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Minor Issues - Others

Discussion in 'Technical' started by gururajanv, Jun 2, 2010.

  1. Sam

    Sam Amatore

    Interesting! I was wondering whether FIAT has really gone very much defensive for MJDs and whether DDIS and QuadraJet can be revved more than MJDs. Also engine goes super loud when approaching 2.5k RPM. Will this same case be with other variants (DDIS/QuadraJet) too?

    I was trying to find the gear ratios for Fiat MJD 75 HP however couldnt locate in the manual. After some extensive research on internet somewhere (italiaspeed.com: Fiat Grande Punto) I got hold of its specs which are as below.

    1st Gear : 3.909:1
    2nd Gear : 2.238:1
    3rd Gear : 1.444:1
    4th Gear : 1.029:1
    5th Gear : 0.767:1
    Reverse : 3.909:1

    Final drive ratio : 3.563

    Essentially 4th matches engine RPM and 5th is overdrive while first and second seems longer. Based on this and wheel diameters we can presume speeds the car will make at various RPMs (Gear Ratio Speed Calculator). So I calculated speed of the car in 5th gear at various RPMs.

    1500 : 60 kmph
    2000 : 80 kmph
    2500 : 100 kmph
    3000 : 120 kmph
    4000 : 160 kmph
    5000 : 200 kmph (redline)
    6000 : 240 kmph (engine about to burst if no auto fuel cut off kicks in :))
    7000 : 280 kmph (engine almost committed suicide the injectors have failed and valves broken :D)

    The car manual states that max speed any variant (except 1.2) can make is 165 kmph which falls probably at 4500 RPM (BTW max power ie 75 hp is generated at 4000 rpm) and probably anything beyond 4.5k can be considered as redlining the engine. Not sure its my conclusion after really googling around to find relations between rpm, torque, power and engine components ;)
  2. Sam

    Sam Amatore

    Double clutching in modern gearboxes with synchromesh


    Couple of days back I was introduced with the term called as "double clutching". I googled around to find what was it all about and found that it is(was) a technique to change the gears of the car smoothly (gearbox rpm matching to engine rpm so as gear teeth don't slip or kill themselves) for gearboxes without synchromesh and were called "crashboxes".

    However, I have seen people using it in modern cars and there are videos on youtube where people have demonstrated how smooth it becomes changing a gear with this technique even with modern gearbox but it takes real practice. Now my question, although I personally find this technique little ugly and impractical in modern traffic but will there by any real benefit if it use it in my Punto or I will just fry my clutch plates?


  3. gurjinder

    gurjinder Staff Member Janitor

    Double clutching and rev-matching are two different things.

    And both not needed in our FIATs. :)
  4. Sam

    Sam Amatore

    Thanks gurjinder for replying. I thought double clutching was actually rev (rpm) matching for unsynchronized gear boxes. This is what wiki says. And although you are right in quoting that its not needed in our FIATs but I was actually keen on knowing whether there be any real benefit if we practice on ours? My common sense says NO but still wanted to know what experts (like you :)) think.

    Wiki (Double clutch - Wikipedia, the free encyclopedia)

    A double clutch (also called a double declutch) is a driving procedure primarily used for vehicles with an unsynchronized manual transmission. The double clutching technique involves the following steps:

    The throttle is released, the clutch pedal is pressed, and the gearbox is shifted into neutral.

    The clutch pedal is then released, the driver matches the engine RPM to the gear RPM either by throttle (when changing down) or wait for RPM to decrease (when changing up) until they are at a level suitable for shifting into the next gear.

    At the moment when the revs between engine and gear are closely matched, the driver then instantly depresses the clutch again and shifts into the next gear. The whole maneuver can, with practice, take no more than a fraction of a second, and the result is a very smooth gear change.
  5. ENKI

    ENKI Esperto

    I don't know how much FIAT is right about that 165 & what i am sensing from the above reply is a claim that MJD can't rev past 4500 rpm:mrgreen:. Not sure about 75 hp but 90 HP does. The other Diesels engines do rev much better & to the likeness of @5500rpm in stock cars as far as India is concerned. Pls refer below link for Fabia 1.2 TDI testing & their top speed.

    Road Test: Skoda Fabia - CarWale

    Well you can scare yourself as much as you wish by those 6000/7000 RPM engine blow ups but that's not diesel engine's RPM. We will talk realistic with stock car's RPMs only. If 1.2 TDI can rev upto 5500 rpm, 90 HP Multijet can surely manage happily (if FIAT would have allowed). May be they wanted to maintain longest service interval & best durability. It doesn't move 1 mm ahead of 5100 rpm. I had my 90 HP on 155 kmph@4th gear@5100 RPM & sudden jerks of fuel cuts. Even then MJD is one hell bent idiot & you can have that enough fun with-in those 5100 rpm. Now i don't know what would be the speed at 5100 RPM in 5th gear but i have taken my 90 HP to just slightly over 185 Km hr. Didn't notice the exact RPM at that moment but engine was surely about to over-revv.

    165 Kmph@4500 rpm is sure for 90HP any day, any time you wish.In-fact,if you start a deep breath @120 & blow it out, you will cross 165, it's that easy. Technically you are correct about the data here but i am sure there are many 90 HP owners who are equally confused on top speed claimed by FIAT (including myself). This engine becomes a total different character after 110 Km.
    Last edited by a moderator: Feb 13, 2012
  6. ENKI

    ENKI Esperto

    FIAT's new DDCT/TCT is ridiculous. It features no torque converter, it improves fuel efficiency, acceleration & emissions even when compared to manuals. Obviously it is far better than those automatics/semi automatic options which costs all these things if one prefers them over manual.
    Dual Dry clutch doesn't need any oil/lubrication, lighter & needs lesser maintenance since it works on hydraulics which FIAT has been very good into (multiair is also Hydraulic valve actuation). One clutch always remains engaged at the time of gear shifting resulting in no loss of torque/acceleration compared to other semiautomatics (It is more or less compared with VW DSG). If FIAT introduces that in even in 1.3MJD/Punto, their 0-100 kmph will at least improve by 2-3 secs due to seamless gear shift & long clutch throws of GM's ancient Gearboxes which are dumped by FIAT already in Europe long ago.So it shouldn't be a bad thing if we get DDCT here so i disagree with Gurjinder here when he says that we don't need that.

    You can refer to one latest review of TCT/DDCT & judge yourself.
    2012 Alfa Romeo Giulietta First Drive
  7. vilas iyer

    vilas iyer Novizio

    Today I touched 170 at 5000rpm on gurgaon highway . i have even tried above 6k rpm but the auto fuel cutoff kicks in at that time . It feels as if there is some thing gone wrong with the car ;)
  8. gurjinder

    gurjinder Staff Member Janitor


    The discussion is on double clutching & rev matching while shifting gears , and not double clutch transmissions! :)

  9. shashanknathani

    shashanknathani Superiore

    1.2 FIRE engine gets it cut off at around 6300-6400 rpm... I have tried the same in my car in third gear. About the fifth gear i never managed to reached the same rpm but ya i did touched 175 knph at little over 6000rpm without AC. With AC i have touched 165 at ~5600rpm.

    I guess for 1.2 FIRE Petrol engine the max speed would be around 175-180 ish and rpm is surely 6300-6400 mark. another point is that the engine makes hell lot of noise post 5500 rpm. till 5500 it feels smooth and not much noise or vibrations are felt inside.
  10. Italia-Linea

    Italia-Linea Staff Member Janitor

    LOL, yeah cast iron is hard.

    but its not like the way we are thinking.

    when the rotor is turned new surface is exposed. with constant or excessive heat generated from brake pads the layer again undergoes metallurgic changes and becomes hard. i.e the brinell hardness number increases like it does in case of heat treatment.

    the brake discs are mostly manufactured from SG iron.

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