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Thread: SOHC vs. DOHC

  1. #21
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    Default Re: SOHC vs. DOHC

    ECU still needs to coordinate the opening & closing & when the spark plug fires.

    timing belt also comes to play.

  2. #22

    Default Re: SOHC vs. DOHC

    Quote Originally Posted by markccm
    ECU still needs to coordinate the opening & closing & when the spark plug fires.

    timing belt also comes to play.
    ahhh.. that the thing I'm looking for.. timing belt.

    The cam shaft is mechnically linked to the engine's shaft via the timing belt. when the engine shaft rotates, it turns the cam shafts which pushes the respective valves open, and the valves will close via spring action. ECU not in this loop.

    I only know the ECU only adjust the flow of fuel and air. All timing related functions are also mechnically linked to the rotation of the engine shaft via timing belt or gears.... I tink even the firing of the spark plug is not controlled by ECU, cus any mis-timed firing can cause the whole engine to self destruct. Cuz I remembered in order to tweak my car's spark plug firing.. I need to physically rotate on the the cable contacts to change the "angle" thingy.

    Or mabbe I too long no follow car technology liao.
    Last edited by CYRN; 3rd February 2006 at 12:52 PM.
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  3. #23
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    Default Re: SOHC vs. DOHC

    but if its controlled using Apexi it would require different intake of fuel or air liao, thus still require ECU control right?

  4. #24

    Default Re: SOHC vs. DOHC

    Quote Originally Posted by markccm
    but if its controlled using Apexi it would require different intake of fuel or air liao, thus still require ECU control right?
    might be.. I'm not that conversant with the current technologies implemented on cars liao.

    I juz tot some safety convention on engine design are still strictly followed... 1 cylinder misfire, you car might jerk, 1 cylinger misfire @ 3000/(num of cylinders your engine have) is gonna kill the engine, the entire bank of cylinders misfires... you car can take part in FW display laio...but it might seem otherwise.

    Only thing I can check is that: are timing belts as important in current cars. If yes, then most probably it ment to avoid mistiming of the firing sequence and taking part in FW displays.
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  5. #25
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    Default Re: SOHC vs. DOHC

    yup, that's y the more the ECU need to control it so as to prevent mis-firing.

  6. #26

    Default Re: SOHC vs. DOHC

    Quote Originally Posted by markccm
    yup, that's y the more the ECU need to control it so as to prevent mis-firing.
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  7. #27

    Default Re: SOHC vs. DOHC

    I don't mean to be rude here, but I see too many errors in this thread of discussion.

    1) SOHC benefit over DOHC: Lower cost of manufacturing and engineering. Period.

    2) DOHC benefit over SOHC: Easier to manage valve opening/closing overlap and valve lift control, and easier to engineer for more than 4 valves per cylinder. This benefit performance.

    3) Both SOHC and DOHC can control 4 valves per cylinder, and both pass stringent emission control equally well. There is not significant difference on fuel consumption.

    4) Many people think that DOHC is not economical on petrol. Since DOHC is mainly tuned for performance, of course it will not be as economical as a SOHC engine that is tuned for economical running. The difference in petrol consumption is therefore the function of TUNING, and TUNING only.

    5) ECU is a box that contains multiple processors. It is the brain of the car. It controls everything including firing, idling, air-flow, gear-changing (for auto gear), cam-angle, radiator fan start/stop and even prevent engine from being over-revved. What those tuninnig parts (such as Apexi) do is only altering the mapping of parameters. They are not ECU-replacement. A ECU-replacement costs thousand of dollars.

    6) Things like timining belt/chain is used to ensure that the valves are lifted and lowered according to the rise/fall of the piston. They are mechanically aligned and need no interferenece from ECU.

    7) For ECU to function, there are many sensors that provide streams of data feed to the ECU. Such sensors include knock sensors, valve-lift angle sensor, water and oil temp sensors, oil pressure sensor, RPM sensor, gear position sensor, air-flow sensor, throttle position sensor, air temp sensor, fan-speed sensor, fuel supply/pressure sensor, brake hydraulic sensor, ... etc. Some time it works with sub-systems such as ABS brake and even SRS so that fuel supply is cut when there is a head-on collision.

    8) For most continental cars and some Japanese cars (especially all modern Honda, Mazda and Subaru), the ECU also has sophisticated immobiliser/theft-prevention features. For Nissan, Toyota and Mitsubishi, many are still not equipped with one. Not sure about Korean cars.

    We can spend many more pages on this topic. But I think I better stop here.

  8. #28

    Default Re: SOHC vs. DOHC

    Wow... the real expert is here.

    Thanks for correcting.
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  9. #29
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    Default Re: SOHC vs. DOHC

    wah professional sia....

    we all better siam

  10. #30

    Default Re: SOHC vs. DOHC

    I'm not pro. Just an enthusiast for too many decades

    Anyway, someone told me that I am wrong about point 8. Many Nissan, Toyota and Mitsubishi are equipped with immobilizer. If what was told to me is true, I apologise for giving out wrong information here.

  11. #31

    Default Re: SOHC vs. DOHC

    For modern cars with variable valve timing technology, ECU does control the valve opening/closing timing to a certain extend.
    But for older mechanical cars without computing powers (no ECU to begin with), all valve timings are mechanically controlled.

  12. #32
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    Default Re: SOHC vs. DOHC

    Sorry to gatecrash, between the Daihatsu Sirion, Suzuki Swift and Hyundai Getz, which is the most fuel efficient? Considering between these few closely priced cars at the moment.

  13. #33
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    Default Re: SOHC vs. DOHC

    Quote Originally Posted by tao
    Sorry to gatecrash, between the Daihatsu Sirion, Suzuki Swift and Hyundai Getz, which is the most fuel efficient? Considering between these few closely priced cars at the moment.
    my guess purely... Suzuki Swift... follow by Daihatsu Sirlion Steak (hehe)... den Hyundai Getz...
    Logging Off. "You have 2,631 messages stored, of a total 400 allowed." don't PM me.

  14. #34
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    Default Re: SOHC vs. DOHC

    Quote Originally Posted by beachbum
    For modern cars with variable valve timing technology, ECU does control the valve opening/closing timing to a certain extend.
    But for older mechanical cars without computing powers (no ECU to begin with), all valve timings are mechanically controlled.
    yup that's wat i tot so also.

    VVT-i, Vtec, i-Vtec, Mivec, VVT.

    all these valves are in a variable timing.
    when to lift & close.

    so should be electronically controlled.

  15. #35
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    Default Re: SOHC vs. DOHC

    In camera term
    CCD vs CMOS which is better?

  16. #36
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    Default Re: SOHC vs. DOHC

    Quote Originally Posted by jeryltan
    The CVT gearbox is weak.. I used to drive the Civic EK3 VTi, changed gearbox twice over 7 yrs.. My current Civic ES8 VTi, just changed CVT gearbox at 3 yrs.. I've also have friends driving Fit / Jazz who's had problem with their CVT, including the Mitsubishi Lancer CVT..
    Wah! The CVT engines so fragile one ah! I am actually looking at the CVT of the NISSAN Latio (Premium).

  17. #37
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    Default Re: SOHC vs. DOHC

    Quote Originally Posted by jeryltan
    The CVT gearbox is weak.. I used to drive the Civic EK3 VTi, changed gearbox twice over 7 yrs.. My current Civic ES8 VTi, just changed CVT gearbox at 3 yrs.. I've also have friends driving Fit / Jazz who's had problem with their CVT, including the Mitsubishi Lancer CVT..
    jeryltan, when you changed the gearbox, it is because the belt of the CVT needed to be changed? Was that the primary reason why the gearbox needed changing?

  18. #38

    Default Re: SOHC vs. DOHC

    think what happened to the older generation of civics (not the new 8th generation) is that there's problems like slippage in the torque convertor, eg, when put to Drive mode, engine RPM goes up but the pickup is significantly slower. the feeling is like wheelspin.

    AFAIK, honda customers owning CVT autoboxes are hit with this problem. and the agent kept changing with a new CVT box and the problem still persists after some time. I heard the last resort was to replace the CVT box with another version that is not designed for the model that the vehicle was intended. something like changing the 1DM2N's cmos imager with a 1D ccd

    hence, the agent got bitten real terok by this CVT thingy and immediately stopped importing hondas using CVT from japan. of cos, thru continuous R&D, they may have solved the problem.

    Quote Originally Posted by Canew
    jeryltan, when you changed the gearbox, it is because the belt of the CVT needed to be changed? Was that the primary reason why the gearbox needed changing?
    Last edited by user12343; 8th February 2006 at 07:32 PM.

  19. #39

    Default Re: SOHC vs. DOHC

    Not sure what was thge problem.. But definitely not start clutch..

    Quote Originally Posted by Canew
    jeryltan, when you changed the gearbox, it is because the belt of the CVT needed to be changed? Was that the primary reason why the gearbox needed changing?

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