Administrators Noble 103 Posted February 12, 2017 Administrators Report Share Posted February 12, 2017 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 strokein 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 Carburetor size formula: 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. Bore and stroke formula's (common combinations given) 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 Mile per hourMPH = (RPM x R) ./. (168 x AR)RPM = revolutions per minuteR = 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 Link to post Share on other sites

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