CRX_B16B
Senior Member
Here is some good info on intake manifolds
Multiport fuel injection (MPI) systems use dry intakes, which allows more flexiblity in design. Still, many variations of runner lengths and plenum size have been used. To date, the most common design for MPI performance cars is the long-runner / small-plenum type. In these manifolds long-runners build torque but also take advantage of a phenomenon known as inertial supercharging through resonance-tuning.
When the piston decends during its intake stroke, air is drawn through the intake runner. This airflow has momentum, and whan the intake valve colses, the air in the runner continues forward and crashes in the back of the valve. The air then "bounces" back, creating a reverse airflow back towards the plenum. When it reaches the wall of air in the plenum, it agin recoils and heads back towards the intake valve. if the intake valve opens at this moment, the incoming air gets a boost from the airflow wave already in the runner, which aids velocity, thus enhancing cylender fill. Resonace tunning is the practice of selecting a runner length and crosssection that will create this situation consistantly. Camshaft profile must be designed to coincide with the runner so that the intake valve opens at the right time to "catch the wave."
While resonance tuning works well to build midrange power, it also creates a narrow margin of efficencyfor the manifold, sinsce the inertial supercharging effect will only really work in a limited rpm range. To get around this, some manufactuers introduced dual runner intakes: one short, one long (as seen on Yamaha-built Ford Taurus SHO engines and the LTS Corvette). This gives the benefits of tuned runners for low rpm and short runners for high rpm.
The down side of a dry intake manifold is that it often transfers a lot of engine heat to the air charge that passes through it. The fuel in a wet manifold acts like a coolant and reduces intake-charge temperature. This is why placing bags of ice on the intake of a MPI engine brings such positive results at the drags.
Thanks to: Terry McGean from HOT ROD MAGIZINE
Multiport fuel injection (MPI) systems use dry intakes, which allows more flexiblity in design. Still, many variations of runner lengths and plenum size have been used. To date, the most common design for MPI performance cars is the long-runner / small-plenum type. In these manifolds long-runners build torque but also take advantage of a phenomenon known as inertial supercharging through resonance-tuning.
When the piston decends during its intake stroke, air is drawn through the intake runner. This airflow has momentum, and whan the intake valve colses, the air in the runner continues forward and crashes in the back of the valve. The air then "bounces" back, creating a reverse airflow back towards the plenum. When it reaches the wall of air in the plenum, it agin recoils and heads back towards the intake valve. if the intake valve opens at this moment, the incoming air gets a boost from the airflow wave already in the runner, which aids velocity, thus enhancing cylender fill. Resonace tunning is the practice of selecting a runner length and crosssection that will create this situation consistantly. Camshaft profile must be designed to coincide with the runner so that the intake valve opens at the right time to "catch the wave."
While resonance tuning works well to build midrange power, it also creates a narrow margin of efficencyfor the manifold, sinsce the inertial supercharging effect will only really work in a limited rpm range. To get around this, some manufactuers introduced dual runner intakes: one short, one long (as seen on Yamaha-built Ford Taurus SHO engines and the LTS Corvette). This gives the benefits of tuned runners for low rpm and short runners for high rpm.
The down side of a dry intake manifold is that it often transfers a lot of engine heat to the air charge that passes through it. The fuel in a wet manifold acts like a coolant and reduces intake-charge temperature. This is why placing bags of ice on the intake of a MPI engine brings such positive results at the drags.
Thanks to: Terry McGean from HOT ROD MAGIZINE
