How do you calculate compression ratio? What’s the best way to figure out engine displacement?
While cheat sheets might have frowned upon in your sixth-grade classroom, we strongly encourage them in the garage, shop, or pits. That’s why we’ve put together this list of 13 key performance formulas you should know when building or tuning your street or race vehicle.
Read it, print it out, and tape it to your beer fridge. (Quick—while your sixth grade teacher isn’t looking!)
Racing Carburetor CFM
Displacement = .7854 x Bore2 x Stroke x Number of Cylinders
Correct Compression Ratio (CCR)
CCR = FCR (Altitude/1,000) x .2
Note: You can also take this Compression Ratio Calculator tool for a spin.
Tire Diameter = (MPH x Gear Ratio x 336) ÷ RPM
Rocker Arm Ratio and Valve Lift
Horsepower = (RPM x Torque) ÷ 5,252
Torque = (5,252 x HP) ÷ RPM
Rod Ratio = Rod Length ÷ Crank Stroke Length
Average Piston Speed
Average Piston Speed = Crank Stroke x RPM ÷ 6
Rear Gear Ratio
Rear Gear Ratio = (RPM at Finish Line x Tire Diameter) ÷ (MPH x 336)
Note: You can also save this link to a handy Gear Ratio calculator.
Volume (CCs) of Deck Clearance
CCs of Deck Clearance = Bore x Bore x 12.87 x Depth of Deck Clearance
Volume (CCs) of Head Gasket
CCs of Head Gasket = Bore x Bore x 12.87 x Thickness of Head Gasket
Combined Chamber CCs + Gasket CCs + Deck CI CCs + (Displacement x (N))
Combine Chamber CCs + Gasket CCs + Deck CI CCs
(N) = 2.0483 for 8-cylinder. (N) = 2.7311 for 6-cylinder. (N)=4.0967 for 4-cylinder.