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Thread: Engine related formulas

  1. #1
    Join Date
    Mar 2005
    Posts
    1,971

    Engine related formulas

    Here are some pretty interesting formulas you gear heads might enjoy!

    How to get Cubic Inch Displacement (CID)
    CID = .7854 x Bore squared x stroke x number of cylinders
    example: .7854 x 3.346" x 3.346" x 2.756" x 1 = 24.23 cid ( 400ex)

    How to convert to Cubic Centimeters (CC's)
    CC = .7854 x Bore (mm) x Bore (mm) x Stroke (mm) x 1 Then divide that answer by 1,000.

    How to convert to Liters
    Liters = .7854 x Bore (mm) x Bore (mm) x Stroke (mm) x 1 Then divide that by 1,000,000

    Exhaust Header Tubing Diameter
    How they figure out the way to make headers.
    Tubing Diameter = The square root of CID (cubic inch displacement) x 1900 then divide by
    Length of exhaust tubing x RPM (where it will be making most of its power).
    Example: 351 x 1900 div. by 20' x 6,000...
    Now take the sqare root of 666,900 div by 120,000 and you should get 2.36" as your answer!

    How to figure out HP and Torque loss by driving in different elevations
    HP Loss= Elevation x .03 x (vehicle rated HP) then take that answer and div. by 1,000.
    Torque Loss= Elevation x .03 x (torque) then take the answer and div by 1,000.
    Dont know your tourque use this...

    How to find Torque
    Torque= 5,252 x HP div. by RPM (your making most power at)

    How to get Horse Power
    HP = RPM x Torque div. by 5,252
    ex: 6200 x 28 div by 5,252 = 33.05 HP

    Compression Readings
    To find the lowest reading you have to get the highest reading and multiply by 0.75.
    ex: 195 psi x 0.75 = 146 psi being the lowest amount you can have throughout all the cylinders.

    Jimmy

  2. #2
    Join Date
    Nov 2004
    Location
    Independence, KY
    Posts
    3,344
    another way to find the displacement of a and engine is
    radiuse of bore squared X stroke X Pi (3.14) X # of Cyl. / (DIvided by) 1000

    Ex. (400ex)
    stock bore=85mm Stroke=70mm

    42.5 (1/2 of 85) ^2(squared) X 70 X 3.14 X 1= 397013.75/1000=397cc's
    Tyler Jones

    2000 426EX, 11:1 wiseco, hot cams stage 3 "stroker" cam, Ported head done by Dr. G, FCR 41, Hot rods crank, running no base gasket, 1 layer of 3 layer head gasket, Klotz 113 race fuel Feather carbon smoothie hood, works tripples w/ressies, Black HMF slip on, AC pro peg nerfs, Azonic fat bars, burgaurd +1 1/4" swinger, Lonestar +1 stem, douglas yellow label front wheels, Pro Armor front bumper, + some others goodies

    AIM: Fourtrax426

    Holeshot Motorsports Wilder, KY
    for all aftermarket parts

  3. #3
    Join Date
    Jun 2006
    Location
    Arizona
    Posts
    200
    really cool post!
    2005 400ex

    Armadillo swinger and body skids

    HMF Sport Series slip-on

    More to come!

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