.:: ENGINE CYL-HEAD WITH NOVEL CROSS-VALVE ARRANGEMENT ::.


.:: Cross-section of the Triflux Cyl-Head ::.

The Triflux cyl-head had an innovative 16 Valve layout which, coupled with Turbo-charging, gave performance advantages compared to the std. layout. With the Triflux cyl-head, Fiat continued their advances in applying boosting techniques to combustion engines, a unremitting tradition started in 1923 by Vittorio Jano who fitted the first Volumetric compressor to a competition vehicle.

.:: "Triflux" cross-valve arrangement: from 2+2 to 2 x 2::.

In order to achieve :
  • High power/cubic capacity ;
  • Efficient combustion ;
  • Low specific fuel consumption.


  • The 4-valve/cylinder with angled valves to create a hemispherical combustion chamber, with a centrally positioned spark-plug, is commonly agreed to be best compromise for an IC gasoline engine.
    The standard valve arrangement is to place the valves in two rows, with all the inlet valves on one side of the head and the exhaust valves on the opposing side, to create the standard "cross-flow" cyl-head. Therefore, the Inlet manifold is positioned on one side of head, feeding the charge air to all inlet valves, and the Exhaust manifold is on the opposing side.
    This arrangement is carried over from naturally aspirated (NA) engines also to turbo-charged (TC) engines. On a high-performance engine, the TC must be near the exhaust valves to recuperate the maximum energy from the exhaust gases and is normally quite large, obstructing the complete length of the exhaust ports. The ideal arrangement to avoid Turbo-lag, caused by the high inertia of a large turbine, would be to have two smaller TC's, but the available space and requisite complex manifold design to get the best through-flow complicates this layout on 4cyl-engines (some 6 cylinder engines use this design). At the time of design of the Triflux, no in-line engines with cross-flow heads were able to run more than one TC.
    To circumvent this problem, Abarth technicians developed a new valve-layout, optimized to allow the use of two TC's. The valves are arranged in a crossed formation, so that each side of the cyl-head alternates inlet and exhaust valves. Therefore, there is an exhaust manifold, connected to each cylinder via one exhaust-valve, on each side of the cyl-head. The inlet ports are connected to a central vertical manifold. This configuration was termed F.I.D. by Fiat and patented. Many configurations were envisaged in this patent, and the one that was chosen for the final design had a single inlet valve port dividing just before the two inlet valves, leaving just enough room for the spark-plug. Since the gas-flows were three (two lateral Exhaust, and one vertical - Intake) , this head was named TRIFLUX and this name was also deposited by Fiat. The valves are actuated by two camshafts, which have alternating profiles for the respective staggered Intake and Exhaust valves.

    .:: Advantages of the Triflux cyl-head arrangement ::.

    With respect to the convential 4 valve/cyl head, the TRIFLUX had several further performance advantages in addition to the layout improvement described above.


    .:: TRIFLUX head advantages ::.


    A cross-flow cyl-head has a cold (intake) and hot (exhaust) side, creating possible thermal expansion deformation and increased risk of local hot-spots causing detonation and cooling difficulties. The Triflux head has a more linear temperature distribution. The alternating layout of the Inlet/Exhaust valves has the same effects. The cooling fluid flow through the cylinder head is also linear, with four passages through the head (one per cylinder) The intake and exhaust manifolds layouts are optimised :

  • Exhaust manifolds are symmetrical ;
  • An optimised wastegate for the TC is possible, or with variable-geometry TC, the wastegate can possibly be eliminated altogether ;
  • The space around the engine cylinder-head and block can be used to create the best flow-paths, radii and speeds for the air-flow with no obstructions, optimizing the engine-performance with tuning of the pipe lengths and resonance frequencies.
  • The TC compressor and intercooler hose and pipe layout can be symmetrical and feeds a single air intake manifold.
  • The space around the engine cylinder-head and block can be used to create the best flow-paths, radii and speeds for the air-flow with no obstructions, optimizing the engine-performance with tuning of the pipe lengths and resonance frequencies.
  • Possibility of modular boosting. The exhaust gas flow from the cyl-head can be directed to a single TC at low engine rpm, permitting a high boost and subsequent high engine-torque to be generated even at low-speeds. At higher engine rpms, when sufficient engine exhaust gas is being generated, the second TC can be unblocked, and both TCs together produce higher top-end power. The two TCs can also be sized differently. The fitting of a smaller TC with lower rotational inertia allows minimum turbo-lag, and the larger TC allows extreme top-end power. The Triflux head, with a corresponding valving arrangement allows management of the exhaust gases to create this responsive system.



  • .:: The twin TC and twin Intercooler arrangement fitted to the Triflux cyl-head ::.


    As is illustrated, at low engine rpm, the valve downside from the TC situated on the LHS of the engine is closed, therefore all the exhaust gas is forced to exit the cyl-head through the RHS TC, which has also it's wastegate completely closed. This allows rapid spin-up of the RHS TC. At higher RPMs, the LHS valve is also opened, and the LHS TC enters into function


    Layout for modular Turbo-charging

    1 - Flow regulating valve for LHS intake air compressor
    2 Flow regulating valve for LHS exhaust gas turbine
    3 Wastegate valve LHS TC
    4 LHS TC
    5 RHS TC
    3 Wastegate valve RHS TC

    .:: APPLICATION ::.

    The Triflux head was ideally suited to competition vehicles required extremely high outputs.
    A smaller lighter engine could be used (4, 5 cylinders maximum) whilst still using two TCs to produce the equivalent power of a 6-8 cyl NA engine, due to the above additional advantages, whilst retaining the good basis of the traditional 4-Valve/cyl layout and combustion chamber.



    .:: PATENT ::.


    .:: The ECV triflux engine patent registered by FIAT AUTO S.p.A. on 5th december 1986 ::.


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