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Thread: Air Intake System Design

  1. #1

    Air Intake System Design

    Hi guys,

    I'm designing my car team's air intake and I have been struggling to find solid information, including reliable calculations with variables explained, for both runner length as well as plenum volume and design. We are working with a Honda TRX 450 cc single cylinder engine and most plenum designs are based on four cylinder engines. Does anybody have any helpful resource (website, book, etc) that has detailed information on plenum volume and design (with calculations) as well as runner length calculations?

    Also, if anyone knows, if the runner length includes a bend, should the length be modified to account for this?


  2. #2
    Senior Member
    Join Date
    Oct 2009
    San Antonio, TX
    Howdy Boydlaf. You should introduce yourself and tell us what school/team you're from.

    The throttle-restrictor-plenum intake design is fairly unique to FSAE and you won't find academic plug-and-play design guidelines out there (plenum volume rules-of-thumb are especially bad). For books, I would suggest Blair's "Design and Simulation of Four-Stroke Engines" and Bell's "Four Stroke Performance Tuning". Runner geometry will closely match theory with sufficient plenum volume to provide a consistent "atmosphere" throughout the induction event. Plenum volume is best left to simulation and physical testing.

    From the acoustic wave tuning/ramming perspective, bends in the runner do not matter. Length and cross-section geometrical discontinuity does.
    Matt Birt
    Engine Calibration and Performance Engineer, Enovation Controls
    Former Powertrain Lead, Kettering University CSC/FSAE team
    1st place Fuel Efficiency 2013 FSAE, FSAE West, Formula North
    1st place overall 2014 Clean Snowmobile Challenge

  3. #3
    Oldie but a goodie, not least because the initial chapter goes through base theory really well.


    Get a copy of the Bosch auto handbook too.

    The FSAE restrictor design is not that unique. Just view it as a nodal pressure network, which also has implications for where you place the intake (e.g. your cylinder pressures at TDC are as much a function of CR as they are inlet pressure and losses along the way).

    If you don't have access to a flow bench, try building one - for a single it's not going to be too hard. You'll learn a ton from it and it's probably more useful than CFD at the FSAE level.

    Also for a single from a 1D gas analysis perspective - copies of Lotus Engine Simulator are free (I think, does someone need to correct me here?). Bear in mind that 1D gas analysis is not a complete picture, but does capture transient behaviours once you have the quasi-static stuff (pressure loss behaviours) understood.

    If you are looking for 'insert numbers into spreadsheet, get instant design' type answer I'm afraid it's not just that simple, however intake/exhaust design (they go together) are an excellent challenge. Lots of fun to design, not too hard to modify and you have a very real effect on how the car drives and feels.

    Plenty of ways to test and validate what's what that aren't too expensive.

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