spencergt66
Full Access Member
Well you just asked a whole mouth full. The camshaft is one of the most important parts of the engine it will make the engine make power in higher rpms or lower rpms depending on how its configured. On a conventional engine N/A usually the more lift and duration you have the better the engine preforms @ higher rpm but with a diesel engine, turbo charged that is, Usually the rpms are lower and the torque is made lower there for the time that the valves are held open during operation or travel of the piston is less cause the engine is being force fed air,turbo charging, instead of relying on vacuum.
Now this is where you need to pay attention to where your valves open and close. On a turbo charged engine before the end of the exhaust stroke both the intake and the exhaust valves should be open for a given amount of time, valve over lap, creating what they refer to as scavenging. This is when the charge air from the turbo is pushing out any remaining exhaust gases before starting the intake stroke usualy the intake valve stays open more than the entire downward travel of the piston (180 degrees of crank shaft rotation) say the intake opens @ 10 degrees BTDC exhaust stroke and stays open until 35 degrees after BDC intake stroke or 35 degrees into the compression stroke.
Right here is where what engine types differ.
Most conventional engines are still letting charge air into the cylinder during the upward stroke or compression stroke, like our engines IDI's, this cause more heat and cylinder pressure at TDCC Where as other engine types close the inlet valve before the intake stroke has ended thus letting the charge air expand in the cylinder. And when a volume of air that is already compressed, from the turbo, and is let re-expand quickly during the downward piston travel it becomes cooler decreasing the amount of cylinder pressure and heat in the combustion chamber. When this system is used it is necessary to have a larger quantity of charge air to make up for the air expansion in the cylinder Therein lies the problem and possibly some solution to the IH IDI turbo engines.
Because the 7.3 IDI inlet valve closes @ 42.8 degrees ABDC , from what i was told, the inlet air is crammed in there to the point where its probably being pushed back out of the cylinder due to the length of upward piston travel.
More then likely if the inlet valve was closed before the bottom of the intake stroke then you could have more charge air less emissions and a better balanced engine
Hope that helps
Now this is where you need to pay attention to where your valves open and close. On a turbo charged engine before the end of the exhaust stroke both the intake and the exhaust valves should be open for a given amount of time, valve over lap, creating what they refer to as scavenging. This is when the charge air from the turbo is pushing out any remaining exhaust gases before starting the intake stroke usualy the intake valve stays open more than the entire downward travel of the piston (180 degrees of crank shaft rotation) say the intake opens @ 10 degrees BTDC exhaust stroke and stays open until 35 degrees after BDC intake stroke or 35 degrees into the compression stroke.
Right here is where what engine types differ.
Most conventional engines are still letting charge air into the cylinder during the upward stroke or compression stroke, like our engines IDI's, this cause more heat and cylinder pressure at TDCC Where as other engine types close the inlet valve before the intake stroke has ended thus letting the charge air expand in the cylinder. And when a volume of air that is already compressed, from the turbo, and is let re-expand quickly during the downward piston travel it becomes cooler decreasing the amount of cylinder pressure and heat in the combustion chamber. When this system is used it is necessary to have a larger quantity of charge air to make up for the air expansion in the cylinder Therein lies the problem and possibly some solution to the IH IDI turbo engines.
Because the 7.3 IDI inlet valve closes @ 42.8 degrees ABDC , from what i was told, the inlet air is crammed in there to the point where its probably being pushed back out of the cylinder due to the length of upward piston travel.
More then likely if the inlet valve was closed before the bottom of the intake stroke then you could have more charge air less emissions and a better balanced engine
Hope that helps