Dynamic Compression Ratio Calculator (Use seat to seat specs for Intake spec for best results) Number of Cylinders. is 160 psi, but pump gas seems like a risky choice. With the big cam in my 12.5:1 BBC, DCR is 8.0 and cranking est. Blower efficiency - blower efficiency is determined by the materials used and the methods of assembly. Engines do not pay much attention to compression ratio, either static or dynamic.Blower size and drive ratio - larger blowers and higher drive ratios can create more boost.CFM available to the blower - carbs that are too small will keep the blower from making maximum boost.Size of the exhaust system - a small, restrictive exhaust can cause high boost readings.If you put a very mild camshaft (194/204. To give an example, lets say youre considering only pump gas for your engine, and it has a static compression ratio of 11:1. Cam Shaft specifications - lift, duration, and lobe center play a big part in boost levels. Unlike Static Compression Ratio, Dynamic Compression Ratio takes into account camshaft timing by considering the intake valve closing point in relation to the piston position.Cubic inches of the engine - more cubic inches means less boost.Aside from the possible differencein blower diameters, there are numerous things that will determine maximum boost levels. The actual boost readings from your system may vary greatly from the figures shown here. The larger bore blower is recommended for 371-500 CID engines in high performance, racing applications. The small bore blower (case thickness 3/4"+) is recommended for 370 CID engines or less for street applications. The large bore blower (case thickness 1/2"-) is approximately 11 percent larger in volume than the small bore. They are the larger diameter blower and the small diameter blower. There are two different 671 blowers commonly used. These boost readings were measured at wide open throttle and with the engine under load at 6000 RPM using a large bore blower unless otherwise specified. The boost levels listed in our charts are based upon an average that was determined by 39 years of experience testing superchargers. To determine the effects of the altitude on a calculated compression ratio, use the following formula:Ĭorrected Compression Ratio = FCR. If the altitude in the area where you normally drive is significantly higher than sea level, then your compression ratios will also vary. The formula for calculating your exact final compression ratio is as follows:įinal Compression Ratio (FCR) = x CRĬR = engine compression ratioAltitude plays an important role in determining compression ratios. Final compression ratios in excess of 12.4:1 are not recommended for use with "pump gas." The higher the final compression ratio, the higher the octane rating of the fuel must be in order to help prevent detonation and serious engine damage. It is to be used as a guideline in determining the proper maximum boost level for a specific application. This chart shows the final compression ratio combining the static compression ratio of an engine and the maximum blower boost from the blower system. download Drive Ratio Chart for 13.9mm & 14mm Pulleys download Drive Ratio Chart for 8mm Pulleys download Drive Chart for 1/2" Pitch Pulleys Back Fire Valves and Intake Accessories.
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