Useful automotive formulas

CALCULATING PERFORMANCE

HP = Torque * RPM/5252

HP = (((MPH / 234)^3) * Weight)

torque = 5252 x horsepower / rpm

brake specific fuel consumption = fuel pounds per hour / brake horsepower

bhp loss = elevation in feet / 1000 x 0.03 x bhp at sea level

FORMULAS FOR SPEED AND GEARING

mph = (rpm x tire diameter) / (gear ratio x 336)

rpm = (mph x gear ratio x 336) / tire daimeter

gear ratio = (rpm x tire diameter) / (mph x 336)

tire diameter = (mph x gear ratio x 336) / rpm

FORMULAS FOR ENGINE STROKE AND VOLUME

cylinder volume = pi/4 x bore^2 x stroke

stroke = displacement / (pi/4 x bore^2 x number of cylinders)

FORMULAS FOR COMPRESSION RATIO

cylinder volume = pi/4 x bore^2 x stroke

chamber volume = cylinder volume / compression ratio - 1.0

displacement ratio = cylinder volume / chamber volume

amount to mill = (new disp. ratio - old disp. ratio / new disp. ratio x old disp. ratio) x stroke

swept vol (cc) = bore^2 * stroke * .0031416 / #cyl

Deck height (cc) = bore^2 * deck height (inch) * .01996

Compression Ratio = (CylVolume + ChamberVolume) / ChamberVolume

Compression Ratio = [swept vol + deck height + head vol] / [deck height + head vol] (all in cc's)

FORMULAS FOR PISTON SPEED

piston speed in fpm = stroke in inches x rpm / 6

rpm = piston speed in fpm x 6 / stroke in inches

FORMULAS FOR AIR INTAKE FLOW

theoretical cfm = rpm x displacement / 3456

volumetric efficiency = acutal cfm / theoretical cfm x 100

street carb cfm = rpm x displacement / 3456 x 0.85

racin carb cfm = rpm x displacement / 3456 x 1.1

FUEL INJECTION FORMULAS

B.S.F.C = brake specific fuel consumption = .50-normally aspirated, .60-forced induction

Inj size (lb/hr) = HP * B.S.F.C. / (.8 * #cyls)

New flow rate = Old flow rate * (new pressure/old pressure)^.5

lb/hr = cc/min / 10.5

gal/hr = lb/hr * 6

FORMULAS FOR G-FORCE AND WEIGHT TRANSFER

drive wheel torque = flywheel torque x first gear x final drive x 0.85

wheel thrust = drive wheel torque / rolling radius

g = wheel thrust / weight

weight transfer = weight x cg height / wheelbase x g

lateral acceleration = 1.227 x raduis / time^2

lateral weight transfer = weight x cg height / wheel track x g

centrufugal force = weight x g

INTAKE RUNNER LENGTH

ECD = Effective Cam Duration
RV = Reflective Value = 2
D = Runner Diameter

ECD = 720 - (Adv. duration - 30)

intake runner length = ((ECD × 0.25 × V × 2) ÷ (tuned rpm × RV)) - ½D

EXHAUST RUNNER LENGTH

Primary tube Length ( inches) = (CID x 1900) ÷ (rpm x pri.OD²)