the "no replacement for displacement" thread

Discussion in 'The Garage' started by tooslow, Jun 10, 2007.

  1. tooslow

    tooslow Active Member

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    i know everyones heard the age old comment and everyone has there own thoughts and opinions about it.

    share yours, i know this topic tends to lead to a immature "e-fight" so lets not go there with this thread.

    last time i put though into it, this is what i came up with.

    my thoughts-

    for the most part displacement is thought of as being equal to the volume of each of the engines cylinders. but, thats not the true definition of displacement.

    displacement is just what it sounds like, the amount of air an engine displaces during one cycle. on a 4 stroke, thats 2 revolutions.

    for naturally aspirated engines every 2 revolutions the amount of air pumped through the engine is directly related to the volume of the cylinders therefor its displacement can be said to be exactly that of the volume of its cylinders.

    for forced induction engines the amount of air displaced every 2 revolutions is not the same as the volumetric amount of its cylinders. Because air is being forced into the engine that air must also exit the engine. since the definition for displacement is the amount of air displaced by an engine during 2 revolutions and a forced induction engine processes more air per every 2 revolutions than the volumetric amount of its cylinders the engine's displacement and cylinder volume are not directly related.

    with that truth said, one more truth needs to be addressed.

    Since the amount of air processed by an engine directly relates to the amount of fuel an engine can process, the more an engine displaces the more powerful it may be. Therefore, there is no replacement for displacement.
     
  2. 19mustang95

    19mustang95 Legend

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    the replacement for displacement is forced induction....
     
  3. tooslow

    tooslow Active Member

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    :-[

    to me, thats a form of displacement.
     
  4. DropTopPony

    DropTopPony Administrator Staff Member Admin SN95 Supporter

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    Tell the no replacement for displacement argument to the guys with 3.0 liters making a reliable 700hp...not to mention our puny 4.6 is also capable of some really high hp potential...Large displacement engines are nice and nostalgic but are not needed on street cars to make power like in the old days.
     
  5. 19mustang95

    19mustang95 Legend

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    exactly, newer 6 cyclinder motors are coming stock with more power than our 4.6 8 cyclinder motors...saddening that is. :'(
     
  6. Paul

    Paul Legend

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    It's all well and good, but you can apply forced induction to large displacement motors too.

    An extreme example - Brad Brand's Outlaw car has a twin-T88 707 ci big block that makes 1100 rwhp at 3psi and pegs the dyno (1800 rwhp) at 11 psi. Let's see a 3.0 or a 4.6 do that.


    Furthermore, my 422 ci Windsor for example can make more power with less pressure than a smaller engine. Thusly, I have more "room" for horsepower before I start needing exotic fuel and such. All FI does is multiply the amount of power that can be made naturally aspirated.

    Larger motors can make more power more easily naturally aspirated. Thusly, they make more power with >1 atmosphere as well. There is no replacement for displacement; technology works here too.

    Paul.
     
  7. tooslow

    tooslow Active Member

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    true true.

    i just look into things deeper than i should really.

    the way i think about it for the most part. a 3.0l with a 60mm turbo does not "displace" 3l or air every 2 revs. it displaces much much more ait than that. so in my eyes it isn't a 3.0l anymore.
     
  8. Paul

    Paul Legend

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    It's still a 3.0L in so many ways.

    For example, my friend now has a 76mm single turbo Supra. It runs 14.1 @ 114+ mph. It makes 450 rwhp with a peaky, high-rpm torque curve.

    His old car car was a 316 ci Mustang with a GT42 (76) turbo. It ran 10.25 @ 141 mph. It made 725 rwhp with a broad, flat torque curve.

    Area under the curve (which is much more important than peak horsepower, especially for streetcars) will be much larger for a larger motor than a smaller one.

    Paul.
     
  9. tooslow

    tooslow Active Member

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    the volume of the cylinders added together doesn't change with boost, so most people consider an engine to be a "3.0" regardless.

    the word displacement throws that thought out the window for my. an engine's air displacement isn't always the same as its cyinder's volume.

    1 atmosphere is roughly 14.7psi right? so a 3.0 with 25psi of boost would actually "displace" 8.2l or air every 2 revolutions. '((3.0/14.7)*25)+3.0'

    a whole new way of looking at it.

    not saying i'm right, just my outlook.
     
  10. AaRoN

    AaRoN King Post Whore

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    power adders have nothing to do with displacement. that saying refers to factory displacement.
     
  11. 94Vert

    94Vert Active Member

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    That seems a little odd. 450 hp and only 14.1
     
  12. Paul

    Paul Legend

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    It had a sweet 2.6 60' time too. LMAO. Supras suck. They make power for about 500 rpm. :rollinglaugh: I almost beat it with my near-stock full weight coupe.
     
  13. Paul

    Paul Legend

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    It's not that simple. The characteristics of a pressurized small motor are not the same as those of an equivalent-displacement (according to your statements) large motor.

    Long story short, it's apples to hand grenades.

    Paul.
     
  14. 97vertstang

    97vertstang Well-Known Member

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    so true!!!!
    u cant beat cubic inches
     
  15. 95PGTTech

    95PGTTech Well-Known Member

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    I agree with your statement that forced induction is displacement, but I also agree with previous comments that the same amounts of forced induction on large and small motors play big differences.

    the saying was a stupid one, in a stupid time, said by stupid people - there are many effective methods to going fast; an engine is an air pump, and anything you can do to improve the volume or the efficiency of air it can send through will increase your power, acceleration, speed, etc.
     
  16. tooslow

    tooslow Active Member

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    haha, that pretty much sums it all up.
     
  17. Paul

    Paul Legend

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    The saying holds true today, and will until the end of eternity for internal combustion engines.

    It is not stupid. It is fact. Yes, there are many ways to go fast, but the fact remains - there is no replacement for displacement.
     
  18. TRUUBLE

    TRUUBLE -Never Forget-

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    This is a timely thread because I've decided to go forced induction on my alky 427 next season (or may be earlier).

    I'm betting that it's going to be a lot easier to make big power than it was with my blown 331.

    FWIW, my 427 NA alky motor is making more power than my blown 331 did with 15 pounds of boost.
     
  19. uncltrvlnmatt

    uncltrvlnmatt Legend

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    If bigger is better, than to much is just right!

    If you get a 289 and a 351W and build them exactly the same, the 351 will whoop the 289's ass every time. Same goes with the 4.6 and the 5.4, the 390 and the 427, the 429 and the 460.

    I used these examples because they are the same engine family.
     
  20. Rantheman

    Rantheman Well-Known Member

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    displacement does play a big roll but that not the only thing it's all in vehicle weight traction what motor setup are you f/i i mean you got a honda with 350 hp with a turbo and then a 350 small block with 400 hp-425 the ratio maybe close so i think of it more as in hp to weight ratio but you can build a lot of power off of c/i