EFI System For Our Hemi Engine Project - A Big Twist

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.

Pros And Cons Of EFI
Pros:

• 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

Cons:

• 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.

Proven Power
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