3.9 Liter V6 Swap

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The highway mileage would be more from the O.D tranny than the V6,
Probably could cut up a 318 pan to fit. If you did similar hop ups to the 6 as a magnum 8 should make 3/4 the power as the 8. I seen one in a early a body at a car show this year but really just look like an 8 until closer inspection. Really no up side to the swap, but if thats what you want go for it , mounts and oil pan and maybe exhaust will be your main problems.
 
Good point about most of the MPG in the O/D trans.

For the same money and labor, I think I'd just do the 5.2
 
For the same money and labor, I think I'd just do the 5.2

Your right, I don't think its really worth rebuilding a V6 for power. I just happen to have a V6 that my uncle had freshened up a few years back, and just pulled out of his '89 Dakota to do a V8 swap.
 
I Have a 92 DAkota with the MAgnum 3.9 with over 250K and the valve covers have never been off . The best I EVER got was 18 mpg in a high state of tune.

I have a 96 Dakota with a 3.9 and a o/d auto. I have gotten 22 on the highway more than once. tmm
 
I had a 94 SWB standard cab 2wd 3.9 mag 5-speed.
When I bought it it had 20K miles on it, my neighbor bought it off me at about 100K for his kid to drive to college, he sold it at 160K still running strong.
It averaged about 20 mpg when I had it.

My daughter has a 88 dakota, 2wd auto standard cab LWB that I gave her last year with over 150K on the clock, milage is only about 14mpg.

The magnum had way more power and got better milage than the LA one.
 
I don't think I would do it. I believe I would stick with the slant. In my experience, the straight sixes were peppier than the V6s right off idle. I don't know the physics of it, but IMO they were. Maybe the crank being so long. Maybe something about the crank phasing, I don't know. But I've worked on a PILE of V6s and not one of them, not even the GM 4.3 had the off idle SNAP any straight six had.

Don't get me wrong, I ain't dawgin on the 3.9. How can you? A 318 V6 pretty much is what it is. Cannot go wrong with that design. It's just not a point I had seen brought up and I think it's a true one. While the V6s have more power overall, I am sure, the little slant has balls right when you crack the throttle that the 3.9 simply does not have.
 
Well rob ive had both lol . Ive run them side by side too . The 3.9 would smoke the slanty from the hit of the gas and never look back every time . Maybe that was not your point lol . I beleave both are good motors . The slanty Has the cool factor put a hyper pak on it and a set for shorty headders . cant go wrong ther ! A 3.9 with a v8 throttle body and a set of headders . Still cant go wrong . the 3.9 has the cool factor too cuz . It just aint done that offen . ... the bigger throttle body takes th mpg away some but hay lol
 
You're how old? And you don't think I've had both?

No it's not what I meant or what I said. You don't get it. I've had both too. Anybody whose had a good running straight six knows what I am talking about. It's got nothing to do with spinnin tires and drivin like a maniac. Not what I'm talkin about AT ALL.

You're not old enough to remember when overhead valve straight six engines were marketed, that was one of their biggest marketing points. How peppy they were. I remember it well. I stand by it. I never said a straight six has more power, in fact, I said the opposite. Stop thinkin about everything like the frikkin dumbass duke boys. lol
 
I think the question of mileage between a 4000lbs + truck and a 2700lbs car will be different. Especially if it's a 4wd Dak. If i couldnt get 25+ out of a magnum V6 (injected) with the OD trans in an early A I'd figure out what wasn't working right.

The 225 has a small carb, small ports, and 3/4" more stroke. It will respond quicker and it's advertised power peaks are (HP)800 rpm & (TQ)1600rpm lower than the 3.9's. But - the 3.9's still 65hp and 40 pound feet higher than the 225. It might feel quicker because of a faster pedal response - but in the same weight and geared package - it's not.
 
How many of th nay Sayers are running slants with money in them? IMO that ain't no different than the v6. Another benefit of the v6 is it weighs less than the slant and the v8 and as stated above, the Dakota weighs a hell of a lot more than the a-body. So there will definitely be a mileage increase. So again, I say go for it!

Asa, the guy I talked to with a v8 throttle bodies v6 saw mpg improvement. Don't ask me how cause I've never done it lol
 
Asa, the guy I talked to with a v8 throttle bodies v6 saw mpg improvement. Don't ask me how cause I've never done it lol

With a ported head, ported throttle body, and ported exh manifold my Neon got an extra 4mpg and a very feelable power boost. I've been driving it that way for 200K miles now - so that work paid off...lol
 
Your right, I don't think its really worth rebuilding a V6 for power. I just happen to have a V6 that my uncle had freshened up a few years back, and just pulled out of his '89 Dakota to do a V8 swap.

If it's free, that changes a lot of the equation.
IIRC a factory 5 speed manual is now a decent option for the 3.9 as well.

My 5.9 CC Dakota will get 23 MPG at 50 MPH all day long
(even though I HATE the phrase "all day long", it really does apply here).

Problem is finding long stretches of road with a 45 MPH speed limit!

I've been driving my mom's truck today after replacing the water pump.
It actually does pretty good getting up to speed from a standing start.
The weak point is passing power at road speeds.
 
With a ported head, ported throttle body, and ported exh manifold my Neon got an extra 4mpg and a very feelable power boost. I've been driving it that way for 200K miles now - so that work paid off...lol

I don't disagree. I'm just not of the science behind it the mpg improvement
 
227,000 miles and 21 mpg with a 5spd in my 03 Dakota and still running strong, however an inject 225 slant would be cool as hell
 
The 3.9 in a early a body hauls *** I put one in my 66 dart wagon the only problem I run in to is the motor mounts are in the wrong place and I had to make some mounts that would work. I avg 24.to 25 on the open road with 3.55 posi in the rear and I missed the car very much. Somebody stole it and the wreck it dam people and the law a worth a ****.

Here you go a picture of the eng bay
 

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Not my favorite engine but I certainly appreciate all the effort that goes into it. That is hot rodding. At least it's not another how do I put a Chevy into blah blah ...done to death.

Besides, I am the guy that wanted to put a 331 Hemi engine into a '74 road runner. I got lots of "why???" about that one.
 
Resurrection: Dodge Magnum 3.9 v6 rebuilt complete engine performance

Dodge Magnum 3.9 v6 rebuilt complete engine performance

From air cleaner to oil pan. all rebuilt drop in and go. has a stage one roller cam, mopar performance roller rockers, 1992 hi flow manifolds, ported and polished hi flow manifolds, lapped valves, surfaced heads, honed cylinders, polished crank,all new bearings, timing set, oil pump, water pump, ported manifold, alternator.....factory 5 hi flow injectors....it is ready to rock.....lubed but never fired. please make an offer
 
Well it must be sea levle or some thing lol Cuz ever one ive talked to In okl thats a had one pulled 25 outta them .
I bought a new '92 Dakota Club Cab, 3.9, 5 Speed, with a 3.55 rear and i would get 28mpg on the highway. Had for 7 years, no real issues.
 
Ive had several Dakotas both 318 and 3.9. The 3.9 is a long lasting engine for sure, many with over 250K and still going.
The biggest problem with them is being an "odd fire" V6 they are harder on timing chains than the V8, which takes the same chain and gears.
same labor as a V8 to change, they arent terrible to do.
BUT I must say that my 318 Dakotas have ALOT more power AND get the same (or better) mileage. and the same longevity with the same amount of care given to each.
My 90 (non Magnum) was the best on fuel MPG if that is what you are after, 16 (worst) 20 (best) my 94 was the peppiest, and my current 99 is the doggiest. My 94 and 99 seem to both top out on MPG at 17/ on the 99 it seems like I have to put my foot "thru the floor" to get it to go. my 94 pulled my popup (same camper) easier it seemed, than the 99. all my v6 Dakotas were 3.55 geared with the "A500" trans (42/44, RH/RE) so no variable there.
my 96 318 Dakota (only 4wd Dakota of the bunch) with 3.91 gears (only one of my 6 Dakotas to have had that ratio) can get 17 on summer blend gas in combo mixed driving. normally it's about 15 to 15-1/2 esp in the winter. My 2wd 318 Dakotas were slightly better. especially my 93 of which I converted to a NV3500 5 speed stick. That truck got an easy 20, and went like a bat outta He11.
You cant get these series trucks off teh showroom floor anymore and I like them overall much better than anything newer, so I take what I can get. V6 or V8. I look 1st for good body and frame and take whatever mechanicals come with the truck at that point. I miss the 93 the most, with its V8/stick and Id still have it if it hadnt been so badly crashed.... I put 72k miles on that truck for very little money. definitely got my moneys worth. the only one of the bunch that I am sorry I bought is the 99.
It has had alot more mechanical issues in a short time than any of my square bodys. and it was the lowest mile "when I got it" of any of them. Came with the biggest pile of reciepts showing it was maintained by the PO. alot of my repairs have been "redo's" of repairs he had paid someone else to do. and some things that you would have thought tehy would have done "while they were in there" but didn't. but I am so behind the 8 ball on the 99 that I have no choice but to run the wheels off of it cuz I surely wont come close to getting what I have into it back out. The rest I drove the wheels off, because I liked them, instead.
But all that said, no, I would not swap/retrofit a 3.9 into anything.
 
I bought a new '92 Dakota Club Cab, 3.9, 5 Speed, with a 3.55 rear and i would get 28mpg on the highway. Had for 7 years, no real issues.
HOW???? I don't see that as possible to get that good out of a 3.9 in a Dakota. occasionally I hear 22-23 but never 28.
 
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