Brake Mean Effective Pressure
This is a calculation that gives you a measurement in bar (pressure). It is intended to be a way to compare engines and their output. It gives you output with respect to engine size as well as RPM (better than just HP/Liter).

(HP * 894.84) / (liters * rpm @ peak HP)

Here are some calculations of common Tercel engines, and similar car's engines:

Engine

BMEP

3E

7.99

3E-E

9.69

1st Gen 4E-FE

10.08

2nd Gen 4E-FE

10.39

4E-FTE

14.18

1st Gen 5E-FE

9.34

2nd Gen 5E-FE

10.41

5E-FHE

10.27

1NZ-FE

10.26

4A-GE

10.59

4A-GZE

14.54

4A-GE 20V

11.93

1ZZ-FE

10.69

Horsepower
Your basic calculation for horsepower. Everyone who tinkers with engines should know this one.

RPM x Torque / 5252 = Horsepower

Injector Horsepower Capacity
Calculations for estimating horsepower and injector size.

Horsepower limit of injectors = (Injector flow rate / 10.5) * Max Injector Duty Cycle / Brake Specific Fuel Consumption * Number of Cylinders

Ideal injector size (cc/min) = (Maximum Horsepower * Brake Specific Fuel Consumption) * 10.5 / (Number of Injectors * Maximum Duty Cycle)

Optimum Muffler Flow Rate
The ideal flow rate for your muffler. Too small and it will cause restriction and thus power loss.

Ideal muffler flow rate (CFM) = HP X 2.2

Suspension

Springrate
A rough calculation of spring rate.

Spring Rate (Lbs/In) = 11,250,000 * Bar Diameter ^ 4 / 8 * Number of active coils ^ 3

Bar & Tube Stiffness
A calculation to measure the stiffness of a bar. Very useful for increasing sizes of sway bars or any type of support bars.

Diameter ^ 4 = Stiffness

If you have a hollow tube, first calculate the outside diameter stiffness. Then, calculate the hollow diameter as if it were solid. Now subtract the first calculation from the second.