1:13 vs 1:14 compression ratio and MPG loss

Discussion in 'Gen III 2010+ Prius Fuel Economy' started by cyclopathic, May 16, 2011.

  1. cyclopathic

    cyclopathic Senior Member

    Joined:
    Apr 15, 2011
    2,176
    298
    2014 Prius C
    Vehicle:
    2010 Prius
    Model:
    II
    US Prii have 1:13 compression ratio and Japanese/European have 1:14.. this is due to different minimal gasoline octane rating 85-87 (R+M) in US and 95 R in other markets.

    theoretically the loss of efficiency ~7.7%, in reality probably ~3-5%.
     
  2. Insight-I Owner

    Insight-I Owner 2006 Insight-I MT + 2011 Prius

    Joined:
    Aug 29, 2009
    505
    96
    Essex, CT
    Vehicle:
    2011 Prius
    Model:
    Two
    Are these the geometric CR's or the effective CR's? If they are geometric CR's, the effective CR's are less due to the late intake valve closing of Atkinson cycle engines like the Prius'. From Wikipedia on Atkinson cycle engines: "Note that the compression ratios shown above reflect the expansion ratio, which is the ratio of the combustion chamber volumes when the piston is at bottom dead centre and top dead centre. The effective compression ratio of the air-fuel mixture in an Atkinson cycle engine, with respect to atmospheric pressure, is lower due to the aforementioned delay in closing the intake valve."

    And is the theoretical CR-vs-efficiency comparison you are using valid for Atkinson cycle engines?

    And what sort of "efficiency" is meant: is it max HP or something more closely related to mpg?
     
  3. GrumpyCabbie

    GrumpyCabbie Senior Member

    Joined:
    Dec 14, 2009
    6,403
    1,833
    North Yorkshire, UK
    Vehicle:
    2010 Prius
    Model:
    III
    So why have different compression ratios for different markets? Why not just leave it the same - surely that would make it easier for parts etc?
     
  4. ken1784

    ken1784 SuperMID designer

    Joined:
    Dec 18, 2003
    2,894
    1,202
    Yokohama, JAPAN
    Vehicle:
    2010 Prius
    Model:
    N/A
    I don't know where you get the numbers, but JP Prius has 1:13 compression ratio.
    JP Prius spec (Japanese language only)

    Ken@Japan
     
  5. ken1784

    ken1784 SuperMID designer

    Joined:
    Dec 18, 2003
    2,894
    1,202
    Yokohama, JAPAN
    Vehicle:
    2010 Prius
    Model:
    N/A
  6. xs650

    xs650 Senior Member

    Joined:
    Jul 2, 2010
    4,525
    1,383
    Northern California
    Vehicle:
    2010 Prius
    Model:
    II
    Thanks for the link. There is a lot of other general interest info there that is semi-readable by English speakers with Google Translate
     
  7. qbee42

    qbee42 My other car is a boat

    Joined:
    Mar 2, 2006
    18,044
    2,969
    Northern Michigan
    Vehicle:
    2006 Prius
    Perhaps his manual has a compressed font.

    ;)

    Tom
     
  8. usbseawolf2000

    usbseawolf2000 HSD PhD

    Joined:
    Sep 22, 2004
    13,570
    2,514
    Fort Lee, NJ
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    Maybe he has info on the secret Gen4 Japanese model Prius. ;-)
     
  9. Lantec

    Lantec New Member

    Joined:
    May 4, 2011
    23
    3
    BC, Canada
    Vehicle:
    2010 Prius
    Model:
    V
    Actually, the octane between US and Europe/Asia is the same. But the rating system is different. It's 95 RON vs 87 (R+M). Like MPH vs KMH
     
  10. xs650

    xs650 Senior Member

    Joined:
    Jul 2, 2010
    4,525
    1,383
    Northern California
    Vehicle:
    2010 Prius
    Model:
    II
    The difference in rating systems is smaller than that.

    US 87 (R+M)/2 Octane is approximately European 91-92 R Octane.

    US 91 Octane is approximately European 95-96 Octane
     
    1 person likes this.
  11. GrumpyCabbie

    GrumpyCabbie Senior Member

    Joined:
    Dec 14, 2009
    6,403
    1,833
    North Yorkshire, UK
    Vehicle:
    2010 Prius
    Model:
    III
    Except that in Europe very few countries (if any) still offer US87/EU92 petrol.

    US91/EU95 Premium is the lowest we get and then US95?/EU98 Super is reserved for high performance cars - and it costs a small fortune!