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  1. #1
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    Default Top end performance.

    Something about my Q4 has bugged me for quite a while now, infact since I had the majority of work done on it and had the chip written on a rolling road.

    Peak power arrives really quite low down, 5400rpm or there abouts. Now the car was running without Cats, and with a different (larger) turbo. Works well around town, but lacks top end power and grunt on track etc.

    Anyone got any ideas about how to address this and open up the top end a bit more.

    Thanks.
    1994 Alfa Romeo 155 Q4: Dozeing in the garage.
    2009 Audi A4 tdi: Everyday drive.
    1994 Alfa Romeo 155 , 1995cc Std Standard Black

  2. #2
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    Is this still an issue or you already solved it ?

    I've got no personal experience but as an armchair engineer I think 5400rpm is pretty top end for our engines
    1995 Alfa Romeo 155 Q4 , 1995 cc Standard Standard Black

  3. #3
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    I've just checked as I posted up the dyno plots for my car ages ago This Thread and max power was at 4800 rpm.
    1994 Alfa Romeo 155 Q4: Dozeing in the garage.
    2009 Audi A4 tdi: Everyday drive.
    1994 Alfa Romeo 155 , 1995cc Std Standard Black

  4. #4
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    Based on that thread I share corriedw's view on the issue and either the turbo not supplying enough air, exhaust manifold limiting turbo, exhaust too restrictive or there is boost leak which prevents your engine to reach higher numbers at the top end rpm range.
    Did you check the AFR numbers during that live road mapping ?
    1995 Alfa Romeo 155 Q4 , 1995 cc Standard Standard Black

  5. #5
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    I actually think its the injectors.

    If you look at this calculator fuel-injector-calculator you can see that with the standard injectors at 3 bar fuel pressure, they are going to be running at 85% duty cycle even to make 250 BHP.

    The turbo is a T3/T4 hybrid so should supply more air than standard, the exhaust manifold is a superspirnt so less restrictive than standard, and it runs up to 1.3 bar of boost.

    From the Air side of things it should be fine, hovever, the injectors, 7 years old at that point so far from perfect, are already theoretically struggling.

    The AFR looked fine on the mapping, just refused to make power at the top of the rev range.
    1994 Alfa Romeo 155 Q4: Dozeing in the garage.
    2009 Audi A4 tdi: Everyday drive.
    1994 Alfa Romeo 155 , 1995cc Std Standard Black

  6. #6
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    You are probably right, our injectors are at the safety limit 90% of duty cycle at roughtly 260bhp so it seems those are the limiting factors in your cars.
    1995 Alfa Romeo 155 Q4 , 1995 cc Standard Standard Black

  7. #7
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    Interesting problem. I make the same torque, but about 325 hp at 6600-6800 rpm with rev limit at 7050 rpm with standard internals, intercooler and injectors. However I have fitted a Wallbro 255 l/h fuel pump and the Delta Integrale fuel pressure regulator, turned up to ?? (don't remember, but as much as possible). I would check the fuel pressure, or just fit a proper fuel pump if you haven't already done that. It is one of the cheaper things to fit. If that is not the problem, I would assume something with the boost regulation. You manage to get a second peak in the dyne plot, which comes from the intake tuning and obviously there is fuel to get power from it, that confuses me.
    -
    155 Q4 -96 (Alfa Rosso 130)
    Giulietta ti -59 (.. will be "Aqua di fonte" blue/grey)
    Giulia 1600 Sprint -62 (.. will be dark grey)
    Stelvio 2.2 Q4 (Trofeo white)
    Fiat 500 TwinAir -11 ("Baby blue")
    Lotus Evora S -11 (Laser blue)

  8. #8
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    I'm ahead of you, a new Walbro 255L pump has been recently installed along with a Deatchwerks adjustable fuel pressure regulator. Once I get a few more things ironed out, I'll be looking at upping the fuel pressure as well, currently the car was setup running 2.5Bar.
    I've got a Kappa\Integrale inlet manifold to install at some point as well.
    1994 Alfa Romeo 155 Q4: Dozeing in the garage.
    2009 Audi A4 tdi: Everyday drive.
    1994 Alfa Romeo 155 , 1995cc Std Standard Black

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