The Recap Last month we showed you the buildup of a Hemi engine project, along with the m
Part 2: The New Technology
Carburetors vs. EFI
EFI is designed to inject fuel into each cylinder, proportionate to the engine's needs. The main difference from a carb is the way the systems approach the problem. A carburetor uses the vacuum created by the airflow in the carburetor to suck in the fuel. this works well because the amount of fuel delivered is directly related to how hard the engine is drawing in air. Get the jets and the intermediate balance right, and the carburetor is going to work pretty darn good. So well in fact, that under wide open throttle (WOT) conditions, the carburetor and the EFI will produce almost the same amount of power. EFI might eek out a bit more power due to a dry manifold, but this is not enough of a difference to amount to anything.
The injectors could be mounted where the carburetor would normally be (throttle-body injection), but this is not ideal because the manifold charge is still wet and distribution problems still exist. The best use of EFI is when the injectors are mounted directly above the intake valve-port injected. EFI can also be either bank-to-bank or sequential. In bank-to-bank, a group of injectors fire together. In sequential, each injector is timed to fire at the same time relative to that particular cylinder's cycle, usually just as the intake valve starts to open.
Notice the extra filtering and the location of the fuel regulator-after the fuel goes thro
EFI System Considerations
An EFI system runs a fairly high fuel pressure, usually around 45 psi. This requires a special fuel pump that can usually be heard. Also, the system returns unused fuel to the tank, so a return line is required. The chart on the next page shows how the plumbing works.
Depending on your engine, you may be able to purchase a manifold that already has the injector bungs installed, but injectors can be added to any manifold by drilling above each intake port and welding in injector bungs. This adds to the overall cost of the system, but is fairly easy to do.
Inputs And Sensors
The EFI ECU needs to know a lot about the engine in real time, so there are quite a few sensors. Here's a short list:
Throttle body-This replaces the carburetor. It's a set of plates with a throttle-position sensor that tells the ECU how far the throttle is open. Some throttle bodies also have provisions for an IAC (Idle Air Control) valve.
MAP sensor-manifold absolute pressure. This is essentially a vacuum gauge that allows the ECU to monitor engine load. A 1-Bar MAP sensor is used for normally aspirated engines where the range is (approximately) from 0 to 15 inches of vacuum. A 2-Bar sensor works from 15 inches of vacuum to 15 pounds of boost.
O2 sensor-Oxygen sensor. This can get confusing, because most O2 sensors used on today's cars are really more of a switch than a sensor. They cannot measure air/fuel ratios over a wide range. They change their resistance quickly right around Stochiometric (14.7:1 air/fuel ratio). ECUs used with these O2 sensors deduce the probable air/fuel ratio by watching this switching frequency. Air/fuel ratios can be measured by looking at the sensors' change in resistance, but only in ranges that are close to 14.7:1. A better type of feedback is called a Lambda sensor, or wide band O2 sensor. These sensors read actual air/fuel ratios from 10:1 to well over 16:1. This type of sensor allows the system to run in closed loop, meaning that your basic engine "MAP" defines the air/fuel ratio you want and the system gives it to you. The trade-off is that Lambda sensors are more expensive than O2 sensors.
TPS-Throttle position sensor. a variable resistor, called a potentiometer, it tells the ECU how far the throttle is open.
CTS-Coolant temperature. engine temperature. Used to control fuel enrichment during warm-up.
ATS-Air temperature. Allows the ECU to adjust for changing ambient air temperature.
IAC-Idle air control valve. This is really an ECU output that controls idle rpm by controlling the amount of air, at idle, that is bled into the engine. Think of it as a second set of throttle plates that the ECU controls, but only at idle. This is sometimes called an Idle Air Control motor.
Crank signal-Crankshaft trigger signal. This is an ignition pulse usually from a reluctive-type input. It can be the typical output from a distributor pickup or a crank trigger itself. This is set up to create an ignition signal at a fixed advance. The ECU then delays from this pulse to control timing and generate the actual trigger pulse.
* Crankshaft Reference AngleThis is the amount of advance the crank sensor is set for. Thi
CAM signal-Camshaft position signal. This is a pulse that signifies the start of an engine cycle (once every two crankshaft revolutions). Since the crankshaft goes through two revolutions per engine cycle, the crank signal cannot be used to determine the engine cycle. This signal is only required for those ECU applications that require engine synchronization-sequential fuel injection and/or a distributorless ignition.
ESC-Knock sensor. This is a sensor similar to a small microphone that bolts to the block and "listens" for spark knock. The ECU can then retard the spark to minimize knock. However, a high-performance engine can generate enough mechanical noise to make this type of sensor ineffective.
Special System Considerations
The CAM Signal (Once Per Engine Cycle)
Many factory EFI engines use bank-to-bank injection schemes, where each injector is not timed to its individual cylinder-four injectors fire at once. This works better than you might think, because the injector is mounted in the manifold runner at the intake valve, the injected fuel hits the back of a hot valve, atomizes, and the atomized charge sits there and waits for the valve to open. Since the charge does not travel back up the manifold runner, distribution problems are minimal. In an aftermarket bank-to-bank EFI conversion system, where a distributor is used, no cam signal is required.
In cases where the engine cycle must be known, a cam signal is required. These cases are sequential EFI and/or an electronic distributor. The normal timing for this cam signal is to have it occur just before TDC on the number-one cylinder. A simple way to create the cam signal is to grind off seven of the reluctor points on a normal distributor. That one remaining reluctor-point is a signal for once every engine cycle. Timing of that signal, how-ever, usually requires that the reluctor be relocated on the distributor shaft. This is because the rotor must still be phased properly to the distributor cap.
The Crank Signal (Once Every 90-Crankshaft Degrees)
A normal distributor generates a pulse every 90-crankshaft degrees. The problem is, the distributor will generate this signal when it wants the plug to fire because there is nothing else in the system that controls the timing. When using an ECU, the signal must occur much earlier, allowing the ECU to determine when to actually fire the plug. In addition, since timing is under control of the ECU, the signal to the ECU must be timing fixed.
A typical EFI crank signal would occur at something like 50 degrees (fixed) BTDC. Then the ECU has enough time to create the ignition pulse between 10 degrees and 40 degrees BTDC.
Since there is only one reluctor in a Mopar distributor, if you have to generate both the cam and crank signals, the normal approach would be to use a crank trigger for the 90 degree crankshaft signal, do the grinding and relocation of the reluctor for the cam signal, and use a simple coil and distributor cap. But this wouldn't work for a distributorless Hemi, because we don't want any distributor at all.
CAM and Crank Signals For The EDIST HEMI
We used a crank trigger for the 90-degree crankshaft signal and fabricated a special mount for the cam sensor. Then we used individual coils for each plug so no mechanical distributor cap was required.
* Crankshaft Reference AngleThis is the amount of advance the crank sensor is set for. Thi
The cam sensor mount was easy since the customer wanted to use a Jesel beltdrive. One nice thing about the Jesel is the cam gear is aluminum and exposed, making it easy to insert a magnet and mount the sensor. If you did not have access to the cam gear, then you would go back to using a single-point reluctor distributor to generate the cam signal. With coil-on-plug, no distributor cap would be required, but there would still be a small module installed where the normal distributor would go. Mopar Engines West is going to be fabricating special distributors for Mopars that generate both the cam and crank signals for sequential EFI conversions using a normal coils and a distributor cap.
Sequential System Timing
So we hear you asking, "What is actually going on here?" Here is a system timing description and diagram that take you through one complete engine cycle.
* The cam signal occurs sometime between the last cylinder fire (number 2 cylinder) and before the crank signal on number one cylinder. This is the beginning of the engine's cycle
* Since this is the compression stroke for number 1 cylinder, the ECU is now starting the injection for cylinder number 6, whose intake valve is just beginning to open. It knows cylinder 6, because it counted crank signals from the last cam signal
* The crank signal occurs at approximately 50 degrees BTDC
* The ECU generates the ignition timing-signal between 10 and 40 degrees BTDC depending on engine conditions (Fuel mixture for this compression stroke was injected into cylinder 1 when cylinder 6 was being fired).
The EDIST (Electronic Distributor) is really a simple box. It receives both the cam and ECU-created ignition signals; then it synchronizes on the cam signal and counts ignition signals to determine which coil to fire. We had to make our own cable between the EDIST and each coil, so we used shielded cable (RG-174) to eliminate any chance of electrical interference.
Timing Diagram For Sequential EFI And EDIST Setup
We used an MSD crank trigger for the ignition, and then we configured our own cam sensor using an MSD universal cam pickup with magnet (PN 2346). We used the MSD Pro-Billet 1,000-cfm throttle body because it came with TPS and IAC, and provided a vacuum tap for our MAP sensor. We mounted the air temp sensor in the air cleaner, and the coolant sensor in the water line going from the block to the radiator. We welded a common O2 bung in the exhaust just after the collector. Once all this was completed we plugged everything into the ECU harness. The harness is well marked with unique connectors, making it almost impossible to plug anything in the wrong place.
The F.A.S.T. ECU also controls the fuel pump and cooling fans when used with external relays. The only harness connection we did not use was for the knock sensor (ESC). The EDIST box needed a trigger signal, which was provided by the ECU. This is the wire that would normally be used to trigger the ignition. The EDIST box also needed to see the cam signal, so the cam sensor wires were connected to both the ECU and the EDIST. We made our own cable to connect the EDIST coil signals to each coil.
We loaded the F.A.S.T. software on our laptop and connected the RS-232 cable. Then we powered up the fuel pump and set the fuel pressure to 45 psi while we checked for leaks.
Before you do anything, you have to make sure the ECU and your laptop are communicating. Once the ECU is powered up, select "connect" and the laptop and the ECU are linked. as long as you are linked, anything you change with the laptop automatically updates the ECU. The ECU has a nonvolatile memory, meaning that it will remember the program even if power is removed.
Initial Software Setup
The system needs to know what kind of engine it's going to be running. We spent a few minutes setting up the basic parameters for the first start.
Ready To Start
There are three phases to getting your EFI system dialed in.
* The first start
* Dialing in the cold-start and idle settings
* On-the-road tuning
The F.A.S.T. software uses "dashboards," which can be configured to view various parameter
The F.A.S.T. system uses tables or maps to allow tuning the EFI and ignition timing. For the first start, make sure the crankshaft reference angle is correct. I usually set the ignition table to all one number such as 20 degrees. This will fix the timing so it won't jump around. Then when the engine fires I use a timing light while I change the crankshaft reference angle value until I get 20 degrees.
From there, adjust the cold start tables in order to keep the engine happy while it warms up. I usually do the initial tuning in open loop so I'm not fighting the ECU. Also, make sure the TPS value is below the point that the system detects you are no longer at idle.
It's a waste of time to try adjusting the basic fuel table until the engine is warmed up and stabilized. This is because the F.A.S.T. system uses warm-up tables that overlay the basic fuel table. You can't set the basic table until the warm-up has been achieved and those tables are no longer adding fuel.
The Basic Fuel Table
Now we look at the most important table in the F.A.S.T. software-the VE table. VE means volumetric efficiency and is a measure of how much of the intake charge is available for combustion. A higher VE value will require more fuel, and will therefore enrich the mixture, thereby bringing down the air/fuel ratio. Typical VE ratios run between 40 percent for a normally aspirated engine at idle, to 100 percent when producing full power. Supercharged engines produce well over 100 percent because the charge is forced in, and is therefore more than the engine could normally do on its own.
Don't let the numbers confuse you. These are not injector pulse widths; they're the VE values with the vertical axis being manifold pressure or vacuum and the horizontal axis being rpm. One hundred KPA equates to approximately zero manifold vacuum (wide-open throttle), and a 0 KPA being approximately 15 inches vacuum.
At all times you get a 3D representation of this table. This is a good visual aid to see if there are any weird spikes or table locations that don't make sense.
Final Tuning In The Car
By the time you've reached this point, you should have an engine that starts, warms up, and idles. But you have not done anything for the load conditions. Once you've verified and entered the correct crankshaft reference angle, then you would change the spark table to represent a typical spark curve. This Hemi belongs to a customer who wanted a roller cam and some serious rpm capability. This is not a typical cam we would choose for the a street application, nor would we typically use a Jesel belt drive on the street, so the numbers we ended up with for the EFI were a little different from what you would normally see.
There are several other tables where you would adjust fuel delivery as a function of the changes in manifold vacuum or throttle position. These emulate the accelerator pump. But I don't change any of these tables until the engine is in the car and I can drive it.
Here's a 3D version of the VE table.
We recommend in-the-car tuning because you can accurately adjust for the "transitions" such as the accelerator-pump shot or off-throttle deceleration. A chassis dyno is great for the steady state conditions, but I've had better success with somebody else driving and me telling him what to do. This is where the closed-loop operation using the air/fuel ratio table comes into play. Most of the previous tuning was done in open-loop operation. Now we want to finish the process, so we decide on the air/fuel ratio we want achieve, put the EFI system into closed-loop operation, and turn on the data logger. The data logger will keep track of how much the EFI system had to adjust in order to maintain the desired air/fuel ratio while driving. What could be better than choosing the air/fuel ratio at any given point and the system giving it to you? After a data log drive, you go back to the basic tables and change the values so the closed-loop air/fuel operation doesn't have to make much of a correction. Once you get the correction percentage below 5 percent, you are assured that the underlying VE table is close to what the engine and car need.
When we first started using the F.A.S.T. system, we were amazed at how we could tame a cammed-up Hemi that was undriveable on the street with carburetors. The combination of a low vacuum caused by the wild cam and the timing jumping all around because the advances weights were on the light side made this car a bear to drive. After we converted this engine to the F.A.S.T. EFI system we were able to get it to start and idle. It was a high idle, but tolerable. We locked in the spark advance, allowing the engine to settle down and then go for it when the engine was ready. This was something we could not do with a normal distributor and weights.
This could have been built using tried and true technology, i.e., carburetor and a distributor. but a challenge was overcome, and it shows another way the hobby can get progressively better. One of the objectives was to get the automatic self-adjustability at all altitudes and weather conditions-hot, cold, dry, whatever. A carbureted engine is finicky when it comes to weather conditions.
It takes about two hours to get the initial no-load conditions set. We usually do this on
Pros And Cons Of EFI
- EFI offers driveability enhancements at all throttle positions
- EFI injectors are mounted directly in front of the intake valve. This allows the intake manifold to run dry (it carries only air), so manifold distribution losses are minimal
- EFI systems monitor the engine and make the appropriate changes automatically
- EFI systems can be adjusted and changed on the fly. In other words, the system is very tunable from within the car
- EFI systems can be precisely tuned, which improves fuel economy at the non-WOT conditions where we normally drive
- Aftermarket EFI is expensive compared to a carburetor
- Are you computer literate? We're talking laptops, the Internet, computer files, downloading software updates, and so on. If you're afraid of computers, EFI may be intimidating
- Are you hardware handy? Installing and tuning an aftermarket EFI system is more than just a bolt-on
- Initial system tuning takes longer. It will take two people a full day, driving around, making adjustments, and dialing it in
All the above simply makes an EFI engine start easier, run better, cleaner, and more efficiently.
With the tuning and timing computer work done, it was time to hit the dyno. The basic rundown of the engine and its components were:
- 528 Hemi 4.5-inch bore with a 4.15-inch stroke
- 10:1 compression ratio on pump gas
- F.A.S.T. EFI with coil on plug and 50-pound injectors
- JE Pistons, Manley H-beam rods, Mopar aluminum heads
- Comp custom solid-roller camshaft 252/260-degrees duration and .640/.638-inch lift and a 112 LSA; installed 4-degrees advanced
- Indy Cylinder Heads Intake
EDIST HEMI project-Mopar Engines West
- Baro: 29.89
- Intake Air: 62 degrees
- Elevation: 52 feet
- Coolant: 165 degrees
- (R+M)/2: 92
- Starting rpm: 2,500
- Finish rpm: 6,500
- Idle Vac: 11.4