AEM Engine Management System - Tech Knowledge

The F/IC-8 uses quick and easy injector calibration software that allows for easy vehicle startup when using larger-sized injectors. Castillo simply input the original injector sizes into the laptop, then installed the 1,000 cc/min injectors and made the calibration change, enabling the car to fire up on the first crank.

Our Infiniti G35 showed significant gains throughout low to mid rpm ranges when tuned with the AEM F/IC-8, and dyno numbers revealed an increase of 70 hp and 100 lb-ft of torque at 3,700 rpm over baseline.

Peak & Hold Vs Saturated
Injectors
By Rc Engineering's John Park
Injectors are classified under two categories: peak-and-hold or saturated. Peak-and-hold injectors are rated at 0.5-5.0 ohms (low impedance), and saturated, at 12.0-16.0 ohms (high impedance), as measured by the Fluke multimeter shown above. The type of ECU will dictate whether the vehicle uses high- or low-impedance injectors, but beware: injector types should never be mixed.

To the naked eye, distinguishing between the two types of injectors can be difficult, but when it comes to how they perform, there's no mistaking the two. The drivers in an ECU system that will handle a peak-and-hold injector will energize the injector with an initial shot of four to six amps. Once the injector is open, the current is dropped to about one to three amps to keep it open. A saturated system requires a more simplified injector driver. Unlike peak-and-hold, a saturated injector remains "on" for the entire pulse width. A high-impedance injector only needs about 1.0 amp to open and stay open. About 99 percent of fuel-injected engines on the market today will use high-impedance systems that are less complex, cost-effective and work very well for their intended use.

In the aftermarket world of high-performance gasoline engine tuning, the trend will always remain to use a low impedance system whenever possible. Some of the advantages include a wider selection of injectors, particularly when high-horsepower applications require injectors with extremely high flow rates. Other benefits include a faster response time, which minimizes the injector's "on" time, resulting in faster response to help extend the dynamic range of the injector, which proves to be especially beneficial for street cars where idle quality is a concern.

This is not to say high-performance applications should stay away from high-impedance injectors due to their slower response times. A state-of-the-art sport bike using saturated injectors can rev to 16,000 rpm without hesitation. The high revs in correlation to injection time supports that high-impedance, although slower than low-impedance, is still considered responsive enough to be capable of dealing with high-rpm demands.

How To Select The Proper Injector Size
Finding the correct injector size to support your vehicle can be found using a simple formula. As a sample, we will be using a four-cylinder engine rated at 200 hp to the crankshaft.

First, we need to determine the B.S.F.C (brake specific fuel consumption). B.S.F.C is the amount of fuel an engine needs to make X amount of power (the lower the number, the more efficient the engine). The B.S.F.C varies, depending if the car is naturally aspirated or turbocharged. For naturally aspirated cars, the B.S.F.C. will be anywhere from 0.45 to 0.50, meaning the engine will use 0.50 lbs of fuel per hour for each horsepower it produces. For turbocharged engines the scale will be at 0.55 to 0.60 lbs per hour or higher, depending on whether the engine is running on pump gas or race fuel. If the car is running race fuel, the B.S.F.C. is slightly lower.

1. Take the target horsepower at the crankshaft (i.e. 200 hp) and multiply that number by the B.S.F.C (0.50) =100.
2. Take the number of injectors (4) multiplied by the injector duty cycle (0.80) = 3.2.
3. Finally divide the 100 by 3.2 = 31.25 lbs/hr is the total per injector.
4. To convert from lbs/hr. to cc/min, multiply 31.25 by 10.50, to get 328cc/min.
5. The proper injector size for this application would be 31 lbs/hr or 330 cc/min.