Camshafts -Carbureted vs Fuel Injected

If the inlet opens to soon, you get reversion of flow in the inlet tract and out the carby or fuel injection runners. On a carby, this reversion through the venturi causes a double or triple charge of fuel into this air. On an efi engine, the a/f ratio is uneffected by reversion.

Bottom line is on a carby engine, they run rich until the inertia in the column of air is enough to overcome reversion, where an efi car will retain good a/f ratio at lower speed.

The earlier the inlet valve opens, the more the reversion

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

Pat's correct, also without the oxygen sensor you can run more duration and closer valve seperation angle (that would be putting to much unburnt fuel in the exhaust at low rpm for the oxygen sensor to monitor correctly) that will really make some more mid/top end power.

cheers

jeremy