Superchargers and turbochargers are essentially pumps that beef air into another air pump equivalent to the engine. All else continuance Identical, two superchargers that are equally efficient at compressing air at a inured RPM and consume the alike dimensions of efficacy to turn Testament fabricate twin potentiality on a habituated engine. There's no x-factor when it comes to supercharger sizing; it's all a argument of balancing variables and choosing a supercharger extent and imitation that Testament manage culminating at the intended RPM.
Instructions
1. Calculate your engine's abstract non-supercharged air intake in cubic feet per minute (CFM). Assumed CFM is not difficult to calculate: multiply the engine displacement in cubic inches by the protest RPM and cut by the fixed 3,456. For instance, a 350 cubic-inch engine theoretically Testament inhale 607 CFM at 6,000 RPM (350 x 6,000 / 3456 = 607) and 202 CFM at 2,000 RPM.
Divide the target horsepower by current horsepower, subtract one, multiply by 100 and divide by between seven and nine (depending on the supercharger type and its efficiency). For our example, we'll use a conservative seven percent to reach at a 9.5 psi of boost (500/300 = 1.66, minus one and multiplied by 100 equals 66.6, which divided by 7 equals 9.5).5. Add your target boost to 14.7 psi (the air pressure at sea level), and divide that figure by 14.7 to reach at the pressure ratio. VE is generally approximately 95 to 105 percent at the engine's torque peak, and tends to taper down to approximately 70 percent dispassionate preceding the engine's horsepower crest. The 350 in our exemplar has a notional 100 percent VE at its 2,500 RPM torque pinnacle, so it uses 240 CFM at 2,500 (350 x 2,500 x 0.95 / 3456 = 240).
3. Calculate the airflow values adjusted for VE within your protest RPM compass. We'll answer the item RPM scale for our 350 engine is from honest below its torque pinnacle to aloof above its horsepower top at 6,000 RPM. We be learned from the Reckoning in method two that the engine uses 240 CFM at its torque summit, and assuming a 70-percent VE at 6,000 RPM gives us 425 CFM (350 x 6,000 x 0.70 / 3456 = 425.9). We pdq keep an airflow compass of 240 to 425 CFM.
4. Impel the desired horsepower exact as a advantage over your naturally aspirated (non-supercharged) levels. For instance, our 350 engine makes 300 horsepower without a supercharger, and we appetite 500 horsepower. One pound of boost is generally reward approximately a seven- to nine-percent breakthrough in power.2. Adjust the notional RPM by multiplying by volumetric efficiency (VE). An engine is an imperfect air pump considering while it can pump with 100-percent efficiency within a undeniable RPM reach, it normally doesn't.
In our example, this works out to a 1.6-to-1 pressure ratio (14.7 + 9.5 / 14.7 = 1.6). Now that you have the desired pressure ratio and CFM range, you can size the supercharger. You may need to convert the flow rates from CFM to metric (meters-squared per second, or M3/s) by multiplying the CFM by 0.00047.
6. Multiply the non-supercharged airflow requirements by the desired pressure ratio to determine how much air your supercharger will need to flow to feed the engine. In this case, our pressure-adjusted airflow range is 384 to 680.
7. Compare your airflow range and target pressure ratio to a supercharger compressor map. A compressor map looks like a series of concentric ovals; the vertical part of the chart indicates the pressure ratio and the horizontal aspect the airflow in CFM or M3/s. The center-most oval indicates the supercharger's peak efficiency range of pressure ratio relative to airflow; each oval further out indicates a drop in efficiency. We would want to utilize a supercharger with a center oval that spans from 384 to 680 CFM along at the 1.6 marking on the vertical pressure ratio line.
