Fuel Systems 101
My experience in the past has been with Turbo and Supercharged cars, like the one I own now. I thought this article would give some newbies some insight regarding what exactly goes into a forced induction car. Enjoy everyone.
This is an article dedicated to the four components that often do not receive the attention and recognition they deserve, yet support the forced induction like Nitrous, Superchargers, and Turbos that are glamorized in every other thread. Today we talk about Fuel Pumps, Fuel Pressure Regulators, Fuel Rails / Hoses and Fuel Injectors.
The Basic Fuel Cycle
On most modern fuel-injected cars, fuel is delivered via an in-tank pump. From the pump, it travels through hoses and is filtered eventually leading to the fuel rail. The fuel rail holds the injectors that support the atomization of fuel for combustion in combination with the air from the intake. The fuel pressure regulator simply maintains the pressure inside the fuel system, and also reticulates excess fuel into the fuel tank to restart the fuel cycle.
Fuel Pumps and Fuel Pressure Regulators
Fuel pumps serve two main purposes. The first is to move fuel from the tank to the engine. And the other is to move enough fuel to maintain pressure within the system. Keep in mind before we get too far ahead here, is that the fuel pressure regulator maintains pressure but it’s the fuel pump that puts the fuel in the system to make pressure. Confused? Don’t be. Simply put, if there’s not enough pressure from the fuel pump, the fuel won’t be able to spray very far. Therefore, the Fuel Pressure Regulator and the Fuel Pump must work together in order to deliver the fuel to support combustion. Fuel pumps are rated in either (Lph) liters per hour or (Gph) gallons per hour. This rating is based on how much fuel the pump is rated to deliver over a given period of time. That number is depended also on the voltage rating e.g. 10V at 100 Gph. The higher the voltage, the more fuel the pump can move. Why is this important? Because if you don’t have the necessary voltage to support the max flow capacity of the pump, you may not receive the adequate fuel required to support your forced induction. Fuel Pressure Regulators on the other hand maintains the pressure within the system to ensure the fuel going through the injectors atomizes properly. The FPR also effects idle, so lowering the FPR may cause your car to stall, or even worse, may cause pre-detonation problems on the high end. Most cars idle at 30-45 PSI, with some exceptions. Raise the FPR too high, fuel volume will decrease and you’ll get a similar problem. There are also different types of FPR’s available to aftermarket performance.
Type 1: A Fuel Pressure Regulator that runs on a proportion like a 1:5 Fuel Pressure Regulator. These are the most common FPR’s available. Two main companies that are widely used are Holley and Walbro (which are actually the same company by the way).
Type 2: A Fuel Pressure Regulator that runs as a variable. This is a new type of FPR that has been seen only on a few newer Turbo and Supercharged cars. This type is commonly seen on the Comptech Superchargers, and some Jackson Racing Superchargers that are more “linear” gains throughout the RPM range. The Comptech Supercharged NSX uses this type of FRP (just as with other Comptech FPR's like that of the Supercharged V6 Accord and S2000).
Fuel Rails
Fuel Rails and Fuel Hoses are not just pretty looking pieces of red and blue in your engine bay, but actually serve one main purpose: Hold those big Fuel Injectors! Your average fuel rail supports up to 400 HP without the use of Nitrous. Larger hoses may also be needed depending on how much HP you goal is. However, most cars car run on stock sizes alone, again depending on what your long term HP goals are.
Fuel Injectors
Fuel Injectors are rated by flow capacity which measure how much fuel is delivered through a wide-open injector over a period of time. On typical imports you’ll see them measured in cc/min, however lb/hr is also common.
To convert from lb/hr to cc/min simply multiply the lb/hr by 10.5 and you’ll get cc/min.
The duty cycle measures how hard the injector works as a percentage of the time open. An engine at redline will normally operate its injectors at about 85 percent duty cycle. Anything in excess of 85% and the injector loses its efficiency because the valve doesn’t have enough time to close before it has to open again. Therefore making sure your duty cycle never exceeds 85, you might want to think about getting bigger injectors. In order to find the correct size, you need to know the BSFC or, Brake Specific Fuel Consumption of the engine. To find this number, normally you would need to do yet another calculation formula (how many pounds of fuel are needed to make one horse power for 1 hour – the more coefficient, the lower the number). Luckily, someone already did this for your car, and just need to look up the number for your engine. Your typical B, H, and D Series Turbo engine will run around 0.55. While your stock engine will be around 0.46.
Ok, so how do you determine what size injector you are going to need? Use this formula and you’ll be well on your way.
(Engine Flywheel Horsepower) x (BSFC)
(Number of Injectors) x (Duty Cycle)
then, multiple that value by 10.5. That value will equal the injector size (cc/min) for your import.
Here’s an example: Vic wants a 400 HP at the crank NSX. The BSFC for his engine is 0.55 (not exact value, just an example). In his 6-cylinder NSX, there are 6 injectors, and he wants to place the max duty cycle at 85% for the injectors.
(400) x (0.55)
(6) x (0.85)
= 220 / 5.1 = 43.13 (lb/hr) X 10.5 = 452 (cc/min).
Vic now knows that he is going to need to look for an injector size around the 452 value. He finds two sizes around the 452 value. One injector is rated at the 441, and the other at 545. Which one does he chose? Since Vic knows the values mean max flow capacity, the 441 injector maxes at that value. Therefore, Vic would more than likely chose the 441 injector and make that a realistic goal at 380-390 at the crank. Since the 545 injector is approximately 90 more cc/min more, he may have idling problems if producing more fuel. Unless of course he increases his HP goals. Keep in mind that these figures are simply an example, and may not reflect exact injectors required with some forced induction kits out there.
Stock cars we meant to run on stock injectors. So, either a piggyback ECU or programmable aftermarket ECU may be necessary to install. Keeping that in mind, you need to make sure there is an aftermarket piggyback ECU or Programmable ECU available for your car. If not, you will have problems since the engine will not properly adjust to these changes. For NSX owners, this means either using the Comptech ESM as a piggy-back or, waiting for another aftermarket piggyback/programmable ECU to be developed.
Source Data:
NOPI Street Compact Magazine, Aug/September 2003 Issue.
Honda/Acura Engine Performance, Written by Mike Kojima.
Comptech USA: Chad the “Technical God”
RPM NYC: Suppy, Tommy, Chan, Jack, and Tony thanks!
My experience in the past has been with Turbo and Supercharged cars, like the one I own now. I thought this article would give some newbies some insight regarding what exactly goes into a forced induction car. Enjoy everyone.
This is an article dedicated to the four components that often do not receive the attention and recognition they deserve, yet support the forced induction like Nitrous, Superchargers, and Turbos that are glamorized in every other thread. Today we talk about Fuel Pumps, Fuel Pressure Regulators, Fuel Rails / Hoses and Fuel Injectors.
The Basic Fuel Cycle
On most modern fuel-injected cars, fuel is delivered via an in-tank pump. From the pump, it travels through hoses and is filtered eventually leading to the fuel rail. The fuel rail holds the injectors that support the atomization of fuel for combustion in combination with the air from the intake. The fuel pressure regulator simply maintains the pressure inside the fuel system, and also reticulates excess fuel into the fuel tank to restart the fuel cycle.
Fuel Pumps and Fuel Pressure Regulators
Fuel pumps serve two main purposes. The first is to move fuel from the tank to the engine. And the other is to move enough fuel to maintain pressure within the system. Keep in mind before we get too far ahead here, is that the fuel pressure regulator maintains pressure but it’s the fuel pump that puts the fuel in the system to make pressure. Confused? Don’t be. Simply put, if there’s not enough pressure from the fuel pump, the fuel won’t be able to spray very far. Therefore, the Fuel Pressure Regulator and the Fuel Pump must work together in order to deliver the fuel to support combustion. Fuel pumps are rated in either (Lph) liters per hour or (Gph) gallons per hour. This rating is based on how much fuel the pump is rated to deliver over a given period of time. That number is depended also on the voltage rating e.g. 10V at 100 Gph. The higher the voltage, the more fuel the pump can move. Why is this important? Because if you don’t have the necessary voltage to support the max flow capacity of the pump, you may not receive the adequate fuel required to support your forced induction. Fuel Pressure Regulators on the other hand maintains the pressure within the system to ensure the fuel going through the injectors atomizes properly. The FPR also effects idle, so lowering the FPR may cause your car to stall, or even worse, may cause pre-detonation problems on the high end. Most cars idle at 30-45 PSI, with some exceptions. Raise the FPR too high, fuel volume will decrease and you’ll get a similar problem. There are also different types of FPR’s available to aftermarket performance.
Type 1: A Fuel Pressure Regulator that runs on a proportion like a 1:5 Fuel Pressure Regulator. These are the most common FPR’s available. Two main companies that are widely used are Holley and Walbro (which are actually the same company by the way).
Type 2: A Fuel Pressure Regulator that runs as a variable. This is a new type of FPR that has been seen only on a few newer Turbo and Supercharged cars. This type is commonly seen on the Comptech Superchargers, and some Jackson Racing Superchargers that are more “linear” gains throughout the RPM range. The Comptech Supercharged NSX uses this type of FRP (just as with other Comptech FPR's like that of the Supercharged V6 Accord and S2000).
Fuel Rails
Fuel Rails and Fuel Hoses are not just pretty looking pieces of red and blue in your engine bay, but actually serve one main purpose: Hold those big Fuel Injectors! Your average fuel rail supports up to 400 HP without the use of Nitrous. Larger hoses may also be needed depending on how much HP you goal is. However, most cars car run on stock sizes alone, again depending on what your long term HP goals are.
Fuel Injectors
Fuel Injectors are rated by flow capacity which measure how much fuel is delivered through a wide-open injector over a period of time. On typical imports you’ll see them measured in cc/min, however lb/hr is also common.
To convert from lb/hr to cc/min simply multiply the lb/hr by 10.5 and you’ll get cc/min.
The duty cycle measures how hard the injector works as a percentage of the time open. An engine at redline will normally operate its injectors at about 85 percent duty cycle. Anything in excess of 85% and the injector loses its efficiency because the valve doesn’t have enough time to close before it has to open again. Therefore making sure your duty cycle never exceeds 85, you might want to think about getting bigger injectors. In order to find the correct size, you need to know the BSFC or, Brake Specific Fuel Consumption of the engine. To find this number, normally you would need to do yet another calculation formula (how many pounds of fuel are needed to make one horse power for 1 hour – the more coefficient, the lower the number). Luckily, someone already did this for your car, and just need to look up the number for your engine. Your typical B, H, and D Series Turbo engine will run around 0.55. While your stock engine will be around 0.46.
Ok, so how do you determine what size injector you are going to need? Use this formula and you’ll be well on your way.
(Engine Flywheel Horsepower) x (BSFC)
(Number of Injectors) x (Duty Cycle)
then, multiple that value by 10.5. That value will equal the injector size (cc/min) for your import.
Here’s an example: Vic wants a 400 HP at the crank NSX. The BSFC for his engine is 0.55 (not exact value, just an example). In his 6-cylinder NSX, there are 6 injectors, and he wants to place the max duty cycle at 85% for the injectors.
(400) x (0.55)
(6) x (0.85)
= 220 / 5.1 = 43.13 (lb/hr) X 10.5 = 452 (cc/min).
Vic now knows that he is going to need to look for an injector size around the 452 value. He finds two sizes around the 452 value. One injector is rated at the 441, and the other at 545. Which one does he chose? Since Vic knows the values mean max flow capacity, the 441 injector maxes at that value. Therefore, Vic would more than likely chose the 441 injector and make that a realistic goal at 380-390 at the crank. Since the 545 injector is approximately 90 more cc/min more, he may have idling problems if producing more fuel. Unless of course he increases his HP goals. Keep in mind that these figures are simply an example, and may not reflect exact injectors required with some forced induction kits out there.
Stock cars we meant to run on stock injectors. So, either a piggyback ECU or programmable aftermarket ECU may be necessary to install. Keeping that in mind, you need to make sure there is an aftermarket piggyback ECU or Programmable ECU available for your car. If not, you will have problems since the engine will not properly adjust to these changes. For NSX owners, this means either using the Comptech ESM as a piggy-back or, waiting for another aftermarket piggyback/programmable ECU to be developed.
Source Data:
NOPI Street Compact Magazine, Aug/September 2003 Issue.
Honda/Acura Engine Performance, Written by Mike Kojima.
Comptech USA: Chad the “Technical God”
RPM NYC: Suppy, Tommy, Chan, Jack, and Tony thanks!
