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Intake tuning is a widely recognized method for optimizing the performance of a naturally aspirated engine for motorsports applications. Wave resonance and Helmholtz theories are useful for predicting the impact of intake runner length on engine performance. However, there is very little information in the literature regarding the effects of intake plenum volume. The goal of this study was to determine the effects of intake plenum volume on engine performance for a restricted naturally aspirated engine for Formula SAE (FSAE) vehicle use. Testing was conducted on a four cylinder 600 cc motorcycle engine fitted with a 20 mm restrictor in compliance with FSAE competition rules. Plenum sizes were varied from 2 to 10 times engine displacement (1.2 to 6.0 L) and engine speeds were varied from 3,000 to 12,500 RPM. Performance metrics including volumetric efficiency, torque and power were recorded at steady state conditions.

Engine startup experiments with intake port sampling were performed in a modified fuel injected single cylinder gasoline CFR research engine. Immediately after fuel injection, port fuel-air vapor sampling was performed in order to quantify the role of the fuel injector in creating a combustible mixture for the first cycle of engine startup. In-cylinder sampling was also performed to clarify the role of other mixture preparation mechanisms in the startup process. Sample analysis was performed using gas chromatography. Experimental data were also collected during steady-state operating conditions at the same intake port pressure and temperature as that of the first cranking cycle for comparison. Results show that approximately ½ to ¾ of a near stoichiometric combustible 1st cycle charge, as a function of first cycle fueling, is produced immediately after enriched cranking fuel injection.

Intake tuning is a relatively simple alternative to turbochargers and superchargers as a means of augmenting engine performance. Capitalizing on air flow harmonics at specific engine speeds, intake tuning forces more air into the engine cylinders, resulting in greater torque and power. Concepts such as Helmholtz Resonance Theory and Reflective Wave Theory help to describe the physical phenomena that contribute to intake tuning, but previous studies have generally found that computer models utilizing computational fluid dynamics (CFD) are needed to accurately predict performance effects. The current research involves testing various intake runner lengths and cross section geometries on a Honda CBR600 F4i gasoline engine typically used to power a Formula SAE car. Also, the effect of adding 180 degree bends to intake runners is evaluated.