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Small engines vs. big engines?

  1. Dec 5, 2007 #1
    If you were a car manufacturer, which of the following cars would you choose to manufacture, supposing you are only allowed to manufacture either kind:

    1) a car with a small engine but with a turbocharger; or
    2) a car with a big engine

    Assume that both cars have other variables constant i.e. the same horsepower, the same acceleration speed etc.

    Next, if you were a car buyer, which of the cars would you decide to buy?
     
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  3. Dec 5, 2007 #2

    JasonRox

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    I love small engines with turbochargers are on them, so I vote small one if I were a buyer.

    Even if I were a manufacturer, I would make the smaller one because of the market is going with car buying.
     
  4. Dec 6, 2007 #3
    Are there any clear advantages of small engines with turbochargers, compared to big engines? Or any clear disadvantages?

    I know that with most turbochargers, turbo lag might occur now and then, and that's something which will not happen for big engines. Any others?
     
  5. Dec 6, 2007 #4
    Of course, there are a lot of variables that boil down to driver preference, but...

    A simplified analysis suggests a small engine is better because it can run at higher RPM and thus move the same amount of fuel-air mixture through its cylinders as the big engine--which translates to power. Unfortunately, the size of the intake and exhaust valves become problematic. Understand that it isn't just a matter of figuring out a way to get the fuel-air through the cylinder (which is what a turbocharger solves, along with a moderate improvement in efficiency because of the higher cylinder pressure). It is a matter of how much power is wasted in the extra turbulence you get by really shoving that air through a smaller orifice. The turbocharger increases the fuel-air flow through the engine and increases efficiency via higher cylinder pressure, but it also takes power from the engine to spin and it increases turbulence of air through those little orifices.
     
  6. Dec 6, 2007 #5

    stewartcs

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    Try searching this forum for "Turbos" or similar phrases. There is a lot of information on how them that might help answer your question.
     
  7. Dec 6, 2007 #6

    turbo

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    Two words: Grand National

    Turbocharged V-6 in a mid-sized Buick that could give 'Vettes a run for their money.
     
  8. Dec 6, 2007 #7

    rcgldr

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    Turbo chargers take up a lot of space, and retain more heat in the engine compartment, but then the engine itself is smaller. A larger V8 is generally smoother (less vibration), and many prefer the sound and feel of a larger V8 (or even a V6). Torque versus rpm curver will generally be flatter with a non-turbo charged curve, more low rpm power.

    It's hard to say which is really better. On the semi-high end, a Corvette Z06 uses a 7 liter V8 to make 505hp, while a Ford GT uses a supercharged 5.4 liter engine to make 550hp. The Corvette weighs 3150lbs, while the GT weighs 3485lbs. The Z06 gets 26 miles per gallon on the freeway, while the GT gets about 19.

    The Z06 7.0 liter engine is light, lighter than the 480hp twin turbo 3.6 liter flat six used in a Porsche 911 Turbo.
     
  9. Dec 6, 2007 #8

    brewnog

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    Turbo, definitely, though it depends entirely on application.
     
  10. Dec 6, 2007 #9

    Danger

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    From the practical standpoint, as a manufacturer, I'd have to go with the smaller engine/turbo. As a consumer, not a chance. There's no replacement for displacement. :biggrin:
     
  11. Dec 6, 2007 #10
    But the larger engine is likely to last longer. The turbo is boosted to stronger action, higher pressures, more tear and wear, limits the life span and boosts the maintenance bill.
     
  12. Dec 6, 2007 #11

    brewnog

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    There's no reason that a turbocharged engine can't last far longer than a nat asp. Average life spans of a typical German turbodiesel are double; possibly triple that of a naturally aspirated engine of equivalent output. Just because an engine has been breathed on doesn't necessarily mean it's going to live less long.

    Both configurations have their advantages; and these advantages are most prominent in completely different markets and applications.

    I know there's some tongue-in-cheek there, but this is exactly the delusional view that just doesn't hold water any more. It's this myth that is largely preventing the North American market from seeing sense and buying (and preparing infrastructure for) 50mpg turbodiesels rather than 20mpg V8s, and arguably getting better performance.

    I was having a conversation with an American colleague the other day, who when hearing that my car 'only' has a 2.4 litre engine, exclaimed "my lawnmower has more power than that!" Considering this guy works for an engine manufacturer, I couldn't believe that he was still equating displacement with power. He was amazed when I told him it develops nearly 200bhp and 380Nm of torque; and that I still get 45mpg.
     
    Last edited: Dec 6, 2007
  13. Dec 6, 2007 #12

    Stingray

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    Can you give an example? I've never heard of anything that could approach that kind of efficiency.
     
  14. Dec 6, 2007 #13

    Danger

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    It'd make a good starter for a real motor.:tongue:
    I personally wouldn't own anything with less than 400hp, and over 1,000 is better.

    Anyhow, the question was based from the manufacturer's standpoint, not the buyer's. While I might be wrong, I'm pretty sure that the costs would be lower for the little motor.
     
  15. Dec 7, 2007 #14
    wow guys, thanks for all the nuggets of information! they came in really useful! :smile:
     
  16. Dec 7, 2007 #15

    brewnog

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    50mpg?

    VW's current 1.9TDI is quoted at 56.5mpg on a combined, 65.7mpg extra urban, in a Golf.
    Audi's 2.0TDI A3 will do 51.4mpg combined.
    Ford's 2.0 Duratorq TDCi will do 58.9 extra urban.

    Just have a look in the back of any car magazine.
     
  17. Dec 7, 2007 #16

    Stingray

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    No. You were claiming that a vehicle normally getting 20 mpg with a V8 could get 50 mpg with a turbodiesel while suffering minimal performance loss. While their efficiencies are very impressive, none of these examples fit that statement.
     
  18. Dec 7, 2007 #17

    brewnog

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    Ok, you could compare (say) a 3 litre Audi turbodiesel (155mph, 0-60 6.1 secs, 43mpg), with (say) a Cadillac STS V8 (155mpg, 0-60 6.2secs, 24mpg).

    Probably not the best comparison, but it shows the point I was making.
     
  19. Dec 7, 2007 #18

    Stingray

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    That's a nice example, although it looks like you're using the figures from an A4. The A6 is probably more comparable to an STS in size, and apparently gets 34 mpg with that engine.

    Still, that's very good. I hadn't realized that diesels improved so much. My only experience in one was a Mercedes 240D from the 70's. That thing was dangerously slow on Los Angeles freeways
     
  20. Dec 7, 2007 #19

    brewnog

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    Yeah that was the A4.

    I think most petrolheads (myself included) are astounded the first time they drive a common rail diesel. My Alfa JTD even sounds like a straight six petrol engine, and pulls all the way to the red line with no perceivable turbo lag whatsoever. The only giveaways that it's a diesel are the 5,000rpm redline, the rattly cold start, and only having to fill up every 550 miles.
     
  21. Jun 22, 2010 #20

    actually small engines rev higher because of the overhead cam...but when you look a the 03 cobra which is dohc (has 4 cams) then rpm isnt an issue. and they come boosted from the factory which gives them 410 hp. u equipt it with just pulleys, intake, exhuast, and a tune, and you get 600 hp to the crank and about 500 to the wheels. i choose v8 over small engines any day. theres no replacement for displacement
     
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