6 ms·

Porsche 919 – Racecar Engineering

60 points by dmmalam 11y ago

ExpiredLink 11y ago
I hope nobody has forged an emissions test.
elektromekatron 11y ago
Is interesting to see how hybrids now dominate Le Mans.
- nialo 11y ago
  An important point about racing cars is how completely their performance is determined by the rules of the series. Hybrids dominating says more about the details of the rules than about hybrids.
  - jdietrich 11y ago
    By design, the LMP1 rules permit a diverse range of solutions. Porsche run a turbocharged V4 petrol engine, Audi use a turbocharged V6 diesel, Toyota a naturally aspirated petrol V8. Audi's hybrid system has half the energy capacity of Porsche's. Teams running a large hybrid system are penalised with a lower fuel rate limit and vice-versa. The technical regulations are significant in any racing formula, but the LMP1 rules are carefully balanced to prevent the dominance of any one technological approach. Diesel engines have been significantly gimped in recent years to curtail the dominance of Audi.
    - magila 11y ago
      None of what you said is wrong, but it also doesn't refute the central point: current WEC regulations are very much designed to make the LMP1 hybrid formula the premiere class. While there is a non-hybrid LMP1 formula, it is a distinctly lower performance class which exists to accommodate privateer teams who can't afford a complex hybrid system.
- abruzzi 11y ago
  Since Le Mans is an endurance race, the vehicles that can run longer with less pit stops have a strong advantage. This is what the Audi diesels dominated for a good part of the 2000s.
sandworm101 11y ago
"the internal combustion engines have no air restrictors or capacity limits which has seen Audi opt for a diesel fuelled V6" Well, I think they might want to take a closer look at that one.
- jdietrich 11y ago
  They're correct. Engine capacity limits and intake restrictors were abolished in 2014 and replaced with a fuel flow limit. This more closely aligns the LMP1 rules with the goal of developing commercially relevant fuel efficiency technology. Engine capacity limits do apply to other classes, and to privateer teams in LMP1 who opt not to use a hybrid system.
  - sandworm101 11y ago
    I meant to imply that, as Audi is owned by VW, that officials might want to look for possible cheating given the current VW controversy re diesel engines. But if one has to explain ...
    - rebootthesystem 11y ago
      What vw has done sucks yet, what you are siggesting is completly without relevance to racing. There is no connection whatsoever.
    - jotux 11y ago
      >But if one has to explain ... Comments this far off topic and irrelevant need explanation.
      - sandworm101 11y ago
        Wow. I have seriously over-estimated this crowd. The saying goes that if one has to explain a joke, then it wasn't funny in the first place. I had assumed that people reading this thread would see the humor behind linking Audi, VW, diesel and cheating. Oops. Then I assumed that readers would understand the "if it needs explaining..." remark as a reference to jokes not being funny if they need explaining. Oops again. I'll set my lowest common denominator a bit lower next time.
vegabook 11y ago
It's interesting how at the high end the piston engine increasingly looks like a jet turbine. In the 919 we essentially have more than half the energy created by a rotating set of turbos, capturing a part of the huge energies usually expelled down the exhaust, in way reminiscent of the rear (hot) turbines in a jet (in this case the "compression stage" is provided by the piston engine). The big advantage, of course, shared with wankel engines, is no waste of energy accelerating and decelerating pistons hundreds of times per second, and lower frictional losses too. Porsche captures this fact by making a small V4, not some big v6 or V8. In essence, we're getting closer to pure turbine style for extracting the available energy in the fuel, because the electric part of the engine creates a way of "buffering" the energy and releasing it on demand, which of course is the major problem with jet turbines (constant output difficult to modulate). Take it to its logical conclusion and, if turbines could be made small enough, we might no longer have a physical link between the fuel-burning part of the engine and the road. Not a ICE engineer myself so happy to be corrected but this seems to be where fuel-burning vehicle engine technology is headed (I note the proliferation of turbos in road cars).
- sokoloff 11y ago
  Jet engines don't dominate airline usage because of good fuel consumption (their BSFC [specific fuel consumption, or "how much fuel is needed to create a set amount of power?] is not competitive with piston engines). Jet engines dominate because of high power to mass, highly reliable power production, and a good match between power available and power required in different phases of flight. Non-flat-rated jet turbines lose power with altitude and temperature right off the deck. Some are flat-rated (higher thermodynamic power capability than physical power capability), but even those lose power at some altitude. This is a good match for high power required at takeoff and less power required at cruise altitudes.
  - vegabook 11y ago
    why do most power stations use turbines and not pistons? There is no need for power to mass ratios there?
Gonzih 11y ago
> The cars power unit was at first thought to be a derivative of the never raced early 2014 spec Volkswagen F1 inline four engine I had no idea VW had f1 engine, is it used? I know that they have some presence in f3 in that sense, had no idea about f1 though.
- mrcarrot 11y ago
  Perhaps F1 is just a model number here? VW certainly don't supply any Formula 1 teams currently, and a 2014 spec F1 engine would have to be a V6, not a four cylinder.
  - Gonzih 11y ago
    I did some research on the topic and apparently audi was planning to jump on to the f1 game (based on redbulls plans). But sadly with recent VW related issues audis presence in f1 will not happen soon.
- zarriak 11y ago
  When they started talking about the changes that were coming to F1 in 2014 the regulations initially called for inline four engines[1], but that had nothing to do with the engines that Ferrari manufactured, so they compromised with V6 turbo hybrids. [1]: https://en.wikipedia.org/wiki/Formula_One_engines#2014.E2.80.93present https://en.wikipedia.org/wiki/Formula_One_engines#2014.E2.80...
zackmorris 11y ago
I'm a little surprised they didn't go with a 4 cylinder boxer engine since vibration was such a problem: https://en.wikipedia.org/wiki/Flat_engine#Porsche https://en.wikipedia.org/wiki/Flat_engine#Porsche
- jdietrich 11y ago
  It's a packaging issue. Boxers are excellent for weight distribution, but their width would restrict airflow to the rear diffuser. V engines fit neatly behind the cockpit, with plenty of space for ancillaries. Rear aerodynamics are a key aspect of Nissan's decision to go front-engined; putting the engine up front allows for an absolutely huge diffuser tunnel. https://s-media-cache-ak0.pinimg.com/736x/1a/4a/73/1a4a737152125a0a74d1b2946c7ca513.jpg https://s-media-cache-ak0.pinimg.com/736x/1a/4a/73/1a4a73715...
  - FrankBooth 11y ago
    Also because it's a stressed member, which is significantly easier to build in a V layout than a flat layout. The lower CoG thing with flat engines is kind of a myth. You end up with the exhaust headers below the engine, so the engine sits higher than an equivalent V layout engine would.

60 points by dmmalam 11y ago

ExpiredLink 11y ago

I hope nobody has forged an emissions test.

elektromekatron 11y ago

Is interesting to see how hybrids now dominate Le Mans.

nialo 11y ago
An important point about racing cars is how completely their performance is determined by the rules of the series. Hybrids dominating says more about the details of the rules than about hybrids.
- jdietrich 11y ago
  By design, the LMP1 rules permit a diverse range of solutions. Porsche run a turbocharged V4 petrol engine, Audi use a turbocharged V6 diesel, Toyota a naturally aspirated petrol V8. Audi's hybrid system has half the energy capacity of Porsche's. Teams running a large hybrid system are penalised with a lower fuel rate limit and vice-versa. The technical regulations are significant in any racing formula, but the LMP1 rules are carefully balanced to prevent the dominance of any one technological approach. Diesel engines have been significantly gimped in recent years to curtail the dominance of Audi.
  - magila 11y ago
    None of what you said is wrong, but it also doesn't refute the central point: current WEC regulations are very much designed to make the LMP1 hybrid formula the premiere class. While there is a non-hybrid LMP1 formula, it is a distinctly lower performance class which exists to accommodate privateer teams who can't afford a complex hybrid system.
abruzzi 11y ago
Since Le Mans is an endurance race, the vehicles that can run longer with less pit stops have a strong advantage. This is what the Audi diesels dominated for a good part of the 2000s.

sandworm101 11y ago

"the internal combustion engines have no air restrictors or capacity limits which has seen Audi opt for a diesel fuelled V6" Well, I think they might want to take a closer look at that one.

jdietrich 11y ago
They're correct. Engine capacity limits and intake restrictors were abolished in 2014 and replaced with a fuel flow limit. This more closely aligns the LMP1 rules with the goal of developing commercially relevant fuel efficiency technology. Engine capacity limits do apply to other classes, and to privateer teams in LMP1 who opt not to use a hybrid system.
- sandworm101 11y ago
  I meant to imply that, as Audi is owned by VW, that officials might want to look for possible cheating given the current VW controversy re diesel engines. But if one has to explain ...
  - rebootthesystem 11y ago
    What vw has done sucks yet, what you are siggesting is completly without relevance to racing. There is no connection whatsoever.
  - jotux 11y ago
    >But if one has to explain ... Comments this far off topic and irrelevant need explanation.
    - sandworm101 11y ago
      Wow. I have seriously over-estimated this crowd. The saying goes that if one has to explain a joke, then it wasn't funny in the first place. I had assumed that people reading this thread would see the humor behind linking Audi, VW, diesel and cheating. Oops. Then I assumed that readers would understand the "if it needs explaining..." remark as a reference to jokes not being funny if they need explaining. Oops again. I'll set my lowest common denominator a bit lower next time.

vegabook 11y ago

It's interesting how at the high end the piston engine increasingly looks like a jet turbine. In the 919 we essentially have more than half the energy created by a rotating set of turbos, capturing a part of the huge energies usually expelled down the exhaust, in way reminiscent of the rear (hot) turbines in a jet (in this case the "compression stage" is provided by the piston engine). The big advantage, of course, shared with wankel engines, is no waste of energy accelerating and decelerating pistons hundreds of times per second, and lower frictional losses too. Porsche captures this fact by making a small V4, not some big v6 or V8. In essence, we're getting closer to pure turbine style for extracting the available energy in the fuel, because the electric part of the engine creates a way of "buffering" the energy and releasing it on demand, which of course is the major problem with jet turbines (constant output difficult to modulate). Take it to its logical conclusion and, if turbines could be made small enough, we might no longer have a physical link between the fuel-burning part of the engine and the road. Not a ICE engineer myself so happy to be corrected but this seems to be where fuel-burning vehicle engine technology is headed (I note the proliferation of turbos in road cars).

sokoloff 11y ago
Jet engines don't dominate airline usage because of good fuel consumption (their BSFC [specific fuel consumption, or "how much fuel is needed to create a set amount of power?] is not competitive with piston engines). Jet engines dominate because of high power to mass, highly reliable power production, and a good match between power available and power required in different phases of flight. Non-flat-rated jet turbines lose power with altitude and temperature right off the deck. Some are flat-rated (higher thermodynamic power capability than physical power capability), but even those lose power at some altitude. This is a good match for high power required at takeoff and less power required at cruise altitudes.
- vegabook 11y ago
  why do most power stations use turbines and not pistons? There is no need for power to mass ratios there?

Gonzih 11y ago

> The cars power unit was at first thought to be a derivative of the never raced early 2014 spec Volkswagen F1 inline four engine I had no idea VW had f1 engine, is it used? I know that they have some presence in f3 in that sense, had no idea about f1 though.

mrcarrot 11y ago
Perhaps F1 is just a model number here? VW certainly don't supply any Formula 1 teams currently, and a 2014 spec F1 engine would have to be a V6, not a four cylinder.
- Gonzih 11y ago
  I did some research on the topic and apparently audi was planning to jump on to the f1 game (based on redbulls plans). But sadly with recent VW related issues audis presence in f1 will not happen soon.
zarriak 11y ago
When they started talking about the changes that were coming to F1 in 2014 the regulations initially called for inline four engines[1], but that had nothing to do with the engines that Ferrari manufactured, so they compromised with V6 turbo hybrids. [1]: https://en.wikipedia.org/wiki/Formula_One_engines#2014.E2.80.93present https://en.wikipedia.org/wiki/Formula_One_engines#2014.E2.80...

zackmorris 11y ago

I'm a little surprised they didn't go with a 4 cylinder boxer engine since vibration was such a problem: https://en.wikipedia.org/wiki/Flat_engine#Porsche https://en.wikipedia.org/wiki/Flat_engine#Porsche

jdietrich 11y ago
It's a packaging issue. Boxers are excellent for weight distribution, but their width would restrict airflow to the rear diffuser. V engines fit neatly behind the cockpit, with plenty of space for ancillaries. Rear aerodynamics are a key aspect of Nissan's decision to go front-engined; putting the engine up front allows for an absolutely huge diffuser tunnel. https://s-media-cache-ak0.pinimg.com/736x/1a/4a/73/1a4a737152125a0a74d1b2946c7ca513.jpg https://s-media-cache-ak0.pinimg.com/736x/1a/4a/73/1a4a73715...
- FrankBooth 11y ago
  Also because it's a stressed member, which is significantly easier to build in a V layout than a flat layout. The lower CoG thing with flat engines is kind of a myth. You end up with the exhaust headers below the engine, so the engine sits higher than an equivalent V layout engine would.