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Understanding FIRE Engine performance

Discussion in 'Technical' started by RaviInTfi, Dec 11, 2015.

  1. RaviInTfi

    RaviInTfi Amatore

    Grande Punto 1.4
    When I read that the 1.4 FIRE Engine has the feature called PDA - Port Deactivation, I did a bit of research on FIRE engines and found a set of interesting info in these links




    The 1.4 16V FIRE engine with Port Deactivation is called the StarJet (an interesting analog to the T-Jet) its specified with a highway fuel consumption of almost 19kmpl (5.2L for 100km)

    Of the interest is also the fact that FIAT has the 8V SOHC version of the same 1.4L FIRE engine capable of 77bhp and the same peak torque of 115Nm at 3000rpm instead of 4500/4250rpm.

    Aside: Like all the 8V designs there is good torque in the low-end, but not much top end power. The 1.4 8V FIRE would have been something like the 1.2 8V, except more powerful.

    So in hindsight: perhaps it was a mistake of FIAT to not have this engine in the lineup for India. For sure this engine would had better driveability and fuel economy.

    The speed-torque maps of the engines explains something else:


    The graphs clearly explains why the 75bhp Multijet can outrun the so-called more powerful 90bhp petrol. At the same engine rpm in the power band the diesel has access to higher power (though this powerband is narrow for the diesel). To access the 90bhp of power in petrol one has to rev to 6000rpm. Whereas the peak power of a diesel is accessible at 4000rpm.

    Therefore even with 90bhp of power of a 1.4 FIRE, it remains inaccessible in normal running making it ironically less powerful than what the figures indicate.

    Coming back to the PDA feature of the "StarJet" engine:

    This is a feature that blocks out one of the intake values (artificially throttling) the airsupply. I found more info on this on t-bhp (found also in Beat) so I quote it here:

    "However there is a different technology involved and that is called Port deactivation. Beat has 2 intake valves per cylinder. In the intake manifold there are 2 passages (generally there is only 1) for the 2 intake valves. Now when pressure in the intake manifold is low or in other words you are not giving too much gas, one of the passages in the intake manifold (intake port) is blocked. So Although the both the valves are physically opening air is coming only through 1. Port deactivation happens in low load. Has nothing to do with RPM.
    Advantage is if you block one of the path, velocity through the other will increase & there will be more turbulence in the combustion chamber. Net result: better efficiency

    A picture is always better to understand so here is the link:


    Notice the turbulence when one of the intake port is blocked. This creates better combustion and lower fuel combustion at lower rpms. But I think it also makes for not so free revving of the engine below 2000rpm.

    Another feature of the 1.4 is the is long stroke of 84mm. This around 0.5 inch more than 1.2. This makes for great thermal efficiency and in turn good torque and fuel consumption, but not so free revving sporty nature!
  2. RaviInTfi

    RaviInTfi Amatore

    Grande Punto 1.4
    A comparison of other 1.4 litre petrol engines in the Indian market :

    The G4FA is a 1.4 L (1396 cc) engine. Bore is 77.0 mm and stroke is 75 mm. It has MPI and makes 109 hp (81 kW; 111 PS) at 6,300 rpm and 101 lb·ft (137 N·m) of torque at 4,200 rpm. Power is dropped to 99 hp (74 kW; 100 PS) at 5,500 rpm and 100 lb·ft (136 N·m) of torque at 4,200 rpm in the Hyundai i20.


    Type K14B
    Number of cylinders 4
    Number of valves 16
    Piston displacement cm3 1,372
    Bore x Stroke mm 73.0 mm x 82.0 mm
    Compression ratio 10.0
    Maximum output kw/rpm 70/6000 rpm
    Maximum torque Nm/rpm 130/4000 rpm
    Fuel distribution Multipoint injection

    And here is the FIAT engine European specs:
    BORE x STROKE 72.0 x 84.0 mm ( 2.83 x 3.31 inches)
    NUMBER OF VALVES 16 Valves
    MAXIMUM POWER - OUTPUT - HORSEPOWER 95 PS (94 bhp) (70 kW) @ 6000 rpm
    MAXIMUM TORQUE 127 Nm (93 lb.ft) @ 4500 rpm

    Tuning of the FIRE engine in India is nothing but bringing it to the European state of tune

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