Stinky211

I have a 2008 300C with a 5.7 hemi and found a used 5.7 hemi from a 2007. The majority of the engine appears correct except the spark plug cois are completely different. Wondering if I can do this swap assuming the ECM from the 2007 will hook up to the 2008

wreklus

If I'm not mistaken, the 2007 and 2008 5.7 Hemi are the same. They should both have MDS, multi-displacement which cuts off 4 cylinders under gentle driving for "economy" (haha!). If so, they're the same internally.
The difference I would look out for is engine mount points, accessories and the connection to the torque converter and transmission. I don't know if the 300 changed much between those years.

I'd guess things would match up really well, but I could be wrong.

Stinky211

Stinky211

The engine and tranny from the 2007 are together so will be a straight forward swap. My concern is the ignition systems are different and not sure if having the original 2007 ECM is the only required component.

wreklus

Without having seen the coil packs, the difference could be several things:
1. Aftermarket parts on one engine
2. Two different engines (a 5.7 vs 4.7, 6.1, etc...) I don't know what options 300s came with.
3. Some modders crossed one wire from the coil pack to the opposite cylinder to get both plugs in each cylinder to fire at the same time (because they thought that would be a good way to initiate spark, clearly knowing zero about clashing flame fronts creating stupid high pressure spikes).

You could:
1. Post pictures here and hope someone knows what they're looking at (low chance I'd have any idea).
2. Take pictures to a dealership and hear the truth from the horse's mouth.
Or both.

Stinky211

This is the 2008 5.7 hemi.

This is from the 2007 5.7 hemi
Can anyone help if the 2007 5.7 engine with original ECM will swap with a 2008 5.7 engine if I swap the ECM for the 2007?

wreklus

Oh. I see what you mean.
Looks to me like you have one engine with dual spark plugs and one with single spark plugs.
I had thought that dodge made that change back in '05.

I don't think the old ECU will have the ability to run 8 extra plugs. That unfortunately is going to cost you, if you don't already have the right ECU.

Stinky211

The 2007 replacement engine includes the ECM

wreklus

Ought to run just fine, then.
Curious about whether the mount points would match up. You might end up having some fabrication work to do for mount points and exhaust manifolds.

mopar5150

Both engines are 5.7L but the one with the crossover spark plug wires is an'03- '05 Ram or '05 LX. All Gen3 hemis are dual plug.

The engine mounts on the bottom photo are from an LX. Truck mounts are large cast iron parts. The 5.7L truck engine uses a different intake (TB on top) and front cover/ accessories. I cant see the intake in the photo.


People will often try to sell an '03-05 as an '06-07 because the early 5.7L engines had issues with exhaust valve seats dropping and are hard to sell.

There are a few differences between the years but as far as a long block is concerned it it a direct swap. Do not mix up the ECUs and throttle bodies as they are "matched".
If you swap throttle bodies the ECM will go into limp mode and the throttle will not work requiring a dealer scan tool to re-cal.

In the LX cars the ECM, TCM ignition switch and other parts are serial number matched.

wreklus

I stand corrected.