efficient. No. Mazdas SkyActiv-G do the exact opposite, because, as Mazda states it: "When you add forced induction the combustion becomes harder to control, resulting in lower efficiency". Car companies collectively research EVs and high compression Atkinson style engines, because the real world efficiency are significantly better. But for driveability, a fast responding turbo makes sense, but a larger NA engine is better. Neither is good for efficiency. My EcoBoost Fiesta, driving 80kmph (50mph), gets around 4.0L/100km (around 59mpg), but 130kmph (80mph), is around 6.5L/100km (36mpg). This is expected due to how drag works, but the kicker is city driving. It's worse, and I can drive a Mazda 6, a significantly bigger car, with a bigger engine, in the same city, same driving, more efficiently.

davewritescode 9y ago
Mazda has a turbocharged SkyActive-G 2.5 these days they're using on the CX-9 and it's been pretty well recieved - https://insidemazda.mazdausa.com/press-release/mazdas-turbocharged-skyactiv-engine-wins-2017-wards-10-best-engines-award/ https://insidemazda.mazdausa.com/press-release/mazdas-turboc... It makes a ton of torque very low down low (300 ft/lbs) which makes it very suitable to push around a midsized CUV.
- hvidgaard 9y ago
  According to their engineers it was a compromise because they needed a more powerful engine, and adding a turbo was simpler and faster, than design larger one in line with their SkyActive-G design philosophy.

driverdan 9y ago

> It was even weirder when the 2005 STI came out with the same engine The 2005 STi has a 2.5L engine, not the 2.0 found in the WRX. It's the same block as the Forester's 2.5L turbo.