This is a listing of a few different mathematical formulas
that I like to use
1. MPH
MPH = (tire radius / 168) X (RPM / Gear ratio)
(example:(13 / 168) x (4500 / 3.73) = 93.35mph)
2. RPM
RPM = (168 X Gear ratio X MPH) / tire radius
(example: (168 x 3.73 x 100) / 13 = 4820)
3. Gear Ratio
Gear Ratio = Tire radius X RPM / 168 / MPH
(example: 13 x 5000 / 168 / 110 = 3.51)
4. Tire Radius
Tire Radius = 168 X MPH X Gear ratio / RPM
(example: 168 x 100 x 3.73 / 4500 = 13.92")
Here is an interesting formula I found
Try it out. Its actually pretty close for being so simple.
5. Horsepower
HP = *Atmospheric pressure X Compression Ratio X *Volumetric effiency
X Cubic Inch Displacement X RPM at HP peak / 5252 / 150.8
(example: 14.7 x 10 x 1.05 x 306 x 5800 / 5252 / 150.8 = 345 hp)
*Atmosheric pressure-nominal is 14.7
for cars with blowers or turbos try adding amount of boost to the AP#,
(example 14.7 + 10lbs of boost = 24.7)
*Volumetric effiency-a well tuned stock motor should be able to get 90%(.90),
a car with bolt on parts should be able to get close to 100%(1.0)
and a car with alluminum heads and cam should easily achieve 110%(1.1)
Here is a few more formulas for finding Horsepower
(NOTE-MPH is 1/4 mile MPH)
6. Horsepower
HP = (0.00426 X MPH)3 x Weight
(example:[(0.00426 x 100)3 = 0.0773] x 3225 = 249.29hp)
7. Horsepower
HP = (MPH / 234)3 X Weight
(example: [(110 / 234)3] = 0.1038 x 3225 = 335hp
8. Horsepower
HP = Weight / (ET / 5.825)3
(example: 3225 / [(11.68 / 5.825)3 = ] 8.0619 = 400)
Ok these next 2 are a litlle complicated unless
you have a scintific calculator with a cube-root function on it
. I tried to locate the formula to figure out a cube-root
to make it a little easier but didnt have any luck.
If anybody knows the formula give me a holler.
9. 1/4 Elapsed Time
ET = The cube-root of (Weight / HP) X 5.825
(example: [the cube-root of(3225 / 400)=] 2.005 x 5.825 = 11.68)
10. 1/4 Mile MPH
MPH = The cube-root of (HP / Weight) X 234
(example: [the cube-root of(400 / 3225)=]0.4987 x 234 = 116.69 mph)
Here are a few very good drag race formulas
11. 1/4 mile to 1/8 mile ET Conversion
1/4 mile ET = 1/8 ET X 1.57 and 1/8 mile ET = 1/4 ET / 1.57
12. 1/4 mile to 1/8 mile MPH Conversion
1/4 mile MPH = 1/8 MPH X 1.27 and 1/8 mile MPH = 1/4 MPH / 1.27
13. 60ft Conversion
60ft = (1/4 mile ET x 0.12) + 0.17 and 1/4 mile ET = (60ft - 0.17) / 0.12
14. Ideal Rear Gear Ratio
IRGR = (RPM X Tire Diameter) / (336 X Trap Speed MPH)
15. Cubic Inch Displacement
CID = Number of Cylinders X 0.7854 X Bore X Bore X Stroke
16. CFM Formula
CFM = CID X RPM X Volumetric Effiency / 3464
(examples: 6.90 x 1.57 = 10.83 and 10.50 / 1.57 = 6.68)
(examples: 90.00 x 1.27 = 114.3 1/4 mile MPH and 120.00 / 1.27 = 94.48 1/8 mile MPH)
(examples: (12.50 x 0.12) + 0.17 = 1.67 60ft and (1.50 - 0.17) / 0.12 = 11.08 1/4 ET)
(example: (5400 x 26) / (336 x 116) = 3.60 ideal Rear Gear ratio)
(example: 8 x 0.7854 x 4.03 x 4.03 x 3.00 = 306.13 CID)
(example: 302 x 5500 x 1.10 / 3464 = 527.45 CFM)