Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

3.9 dodge to a 5.7 (340) dodge

i planing on getting a dodge dakota with a 3.9 auto and was woundering if a 340 will bolt up. becuse i was told that the 3.9 dodge motor was the same as a 318 but with to pistons takin of. but i could be worng.

Ya, you wrong. Wrong like a soup sandwich.

For all things Dakota, this is an excellent site. They could answer any questions about an engine swap. I don’t recall any 340 swaps when I frequented the site though.

Off the top of my head, Gen I Dakotas (87-91) were not available with a V8 (exc. Shelby Dakota). The length of the engine compartment was increased to accomadate a V8 with the Gen II (92 -96) Dakota. According to the my 95 Dakota shop manual the V8 was a 318 (5.2). The V6 trans was a 42RH and the V8 was a 46RH. The Gen III Dakotas (97+) were also available with a 360 (5.9) in the RT trim. Around 2000 or so the V6 and V8 engines used were the 3.7 and 4.7 respectively.

Ed B.

Uhh. the 3.9 is a V6 that displaces 239 Cubic Inches. It is not a 318 (5.2L V8). The 340 V8 is basically a stroked 318. However the 340 has not been used in production vehicles for many year. The 5.7L engine that Dodge makes now is their much touted “hemi” V8. It has very little in common with the LA series engines (the magnum line)

Actually, the 3.9L V6 IS essentially a 318 minus 2 cylinders (same bore & stroke, cylinder bore centers). Heck, some engine parts are interchangeable between the two. (So much for the “soup sandwich”, Norm.)

Ed’s post has some good information. A V8 CAN be shoehorned into an early Dakota, but you’ll have to monkey with the cooling system. There isn’t enough room for the waterpump-mounted fan.

A bigger problem is the transmission. The V6 trucks have a lighter duty automatic that won’t stand up to the torque from a V8 for long. You also will have a problem if emissions testing is required where you live.

With all of the used dakota’s out there, why buy one and then put a lot more money into an engine swap? Just get one with the engine you want already installed from the factory and save yourself a lot of headaches and money.