20% higher then what the engine actually sees. Readings from this port will always be approx. Interruption of the vacuum signal to the fuel rail pressure sensor can affect the fuel pressure reading to the PCM, which can result in engine failure! Furthermore, this port reads pressure before the intercooler, and therefore is before the inherent intercooler pressure drop. There is currently a plug sealing the hole, which can be removed, and replaced with a fitting to adapt to your sensor.ĬAUTION: Never cut into the vacuum lines leading to the fuel rail pressure sensor and bypass actuator, on the driver's side of the manifold, for the purpose of tapping in a boost gauge. Your supercharger has been pre-drilled and tapped for a 1/8' NPT fitting. The second option is to utilize the pressure port at the rear of the passenger side intake runner flange. Also, detonation will occur with spark advanced only 3 degrees to 5 degrees over best timing and detonation will cause 1% to 10% torque loss, immediately, and engine damage if allowed to persist.Ģ. Rule: Expect 0.1% to 0.5% loss in Torque for each 1 degree error in spark timing advanced or retarded from best timing.

And even engines of equal CID but different CR require their own unique spark advance profiles. Different engine families require distinctly different spark advance profiles. Spark timing must be matched to Volumetric Efficiency because VE indicates the quantity of charge in each cylinder on each stroke of the engine. On the newer computer controlled vehicles it is also important to ensure that all emissions control devices, and especially the O2 sensor, still work as intended. This will not happen if the exhaust valve dumps into a big header pipe. Improving an engine’s Volumetric Efficiency depends on high exhaust gas velocity to scavenge the cylinder. But headers are often too big especially for Performer and Performer RPM levels. Tube style exhaust systems are preferred. Cast iron, log style manifolds hamper the exhaust process. To break 100% Volumetric Efficiency, however, better cylinder heads or OEM “HO” level engines are usually needed.Īn engine must exhaust burned gases before it can intake the next fresh charge. When it is not possible to replace the cylinder heads because of cost, a better matching carburetor, manifold, cam and exhaust can increase HP of most stock engines by 10 to 15 points. That is why installing only a large carburetor or a long cam in a stock engine does not work. An increase in camshaft lobe duration of 10 degrees will move the HP peak up 500 RPM but watch out it may lose too much HP at lower RPM.Ĭylinder heads are usually the limiting component in the whole air flow chain. These losses come from the wrong lift and duration which try to create air flow that does not match the air flow characteristics of the carburetor, manifold, head and exhaust so volumetric efficiency is reduced. With the proper carburetor and manifold it is possible to select a cam that loses 5% to 15% of the potential HP. Because manifolds are made for specific engines, select manifolds based on the RPM range. Manifolds must be sized to match the application. For dual-plane manifolds use 120% to 150% higher. A 1050 probably would cause actual loss of HP below 4500 RPM. An 850 probably would cause driveability problems at lower RPM. Example: If the engine needs 590 CFM, select a carburetor rated in the range of 650 to 770 CFM for a single-plane manifold. Use 110% to 130% higher on single-plane manifolds. Rule: For maximum performance, select a carburetor that is rated higher than the engine CFM requirement. 4V carburetors are rated at 1.5 inches (Hg) of pressure drop (manifold vacuum) and 2V carburetors at 3 inches (Hg). Answers will be approximate but generally will be close enough for use as a guideline.Ĭarburetors are rated by CFM (cubic feet per minute) capacity. The equations have been simplified for ease of understanding. Please Note: The above equations and rules apply only to four-cycle engines. (volume of piston depressions - volume of piston bumps)Įxample: What is CR of the engine in #9 if heads have 72 cc chamber, head gasket is compressed to 0.040 inch and flat top pistons give 0.025 deck clearance at TDC? PDV = (0.7854 x bore x bore x deck to piston distance) + PDV = (Piston Deck Volume) + (Piston Dome Effective Volume) HGV = Head gasket compressed thickness x 0.7854 x bore x bore HGV = Head Gasket Volume, in cubic inches,

Note: if volume is given in cc’s then ÷ 16.4 to get cubic inches. VOLUME BDC ÷ CYLINDER VOLUME TDCĬR = 1+ (0.7854 x BORE x BORE x STROKE) ÷ (CCV + HGV + PDV)ĬCV = Combustion Chamber Volume, in cubic inches

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