.                                                                  Current version: 3.2.1

German and English manual available at the bottom !

This text based software covers time-area calculations of all intake types.
The time-area (a measure of flow capability) can be varied against port/piston/reed/disc dimensions and rpm. The specific time-area target is calculated from desired maximum horse power (or Braked Mean Efficient Pressure (BMEP) or kW) and corresponding crank speed and is a measure of the ports time-area divided by the engine displacement, ms*mm^2/cc. (milliseconds*mm^2/cc).
It also calculates the Yamaha Energy Induction System (YEIS) which is also known as the magic boost bottle. At some engine configurations this box will remove low rpm flat spots and/or increase the power in the low rpm range.
A brief presentation is shown below.
More details and print outs are found in the Bimotion Intake Manual at the bottom of this page. 

System requirement: Dos 32 bit systems (all Dos 32 bit Windows OS including Vista)

For other platforms as Windows 7, Linux, etc., an emulator is needed. There are two free emulators available, Microsoft's Virtual PC and dosbox. Special instructions about the emulators can be found here.

First, Time-Area targets will decide how much flow is needed for a specific tuning degree and rpm. Example:

Tuned crank speed [rpm] ? 11000


  Target      Bmep(bar)


 Road racing   >11

 Motocross       9

 Enduro          8



 Enter your targets in hp .... (1)

                       kW .... (2)

                       Bmep..  (3)

 hp target   _?

If the target becomes 16 units then...


Maximum piston skirt length: ? 58

Minimum piston skirt length: ? 50

Increment:                   ? 1


Recommended sp. t-a 15-20 ms-sq mm/cc

Length,mm   s-sq mm   ms-sq mm/cc

   58         1.1       14.9 

   57         1.14      15.6 

   56         1.18      16.2 

   55         1.21      16.9 

   54         1.25      17.5 

   53         1.29      18.2 

   52         1.33      18.9 

   51         1.37      19.6 


 Enter required length:  _?


...the port (or flow) is obviously too large in this example. It does not meet the target at 10000 rpm and will nor pull below 6000 rpm as seen in the list below. (t-a over 30)
The port dimensions need to get a correct range of time-area within the rpm range.


  Specific t-a >30 => bad effect.


  Crank     Time-area    Sp t-a

  rev/min   s-sq mm      ms-sq mm/cc

   4000       2.82         48.5 

   5000       2.26         38.8 

   6000       1.88         32.3 

   7000       1.61         27.7 

   8000       1.41         24.3 

   9000       1.25         21.6 

   10000      1.13         19.4 

  End of list.


The procedure is the same for all intake types.

The port and piston dimensions can be varied against time-area at the specific rpm, as in the left example.


If 56 mm skirt length also meets the port duration requirement then it's ok, otherwise the port have to be wider instead. There are also difference in working with the piston skirt/port lower edge/port upper edge/port width. Either is the area affected or the duration or both. This effect is easily tested in the program and must be conformed.

Previous values appear in front of the input and are accepted by enter.

Rotary valve input example:

 Accept by enter.


 Port top radius, ...  50 _?

 Port height, .......  18

 Port mean width, ...  22

 Port upper radii, ..  4

 Port lower radii, ..  3

 Disc opens, deg ....  120

 Disc closes, deg ...  65


The program calculates reed petal resonance frequency and a lot more of measures. Warnings are sent when the specifications are out of the limits. Example:



 Tip lift is higher than stop plate height.

 Reed plate is close to natural freq.(18 %)

Petal resonance frequency is crucial, if the  resonance frequency is too close to the operational rpm range then the petal will be overloaded and fail from fatigue.

Reed valve input example:


  Accept by enter.

  Block dimensions.


  No of ports ...... (6)   _?

  Width, ........ Xp (19.6)

  Length, ....... Lp (32)

  Radii, ........ Rp (1)

  Angle, ..... Fi_Rb (23.5)


  Reed petal dimensionsionsions


  Width, mm ..... Xr (22.7)_?

  Length, mm .... Lr (38)

  Mount distance, Xs (4)

  Thickness, mm . Xt (.42)

  Reed mtrl, (C)Carbon


             (S)Steel           (Glass)

  Duration (170-210), Default 200 (200)

  xtip/Lr max, % .... Default 30% (30)

A boost bottle must be calculated exactly to the specific engine. There is no working ”one fit all” bottle as can be found at many dealers. The function is dependent on engine size, carb dimension, bottle volume, branch pipe dimensions, rpm and can be optimized within a certain rpm range. The bottle and pipe must be manufactured from a stiff material.

Download the user manual
by clicking a flag  !

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