The Effects of Intake Plenum Volume on the Performance of a Small Normally Aspirated Restricted Engine

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. Experimental results showed that engine performance increased modestly as plenum volume was increased from 2 to 8 times engine displacement. Increasing plenum volume beyond 8 times engine displacement resulted in significant improvement in performance parameters. Overall, peak HP was shown to increase from 54 kW to 63 kW over the range of plenums tested. While it was clear that larger intake plenums yielded better steady state performance, their effect on transient performance was not explored and will be the subject of further research.