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  • #16
    on a non-forced induction car, the bellmouths are absolutely critical for intake efficiency, that is assuming everything else flows well, the engine will create vacuum, the air will try to fill it, being that it's a suck not a blow, as long as the ports are part of a large chamber or fully exposed they will evenly suck the air in..... here you truly never have to worry about exceeding 100% of the bellmouth, the diameter of the runners are the maximum

    in a forced induction scenario, the flow is more complicated, since you compress the air, the air will go wherever it can as quickly as it can, and that's where the problems start, it might be easier or quicker to go one way, and that will lead to lean cylinders.... this is why log manifolds always have a dome or otherwise protruding end beyond the last port, as the pressure tries to force it's way to the end and make a direction change, you would be over-flowing the last port and much less on the first, the extra dead-end does two things, it stops the forward momentum of the bulk of the air and the pressure waves will be directed back towards the front.... and the air will split itself apart at each port

    pressure fronts and reflections do play a role in forced induction efficiency, and the simplest way to cure it is seperate the ports with longer runners and/or less chamber volume.... aside from that, tuning and shaping will always lead to an efficiency band just like the turbo itself, what works well at steady flow might not be optimal for quickly rising boost.... you could very well design something that will help out the low boost and give you power sooner that will limit you at high boost

    engineers and aftermarket companies all guess and test, everyone has their own tricks, their own truisms, theories and whatever baggage they carry, the fluid modelling is done after the basic design, and is used to tweak it based on what they find

    modern engines run closer to the safety threshold than before, design and manufacturing have improved, but so has engine management, there are hardly any cars not equiped with temperature and knock monitoring to stay in the safe zone... so even if they have problems they can adjust quickly and keep it like that as long as needed

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    • #17
      Very interesting... thanks for the info man!
      8.5 custom arias pistons (.020 over)
      eagle rods
      t70 turbo (man was that a squeeze)
      38 mm external wastegate
      mild port/polish
      3 angle valve job
      custom intercooler piping
      twin external intakes with z32 maf
      rad moved back
      3" exhaust with only a resonator
      romulator
      420cc injectors
      custom body work, homemade oil lines and fittings..
      walbro 255lph in-line fuel pump.... and lots of headaches... lol

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      • #18
        G-E:

        Good info man. Much appreciated here.

        As you stated, engineers and everyday guys like us have our own ideas about air flow, be it right, wrong or somewhere in between. The whole thing is really a science based on the application and the desired results.

        Again, good stuff, thanks. :wink:
        Just stand back and throw money.
        Performance costs money.
        Reliable performance costs more.

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