It may seem hard to believe, but back in the mid-'70s it wasn't unheard of for Hemi car owners to swap out the Hemi in favor of a Wedge engine. It seems that--at no fault of the Hemi--the engine didn't have a great reputation among get-in-your-car-and-drive-to-work commuters. We're talking the Street Hemi now, not the two four-barrel cross-rammed racing version. They were (and still are) known to be temperamental, hard to start sometimes, and certainly not easy to operate in heavy traffic.
It also didn't help that insurance companies didn't like them and that the country was in the middle of a gas crisis. There were long lines at the pumps that did happen to have fuel, and if they did you sometimes couldn't buy enough (at less than $.60 a gallon, by the way) to fill up your tank.
Times have changed, and engine builders have learned a lot and can do things never dreamed of back then. So as long as there is gasoline for purchase, the Hemi will hold its rightful place in automotive legend. Still, these things were designed to make brute power, not to take grandma to the store.
Part of the problem was and is our own fault. We've never gotten over the bigger is always better stigma. If one four-barrel was good, then two must be better. Two four-barrels might double the cool factor at the local hang out, but not so much if you drive it every day.
01 We're beginning with an...
01 We're beginning with an off-the-shelf aluminum street Hemi manifold. Besides the need to install injector bungs, there are a couple of not so obvious tricks that need to be done as well. Remember that these engines were originally equipped with Carter AFBs, This means that they have a different bolt pattern than that of the Holley style bases that the FAST throttle bodies use.
02 Not only is there a different...
02 Not only is there a different carburetor mounting pattern, but the factory butterfly openings will interfere with the butterflies of the throttle bodies and will need to be removed. Another modification done to the intake has to do with the fact that the intake is now dry, meaning it only flows air, not an air/fuel mixture. Since the manifold will now only flow dry air, there is no longer any need for the factory plenum dividers that aid with air/fuel mixture and distribution.
03 The XFI kit uses rail-mounted...
03 The XFI kit uses rail-mounted injectors, and for this application, we had to add holes in the intake runners for the injector bungs. The 3/4-inch holes for the bungs are drilled at a 15-degree angle from vertical with the bore centerline .950 inch from the manifold edge. Spacing is on 4.8-inch centers, which is of course the same as the bore spacing for this engine.
These days, any real Mopar guy can handle the drivability issues, but what if you've built a 472-inch Hemi with a solid roller cam, a 10.0:1 compression ratio, and an inline two four-barrel street Hemi manifold? Add to it the fact that you expect to top 600 horsepower and you want this thing to be hassle free so your girlfriend will be able to drive it.
While Muscle Car Restorations in Chippewa Falls, Wisconsin, was restoring Frank Dorsey's '70 'Cuda, Frank mentioned the Hemi that he and his cousin Jesse had been working on for the car, and how he liked the idea of electronic fuel injection. So, once the Hemi was in the hands of the guys at MCR, it was quickly sent to Gary Schmidt of Wheeler Racing Engines in Blaine, Minnesota, for Gary to finish the engine build and solve Frank's EFI dilemma by modifying the inline carbureted manifold to accept a FAST XFI fuel injection system. FAST's XFI fuel injection is a little different than their bolt-it-on-and-go EZ kit, the XFI uses a fully user-programmable Engine Control Unit (ECU) and can be tuned with any laptop or desktop computer. This tunability helps when using aggressive camshaft profiles, high compression, and all other horsepower-increasing modifications. Keep in mind that with the XFI injection kit, you will need to either modify your existing intake to accept fuel injectors, or source an intake already designed for them. We chose to modify an existing Street Hemi intake. The reason we did this was that we wanted to keep the factory look (albeit with fuel injectors), and with the Shaker being installed on the E-Body, height was a concern.
While fuel injection might not yield greater maximum power than a pair of well-tuned carburetors in all applications, it can dramatically improve the drivability of the engine.
04a When installing the injector...
04a When installing the injector bung in a dual-plane intake, the depth of the bung into the runner is determined by the lower plane runners on each side of the manifold. The bungs will protrude farther into the higher-plane runners, but as this manifold is only flowing dry air, this will not appreciably affect airflow.
04b The reason for this placement...
04b The reason for this placement is to keep all eight of the injectors at the same distance from the valve. Do not grind the bungs flush to the runner's roof. Their exact length is designed to produce optimum injector spray atomization.
05 There are bracket-mounting...
05 There are bracket-mounting bosses on the passenger side of the manifold that will be affected by the boring/drilling process. Gary had to remove enough material from them to provide clearance for the bung but leave the intake bolt-seating surface intact.
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.