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Thread: Car engines squeeze power out of every drop of gas

  1. #61
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    Re: Car engines squeeze power out of every drop of gas

    So FWD is like the Celeron...
    ROFL
    Quote Originally Posted by regomodo View Post
    My maths and physics may be a little rusty but as far as i remember pushing at an object is better than pulling if the force applied is at an angle (for push, force down to the object). In FWD when torque is applied the weight is shifted to the rear of the car thus not over the front wheels. You'll notice the bonnet rise.
    In RWD the torque causes the bonnet to rise (if going forwards) shifting the weight to the back therefore over the rear wheels more.

    Of course i may be wrong which is why i did a masters in Elec Eng instead of Mech
    The weight does shift backwards when accelerating, however pulling on a slippery surface is better than pushing. Reason for this is that when you are accelerating rotating tires have less traction than stationary tires and that makes the rear swing out. You can see that with high powered RWD even in the dry.

    Weight shift is also a tricky beast, no matter how much weight transfer you are doing the engine is still the heaviest part of the car and it is still on the front tires (unless we are talking midships and rear engined cars like Porsche's). There is also suspension set up that can change your weight transfer. Most sports tuned cars have very hard suspension setup making weight transfer minimal.
    Since I get asked alot, I am originally from Ukraine but am Russian by nationality. My nick means specter in Russian.

  2. #62
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    Re: Car engines squeeze power out of every drop of gas

    Quote Originally Posted by Whiffle View Post
    You're confusing different things here.

    A supercharger requires power, no matter what you're doing with it, or how you're driving it. If you run it with a belt, you're giving it power directly off the engine. If you run it electrically, you have to run the alternator, which converts the energy into electrical energy, send it over some wires, and then spin a motor which converts it back into mechanical energy. Its 6 one way and half a dozen the other, you're still sending power to the supercharger, except electrically is less efficient because you have to convert it from one form of energy to another, twice.
    My understanding is the alternator runs permanently while the engine is running. It has no clutch to disengage it. So if it is going to run permanently then you might as well use it to power another electrical device. So how does it rob more power from the engine if it is already running and you want to supply power to another device?

  3. #63
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    Re: Car engines squeeze power out of every drop of gas

    Quote Originally Posted by mips View Post
    My understanding is the alternator runs permanently while the engine is running. It has no clutch to disengage it. So if it is going to run permanently then you might as well use it to power another electrical device. So how does it rob more power from the engine if it is already running and you want to supply power to another device?
    Cranking a generator (of electrical power) uses some energy even when there is no load on it, i.e. no device using the energy offered by the generator.

    As soon as you apply a load (connect a light bulb, a toaster or motor to the generator), the generator uses the energy drawn by the load in addition to the energy it used when empty.

    You can easily test this by manually cranking a generator (such as the one often found on bicycles used to drive the lamp). Cranking becomes much more harder when the power is being consumed.

    It is much the same as a motor car: the engine consumes more fuel at the same rpm when climbing uphill while hauling heavy loads than when coasting down hill.
    ch
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  4. #64
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    Re: Car engines squeeze power out of every drop of gas

    Quote Originally Posted by mips View Post
    My understanding is the alternator runs permanently while the engine is running. It has no clutch to disengage it. So if it is going to run permanently then you might as well use it to power another electrical device. So how does it rob more power from the engine if it is already running and you want to supply power to another device?

    Alternators run all the time, but they aren't putting out their full power all the time. If they were, your battery would probably boil and burst, as the energy has to go somewhere. (this happens when the alternator regulator fails) They only produce as much electricity as is needed. The higher the electrical load, the harder it is to turn the alternator, the more power it takes off of the engine.

    In addition, I'll give you a little math on the inpracticality of electric superchargers. According to this site:
    http://www.aa1car.com/library/supercharge.htm
    It takes about 50-60 hp to run an OEM belt driven supercharger at full throttle. 50 hp is equivalent to 37,284.9 watts. Now, in order to transmit that much power on a 12 volt electical system, you'd need (according to the equation Power=Current*Voltage) an electrical current of 3,107 amps, the wiring to handle it, and an alternator big enough to provide that kind of power (the alternator on my truck is 130 amps...). Thats why nobody uses electric superchargers, its nearly impossible to run one big enough to be as effective as a belt driven one.

    On turbos being more efficient, maybe maybe not. Exhaust gases are pushed out of the cylinders by the pistons, which are connected to the crankshaft, the harder it is to push the exhaust out, the more energy is robbed from the engine. Thats why people put free flowing exhausts on. One thing for certain is that they make their power in a different range than a supercharger. Its personal preference as far as I'm concerned.
    Last edited by Whiffle; January 21st, 2008 at 07:27 PM.
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  5. #65
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    Re: Car engines squeeze power out of every drop of gas

    Quote Originally Posted by popch View Post
    Cranking a generator (of electrical power) uses some energy even when there is no load on it, i.e. no device using the energy offered by the generator.

    As soon as you apply a load (connect a light bulb, a toaster or motor to the generator), the generator uses the energy drawn by the load in addition to the energy it used when empty.

    You can easily test this by manually cranking a generator (such as the one often found on bicycles used to drive the lamp). Cranking becomes much more harder when the power is being consumed.

    It is much the same as a motor car: the engine consumes more fuel at the same rpm when climbing uphill while hauling heavy loads than when coasting down hill.
    I don't get it yet.

    How does the alternators physical load on the engine change? The alternator is a free spinning device with certain losses due to bearings etc which basically stays constant throught the engines rpm range. Does the alternator have feedback to the cars ecu so it can tell the engine to rev higher when it needs to generate more power?

    Why do you guys call it a generator (which is DC) when you are actually referring to something genrating AC power?

  6. #66
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    Re: Car engines squeeze power out of every drop of gas

    An alternator is a free spinning device when it has no load, but when you put a load on it, it becomes harder to turn, its physics. When you spin the magnetic core of an alternator, it induces a current in the coils surrounding it. This is what produces the electrical power. In addition, the current in the coils also create their own magnetic field, which pushes back on the rotating core, making it harder to turn. The higher the current being generated, the stronger the magnetic field, and the more power it takes to turn.
    100 buckets of bits on the bus,
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  7. #67
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    Re: Car engines squeeze power out of every drop of gas

    Quote Originally Posted by Whiffle View Post
    An alternator is a free spinning device when it has no load, but when you put a load on it, it becomes harder to turn, its physics. When you spin the magnetic core of an alternator, it induces a current in the coils surrounding it. This is what produces the electrical power. In addition, the current in the coils also create their own magnetic field, which pushes back on the rotating core, making it harder to turn. The higher the current being generated, the stronger the magnetic field, and the more power it takes to turn.
    Thank you, now I get it. When I read this I had flashbacks of my "Electrical Machines II" course/class and it all makes sense now.

  8. #68
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    Re: Car engines squeeze power out of every drop of gas

    Regenerative braking on electric cars is a good example of the resistence to rotational motion of generators and alternators. The electric motors in the drive train are capable of being used as generators to convert the forward motion of the car back into electricity to charge the batteries. The more charging load on the motor/generator, the harder it is for the wheels to turn and the faster the car stops.
    Last edited by azimuth; January 21st, 2008 at 08:57 PM.
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  9. #69
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    Re: Car engines squeeze power out of every drop of gas

    Quote Originally Posted by Whiffle View Post
    An alternator is a free spinning device when it has no load, but when you put a load on it, it becomes harder to turn, its physics. When you spin the magnetic core of an alternator, it induces a current in the coils surrounding it. This is what produces the electrical power. In addition, the current in the coils also create their own magnetic field, which pushes back on the rotating core, making it harder to turn. The higher the current being generated, the stronger the magnetic field, and the more power it takes to turn.
    Ahh thanks for the explanation, I was operating under the wrong assumption that power output is constant (couldn't figure our where extra power went either). Then yes it makes sense to have a belt driven supercharger.
    Since I get asked alot, I am originally from Ukraine but am Russian by nationality. My nick means specter in Russian.

  10. #70
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    Re: Car engines squeeze power out of every drop of gas

    Quote Originally Posted by prizrak View Post
    As tgalati4 put it the worst thing about the turbo is that it burns out quickly. About 80,000 miles is an average life span of a turbo.
    Please support this assertion - I doubt it's true now. I drive a 1989 Volvo 740 turbo (original) and @ 140K miles, it has no impending sign of turbo death.

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