Torque Cars

How to lower the engines compression ratio

Discussion in 'Engine questions' started by obi_waynne, 31 December 2014.

  1. obi_waynne

    obi_waynne Administrator Staff Member Moderator

    Messages:
    41,082
    From:
    Deal, Kent UK
    Car:
    A3 1.4 TFSI 150 COD
    Reducing the compression ratio is required if you want to run a high boost supercharged engine. High compression NASP engines are quite efficient but when adding forced induction you want to lower the compression ratio. The compression ratio has a dramatic effect on an engines performance and the problem of knock, (where the air fuel mix prematurely ignites) is controlled to a large degree by the compression ratio.

    Continue reading... or post your comments below on this article.
     
  2. TCJBOLDIE

    TCJBOLDIE Torque King

    Messages:
    4,635
    From:
    Brisbane
    Car:
    JB Starion
    To low CR in a turbo car makes it sluggish off boost but can cope with higher boost levels.
    My car has 8.7-1 static CR and if's fine off boost.
    IMO it comes down to tune/mapping with any turboed car AND the quality of fuel used regardless of CR

    What is "high " boost I have 20 psi and the Yanks call that low as they seem to use 25-40 lbs in DD cars ?
     
  3. lostviking

    lostviking Wrench Pro

    Messages:
    20
    From:
    San Diego
    Car:
    2015 Optima LX
    Thicker head gasket is the first thing that comes to mind. Polishing the cumbustion chambers also will remove a small amount of metal and enlarge them. You can recess the valves a bit also. Stuff like that can move the compression around up to a point (ratio point).
     
  4. HDi fun

    HDi fun TC ModFather

    Messages:
    15,384
    From:
    Buckinghamshire UK
    Car:
    Passat 2.0 TDi
    Loosen the head bolts :)
     
    Ronbros likes this.
  5. TCJBOLDIE

    TCJBOLDIE Torque King

    Messages:
    4,635
    From:
    Brisbane
    Car:
    JB Starion
    ^^^ .V( there's always one :lol:

    Fit the correct low compression pistons |B
     
    TAZ67 and Ronbros like this.
  6. TAZ67

    TAZ67 New member

    Messages:
    7
    From:
    Scotland
    Car:
    Vauxhall Astra mk4
    The best way is to get proper low compression pistons and having a low squish/quench area by keeping the piston to head clearance no more than 1mm, helps to reduce detonation. Also making sure that any sharp edges are reduced in head and pistons.
     
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