Continued studies with full-scale engines in the laboratory have provided additional information about the parameters that affect ORI in today's cars. Reduced coolant temperature studies showed an average decrease in ORI of about two units in two popular make engines and no effect in a third make. Coolant temperature had no significant effect on exhaust emissions from any of the engines tested. Tests conducted on gasoline “tail” end properties showed that gasoline endpoint had no effect on ORI, while an increase in polycyclic nuclear aromatics increased it. A manganese antiknock additive reduced ORI in one make engine. Lube oil metal additive type and type of viscosity index (VI) improver affected ORI whereas, sulfated ash content did not affect it. A shortened laboratory test cycle produces ORI comparable to our previous laboratory procedure
