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A turbocharger or supercharger increases power output by compressing air, in other words it stuffs in more air in the same volume ultimately increasing air pressure and air mass inside the engine beyond what the engine could achieve relying on atmospheric pressure alone.
However for the engine to operate properly it must operate at the correct air fuel ratio. This means that when adding forced induction and increasing the amount of air going into the engine we must also increase the amount of fuel coming into the engine.

In my example I'm turbocharging a Toyota 4AFE engine which is naturally aspirated in stock form and makes 110 horsepower. My goal is to try and increase the output to 300 horsepower by adding a turbocharger.
In stock form my engine is equipped with 200 cubic centimetres per minute fuel injectors
And my car is equipped with a fuel pump that flows 80 liters of fuel per hour.

So our fuel pump is capable of flowing more fuel than the engine will realistically ever need. This done to ensure that the fuel pump lasts a long time and isn't strained to maximum capability and it also ensures that correct fuel pressure can be maintained even as the fuel pump ages and wears.
Now let's talk about upgrades. Since I'm planning to almost triple my horsepower output I will also be pretty much tripling the amount of air coming into the engine which means that I will also need to triple the amount of fuel delivered to the engine. So a rough estimate tells us that for 300 horsepower I would need injectors that can flow around 600 cc of fuel per minute.

Now if we multiply our injector flow rate by 4 which is the number of injectors we get a result of 2400cc per minute. This is the maximum amount of fuel my injectors can flow and also the maximum amount of fuel they require. If we convert cc per minute to liters per hour we will see that this is 144 liters per hour which is well beyond the maximum amount of fuel my stock fuel pump can supply, which means that the fuel pump must also be replaced.

I have chosen to replace my stock fuel pump with an AEM High Flow In-Tank Fuel Pump.
I chose this pump because it's very compact and has the same inlet and outlet orientation as my stock pump so it will fit inside the same enclosure and bracket without modification. It's also compatible with ethanol and methanol based fuels in case I decide to run these in the future.
This fuel pump flows 340 liters per hour which is more than twice what my injectors will ever need so you might think this pump is overkill? Well not as much as you'd think and that's because this is a forced induction application. I'm trying to push a 1.6 liter 4 cylinder engine to 300 horsepower and to achieve that I will realistically need at least 20psi of boost.

This means that when the fuel injector opens and tries to spray fuel out into the intake port it will be facing 20 psi of boost pressure fighting against it. So if our fuel pressure is let's say 40 psi then the injector will essentially „waste“ 20 psi of fuel pressure just to overcome boost pressure and the result is that the injector actually discharges fuel with only 20psi behind it.

So how do we fix this? With a boost referenced adjustable fuel pressure regulator. A hose from your intake is connected to the fuel pressure regulator which then „senses“ boost pressure. The regulator has a 1:1 Boost dependent rising fuel pressure rate meaning that it will increase the fuel pressure by the amount of boost pressure it senses. So if it senses 20 psi of boost pressure it will also increase fuel pressure by 20 psi. By doing this we prevent boost pressure from reducing the discharge pressure at the injectors and distorting our air fuel ratio.
But this also means that when our turbo generates 20 psi of boost pressure, our fuel pressure will ramp up from 40 to 60 psi. And the higher the fuel pressure the more difficult it becomes for the fuel pump to maintain the same flow rate. The fuel pump itself does not produce pressure, it produces flow and the pressure level is a consequence of what your fuel pressure regulator does as well as the diameter of your fuel lines, fuel filter and other secondary factors that contribute to fuel pressure.


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#d4a #projectunderdog #boostschool

00:00 More air needs more fuel
02:30 Injector sizing formula
05:03 Boost referenced fuel pressure regulation
07:57 How to replace injectors
09:11 How to replace the fuel pump