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First we look at what exactly an intake manifold is and what it does.
An intake manifold is a device that connects between your throttle body and your cylinder head. It’s comprised of four main parts, the inlet, the runner, the surge tank and the fuel delivery method.
Easiest to explain is the inlet, this is the part where the throttle body or carburettor meets with the surge tank or in some cases, the runners directly.
The runners are the individual tubes connecting the cylinder head to the surge tank and in multi-port injected engines (2.0T, MPI 3.8) also house the injector boss, the hole that supports the injector and allows it to deliver fuel.
The surge tank is typically a tank of sorts that acts as a reservoir to feed the runners air. It comes in many shapes and sizes and in some applications is a separate piece such as the 3.8. It usually has the throttle body directly connected to it and connects directly to the runners.
The fuel delivery method can be carburettors, port injection or multi-port injection. I won’t cover these in length but the 2.0T and the MPI 3.8 are multi-port meaning they have a single injector per runner. GDi’s deliver the fuel directly to the cylinder, such as the GDi 3.8.
Intake manifolds are only applicable to vehicles that do not have independent throttle bodies. In diesels it’s typically called a plenum as they don’t have throttle bodies or need to mix the fuel and air prior to entering the cylinder. GDi’s would also be more appropriate to use the word plenum as well. This is because of how the function of an intake manifold is defined.
The primary function of the intake manifold is to evenly distribute the air fuel mixture into each port of the cylinder head. Other functions are a mount for fuel delivery devices, sensors and whatever else you can come up with to put on there.
Engines can have more than one intake manifold, though it’s uncommon in modern vehicles as it’s more efficient and less expensive to share a single unit.
Next we look at different applications for intake manifolds and requirements for those applications.
In naturally aspirated engines (from here on shortened to NA) the runner length of the intake manifold seriously affects the performance of the engine. Longer runners are better for torque while shorter runners are more adept at supplying air at higher RPM’s. Some companies go as far as to make variable length runners, these self or computer adjusting runners vary in length to provide the best of both situations at the expense of added complexity and cost. NA engines also benefit from large surge tanks; these are basically air boxes post throttle body that allow the engine to breath between shifts as the throttle plate closes. It also helps with runner balance as the runners don’t try to steal air from their neighbour when their time to flow into the cylinder is up.
In turbocharged engines (from here on shortened to TE) the design of the intake manifold differs a bit. This is because the engine is not scavenging for air under load as its being provided by the turbocharger. For optimal performance a TE would have the shortest runners possible with little to no surge tank for maximum performance under load, however when driving outside of load such as cruising, it can cause some decline in performance and responsiveness. When not driving with a positively charged intake (from here on called boost) the engine acts and performs very similarly to a NA engine. Due to the fact that the surge tank is usually reduced in size for under load performance the engine is usually ran at a higher RPM for similar function to increase responsiveness and load the turbocharger readily. This has a negative effect on fuel economy that is usually mitigated by the turbocharger maintaining a small amount of turbine speed to compensate for the extra RPMs demand on the engine, it also helps provide improved low end torque to compensate for the shorter runner length.
In supercharged engines (from here on shortened to SE) you don’t want or need a surge tank and runner length is a near moot point. This is because the supercharger reacts directly with engine RPM. The supercharger housing will have a specific volume (unless centrifugal) and that volume will act as a surge tank for the supercharger, air beyond that point is ideally compressed and best acted in a similar fashion to a TE. This type of setup is really only useful to the 3.8 and most setups for the 3.8 modify the existing surge tank and use it to house the water-air intercooler, thus reducing its surge tank capacity.
Now that we have an understanding of the different designs and needs of each induction type we have to look at a few other things specific to our engines.
An intake manifold is a device that connects between your throttle body and your cylinder head. It’s comprised of four main parts, the inlet, the runner, the surge tank and the fuel delivery method.
Easiest to explain is the inlet, this is the part where the throttle body or carburettor meets with the surge tank or in some cases, the runners directly.
The runners are the individual tubes connecting the cylinder head to the surge tank and in multi-port injected engines (2.0T, MPI 3.8) also house the injector boss, the hole that supports the injector and allows it to deliver fuel.
The surge tank is typically a tank of sorts that acts as a reservoir to feed the runners air. It comes in many shapes and sizes and in some applications is a separate piece such as the 3.8. It usually has the throttle body directly connected to it and connects directly to the runners.
The fuel delivery method can be carburettors, port injection or multi-port injection. I won’t cover these in length but the 2.0T and the MPI 3.8 are multi-port meaning they have a single injector per runner. GDi’s deliver the fuel directly to the cylinder, such as the GDi 3.8.
Intake manifolds are only applicable to vehicles that do not have independent throttle bodies. In diesels it’s typically called a plenum as they don’t have throttle bodies or need to mix the fuel and air prior to entering the cylinder. GDi’s would also be more appropriate to use the word plenum as well. This is because of how the function of an intake manifold is defined.
The primary function of the intake manifold is to evenly distribute the air fuel mixture into each port of the cylinder head. Other functions are a mount for fuel delivery devices, sensors and whatever else you can come up with to put on there.
Engines can have more than one intake manifold, though it’s uncommon in modern vehicles as it’s more efficient and less expensive to share a single unit.
Next we look at different applications for intake manifolds and requirements for those applications.
In naturally aspirated engines (from here on shortened to NA) the runner length of the intake manifold seriously affects the performance of the engine. Longer runners are better for torque while shorter runners are more adept at supplying air at higher RPM’s. Some companies go as far as to make variable length runners, these self or computer adjusting runners vary in length to provide the best of both situations at the expense of added complexity and cost. NA engines also benefit from large surge tanks; these are basically air boxes post throttle body that allow the engine to breath between shifts as the throttle plate closes. It also helps with runner balance as the runners don’t try to steal air from their neighbour when their time to flow into the cylinder is up.
In turbocharged engines (from here on shortened to TE) the design of the intake manifold differs a bit. This is because the engine is not scavenging for air under load as its being provided by the turbocharger. For optimal performance a TE would have the shortest runners possible with little to no surge tank for maximum performance under load, however when driving outside of load such as cruising, it can cause some decline in performance and responsiveness. When not driving with a positively charged intake (from here on called boost) the engine acts and performs very similarly to a NA engine. Due to the fact that the surge tank is usually reduced in size for under load performance the engine is usually ran at a higher RPM for similar function to increase responsiveness and load the turbocharger readily. This has a negative effect on fuel economy that is usually mitigated by the turbocharger maintaining a small amount of turbine speed to compensate for the extra RPMs demand on the engine, it also helps provide improved low end torque to compensate for the shorter runner length.
In supercharged engines (from here on shortened to SE) you don’t want or need a surge tank and runner length is a near moot point. This is because the supercharger reacts directly with engine RPM. The supercharger housing will have a specific volume (unless centrifugal) and that volume will act as a surge tank for the supercharger, air beyond that point is ideally compressed and best acted in a similar fashion to a TE. This type of setup is really only useful to the 3.8 and most setups for the 3.8 modify the existing surge tank and use it to house the water-air intercooler, thus reducing its surge tank capacity.
Now that we have an understanding of the different designs and needs of each induction type we have to look at a few other things specific to our engines.
