OK, back to our install. Since we are modifying a factory intake, how do we know where to weld the injector bungs in place? And do the injectors need to be installed at a particular angle and/or depth in the runner? In a perfect world, most EFI developers agree that the fuel injection nozzle's location should be as parallel to the airflow stream as possible. The relation between the airflow stream and the nozzle angle is called the intercept angle. The intercept angle should not be greater than 45 degrees. It can be at a lesser angle, but not greater. While maintaining a proper intercept angle helps low-speed driveability, we're also told that the slower the inlet airspeed at idle (like with a large intake runner), the more critical it is to maintain the ideal intercept angle. But should the injector be placed closer to the intake valve, or closer to the top of the intake runner?
The answer to that depends on the engine and its intended application. For instance, a car owner with a mostly stock engine is primarily concerned with idle quality and fuel mileage. For this reason, his stock engine can characteristically use a smaller injector (rated in lb/hr). Since the spray pattern of a small-capacity nozzle properly disperses the fuel into the incoming air flow, the nozzle can be located closer to the valve.
Larger injectors, like those used in a modified engine, have been known to develop larger "droplets" of fuel simply because of their larger "pressure" rating. If you place a large injector too close to the valve, it's safe to think that there will not be enough time for the fuel and air to properly mix before hitting the combustion chamber. We all know that lumpy cams—like those used in modified engines—generate poor idle vacuum, and modified engines also typically utilize large-volume inlet runners. This larger volume runner also equates into a slower intake-charge velocity. All of these mentioned conditions adversely affect proper fuel atomization, and by moving the injector farther away from the valve, you essentially give the air and fuel more time to properly mix. In other words, location depends on different factors that you will need to determine for your application.
In our case, although the Hemi is fairly large, at 472 inches, it's not what most would consider high-powered (for a Hemi at least), and the intended factory intake with its shorter runners means we can use a fairly small injector. Once we decided on the proper location for our injectors, we started drilling and welding to get the bungs in place. If you're so inclined to do this conversion by modifying an intake, you will need some specialty tools like a welder set up for aluminum, and a way to consistently drill the intake in the proper location for the bungs. If you don't have the proper equipment, you can have a competent machine shop do the work for you, or, like we said earlier, you can purchase an EFI-ready intake and bolt it on.
|XFI ECU Box|| 301000||$1,666.45|
|Main Wire harness||301100||$356.95|
|Injectors||Varies by requirements|
|Total||$2,420.55||*Editor's note: If you have no problem with using an aftermarket intake, an EFI-ready part is available. We found one at Indy Cylinder Head. The single-plane manifold comes with the fuel rails and is $795. Keep in mind that with this taller intake, you will need to check hood clearance before you try to slam it shut.
06 The upper-plenum runners are the ones that actually dictate the angle of the injectors
07 There is no XFI kit actually designed to fit our application. So we needed to contact
08 In order to mount the throttle bodies to the stock intake, Gary machined a 1-inch-thic
09 You can get as fancy with these as you like, but this is all that's required to hold t
10 Using old injectors, the fitment of the rail and mounting brackets can be finalized. T