Effects of Intake Valve Deposits on Driveability

During the Coordinating Research Council's (CRC) program to select an engine to replace the BMW 31 8i as the industry standard intake valve deposit test engine, an opportunity was identified to compare the driveability performance of the engines evaluated with and without deposits.

This Coordinating Research Council project confirmed that intake valve deposits increase driveability demerits as measured by the BMW Driveability Test Procedure. This was true for the BMW 31 8i reference vehicles as well as the three candidate engines. The driveability demerits for the reference engine as well as the three candidate engines increased with decreasing fuel volatility of the engines considered. The BMW 31 8i was by far the most sensitive to intake valve deposits. A modification of the CRC Driveability Test Procedure did not produce the clear separation found with the BMW Driveability Test.

It is recommended that additional driveability studies be conducted with next generation engines since it is possible that sensitivity to intake valve deposits will increase as engines are recalibrated to meet more restrictive exhaust emission regulations.