Build Turbo Kits
Learn How To Build Turbo Kits
|Turbo How To E-Book Guides FREE! - Learn how to turbo your car.|
This informative EBook guide teaches you everything that you need to know about building your own turbo kit. It covers the hot and cold sides, turbo sizing, wastegates, BOVs, tuning and more. (57 pages, lots of photos and diagrams).
After reading this guide, you will be able to build your own LS1 (LSx) turbo kit. The guide covers all aspects of turbo charging the LS1 including heads, manifolds, cams, pistons, truck headers, tuning and more. (62 pages, lots of photos and diagrams).
FBody Rear Turbo Guide
Learn how to build your own rear mount turbo. This guide teaches you everything that you need to know about rear mount turbos. Covers the GM FBody, but there is a lot of good information that can be used on any car or truck. (42 pages, lots of photos and diagrams).
Learn how to build a turbo system for your 5.0 Mustang. You will learn about the correct turbo(s) to use, how to route tubing, engine internals (pistons, cams, crank), headers, manifolds, tuning and much more. (56 pages with lots of photos and diagrams).
|The EBook is Free, but we ask you to donate a small amount so we can pay the bills. Thank you! Download Now!||The EBook is Free, but we ask you to donate a small amount so we can pay the bills. Thank you! Download Now!||The EBook is Free, but we ask you to donate a small amount so we can pay the bills. Thank you! Download Now!|
Chapter 7 - Fuel Systems
Most stock fuel systems are not designed to work with forced induction. The stock fuel injectors combined with the stock fuel pump cannot provide enough fuel at a high enough pressure to maintain a safe air fuel ratio. Upgrading the fuel pump and injectors is a requirement for almost any forced induction.
The stock fuel pump should be replaced with an aftermarket high flow unit. These can be found for your specific application at any of the finer speed shops and large aftermarket retailers.
What size fuel pump do you need? There are a few simple calculations that will help you decide what fuel pump to use. The calculations depend on a few factors including your Brake Specific Fuel Consumption, fuel pump flow and horsepower output of your engine.
Here is a calculation that finds out how much horsepower a pump will handle.
horsepower = lb/hr (fuel) / Brake Specific Fuel Consumption (BSFC)
BSFC is a measure of an engine’s efficiency. It’s the rate of fuel consumption divided by the rate of power production.
On naturally aspirated engines, it is safe to use .5 for the BSFC. This of course varies depending on modifications etc. For a forced induction engine, the BSFC is a bit higher. We will use .6 for our calculation, but again this will vary from engine to engine.
Let’s use a 190lph fuel pump for our first example.
190lph = 50gph (One gallon of gasoline is roughly six pounds) Therefore: horsepower = 50gph x 6lbs / .6 = 300lb per hr / .6 = 500FWHP
Quite frankly, I wouldn’t want to try my luck with a 190lph pump and 500 force-fed horsepower. Some people do it, but why take a chance spending thousands of dollars in engine repair, when a $250 fuel pump can make it safe. An ounce of prevention comes to mind. Let’s take a look at a 255lph pump using the same calculation.
255lph = 67gph * 6lbs = 402 pounds per hour
Therefore: horsepower = 402 lb per hr / .6 = 670FWHP
A bit better. I’d feel safe running up to 650FWHP with a single 255lph fuel pump. If you are looking for extreme horsepower, you can always run two 255lph fuel pumps. Kits are available to run two fuel pumps inside, or outside of your fuel tank.
External Fuel Pumps
External fuel pumps can help provide extra fuel for high horsepower applications, however it will be restricted by the smallest fuel pump. If you are running a stock in-tank fuel pump with an external 255lph fuel pump, the fuel flow will be limited to the stock fuel pump’s output.
Some of the serious horsepower FI people choose to do away with the stock intake fuel pumps altogether. Instead, a custom fuel tank is used that has a sump to prevent fuel from sloshing away from the fuel lines. External pumps are used to feed the fuel rail. This gives unrestricted choices for fuel pump usage since external fuel pumps tend to be universal types.
It is required that the stock fuel injectors be replaced for almost any forced induction application. The stock fuel injectors cannot supply enough fuel to maintain a safe AFR. Your desired horsepower level will determine what size injectors to use.
Calculating Required Fuel Injector Rate
A simple calculation can be used to determine injector flow requirements. Use the following formula to match fuel injectors with your application.
Injector Flow Rate (lb/hr) = Horsepower x BSFC / Number of Injectors x Duty Cycle
An injector’s duty cycle is the percentage of time that it is powered on. The injector’s pulse width is the actual time that the injector is powered. The injector fires one time during the four cycles of its associated cylinder or once per two crank revolutions. To calculate an injector’s duty cycle, we need to know the time it takes for the crankshaft to turn two times at a given RPM, and the injector pulse width (IPW) at that RPM. Let’s take for example an engine turning 6000 RPM and an IPW of 18ms.
It takes 20 milliseconds (6000/60s = 100RPS and 1/100 = .01s and .01 x 2 revolutions = .02s) for the crankshaft to turn twice at 6000 RPM. If the injector IPW is 18ms then we have a duty cycle of 18ms/20ms = .9 or 90%.
Most fuel injectors should not be operated at above 85% duty cycle for extended periods. Therefore, when calculating our fuel injector size requirements, we will use an 85% duty cycle in our computation.
Let’s go back to our injector flow rate calculation and plug in our numbers. We will compute for 500HP with a BSFC of .6 and an injector duty cycle of 85%.
Injector Flow Rate (lb/hr) = Horsepower x BSFC / Number of Injectors x Duty Cycle
Injector Flow Rate (lb/hr) = 500 x .6 / 8 x .85 = 300/6.8 = 44lb/hr
In the example above, we may be able to get by with 42lb/hr injectors as they are rated at 42lb/hr at 40psi fuel pressure. This example would need to run around 60psi fuel pressure with forced induction. The 42lb/hr injectors will actually flow around 50lb/hr at 60psi fuel pressure.
Other common flow rates for turbocharged engines are 60lb/hr and 96lb/hr. Most engines use high-impedance (high-Z) type injectors. Drivers can be purchased to run Low-Z injectors on high-Z computers, however Motron and Siemens as well as others manufacture high-Z injectors for some engines. It is also wise to have your injectors flow-matched to insure that there is not any variation in fuel supply between cylinders.
Fuel Pressure and Forced Induction
If your fuel system is set up correctly, with the correct pump and injectors, your fuel pressure should not drop at the fuel rail during wide open runs. A drop in fuel pressure can bring the AFR dangerously high, and is an indication that the fuel system is not adequate for the required f
Return Type Fuel System and Boost Referenced Fuel Regulator
In a forced induction application, the intake manifold becomes pressurized. Therefore, the injectors need to overcome this positive pressure to provide the correct amount of fuel.
Say for example, you are seeing 10psi of boost and 60psi fuel pressure at the rail. The effective pressure of the fuel injectors now becomes 50psi and they are no longer flowing at 60psi. To overcome this problem, a boost referenced fuel pressure regulator can be used.
A boost referenced fuel pressure regulator (BRFPR) senses boost and raises the fuel pressure at a ratio of 1:1 with boost pressure. So in our example of 10psi boost and 60psi fuel pressure, the BRFPR raises the fuel pressure 1psi for every 1psi boost to make 70psi of fuel pressure at the fuel rail, allowing the injectors to flow 60psi (70psi fuel pressure – 10psi boost pressure).
In a return type system, fuel is pumped into the fuel rail and an on-rail regulator restricts the amount of fuel that exits the rail and returns to the fuel tank, keeping the fuel pressure at the rail constant. A BRFPR actually controls the fuel pressure in the fuel rail by restricting more fuel as boost pressure rises, actually raising the rail pressure rather than keeping it constant.
Do not confuse the BRFPR with a rising rate regulator or FMU. These units are designed to increase fuel pressures at ratios higher than 1:1 for use with undersized fuel injectors. An FMU is not an advisable way to go with forced induction. They were common a few years ago before EFI programming and standalone fuel injection solutions became available at reasonable costs.
The return type fuel system combined with a BRFPR is the ideal setup for high powered forced induction systems.
Air/fuel ratio or AFR, is the ratio of air mass to fuel mass in a combustion chamber during combustion. In gasoline engines, the air and fuel are chemically balanced in the combustion chamber to a stoichiometric mixture of 14.7:1 by the engine management system. A lower ratio is a rich mixture, and a higher ratio is a lean mixture.
In forced induction applications, a richer fuel mixture is needed under boost conditions to stave off detonation. Most tuning pros agree that an AFR of 11.5:1 is ideal for a turbocharged engine under full boost. Anything lower is too rich, and anything higher could cause detonation or fuel starvation leading to broken pistons.
Wideband O2 Sensor
A wideband oxygen sensor is used to monitor the AFR. The stock narrowband O2 sensors can only read the stoichiometric ratio of 14.7:1 for gasoline. A wideband O2 sensor can read a much wider band of ratios, from 9.65:1 to 20:1. They can also sense changes in AFR much more accuratley.
A wideband O2 sensor and gauge are a requirement for both tuning and monitoring your turbocharged engine. Without one, there is no way to be sure that your tune is correct. A wideband gauge should be mounted on the dashboard and closely monitored. It will likely be the first indication of fuel system problems.
The installation of a wideband system is relatively easy. A bung is welded into the exhaust before the catalytic converters, and the wideband sensor is screwed in. The wiring harness is plugged in and is attached to the gauge, and or tuning computer. A tuner uses the values read from the wideband to adjust parameters in the PCM, adjusting the AFR at a safe value.
|<< Turbo Oiling Systems - Previous Page Turbo Tuning - PCM and ECUs - Next Page >>|
All content on the Turbo Kits web site is copyrighted ©2013