 One Emmy here again and welcome to another episode of Cobb U. A supplying fuel to our engines has come a long way since carburetors. Now while that's still a go-to method for old school hot rodders, most modern engines take advantage of the additional control that electronic fuel injection provides. Modifications that make more power often require increased fuel delivery, where people used to upgrade carbs, now they upgrade injectors. But the reason for upgrading is the same. Your stock fuel system can usually accommodate a small increase in power, but can only supply so much fuel. So if you're wanting to increase power enough, you're going to need to upgrade your fuel system. So to gain a better understanding of how your fuel system works, let's take a closer look at the various types of modern systems, the basic components, and how all the parts work together. We'll start by looking at the various systems. Electronic fuel injection in gasoline burning engines has predominantly used port injection over the last few decades. Now I specify gasoline because, well, diesel, for example, works differently, and that's beyond the scope in this series. With port injection, fuel is injected upstream of the cylinder head intake ports, usually in the intake manifold or an intermediate housing between the intake manifold and cylinder head. As air flows from the intake manifold into the combustion chamber, fuel from the injectors is carried with it. Recently, direct injection or DI systems have become more widely used. Where port injection injects fuel before the combustion chamber, direct injection, as the name implies, involves injecting fuel directly into the combustion chamber. Direct injection allows for extremely precise timing of fuel delivery, with greater atomization and evaporation of fuel. Now with greater control and cooling from the extra evaporation, you can create more power, all while being more fuel efficient and reducing emissions. While DI is the new hotness and port injection is less common on new cars, performance enthusiasts still love port injection because there are proven upgraded injector and pump options, making the system more desirable to those who want to add lots more power through modification. Fuel systems can be separated into two styles, return and return lists. They differ in layout, but much of the system is very similar. Both pump fuel from the tank to the engine bay, and both use an aptly named fuel pressure regulator to regulate the fuel pressure. Return style systems generally regulate pressure near the injectors in the engine bay. Some fuel is injected into the engine and excess fuel, released by the regulator, travels through a return hose back to the fuel tank. In a returnless system, fuel pumped forward can only exit the system through the injectors and into the engine. It's a one-way trip. The regulator is generally located in the fuel tank after fuel exits the pump, but before the fuel flows forward to the engine bay. Excess fuel bypassed by the regulator stays in the tank. Port injection systems can be return style or return lists, while direct injection systems are only return lists. In DI systems, fuel coming from the in-tank pump is boosted to high pressure by a secondary high-pressure fuel pump mounted to the engine, which uses an electronic solenoid to control output. There are pros and cons to both systems. For example, in a return system, regulating pressure close to the injectors can provide more precise and consistent fuel pressure supply to the injectors, especially during rapidly changing conditions. On the other hand, they have more plumbing, and some of the fuel ends up making a loop from the tank to the engine bay. Out the regulator and right back to the tank where it started without being used. Now that we've gone over different fuel system styles, let's take a look at the components. For today's demonstration, we'll be using components from a Subaru WRX STI, which has a port injection return fuel system. For those of you with direct injection, hang in there with us because some of this will still apply and we'll go over the unique components and controls of direct injection in just a moment. The primary components we'll be looking at are the fuel pump, the fuel filter found in the pump housing, injectors, and fuel pressure regulator. Granted, these aren't the only components of our fuel system, but they are the ones that are commonly upgraded in the search for more power. First up, the fuel pump. This is the component that sucks fuel from the tank and sends it through the system. It has a pre-filter or fuel suck, inlet fitting, the pumping mechanism, outlet fitting, side clips to hold the pump in place, and electrical connector. Then we have our main filter, which is inside the pump housing and prevents harmful debris from getting into your injectors. Next we have our injectors, which control fuel flow into your engine. Here's the inlet, the body, outlet, electrical connector, adapters, and O-rings. Last we have our fuel pressure regulator, which controls the pressure of the fuel being supplied to the injectors. There's an inlet where fuel enters here. A hose connects from the intake manifold to the reference port here. That controls the diaphragm and valve inside the body, which manages fuel flow that ultimately controls the pressure. And last, the outlet, also called the return. This is where excess fuel gets diverted back to the fuel tank. Now that we've seen all the components, how does it all come together? One note, to make it easier to see on camera, we've used generic red hoses to represent the feed and return lines. So on your car, these are going to look a lot different. Beginning in the rear, in a port injection setup, we have the fuel tank, which houses the fuel and the fuel pump. The pump sits inside a housing near the bottom of the tank, and the pre-filter prevents large debris from entering the inlet. Fuel is pumped out of the tank, then travels through the main fuel line, known as the feed line, because it feeds the injectors. Fuel travels the length of the car through a combination of hard and soft lines until it reaches the engine bay. Once the fuel has made its way to the engine bay, it gets routed to the fuel rails. From the fuel rails, fuel will go one of two places, either through the injectors, or through the fuel pressure regulator, then down a return hose and back to the fuel tank. The fuel pressure regulator bypasses excess fuel back to the tank to maintain the appropriate fuel pressure to the injectors. So how does the regulator know what's going on inside the intake manifold? Well, like a few other components on our engine, it operates off a diaphragm in spring. This air hose connects the top side of the diaphragm in the fuel pressure regulator to the intake manifold. If there's vacuum in the manifold, it helps pull the diaphragm and causes the fuel pressure regulator's valve to open and bypass more fuel back to the tank. If there's boost in the manifold, it helps close the regulator's valve, increasing the fuel pressure to the injectors. In a returnless system, the fuel pressure regulator is in or near the tank, so this regulator and return hose wouldn't be here. Now let's get back to fuel pressure, why it's important in how the regulator controls it. When you hear people talk about their fuel injectors, you'll hear them throw out numbers like 1,000s or 1,300s. What they're telling you is the maximum fuel volume the injectors can flow. A key factor that isn't mentioned is the amount of pressure that was used to create that amount of flow. Take back to our episode on turbos, where we talked about how naturally aspirated engines can only breathe in so much air. When you add a turbo, that added pressure drives more air into the engine. Our injectors work similarly, and that the higher fuel pressure in the rails, the more the injectors can potentially flow. Fuel injectors are often rated for flow based on 43.5 psi of fuel pressure, which happens to be the base fuel pressure of a Subaru WRX STI. Cobb 1300cc injectors, or 1300s, get their name because they can flow about 1300ccs, or cubic centimeters, of fuel per minute if the injectors provide their maximum output with 43.5 psi of supply pressure. Those same injectors flow about 1600cc of fuel per minute if they're supplied with 60 psi instead of 43.5 psi. By the same token, if we have less fuel pressure than we should, perhaps 30 psi, the injectors can't flow as much and may not atomize fuel as well. This reduces cylinder cooling and makes for poor air-fuel mixing, which can cause misfiring and poor combustion in general. There's another big factor to discuss when talking about fuel pressure. The injector has an inlet and an outlet, and to get the fuel to go from the rail into the inlet, out the outlet, and into the engine, we need to do more than just ask our injector to move the fuel along nicely. So although you'll most likely never need to do the math to explain this, I'm going to go back to our old school high school days and be using a lot of algebra in this episode. So for those of us that gave our algebra teachers a lot of heat back in school, they're about to feel really justified. Fuel like air will always move from an area of higher pressure to an area of lower pressure. Fuel pressure on the inlet side of the injector has to be higher than the air pressure on the outlet side for fuel to flow in the direction we want. If the air pressure on the outlet side is higher than the fuel pressure because we're making a bunch of boost, we won't inject any fuel into the manifold. Instead, we'd inject air from the manifold into our fuel system, which is the opposite of what we're trying to do here. As I mentioned earlier, our Subaru runs 43.5 pounds of base fuel pressure. That number is actually based on the difference between the fuel pressure and manifold air pressure. If you key the car on without starting it, the fuel pump runs for a few seconds and the system builds about 43.5 psi. Because the engine isn't running, there is zero pressure in the manifold. When you want to find the difference between two things, you subtract. So 43.5 minus zero equals 43.5. So the difference between the inlet and outlet pressure is 43.5 psi. From here on out, I'll be referring to that pressure across the injector as differential fuel pressure, which is the difference between the intake and outlet pressures. When we start our engine and let it idle, the engine sucking air in through the almost closed throttle body creates a vacuum in the intake manifold. Now to get the difference of 43.5 psi from the inlet of our injector to the outlet and to keep the injector flow consistent, we now actually need less fuel pressure because that vacuum in the intake manifold is trying to suck fuel out of the injector into the engine. When doing the math, keep in mind that vacuum is a negative pressure compared to atmospheric pressure and boosts as a positive pressure. Intake manifold vacuum at idle on this car is about negative 10 psi. If we supplied the injector with 43.5 psi of fuel pressure, the math would look like this. 43.5 minus negative 10 psi equals 43.5 plus 10, which equals 53.5 psi. At 53.5 psi of differential fuel pressure, we have 10 more psi across the injector than we want. To avoid this, the fuel pressure regulator uses the reference hose to the intake manifold vacuum to open the regulator up more. This bypasses more fuel from the rail back to the tank, kind of like a wastegate bypasses exhaust gases to reduce turbine pressure. So how much fuel pressure do we need to supply to our injectors to maintain that 43.5 psi differential fuel pressure when our intake manifold is at negative 10 psi? Let's bring back that algebra and solve for x, which is going to be our fuel pressure that we need to supply. The equation will look like this. X minus intake manifold pressure equals 43.5 psi. So in this case, X minus negative 10 equals 43.5, which converts to X plus 10 equals 43.5. So X equals 33.5 psi. So 33.5 psi of fuel pressure is what we need to supply our injectors in this idle condition to keep the difference of 43.5 psi across our injector. Now going in another direction, let's say we floor it and we're making 10 pounds of boost in the intake manifold. How much fuel pressure do we need to maintain that differential fuel pressure that we're looking for of 43.5 psi? Now in this case, positive 10 is our intake manifold pressure. So X minus 10 equals 43.5 psi. So X is going to be 53.5 psi. So there you have it, 53.5 psi of fuel pressure is what you need. Keep turning up that boost and you'll need to keep increasing your fuel pressure so that your injectors can do their job properly. Now that we've gone over the major components and you have a basic understanding of how your fuel system works, let's talk about how upgrading those fuel system components can help support your other modifications, like upgrading your turbo. It's going to require more fuel for the more air you'll be pushing. Or maybe you want to run a higher concentration of ethanol, which compared to gasoline, can require over 40% more fuel by volume in order to achieve that balanced air fuel mixture. In many cases with the added fuel demand these modifications require, upgrading your injectors and fuel pump are necessary and you'll usually want to perform this at the same time and here's why. If you upgrade to higher output injectors but your fuel pump can't provide adequate fuel pressure, well then those bigger injectors aren't going to let you make any more power. By the same token, if your injectors are operating at max flow held wide open and your fuel pressure is on target, upgrading your fuel pump alone isn't going to allow you to inject any more fuel. In regards to tuning, upgrading your fuel pump alone you might not necessarily need a tune. If your regulator can manage your fuel pressure despite the increased flow then you're good to go. When it comes to fuel pressure regulators and injectors however, that's a different story. If you plan on running anything other than your stock injectors, you're going to need to plan for a tune. When considering injectors, you'll want to look at a set that meets your needs with a little headroom without going too big. There's no point in running a massively large 2200cc injector on a street car you're going to be driving to work. The trade-off and drivability just isn't worth it. So how do I figure out what injectors I need for my engine? Well, this is actually a loaded question. Many companies will have kits or stage packages that are designed to go with specific injectors or the proper injector will come with your purchase. If you're wanting to go the custom route, you should contact your local pro tuner so that they can find the injector that meets your engine's needs and their tuning preferences. If you want to learn more about injector sizing, visit the extra credit below. Lastly, when doing this type of part install, you will generally use these kinds of tools. Ratchet, sockets and extensions, screwdrivers, zip ties and dykes, lube, rags, hose pinching pliers, eye protection and fire extinguisher, and most importantly, no open flames. That's going to do it for this episode. In our next video, we're going to talk about what happens when the air and fuel mix in the cylinder to create that power that drives your engine. Thanks for joining us. Be sure to subscribe to our YouTube channel so you can check out future episodes. I'm Emmy, your host for Cobb U. Remember, check out Cobbtuning.com for all your parts and tuning needs. Do you like the storage solutions featured in our studio? 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