fuel injectors

[fismail]

Fuel Injectors
by:Titan

There are 6 basic types of metering devices used in fuel injectors today but I will only cover the 3 that I feel will have the most impact. The first is the pintle type made by Bosch/Nippon/Denso. This single pintle discharge injector tends to increase atomization and pattern width at higher pressures. Next, is the disk type fuel injector manufactured exclusively by Lucas. This injector possesses stainless steal internals and a unique metering disk that is years ahead of the 40 year old pintle type injector. The Lucas injector is the best at maintaining its spray pattern cycle to cycle, under varying pulse widths and fuel pressures. Lastly, there is the diffuser/pintle type injector found on Toyota and various other makes and models. Diffuser/pintle type injectors do not change atomization quality at higher fuel pressures like the Bosh/Nippon Denso type injectors. Diffuser/pintle injectors are not high atomizers, they are used to target fuel toward the valve stem reducing intake wall wetting or "puddling" of the fuel. This targeted approach is accomplished by the impact of the fuel on the diffuser surface, which concentrates the fuel at the center of the cone producing a tighter pattern. The distance from the injector to the valve and the cross sectional area of the intake must be considered when incorporating this injector.

Injector types
Peak and Hold injectors, also called low impedance, are initially fired at 4-6 Amps, through a ballast resister, and then fall back to 1-2 Amps for the rest of the injection event. This injector is often used on high fuel pressure systems (75-100psi+) where the increased initial amperage overcomes the high hydrostatic pressures of the fuel pressure. Peak and Hold injectors These injectors tend to respond faster than Saturated injectors
Capabilities
The minimum pulse width cycle time for most pintle type fuel injectors (Bosh/Nippon-Denso) is 2.0Ms for the Peak and Hold and 2.5Ms for the Saturated injectors. Alternatively, disc type injectors (Lucas) will cycle as low as 1.0Ms for Peak and Hold and 2.0Ms for Saturated. The difference in pulse widths between the pintle and disk type injectors can be attributed to weight differences. The Lucas disk only weights .4g while the pintles used by Bosh/Nippon-Denso weight 4g ten times heavier! The disk's lighter weight offers reduced inertial loading allowing it to overcome hydro-static load faster and return to its seat quicker. This decreases response times of the pulse widths and also provides a more constant cycle to cycle flow.
Most pintel injectors tend to fail at around 86% duty cycle while the disk type injectors can usually go to 90% duty cycle. This means that the injectors will increase their flow rates until they reach their highest duty cycle (listed above) and then go semi-static or half-open just before going full static. At semi-static the injectors are only delivering a 50% duty cycle flow rate and at static they lock closed. This usually occurs when you are running WOT, high RPM, and or max boost when you need 100% fuel delivery and your only getting 50%. This situation creates a lean condition that will have you shopping for a new engine fast. If you plan on running higher fuel pressures be warned that at higher fuel pressures this situation seems to be amplified a bit more. When choosing an injector a larger than necessary injector running at a 70% duty cycle will provide more controllable performance than one being pushed to 90%+. Remember, when choosing an injector a larger than necessary injector running at a 70% duty cycle will provide more controllable performance than a smaller one being pushed to beyond 90%.
Atomization
When you consider that at 6000 RPM the intake valves are opening 50 times a second leaving only about .010 seconds to provide all the necessary fuel. With such a brief intake valve open time you may feel that having a fuel injector that delivers a wide highly atomized pattern into the intake would be ideal to ensure a homogenous mixture but this is not necessarily the case. At low RPMs highly atomized fuel has enough time to pass by the intake valve and create a homogenous mixture but as the RPMs increase problems start to develop. In an engine running at high RPMs there is limited time for the fuel to reach the combustion chamber. This is compounded by the fact that often there is residual exhaust pressure present when the intake valve is opened. The residual exhaust pressure tends to blow the lighter drops of atomized fuel back into the intake, which tends to adhere and condense to the intake walls. This presents a few problems. Fuel "puddling" in the intake increases drag thereby reducing airflow, large quantities of highly atomized fuel can displace air in the port, and if the "puddled" fuel does reach the combustion chamber it will cause air/fuel ratio variances between cylinders.
Remember that by choosing the proper size of the injector based on flow rate and duty cycle you will be able to avoid any injector pit falls. This will leave you with plenty of time to worry about other things such as, "how to increase the amount of fuel being delivered to the injectors?"

[Henk]

Fuel Injectors: Flow Rates and Horsepower Levels
by: icu_runnin

Fuel injectors meter the amount of fuel delivered into the combustion chamber, which is constantly adjusted by the car’s computer (ECM) via the oxygen sensor feed back. Basically, there are two different types of fuel injectors, saturated and peak and hold. The saturated type injector is a high ohm impedance injector that works fine for a performance vehicle but only up to a certain extent. The larger this type of injector gets the harder it is to deliver fuel precisely. The impedance of these injectors range from 11-13 ohms depending on the injector and the manufacture. All Saturn vehicles from 96+ have this type of injector in them.
The second type of injector is called a peak and hold injector which, is a low ohm impedance injector. This injector is more commonly used in high performance applications because large injectors are easier to control. The peak and hold injector’s ohm impedance ranges from 1.5-3 ohms depending on the manufacture. These injectors are found on first generation Saturn vehicles 91-95.
Converting Injector Flow Rates
To convert cc's to lbs/hr divide the rated cc's by 10.5
450cc / 10.5 = 42.85 lbs/hr or rounding up a 43lb injector.
To convert lbs/hr to cc's multiply the rated lbs/hr by 10.5
26lb * 10.5 = 273 cc/min injector.
When upgrading the injectors on your vehicle there are a few things you need to keep in mind. First, you must know what type of injector is currently on your car. Using a voltmeter can easily do this. Simply take the injector harness off your injector, set the voltmeter to read ohms, and then apply the two terminal leads from the voltmeter to the two male connections on your injector. It does not matter which lead you test with if the test leads are reversed the voltmeter will display a negative sign next to your ohm reading. Now that you have know the type of injector on your car the next step is to find out what the injector is rated at.\

Brake Specific Fuel Consumption

Locating information about stock injector flow rates can sometime be quite difficult. If you can’t find your car’s injector size you can get a good idea of the injector flow rate using your car’s factory horsepower rating. To do this calculation you will need to determine your Brake Specific Fuel Consumption (B.S.F.C.). The B.S.F.C. is the number of pounds of fuel it takes to make 1 horsepower for 1 hour.
The B.S.F.C. values very from engine to engine depending on its efficiency. The more efficient the engine the lower the B.S.F.C. value, which translates into needing less fuel to make 1 horsepower for 1 hour. This changes for forced inducted applications as the extra fuel is used to cool the combustion chamber helping to prevent detonation. Here are some basic B.S.F.C. values.
Low to medium performance = .50
Performance engine with head work = .45
Performance engine with expert head work = .40 - .45
Supercharged and turbocharged engines = .55 - .60

Injector Duty Cycle

An injectors duty cycle defines how long the injector stays open. Injectors are always rated at 100% duty cycle so, a 26lb injector will put out 26lb's of fuel under 100% duty cycle. You never want to run your injectors above .85 or 85%. Anything higher puts you at risk of the injectors locking up. Choose an injector that puts out your desired lbs/hr at an 85% duty cycle rather than one at 100% duty cycle. If there isn’t an exact match you can raise your fuel pressure, which makes the injector act like a larger one but this trick is only good if you need a few extra lbs/hr.
Now that you have determined your B.S.F.C. and duty cycle it's time to calculate what your stock injector is rated at.
Here is the formula:
( H * B ) / ( C * D ) = estimated injector size.
H = horsepower
B = B.S.F.C.
C = number of cylinders
D = duty cycle
This is what it should look like for a Saturn.
( H * B ) / ( C * D ) = estimated injector size.
124 * .50 / 4 * .80
62 / 3.2 = 19.375 lbs per hour.
Saturn injectors are rated at 19lbs/hr.
Now that you know what size injector you have lets find out how much larger you can go. Typically you should only go 10% over your stock injector anything larger you may run into idle problems when cold and your car may stumble until the vehicle reaches operating temperature. When changing to a larger injector you should reset the computer so it can adjust to the new fuel injector. Resetting the ECM can be accomplished by pulling the battery cable off or pulling the ECM fuse and letting the car sit for 3-5 minutes. If you’ve installed too large of an injector and your car exhibits erratic idle during cold start or stumbling after it is warm you can attempt to remedy this by lowering the fuel pressure. But beware if you lower the fuel pressure to much it will effect your fuel injectors spray pattern so be careful of how much you lower it.

Injector Upgrade

If you want to upgrade your stock 19lb injectors by 10% but your not sure what the new flow rating will be simply multiply the injector’s lbs/hr rating by .10 then add the original lbs/hr rating of the injector. Example:
19 * .10 = 1.9 + 19 = 20.9 or a 21lb injector.
So this means we can upgrade to a 21 lb injector with no problem.

Injector Flow Rate based on Pressure Changes

To calculate an injector’s flow rate at a new desired fuel pressure you will need a calculator that has a Square Root function. Now this one can get a little tricky but pay close attention and this can help you out tremendously. Most of the injectors on the market today are rated at 43.5 psi. So, when you say you have a 19lb injector what you are saying is that your injector puts out 19lbs of fuel per hour at 43.5 psi of fuel pressure. So, how do we find out what our new desired fuel pressure going to be?

Here's an example:

Lets say we want to up the factory fuel pressure to 55psi. You will need to know the following information lbs/hr of the injectors you currently using (19lbs), original fuel pressure (43.5psi), and the new fuel pressure 55psi.
Here is the formula:
The square root of x multiplied by z divided by the square root of y = new injector flow rate
Where:
X = new fuel pressure
Y = original fuel pressure
Z = lbs per hour
First, find the square root of the new and original fuel pressure.
New fuel pressure: square root of 55 = 7.416
Original fuel pressure: square root of 43.5 = 6.595
Then divide the new fuel pressure square root sum by the original.
7.416 / 6.595 = 1.124
Then multiply this total by the size of the injector. In this case we are using the stock Saturn 19lb injectors.
1.124 * 19 = 21.35

At 55psi the injector now flows 21.35lbs/hr

Injector Flow Rate Chart

30psi 35psi 43.5psi* 45psi 50psi 55psi 60psi
16lb 17lb 19lb 19lb 20lb 21lb 22lb
20lb 22lb 24lb 24lb 26lb 27lb 28lb
22lb 23lb 26lb 26lb 28lb 29lb 30lb
29lb 31lb 35lb 36lb 38lb 39lb 41lb
32lb 35lb 39lb 40lb 42lb 44lb 46lb

*Stock injector size 19lb @ 43.5psi

Injector Size vs. Horsepower

Calculating how much horsepower the injectors can support is relatively straightforward using the following four variables:
Injector size: 26lb in this example
Number of cylinders: 4
Maximum duty cycle: .85
B.S.F.C. .50
Here is the equation:
Q * W * E / R = estimated horsepower for injectors.
26 * 4 * .85 / .50 =176.8 horsepower is what four 26 lb injectors will support.
Q = size of injector
W = cylinders
E = duty cycle
R = B.S.F.C.