If you’re looking to build up a 3.9 Magnum engine, theres a few things you should know about what’s really inside the engine. Because in reality, building a stout 3.9 is not that hard! To begin, the first thing you should know is Chrysler never really changed much over the years when it came to engines, only in 2000 they really started to make significant changes when the new 4.7l V8 replaced the 5.2l V8. And the 5.2l magnum is really just a updated version of the legendary 318. So back in 1987 when Chrysler needed to add a V6 to their truck lineup, they just took the 318 and just lopped off two cylinders, and presto, the 239ci (3.9l) V6 was born. It shared a number of the same components, and served it’s job well. It was in use till about 1993 when agian, they took the block, updated the heads, cam and intake, and introduced it as the new 3.9l Magnum engine. The term new really just applied to the name, but it launched Dodge’s truck line to the next level. But in reality it was just new packaging of a really old engine.
So to wrap it up nicely, the 3.9l shares a LOT of parts with the 5.2l engine. The pistons, piston rings, and rods are the same, with the only exception being that the 3.9l ‘s mains are a little bit narrower than the 5.2l’s. So you can buy a set of 318 pistons, rods, rings and bearings, have your machine shop narrow the mains, and install everything very easily. The oil pump, timing chain, cam bearings, and all the little parts are the same. So building up the short block is the easy part!
Where things get a little complicated is on the top end with the heads, cam, and intake. Since there’s very little after-market parts in this department, you’re best bet is going to someone like KRC Performance and ordering a cam, or sending a core cam in to Comp Cams or Crower for a regrind. After that, you’re lifters, pushrods, and rockers are the same as the 5.2’s so that’s an easy order. When it comes to heads, the only option is to port the stock heads. Since the heads are the same design, you can use a 318 porting template, then add the Mopar Performance valves, springs, locks, seals, and retainers. The intake manifold is another item that all you can do is port the stocker, just some simple port matching and shortening of the runners.
Stroker cranks are available for the 3.9, but at $2000.00 for just the crank alone. And really, $2000.00 can build you a nice 5.2 or 5.9, which would give you even more horsepower and a wider variety of parts to choose from. And an engine swap is not that hard with Dodge’s trucks!