Swap A New Hemi Into An Old Mopar

LaPaglia was able to keep his Challenger's stock power steering box. Dart, Duster, and Valiant owners won't be so lucky.

LaPaglia was able to keep his Challenger's stock power steering box. Dart, Duster, and Val

Power Steering
B- and E-Body Mopars can also keep the factory power steering gearbox, but it's a really tight fit, too. A-Body owners aren't so lucky. There simply isn't room for the power steering box, and you'll likely need to convert to the smaller manual steering box. The new Chrysler pump operates at around 1,600 psi--too high for the older car's components, according to most people we talked to. They warned of blown seals and chronic leaks. The solution most recommended was to replace the Chrysler pump with a GM because they operate at lower pressures, about 1,100 psi. However, for the guys who just can't bring themselves to put any GM part on a Mopar, Bouchillon offers a reduced-pressure Chrysler. He says they're such a popular item, he can't keep them on the shelves.

Engine Management
To control your new engine, there are three different options: two stand-alone systems and one that uses a factory ECM. The simplest option is to use the factory ECM. A stock Chrysler ECM can be reflashed to run the new engine in the older car and ignore certain sensors and operations like EGR solenoids and fuel tank pressure sensors. A limitation with a factory ECM is it will need to be reprogrammed if you decide to change things like cams and cylinder heads or add boost or nitrous oxide at a later date. These things would increase airflow through the engine past the limits the base ECM programming can compensate for. Obviously, this would only be an issue if you plan on adding more power down the road.

The Bouchillon low-pressure Mopar power steering pump kit is in this photo.

A better option for guys who are always tinkering is a stand-alone engine management system, and there are two big players you can choose from. FAST and Mopar Performance make systems that are fully programmable via a laptop computer and the accompanying software. Of the two, the Mopar Performance system is a little easier to use. It comes loaded with a basic program that will allow you to start the car and drive it around on a very basic tune. The FAST XFI computer comes with no base program, so you'll have to dial in a basic program yourself. It does offer a dizzying array of parameters to fiddle with, though, and would be perfect for the nerdy, electronics types. No matter which system you choose, your engine will run best when tuned on a chassis dyno, so find a shop you can work with.

There are several options available to run the new engine. LaPaglia uses a Mopar Performance stand-alone computer mounted in his glovebox.

There are several options available to run the new engine. LaPaglia uses a Mopar Performan

Drive By Wire
All new Hemis come with an electronic throttle body, or drive by wire. This poses a problem because you need to use a matching electronic accelerator pedal, and we can guarantee the new one will look odd and out of place in your older car. Mopar Performance makes a traditional cable-operated throttle body that includes a throttle-position sensor to communicate with the ECM. You'll need to come up with a properly routed bracket, however. Another option is to use what's known as the black box. Fullsize pickups use a cable-style gas pedal, and that cable is connected to a box under the hood that converts the input to a digital signal that then operates the electronic throttle. This cable-operated box can be adapted to your old car's throttle cable, and you can keep the engine's electronic throttle body.

Airbox
LaPaglia recommends making some sort of cold air intake ducting rather than using a conical air filter clamped to the throttle body. He tells us he was seeing intake air temperatures of more than 180 degrees before he installed his. At intake temperatures that high, engine performance is greatly diminished because the computer retards timing to prevent detonation. He made a great-looking airbox out of ABS plastic, routing the inlet just behind the lower grille opening.

Do It!
Yes, this is a complicated job. But the good news is there are more people doing it than ever before. That means there are more sources for information and more aftermarket engineering and support, so it's likely you'll be able to find a solution to any problem you encounter while doing the swap. If you like a challenge, this is the swap for you. The new Hemis are great engines with a ton of potential.

See the May '08 issue of CC for a feature on Jonathan's car.

By John McGann

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