Roller rockers (Page 2/2) Patrick MAR 27, 03:22 PM quote Originally posted by kevin: ...would the SMOG referees know that my engine was upgraded? A keen ear might be able to pick out a slight lope to the idle. (You can hear my Formula Here.) I suspect the idle readings for smog testing aren't helped either. pmbrunelle MAR 27, 04:00 PM Usually when an engine is souped up, the camshaft lobe duration is increased, and then there is more overlap between the intake and exhaust valve openings. When there is more overlap, there is more potential for air/fuel mixture to go straight from the intake valve, out the exhaust valve (versus remaining trapped inside the cylinder). This will be reflected as more unburned hydrocarbons and air in the exhaust gas. Keeping the camshaft timing stock, but simply inceasing the lift with greater-ratio rockers, I don't think would cause any emissions disaster. La fiera MAR 27, 05:00 PM quote Originally posted by pmbrunelle: Usually when an engine is souped up, the camshaft lobe duration is increased, and then there is more overlap between the intake and exhaust valve openings. When there is more overlap, there is more potential for air/fuel mixture to go straight from the intake valve, out the exhaust valve (versus remaining trapped inside the cylinder). This will be reflected as more unburned hydrocarbons and air in the exhaust gas. Keeping the camshaft timing stock, but simply inceasing the lift with greater-ratio rockers, I don't think would cause any emissions disaster. 1.6 rockers also increase duration, about 3 degress more.