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Here is our very own James Kostuchowski's article on direct injection versus port injection!
James Kostuchowski is a senior account manager at Tri Star Engines. Jim has been with the company over a decade and was even previously employed at one of our largest competitors. His sales territory has ranged from all of Wisconsin to parts of the Upper Peninsula of Michigan. In his free time he enjoys attending car shows with his Grabber Orange Ford Mustang and Cadillac CTS, collecting vintage signs and gas pumps and working with investments. Jim is a vault of automotive knowledge packed with positive energy, and if you are an automotive parts store or repair shop in Central Wisconsin, you may just find him knocking on your door. Reach out to Jim by emailing firstname.lastname@example.org!
Direct Injection and Port Injection use computer-controlled electric injectors to spray fuel into the engine. The difference is where they spray the fuel.
Direct injection has the injectors mounted in the cylinder head and the injectors spray fuel directly into the engine cylinder. It then mixes with the air. Only air passes through the intake manifold runners and past the intake valves with direct injection.
There are advantages and disadvantages of both systems. The advantages of direct injection is better fuel economy, less emissions, and better performance. Fuel economy improvements can be as much as 15%, allowing much less fuel to be wasted.
It delivers fuel more precisely to increase better combustion with more power while maintaining better fuel economy and lowering emissions. A 25% emission drop at cold-start is possible.
Direct injection meters the amount of fuel exactly into each cylinder for optimum performance and it’s sprayed under very high pressure, up to 15,000 PSI on some vehicles, so the fuel atomizes well and ignites almost instantly.
The big disadvantage of direct injection is carbon buildup on the backside of the intake valves. This can throw a computer code, and could result with an engine miss or a ignition failure.
The other disadvantage of direct injection is cost. The injector tips are mounted right into the combustion chamber, so the materials of the injector have to be very good quality.
High pressure is needed to inject fuel directly into the cylinders which means expensive high-pressure fuel pumps are needed. They are typically mechanically driven from the engine, which adds to the complexity.
The main reason we are seeing vehicles on the market with direct injection, is tighter fuel economy standards.
Port injection sprays the fuel into the intake ports where it mixes with the incoming air.
Port injection systems are much cheaper to manufacture. The injectors are not exposed to the high heat and pressure of the combustion chamber and they don’t have to handle high fuel pressures.
Port injection systems typically operate in the 30 to 60 PSI range, which is dramatically lower than direct injection systems. Support systems such as fuel pumps are also cheaper, because fuel pressures are lower.
Port injection systems spray the fuel on the backside of the intake valve and the fuel has to wait till the valve opens. The fuel sprayed on the backside of the intake valves, also cleans the valves.
The injectors are often mounted in the intake manifold runners and the fuel sits in the runners until the intake valve opens and the mixture is pulled into the engine cylinder.
I can see a time when port injection systems will be completely replaced by direct injection. Port injection, although much better than the old carburetors, throttle body systems, just can’t match the power and economy produced by direct injection.
Some manufacturers like Ford, Lexus, Toyota, and Audi, are going to a combination of port & direct injection called duel fuel delivery. The latest Ford Mustang and Shelby GT350 has a combination of port & direct injection.
As fuel costs increase, the difference in manufacturing cost between port and direct injection systems will diminish. As of right now, both systems are available on new vehicles, depending on the model you select.
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