Cx's Flawed Torque Curve - Twin Peaks?
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Thread: Cx's Flawed Torque Curve - Twin Peaks?

  1. #1
    Join Date
    Feb 2015
    Northern Ireland

    Default Cx's Flawed Torque Curve - Twin Peaks?

    The DS 2.3L efi engine has a single peak torque of 144 ft.lbs @2500 rpm before dropping off.


    The Cx 2400 GTI engine, which is the same engine as the DS 2.3L efi engine, but with L-Jetronic injection instead of D-Jetronic and differences to the intake and exhaust plenum design, has a max torque of 145 @3600 rpm, but I cannot say whether this has a single or twin peak torque curve like the CX 2500 GTI engine.

    The Cx 2500 GTI engine appears to only differ only from the Cx 2400 GTI engine by size and slight differences in valve duration and valve timings, but unlike both of the above, has a twin max torque curve of 146 ft.lbs @2500 rpm & 152 ft.lbs @4000 rpm, why should this be?

    One suggestion is that a twin peak torque engine has a design flaw affecting torque in the 2500 - 4000 rpm range, which should have only a single torque peak curve, can anyone explain what has caused the rpm change in peak torque between the DS and Cx for the 2.3L engines and the twin peak to occur in the Cx 2500 GTI engine power curve.

    Whereas the differences between the DS 2.3L efi and Cx 2400 GTI engine power curves might be explained by the differences to the intake and exhaust plenum designs, I am at a loss to explain the reason for the twin peak torque curve, can anyone provide any insight as to why this might be?

    References, Cx Manual S1 vol1 and Cx Manual S2 online pdfs and

  2. #2
    Fellow Frogger!
    Join Date
    Sep 2001


    At a cursory glance it appears the 2500 Gti has only one torque peak, 152lb/ft @ 4,000 rpm. Any lesser torque is below peak. The second torque figure is very close to the DS torque and seems to me that someone has got confused and quoted the wrong torque figure. It is common for technical writers to look up information from other sources and sometimes misinterpret it. Once a mistake is made it is easy for it to be copied by someone else and then become "fact".
    I found a similar situation with 2cv ride heights which changed between old and new models and some writers did not pick up on the change.
    shanadoo likes this.

  3. #3
    Fellow Frogger! marc61's Avatar
    Join Date
    Jul 2013
    Stamford, UK


    It may be because the 2500 was a 3 speed auto, so they tried to broaden the torque curve to help it pull reasonably well when changing up (driver wanting to accelerate swiftly rather than at max acceleration). When introduced the general opinion of large Citroens was that they were a bit sluggish (unless you floored it) so if this torque curve was intentional, maybe it was trying to address that and provide a firmer smoother pull across the mid range.

    With a 5 speed box the 23EFi will land near to peak torque if changing up at 3000-4000rpm and move swiftly, but most of the time it's capability as a damn good lugger meant it was driven that way. The 24GTi just encouraged a bit sportier driving, revving it a bit more before changing up so buyers kind of believed they were getting a better car than the D for very little change in the torque and power figures.
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

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