I am listing some of the formulas I use, these are helpful, there are many more out there, virtually for any movement, weight, power, the list just goes on and on.
How To Calculate CFM:
Engine size (CID) x maximum RPM / 3456 = CFM
CFM @ 100% volumetric efficiency
Cylinder volume (displacement) =3.1416 x bore x bore x stroke
Compression ratio = Vi ñ
V2
(Where Vi is total volume of one cylinder and
V2 is volume of space above piston at top of stroke)
Brake Horsepower (BHP) = RPM x torque
(in lbs
ft.) = 5252
(Note: Formula is actually 6.28 x RPM x torque by dividing
6.28 into 33,000 we get 5250Piston speed (ft. per mm.) = 2 x RPM x stroke in
feet)
1 mile per hour = 1.467 feet per second
Engine displacement = Cylinder volume times number of cylinders
Piston speed (ft. per
mm.) = 2 x RPM
x stroke
in feet
Torque = BMEP x Swept volume (in cc)
2473
MPH (RPM x wheel diameter in inches)
=
gear ratio x 336
(Note: Wheel diameter is overall diameter of the
inflated tire, not the nominal diameter of the wheel.)
Engine Displacement
Formula: Engine Displacement = #Cylinders
x pi/4 x Bore(2) x Stroke
Cylinder Volume = pi/4 x Bore(2) x
Stroke
Example: 6 cylinder engine with 86mm
Bore and 79mm Stroke
6 x .7853982 x
8.6cm(2) x 7.9cm = 2753cc
Static Compression
Ratio
Formula: Compression Ratio = Cylinder
volume + Chamber Volume/Chamber Volume
Cylinder Volume =
pi/4 x Bore(2) x Stroke
Chamber Volume = Cylinder head cc + gasket cc + dish of piston cc (or) - dome of
piston cc
Example: Cylinder Volume = 458.9cc
(From above)
Chamber Volume =
44.6cc(Cyl. Head Vol) +
7.6cc(Gasket Vol) +
10.9cc(Piston Dish cc) = 63.1cc
Compression Ratio = 458.9cc + 63.1cc/63.1cc = 8.3:1
Piston
Speed
Formula: Piston Speed in fpm (Feet per
Minute) = stroke (in.) x rpm/6
Example: 3.11" x
6000rpm/6 = 3110 fpm
HP &
Torque
Formula: Horsepower = rpm x torque/5252
or Torque = 5252 x hp/rpm
Example: 140 ft.lbs @5600rpm = 140 x 5600/5252 = 149 hp
Example: 149 hp @5600rpm = 5252 x 149/5600 = 140 ft.lbs
CID x RPM x volumetric efficiency* /3,456 = CFM
Volumetric efficiency is how well your engine can breathe. For a street stock (slight modifications) plugin .80. For a full race engine use .90.
How to calculate your compression ratio.
Compression ratio = V1+V2+V3+V4 / V2+V3+V4
V1 = calculated swept volume (bore x bore x stroke x .7854)
V2 = deck height volume (bore x bore x .7854 x measured deck height)
V3 = head gasket volume (bore x bore x .7854 x compressed gasket thickness)
V4 = combustion chamber size converted to cubic inches (1 cc = .061 ci)
Note: Be sure to allow for valve relief's and subtract dome size when computing effective chamber size.
CID = bore x bore x stroke x .7854 x # of cylinders
350 Chevy Block w/ 400 crank
4.000 bore x 3.750 stroke = 377 CID
4.030 bore x 3.750 stroke = 382 CID
4.060 bore x 3.750 stroke = 388 CID
How to determine your transmissions gear ratio.
1. Index the input (the part that goes in the engine) and the output (the part that goes to the drive shaft) shafts with a thin line. Make corresponding lines on both ends of the transmission case to use as your pointers.
2. Put the transmission in the gear you want to check.
3. Turn the input shaft until the tail shaft makes one full revolution. The number of turns made by the input shaft, including fractions, is the ratio for that gear.
High gear is almost always 1:1, over drive will be more than that but the lower gears will normally produce less than one full revolution of the tail shaft. To make this process even more accurate turn the input shaft until the output shaft makes ten revolutions, then divide the number of revolutions made by the input shaft by ten (duh!).
4. To determine the final ratio for running in that gear multiply the transmission ratio by the rear end ratio. Do you know the rear end ratio?
To find out, index the input shaft (yoke) and the rear axel. Turn the yoke until the axel makes one full turn. The number of turns made by the yoke including fractions is your ratio.
Other formulas.
Calculate tire diameter: circumference divided by 3.14159 (pi)
Torque = Brake HP x 5,252 RPM
Brake HP = RPM x Torque 5,252
MPH = RPM x Tire Diameter in Inches Gear Ratio (final) x 336
RPM = MPH x Gear Ratio x 336 Tire Diameter
Drill sizes for tapping threads.
COARSE
|
Screw Size |
N.C. Pitch |
Drill Size |
Decimal Equivalent |
|
1/4" |
20 |
#7 |
.2010 |
|
5/16" |
18 |
1/4 |
.2570 |
|
3/8" |
16 |
5/16 |
.3125 |
|
7/16" |
14 |
23/64 |
.3680 |
|
1/2" |
13 |
27/64 |
.4219 |
|
9/16" |
12 |
31/64 |
.4844 |
|
5/8" |
11 |
17/32 |
.5312 |
|
3/4" |
10 |
21/32 |
.6562 |
Fine
|
Screw
Size |
N.C.
Pitch |
Drill
Size |
Decimal
Equivalent |
|
1/4" |
28 |
#3 |
.2130 |
|
5/16" |
24 |
17/64 |
.2720 |
|
3/8" |
24 |
21/64 |
.3320 |
|
7/16" |
20 |
25/64 |
.3906 |
|
1/2" |
20 |
29/64 |
.4531 |
|
9/16" |
18 |
33/64 |
.5156 |
|
5/8" |
18 |
37/64 |
.5781 |
|
3/4" |
16 |
11/16 |
.6875 |
Gear Ratio Formula
|
DATA | |||||||
|
Type |
1st |
2nd |
3rd |
4th |
5th |
Diff Ratio |
Tire Diameter |
|
280Z |
3.321 |
2.077 |
1.308 |
1.00 |
0.864 |
3.54:1 |
24.0" |
Transmission Gear Spacing
Ratios
Formula: Gear spacing ratio = Gear (new) /
Gear (old)
Example: Difference between 280Z 5spd
1st and 2nd gear.
2.077 (2nd gear) /
3.321 (1st gear) = 0.625 or 2nd gear is 63% of 1st gear.
Overall Gear Spacing
Ratios
Formula: Overall Ratio = Transmission gear
ratio xFinal
Drive (Differential Gear ratio)
Example: 280Z 5spd 1st gear with 3.54:1 Differential Ratio
3.321(1st gear) x
3.54(diff gear) = 11.75:1
Maximum MPH in each
gear
Formula: MPH = rpm x tire diameter (in) /
gear x final gear ratio (diff) x 336
Example: Maximum mph
in 280Z 5spd 1st gear using 6500rpm redline.
MPH = 6500rpm x 24.0"(tire
dia.)/ 3.321(1st gear) x 3.54(diff gear) x 336 =
39.5mph
Note: Top gear is most likely hp
limited, and would not be able to reach max rpm.
RPM @65mph (Derived from Max
MPH formula)
Formula: RPM = mph x gear x final ratio x
336/tire diameter
Example: RPM at 65mph for stock 280Z
5spd
65mph x 0.864(5th gear)
x 3.54(diff gear) x 336/24.0"(tire dia.) =
2783rpm
Shift
Points
Formula: RPM desired = RPM shifted at x
(gear shifted to/gear shifted from)
Example: 4000 is
desired rpm after shift into 2nd gear from 1st gear.
4000rpm / (2.077/3.321)
= 6396rpm is when you shift from 1st to 2nd.
Valve Spring
Rate
R = (OL - CL)
./. (IH - OH)
R = valve spring rate
OL = open load
CL = closed load
IH = installed height (closed
height)
OH = Open height
Rod
Ratio
RR = L ./. R
RR = Rod ratio
L
= center to center length of rod
R
= stroke
Starting
Ratio
Manual transmission
SR = AR x FG
SR = starting ratio
AR = axle ratio
FG = first gear ratio of
transmission
Automatic transmission
SR = AR x FG x TR
TR = torque converter torque ratio at
stall
Mile per
hour
MPH = (RPM x R)
./. (168 x AR)
RPM = revolutions per
minute
R = rolling
radius of driving tire (inches)
AR = Overall gear re Formulas for
weight distribution
percent of weight on wheels = weight on
wheels / overweight x 100
increased weight on wheels = [ distance
of cg from wheels / wheelbase x weight ] + weight
Formulas for center of gravity
cj location behind front wheels = rear
wheel weights / overall weight x wheelbase
cg location off-center to heavy side =
track / 2 - [ weight on light side / overall weight ] x track
cg height = [ level wheelbase x raised
wheelbase x added weight on scale / distance raised ] x overall weight duction
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