Two-Stroke Software Review - Using Bimotion v 2.1

Two-Stroke Software Review

Part 1 - Introduction to Two-Stroke Software

Bimotion v 2.1 - Blair S.A.E. - Dynomation 2 - MOTA v 5.0 - TSR

Using Bimotion v 2.1

1989 Blaster Engine Rebuild

Using Bimotion
The Bimotion menu consists of 10 choices. They are Time Area Targets, Piston Controlled Intake, Exhaust, Transfer, Expansion Chamber, Cylinder head, Piston Load/Acceleration, Gearing and Road Loads, Yamaha Energy Induction System (YEIS) and Quit.

To start the program I choose Time Area targets. I entered the basic engine parameters (66.5 mm bore x 57 mm stroke) and target HP (17 stock and 25 HP, 29 HP modified) and peak RPM that maximum HP will be achieved. The High Output version of this engine in the far right hand column is designed using the long rod (115 mm) and has a bore and stroke that measures 68 x 57 for a displacement of 207 cc^3. Bimotion calculated the TA Targets as follows:

Stock - 17 HP @ 7000 RPM Modified - 25 HP @ 8000 RPM Modified - 29 HP @ 8400 RPM Modified - 33 HP @ 8700 RPM - Long Rod 68 mm Bore (207 cc)

Output data

Intake - 9
Transfers - 6.3

Exhaust - 10.8

Exhaust Blowdown - .4
Intake -11
Transfers - 6.9

Exhaust - 12.3

Exhaust Blowdown - .6
Intake -11.9
Transfers - 7.2

Exhaust - 13

Exhaust Blowdown - .7
Intake -12.8
Transfers - 7.5

Exhaust - 13.7

Exhaust Blowdown - .8

These numbers are not the "as measured" areas of this engines ports. They are what Bimotion determined would be necessary to produce 17 HP @ 7000 RPM.

These numbers are a reflection of what is necessary to produce the given power at the RPM I entered. it is easy to see that more time area is needed for more HP. These output numbers are easily understood. I can tell there is a multiplier involved or else they would be more like .00011 or .00007. It is usually 1000 for all ports and 10000 for blowdown. This is done to make the numbers more friendly.

Exhaust Port Data - (as measured from BDC)

Port height - 24 mm - opens @ 91.5 ATDC
Port Duration - 177 degrees open

Port width - 43 mm

Percent of bore - 64.7 %
Port height - 25.5 mm - opens @ 88.5 ATDC
Port Duration - 183 degrees open

Port width - 43 mm

Percent of bore - 64.7 %
Port height - 26 mm - opens @ 87.3 ATDC
Port Duration - 185.4 degrees open

Port width - 45 mm

Percent of bore - 67.7 %
Port height - 27 mm - opens @ 85.5 ATDC
Port Duration - 189 degrees open

Port width - 46.5 mm

Percent of bore - 69.9 %

Squish Area Data - MSV (Maximum Squish Velocity) Expressed in m/s (Meters/Second)

Volume Trapped @ TDC = 22.4 cc
Uncorrected Compression Ratio (full stroke) = 9.8:1

Corrected Compression Ratio = 6.1:1

Squish Band Width = 17 (76% of bore)

Squish Band Thickness = 2.7

Maximum Squish Velocity = 21.6

Max Squish Pressure Ratio of 1.048 occurred @ 14.5 Degrees BTDC
Volume Trapped @ TDC = 17 cc
Uncorrected Compression Ratio (full stroke) = 12.6:1

Corrected Compression Ratio = 7.4:1

Squish Band Width = 11 (55% of bore)

Squish Band Thickness = 1.1

Maximum Squish Velocity = 30.1

Max Squish Pressure Ratio of 1.082 occurred @ 10.5 Degrees BTDC
Volume Trapped @ TDC = 15.5 cc
Uncorrected Compression Ratio (full stroke) = 13.8:1

Corrected Compression Ratio = 7.9:1

Squish Band Width = 10 (51% of bore)

Squish Band Thickness = 1.0

Maximum Squish Velocity = 29.4

Max Squish Pressure Ratio of 1.085 occurred @ 10.3 Degrees BTDC
Volume Trapped @ TDC = 15.4 cc
Uncorrected Compression Ratio (full stroke) = 14.4:1

Corrected Compression Ratio = 8:1

Squish Band Width = 9 (46% of bore)

Squish Band Thickness = .9

Maximum Squish Velocity = 27.6

Max Squish Pressure Ratio of 1.089 occurred @ 9.5 Degrees BTDC

Boost Bottle Information - Data is CC's based upon stock 26 mm carburetor. Tuned for 5000 RPM.

Boost Bottle Information - Using 34 mm carburetor.

Boost Bottle Information - Using 34 mm carb & other changes.

Bottle Volume = 495
Tube Diameter = 12.7 mm

Pipe Length = 98

Bottle Volume = 517

Tube Diameter = 12.7 mm

Pipe Length = 93

Bimotion 2.1 is more well rounded than the earlier versions I tried. The squish velocity feature is very welcome and necessary. The boost bottle program is also very interesting and different than the program from TSR.

More to come - Rick

Two-Stroke Software Review

Part 1 - Introduction to Two-Stroke Software

Bimotion v 2.1 - Blair S.A.E. - Dynomation 2 - MOTA v 5.0 - TSR

Using Bimotion v 2.1

1989 Blaster Engine Rebuild

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