WHAT IS REVERSION??? Reversion is simply the intake and exhaust gases momentarily flowing backwards during the overlap phase of the camshaft at low cycling rates. Overlap means just what the word implies. The intake event overlaps the exhaust event and the exhaust event overlaps the intake event. The overlap event starts with the piston on the exhaust stroke. As the piston is pushing out the last of the exhaust gases and about 30 or so degrees before the piston reaches top dead center the intake valve begins to open. At low cycling rates the intake charge and the exiting exhaust pulse have not yet created any momentum. Thus the piston pushes some of the spent exhaust gas into the intake manifold. That is why engines with big camshafts have that radical sounding idle. The exhaust pulses shoots up into the intake manifold causing a major disturbance. The cylinders receive an uneven mixture of air, fuel, and spent exhaust gas.
Why??? Today's performance engines evolved from cars that never intended to have water mix with the exhaust. This is where the car camshaft (Summit) and the marine camshaft (Lightning) separate. The extensive overlap found in the car camshaft engine will tolerate water in the exhaust. In the Lightning Reversion Reducing Performance Camshaft and Lifter Combs every effort is made to reduce overlap especially in regards to exhaust valve closing point. With reversion greatly reduced, if not totally eliminated, the presence of water in the form of steam is still present and water migration is still an issue.
How??? Anti-reversion camshafts and lifter combs until recently were thought not even conceivable. But with today's modern engine development technology these new camshafts were created. Hours upon hours of testing have shown that with proper lobe phasing, including a increased LSA , lobe profile, and installation phasing, along with headers options and specialized lifters, that a powerful camshaft can now be produced that greatly reduces engine reversion commonly found in engine with these types of performance specifications.
