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Originally Posted by ChItalian1027  So my engines teacher gave the class a question. Does FI require more overlap, I would assume he means valve overlap. |
No never more overlap on a boosted motor. Overlap on a N/A motor will cause a scavenging, meaning the exiting exhaust gas helps pull in the intake charge into the cylinder, good thing. The more overlap and duration in your cams will cause the motor to lose low end power but the motor will make lots of power in the high RPM's
If you run overlap on a boosted motor the boost which is being crammed through the intake, slammed by the intake valve on its way into the cylinder to create much higher cylinder pressures will just blow right through the open exhaust valve during overlap.
Ok so no overlap or very little on boosted motor: exhaust valve lets out the spent combustion gasses. That exhaust valve closes completely and the intake valve opens. With little or no overlap the cylinder gets crammed with the full boost charge and no boost blows out or is lost by the exhaust valve being open.
Every 14.7 psi of boost doubles the HP/TQ of the motor.
Nitrous motors or as we call it down here "Running the Squeeze or Juice" run good with or without overlap. You just need the right amount of enrichment fuel or it will melt pistons in less then a second.
Hope this helps, John S
Dang when I started typing this post there were no replies. No I see there are multiple replies. Ok I'm offically jacked up here and I'm drug and drink free....