2 Stroke Calculators
average piston velocity
average piston
max RPM piston stroke m/sec velocity
10000 50.0 16.7
trapped cc engine compression ratio
above exhaust engine
port (ml) above TDC cc compression ratio
72.5 8.4 8.6
(same in oz.) (same in oz.) Compression Ratio
2.03 0.29 7.05
Mikuni jet crossover
Mikuni 4/042 equivalent
main jet N100.64 jet hole diameter
150 113.9 1.09
Mikuni N100.64 equivalent
main jet 4/042 jet hole diameter
114.0 150 1.09
engine size (conventional)
cyl bore mm stroke mm cc size
50.0 50.0 98.1
engine cc transfer duration max RPM
250 125 8000
cylinder bore vol. efficiency
66 0.78
compression ratio ft elevation cranking PSI
8.5 500 170
0.96
piston stroke 50
Con Rod mm 110 Hot Port Durations C
Above Port mm exhaust
cold hot duration
exhaust cold exhaust hot 205
27.85 28.10 200
transfers cold transfers hot 195
39 39.25 190
185
Estimated Durations 180
exhaust cold exhaust hot 175
180.0 178.9 170
transfers cold transfers hot 165
123.7 122.2 160
NEEDLE CALCULATOR
(Start diameters Taper Angle Finder
are "up" on the length between dia's start diameter (bigger)
needle and "end" 6 2.13
diameters are end diameter taper angle (full)
down from there.) 1.805 3.100
End Diameter Finder
taper degrees start diameter
2 2.72
segment length end of segment dia.
0.62 2.698
Taper Length Finder
taper degrees start diameter
1.57 2.67
end diameter length between diameters
2.515 5.66
Start Diameter Finder
taper degrees end diameter
1 2.105
segment length start diameter
7.5 2.236
Motorized Bicycle (Grubee 2 stroke) Speed Calculator
max RPM 9000
rear sprocket teeth 44
feet tire circumference 6.66
max MPH 37.6
max RPM 7300
rear sprocket teeth 44
meters tire circumference 2.03
max KPH 49.1
Pipe Powerband RPM Calculator
exhaust port duration 175
millimeters ==> piston to end of belly mm 670
end of powerband RPM 10657
start of powerband RPM 7779
exhaust port duration 184
inches ==> piston to end of belly inches 23
end of powerband RPM 12848
start of powerband RPM 9379
Pipe Cone Pattern Maker
large diameter mm small end diameter pipe angle from center
70 25 8
(Dimeters are inner diameters plus sheet metal thickness)
Resonant Intake Length
top RPM (end of powerband)
transfer duration
intake period in seconds
Intake tract length in feet
Intake tract length in cm
Click here for a listing of for-sale 2 stroke calculators
NEEDLE ANGLE FINDER
Needle Diameters Every 3mm
Dia. 1 Dia. 2 Dia. 3
2.51 2.41 2.57
ANGLES --> 1.91 -3.05
-4.80 0.60
TRANSITION --> 0.60
Needle Diameters Every 5mm
Dia. 1 Dia. 2 Dia. 3
2.515 2.515 2.4
ANGLES --> 0.0 1.3
3.08 -0.01
TRANSITION -->
Needle Diameters Every 10mm
Dia. 1 Dia. 2 Dia. 3
2.515 2.4 1.9
ANGLES --> 0.7 2.9
-0.01 22489894542832
TRANSITION -->
web page
alculators by Michael Forrest
updated Mar 12 '22
Cranking Engine PSI
max allow- engine
able RPM compr ratio feet elevation
15000 8.3 0
head volume
above exhaust engine above
port cc (ml) compr ratio TDC cc
60 7.1 8.5
trapped engine volume
above exhaust mm piston edge
port mm to cylinder top cylinder bore
27.850 0.00 50.0
ounces cubic centimeters
1.0 29.6
cc ounces
30 1.01
Carb Air Speed & Size Calculator website page
mm carb Intake Carb Flow
diameter Volume L/min Velocity m/sec type of riding
38 1552 22.9 enduro/street
cm^2 carb 242.5 racing
area
11.34
idle slide area idle slide height This figures in the bore and comp
125.1 6.4 type of riding
0.110 enduro/street
racing
Hot Port Durations Calculator website page
0.99423 exhaust 0.99423 transfers
above port duration above port duration
22.3 207.5 21.8 130.0
23.4 202.5 22.9 127.5
24.6 197.5 24.0 125.0
25.7 192.5 25.1 122.5
26.8 187.5 26.2 120.0
27.9 182.5 27.3 117.5
28.9 177.5 28.4 115.0
30.0 172.5 29.5 112.5
31.0 167.5 30.5 110.0
32.1 162.5 31.6 107.5
Engine Oil Weight Calculator, Grams
Engine Oil grams of a volume of water 100
Motul 510 grams of same volume of oil 87
measured oil density gas/oil ratio 27
0.87 liters gasoline 0.48
needed grams engine oil 20.4
Engine Oil Weight Calculator, Ounces
ounces of a volume of water 2.8
ounces of same volume of oil 2.43
Oil Density gas/oil ratio 27
0.87 gallons gasoline 3.75
needed ounces engine oil 20.5
Motorized Bicycle (Grubee 2 stroke) RPM Calculator
max MPH 22.5
rear sprocket teeth 56
ft tire circumference 6.66
max RPM 6851
max KPH 46.2
rear sprocket teeth 44
meters tire circ. 2.03
max RPM 6868
MPH to KPH KPH to MPH
mph 60 kph
kph 96.5 mph
Pipe Radius Calculator
belly length in mm 220
pipe angle 60
radius in mm 210
Pipe Cone Angle Calculator
cone length mm small end dia. large end dia.
220 9.5 70.0
length a length b length of chord angle A
89.8 251.5 203.3 77.9
161.7
BlowDown Calculator
peak power RPM 8000
exhaust port duration 180
transfer port duration 115
blowdown time (ms) 0.677
blowdown degrees 32.5
new peak power RPM 9000
needed blowdown deg 36.6
needed exh/transfer
additional separation 4.06
needed exh duration 184.1
Intake Length
12000
120
0.0017
0.47
7.1
NGLE FINDER
Dia. 4 Dia. 5 Dia. 6 Dia. 7
2.57 2.53 2.49 2.45
0.00 0.76 0.76 0.76
0.00 #DIV/0! -12055623884.80 #DIV/0!
#DIV/0! #DIV/0!
Dia. 4 Dia. 5 Dia. 6 Dia. 7
2.1 1.8 1.5 1.2
3.4 3.4 3.4 3.4
#DIV/0! #DIV/0! #DIV/0! #DIV/0!
#DIV/0! #DIV/0! #DIV/0! #DIV/0!
(end of taper dia.)
Dia. 4 Dia. 5
1.4 0.9
2.9 2.9 2.9
22489894542816
(data entry cells are light blue)
(distances are in millimeters unless stated otherwise)
meters feet
ngine PSI 2 6.8
millimeters
cranking psi inches (mm)
172 1.00 25.4
Maximum Delivery Ratio RPM
crankcase mm from top
cylinder compression of transfers
bore mm ratio to TDC
47 1.5 30.4
trapped piston dome above piston cc
head cc engine cc cc volume @ TDC
5.85 61.68 0.8 7.0
head gasket cc volume
mm thickness 5.85
1.00 1.96
piston dome 0.00
mm height 0.79
0.8 55
This chart shows what the bike manufacturers went by, increas
to emphasize mid range power so the engine could carry the R
mm ideal
ideal velocity carb diameter
38.9 29
23.9 37
% cutaway max carb size
10 48
This figures in the bore and compression ratio:
ideal velocity carb diameter
37.9 30
22.9 see web page
38.0
0.99704
above port
37.9
38.4
38.8
39.2
39.6
40.1
40.4
40.8
41.2
41.6
Liters Gasoline Calculator
grams of same
volume gasoline 72
gasoline density 0.72
grams gasoline 345 NOTES : ENGINE OIL
liters gasoline 0.48 Castor 927
Blowdown Calculator Motul 510
exhaust duration 180 Super M
transfer duration 115
peak power RPM 8000
1 or 3 port exhaust? 1 Change to this exhaust or transfer duratio
existing blowdown 32.5 exhaust duration
needed best blowdown 33.3 181.7
needed so-so blowdown 29.7 174.4
Mikuni Main Jet Mikuni Idle Jet Keihin Main Jet
Size Calculator Size Calculator Size Calculator
4/042 main jet # 22/210 Idle Jet Main Jet #
73 7.5 160
N100/604 Main Jet hole diameter hole diameter
0 0.244 1.467
mm hole diameter hole area hole area
0.762 0.047 1.689
main jet hole area
0.456
96.5
59.9
(see video)
(from center)
cone angle
7.8
Needle Shroud Calculator
shroud height % jetting change
+3mm height 29% 240
+2mm height 19% 222
+1mm height 10% 204
current shroud height 6.0 186
-1mm height -10% 168
-2mm height -19% 150
-3mm height -29% 132
Dia. 8 Dia. 9 Dia. 10 Dia. 11
2.41 2.37 2.28 2.19
0.76 0.76 1.72 1.72
3.0 0.00 3.00 0.00
3.000 3.00
(end of taper dia.) NEW JET DIAMETER CALCULATOR
Dia. 8 Previous Carb Dia. Previous M. Jet Dia.
0.9 20 0.74
3.4 3.4 314 0.43
New Carb Dia. New M. Jet Dia.
24 0.89
452 0.619
Mikuni Main Jet Mikuni Idle Jet Keihin Main Jet
Size Calculator Size Calculator Size Calculator
4/042 main jet # 22/210 Idle Jet Main Jet #
73 7.5 160
N100/604 Main Jet hole diameter hole diameter
0 0.244 1.467
mm hole diameter hole area hole area
0.762 0.047 1.689
main jet hole area
0.456
Longer Stinger Diameter
mm length inner diameter C.S. area
original dimensions: 100 26.6 555
new longer length new diameter C. S. area
new dimensions: 400 35.8 1005
922 1005
34.3 35.8
maximum
Intake Crankcase delivery
Volume cc Volume cc ratio RPM
52.7 105.4 10639
engine
compr ratio feet elevation cranking psi
8.8 5000 134
head
gasket
deck
piston dome
port to TDC
nufacturers went by, increasing the velocity for small engines
he engine could carry the RPM up to the pipe powerband.
Gas/Oil Ratio Oil Density
45 @ 7300 0.97
27 @ 7300 0.87
42 @ 7300 0.86
s exhaust or transfer duration (keeping the other existing one the same)
transfer duration
113.3
120.6
Keihin Idle Jet Dellorto Jet
Size Calculator Size Calculator
Idle Jet # Main or Idle Jet #
70 150
hole diameter hole diameter
0.700 1.500
hole area hole area
0.385 1.766
Equivalent Compression Ratio Calculator
full stroke 170* exhaust above 180* exhaust above
Compression Ratio port Compr. Ratio port Compr. Ratio
14.0 7.80 7.25
190* exhaust above 200* exhaust above
port Compr. Ratio port Compr. Ratio
6.68 6.08
(end of taper dia.)
Dia. 12 Dia. 13
2.07 1.95
2.29 2.29 2.3
628363684747.64
TER CALCULATOR
Previous Idle Jet Dia.
0.51
0.20
New Idle Jet Dia.
0.61
0.294
Keihin Idle Jet Dellorto Jet
Size Calculator Size Calculator
Idle Jet # Main or Idle Jet #
70 150
hole diameter hole diameter
0.700 1.500
hole area hole area
0.385 1.766
