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1979 Dodge Demon - The EBay 5.7 Hemi Engine

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We promised to install a Hemi engine into our Dodge Demon, and that time is here. A quick search using the keywords "5.7 Hemi engine" on our eBay Mobile app netted us about 50 different used Hemi engines of various years with a wide range of mileage. As this is written, the average was $2,000 for a 5.7 Hemi engine from a truck and $4,500 for one from a Charger or 300C. We chose a 5.7 hemi truck engine with 65K on the clock for $1,900 from eBay seller Knox Auto Parts. Knox is a wholesale salvage yard in Knoxville, Tennessee. The total price of the Hemi engine with shipping was $2,203.99. For that, we received the complete engine, a wiring harness, and a starter.

After the engine arrived, we needed to learn how to get it running. To get some advice, we called the guys from Street and Performance, MegaSquirt, local tuner DC Motorsports, and even the guys at Comp Cams to get the rundown on what is available to control and tune a Hemi-swapped vehicle.

The options in this story will work on a stock 5.7L truck engine or one pulled from a passenger vehicle. If you go cheap and buy the truck version, you are stuck with a dedicated factory manifold. Passenger-car fuel-injection manifolds crash into the timing-chain cover, making that swap impossible without also swapping the matching front dress. That adds at least another $300 for the cover, plus about $75 more for a plastic intake. The aluminum 6.1L intakes and fuel rails can cost as much as $1,000, and unless you plan to use an alternator-only front-engine accessory drive (FEAD), as we are, you will have to change the FEAD as well. Picking the wrong combo of parts can get expensive, fast. Keep that in mind when you make your choices.

Hemi Engine Factory Harness And Tune

We are adding this option because, in theory, you can add 12-volt power to the stock wiring harness and get the Hemi engine to fire and run on the factory tune. Yes, this is the cheapest way to go, but if there is a wiring problem somewhere in the nest, there is no tech line to help you. Mark Campbell from Street and Performance (S&P) in Mena, Arkansas, explained that the key to making this work is knowing the year of the engine and computer and getting the VIN of the vehicle. Campbell says the '03 to '05 computer is the best. It is less complex because it does not run the computer signals back and forth through a single wire like on the '06 to '08 harness, and S&P hasn't been able to get the '09-and-later system to function with the variable cam timing outside of the vehicle. He also mentioned that some vehicles were equipped with antitheft from the factory. It will kill the ignition if it is not removed from the computer. (Call Mopar and check the VIN for this feature.)

Campbell agrees that the simplest way to get a used Hemi engine running is to use an '05 factory harness and computer, a truck gas pedal, and a pedal-positioning switch (PPS), assuming you use a manual or early-style automatic transmission and an adapter plate (which can be purchased from S&P). If you do not need a detent cable (if you have a manual trans or a manual valvebody in an automatic, for example), you can use an '05 truck pedal with a built-in PPS. If you want to use your stock muscle car pedal or need a detent for a kick-down, you can use a stand-alone PPS and a set of Lokar cables to get it all to work.

If you want to add more power later, you can tune the computer with a handheld tuner and a dyno day. If you want tech support, we'd recommend purchasing a dedicated harness. S&P's team can only answer questions if they know what you are working with.

How Much?
Description Source PN Price
5.7 Hemi engine harness (manual trans) Street and Performance N/A $927.95
Dodge truck pedal Street and Performance N/A 139.95
Pedal-position switch Street and Performance N/A 259.95
Total $1,327.85

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