A question was asked in another thread about upgrading or adding direct injection or DI to a standard port injected coyote motor, and I realized that maybe a small tutorial was needed.
First off a little background, port injected uses injectors in the intake port to inject fuel into the air stream just before the intake valve. The air fuel mix is then sucked into the combustion chamber and compressed during the compression stroke. Because of this setup most naturally aspirated engines can only have a max of 11-11.5:1 compression ratio on pump gas (93 octane) as they are susceptible to detonation or pre-ignition. With the ever tightening federal C.A.F.E. standards the auto manufactures developed direct injection to try to meet the new standards.
What is direct injection? Well the manufactures borrowed technology from the diesel engine to develop DI, the fuel injector was moved from the intake port right into the cylinder head injecting fuel directly into the combustion chamber, hence the name direct injection. Along with the new high pressure injectors, new seals are required at the point where the injector goes into the head and at the fuel rail due to the extreme pressures and higher temps. Since the pressure inside the combustion chamber can reach 7-800 psi or higher, the fuel pump has to be able to create at least that much much pressure. If the fuel pressure is lower than the pressure outside the tip of the injector the combustion gases will backflow into the injector. Remember pressure flows from the higher pressure area to the lower pressure area. Because of this a new mechanical engine driven fuel pump is needed, as the standard electric powered impeller type pump is not capable of more than roughly about 100 psi.
Why direct injection? Well, DI allows for a higher static compression ratio. The 2.0 DI engine ford uses in the 2012 to current ford focus makes a 160 hp and has a 12:1 comp ratio and can run all day on 87 octane. How can this happen? Well DI injects the fuel right at the last split second before the spark plug ignites the air/fuel mix. Because of this, the chances of detonation is greatly reduced as the air/fuel mix does not have time to pre-ignite, and an added benefit is the slight cooling effect the fuel has during the injection process there-by reducing the chances of detonation even further. Why bother with higher compression ratios in the first place? Well higher compression allows for higher hp output out of a given displacement. 20 years ago extracting 160 hp out of a 2.0 liter 4 cylinder was unheard of from an american manufacturer, the norm back then was around 100-110 hp. And getting more power out a smaller engine equates to better fuel economy.
The drawback to DI is accelerated carbon buildup on the backside of the intake valve. A normal port injected engine has fuel sprayed onto the back of the valve washing off the oil/carbon residue and they rarely have any carbon buildup problems. Since DI engines no longer have fuel spraying the back of the valve, they get carbon buildup. How does the carbon get there in the first place? Simple answer, the PCV system. Some think that by using a high quality fuel you can reduce or eliminate the carbon buildup, personally I think that is hogwash. The carbon/oil gets there thru the PCV system in the first place, so that means the buildup is a byproduct of blowby, so when you have a higher load on a DI engine you get more buildup, it's that simple. To reduce or eliminate buildup you either have to drive like a granny to reduce the load on the engine or eliminate the PCV system all-together and run breathers like the old cars did back in the early sixties.
Ford found an elegant and an environmentally friendly solution to the buildup problem, they added back in port injection on DI engines. The DI system is kept as the primary fueling setup and port injection is added in small amounts just to wash the back of the intake valves. The first DI engine to get the new dual fuel setup is the second generation 3.5 ecoboost used in the 2017 f150. The fist gen had 365 hp with only DI and twin turbos. The second gen gets 375 hp with dual injection in the standard version. The high output version only available in the 2017 raptor gets 450 hp, and the the new ford GT gets a special 600 hp version, all out of a 3.5 L v-6. The 2018 5.0 coyote is slated to also get this new dual fuel setup and is rumored to get 455 hp in the mustang.
First off a little background, port injected uses injectors in the intake port to inject fuel into the air stream just before the intake valve. The air fuel mix is then sucked into the combustion chamber and compressed during the compression stroke. Because of this setup most naturally aspirated engines can only have a max of 11-11.5:1 compression ratio on pump gas (93 octane) as they are susceptible to detonation or pre-ignition. With the ever tightening federal C.A.F.E. standards the auto manufactures developed direct injection to try to meet the new standards.
What is direct injection? Well the manufactures borrowed technology from the diesel engine to develop DI, the fuel injector was moved from the intake port right into the cylinder head injecting fuel directly into the combustion chamber, hence the name direct injection. Along with the new high pressure injectors, new seals are required at the point where the injector goes into the head and at the fuel rail due to the extreme pressures and higher temps. Since the pressure inside the combustion chamber can reach 7-800 psi or higher, the fuel pump has to be able to create at least that much much pressure. If the fuel pressure is lower than the pressure outside the tip of the injector the combustion gases will backflow into the injector. Remember pressure flows from the higher pressure area to the lower pressure area. Because of this a new mechanical engine driven fuel pump is needed, as the standard electric powered impeller type pump is not capable of more than roughly about 100 psi.
Why direct injection? Well, DI allows for a higher static compression ratio. The 2.0 DI engine ford uses in the 2012 to current ford focus makes a 160 hp and has a 12:1 comp ratio and can run all day on 87 octane. How can this happen? Well DI injects the fuel right at the last split second before the spark plug ignites the air/fuel mix. Because of this, the chances of detonation is greatly reduced as the air/fuel mix does not have time to pre-ignite, and an added benefit is the slight cooling effect the fuel has during the injection process there-by reducing the chances of detonation even further. Why bother with higher compression ratios in the first place? Well higher compression allows for higher hp output out of a given displacement. 20 years ago extracting 160 hp out of a 2.0 liter 4 cylinder was unheard of from an american manufacturer, the norm back then was around 100-110 hp. And getting more power out a smaller engine equates to better fuel economy.
The drawback to DI is accelerated carbon buildup on the backside of the intake valve. A normal port injected engine has fuel sprayed onto the back of the valve washing off the oil/carbon residue and they rarely have any carbon buildup problems. Since DI engines no longer have fuel spraying the back of the valve, they get carbon buildup. How does the carbon get there in the first place? Simple answer, the PCV system. Some think that by using a high quality fuel you can reduce or eliminate the carbon buildup, personally I think that is hogwash. The carbon/oil gets there thru the PCV system in the first place, so that means the buildup is a byproduct of blowby, so when you have a higher load on a DI engine you get more buildup, it's that simple. To reduce or eliminate buildup you either have to drive like a granny to reduce the load on the engine or eliminate the PCV system all-together and run breathers like the old cars did back in the early sixties.
Ford found an elegant and an environmentally friendly solution to the buildup problem, they added back in port injection on DI engines. The DI system is kept as the primary fueling setup and port injection is added in small amounts just to wash the back of the intake valves. The first DI engine to get the new dual fuel setup is the second generation 3.5 ecoboost used in the 2017 f150. The fist gen had 365 hp with only DI and twin turbos. The second gen gets 375 hp with dual injection in the standard version. The high output version only available in the 2017 raptor gets 450 hp, and the the new ford GT gets a special 600 hp version, all out of a 3.5 L v-6. The 2018 5.0 coyote is slated to also get this new dual fuel setup and is rumored to get 455 hp in the mustang.
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