So why do 3.9's suck

[moparmarks]

I had a 93 Dakota 3.9 5-spd 2-wd and I wasn't overly impressed. Wasn't that great here in the Colorado Rockies. My 97 Dakota 5.2 auto 2-wd had way more power and about the same gas mileage. Not saying it's a bad motor but it didn't compare to my GM 4.3 V6.

 

[toolmanmike]

I had a 93 Dakota 3.9 5-spd 2-wd and I wasn't overly impressed. Wasn't that great here in the Colorado Rockies. My 97 Dakota 5.2 auto 2-wd had way more power and about the same gas mileage. Not saying it's a bad motor but it didn't compare to my GM 4.3 V6.

4.3 to 3.9 comparison? That's about a half liter difference. Like the difference between a 318 and a 340. Of course the bigger engine will have more power.

 

[YY1]

The gm 4.3 is one of the few gm engines I sing the praises of.
The county office I worked for had a fleet of 4.3 powered s-10's and astro vans.
They all had plenty of power and were consistent.
All about 18 MPG.
For a while I drove a short cab, short bed s-10.
It would bark 2nd.

Around the same time, I had a 93 3.9 Dakota and later my mom had a 93 3.9 Dakota, both ext cabs.
My truck was a DOG. Hers was peppy.
...and that's what I've come to see across the board. They are inconsistent with respect to power.
Mom now has an '02 3.9 crew cab Dak.
The power is "OK", but be careful about pulling out in traffic.
All of our 3.9 engines got about 18 MPG.

Previous to the 93 Dakota, mom had a 1980 gran prix 3.8.
TURD for power.
Could not kill it, though.
Unsure of MPG.

 

[YY1]

The Mopar 3.6 is a winner power and economy wise at give or take 300HP.
We've rented several minivans and all had great power and returned an average of 27 MPG.

 

[moparmarks]

4.3 to 3.9 comparison? That's about a half liter difference. Like the difference between a 318 and a 340. Of course the bigger engine will have more power.

True but my 4.3 van got better mileage than the 3.9. I just thought the 3.9 should have got better mileage that it did. At least mine anyway.

 

[AJ/FormS]

3800 in my 2000 Buick Park Avenue and it's a fantastic engine,

I had a 3800FWD in a 2008 Buick LaCross, plenty of power, and mileage tickling 30mpg US. I chose that car for that engine.
Hyup, I loved that car, right up until the wife wrote it off.
She writes nearly all our cars off; and never gets hurt. I think God loves her.
I don't let her drive our 2014 Orlando much, cuz I want it to be with us until they take my driving privileges away. After that, she can crash it.

 

[nitro_rat]

The 3.9 also gets the distinction of having one of the WORST exhaust notes of all time. Considerably more annoying than a 4.3 Chevy or 3.8 Ford. Even the 2800/3100 GM v-6's are less annoying, at least they sound mean when uncorked. Whatever you do with a 3.9, keep quiet exhaust on it!!!

 

[volaredon]

I had a 3800FWD in a 2008 Buick LaCross, plenty of power, and mileage tickling 30mpg US. I chose that car for that engine.
Hyup, I loved that car, right up until the wife wrote it off.
She writes nearly all our cars off; and never gets hurt. I think God loves her.
I don't let her drive our 2014 Orlando much, cuz I want it to be with us until they take my driving privileges away. After that, she can crash it.

2014 Orlando? Never heard of it

 

[AJ/FormS]

That's a Chevy CUV, barely bigger than a hatch back, but with a higher roof and seats, for us older guys. We luv it.
She boasts 167hp@6700, and does it with VVT, DI, 2.5 liter, Eco-something, with a 6-speed+LU auto. I have yet to fault the shift programming.
The switchover in the VVT happens at 4500. In 4 years, I've only ever felt it once, cuz the bottom end, which cranks 220psi on my gauge, is more than enough for what it is. The one time I needed it, was during a pass; I thought I had misjudged the distance available, which, as it turned out, was false as there was plenty of room, lol.
It seems the USA never got them, which is a shame, cuz IMO, it's a great vehicle.

 

[RustyRatRod]

The gm 4.3 is one of the few gm engines I sing the praises of.
The county office I worked for had a fleet of 4.3 powered s-10's and astro vans.
They all had plenty of power and were consistent.
All about 18 MPG.
For a while I drove a short cab, short bed s-10.
It would bark 2nd.

Around the same time, I had a 93 3.9 Dakota and later my mom had a 93 3.9 Dakota, both ext cabs.
My truck was a DOG. Hers was peppy.
...and that's what I've come to see across the board. They are inconsistent with respect to power.
Mom now has an '02 3.9 crew cab Dak.
The power is "OK", but be careful about pulling out in traffic.
All of our 3.9 engines got about 18 MPG.

Previous to the 93 Dakota, mom had a 1980 gran prix 3.8.
TURD for power.
Could not kill it, though.
Unsure of MPG.

They're ok. Good power, torque and decent mileage. But GM never managed to get the inherent vibration out of them. We had one at the Chevy dealer when I worked there that was under warranty. I don't know what the GM rep was thinking, but he authorized us to pull the engine and send it to a local machine shop, have them disassemble it and balance it to the nth degree, which we did. Got it back, put it back and no difference. I think that particular warranty rep was trying to prove to his managers that this was something that was going to be "the way it was" with those engines. If that was his point, he was successful. I've never seen one newer or older that did not have that vibration.

 

[Syleng1]

Easy boy. lol

Bahahahahajahahhhhaaa!

 

[MopaR&D]

I had a 3800FWD in a 2008 Buick LaCross, plenty of power, and mileage tickling 30mpg US. I chose that car for that engine.
Hyup, I loved that car, right up until the wife wrote it off.
She writes nearly all our cars off; and never gets hurt. I think God loves her.
I don't let her drive our 2014 Orlando much, cuz I want it to be with us until they take my driving privileges away. After that, she can crash it.

That was Series 3, they fixed the leaking lower intake gaskets by that time. Multiple options exist now for improved LIM gaskets that eliminate coolant leakage into the crankcase. One of those stupid seemingly harmless cost-cutting moves by GM that just happened to cause total engine failure if not caught quickly on the Series 2 engines. Same with the stupid plastic coolant tubes going from the timing cover to alternator housing (WHY are they there in the first place?), every auto parts store carries aluminum ones in stock lol. Once those issues are fixed the NA ones easily go 300k miles, usually the cars fall apart around the engine by then.

Put the aluminum tubes in mine as a preventative "repair" and keeping a close eye on coolant levels as I haven't done the LIM gaskets but the SC engines are more forgiving since the lower intake (blower base) is aluminum instead of plastic like the NA ones are.

Back to Mopars... tbh the 3.8L was pretty good in the minivans, drove a couple of those (2001 and 2003) and they had good power and reliability. Idk what happened when they put them in Wranglers, maybe the extra weight and terrible aero was too much for them to overcome... Might have had too tall of gearing as well, idk. I'd consider swapping one of those in a hotrod if I really wanted to use a Mopar V-6.

 

[RustyRatRod]

That was Series 3, they fixed the leaking lower intake gaskets by that time. Multiple options exist now for improved LIM gaskets that eliminate coolant leakage into the crankcase. One of those stupid seemingly harmless cost-cutting moves by GM that just happened to cause total engine failure if not caught quickly on the Series 2 engines. Same with the stupid plastic coolant tubes going from the timing cover to alternator housing (WHY are they there in the first place?), every auto parts store carries aluminum ones in stock lol. Once those issues are fixed the NA ones easily go 300k miles, usually the cars fall apart around the engine by then.

Put the aluminum tubes in mine as a preventative "repair" and keeping a close eye on coolant levels as I haven't done the LIM gaskets but the SC engines are more forgiving since the lower intake (blower base) is aluminum instead of plastic like the NA ones are.

Back to Mopars... tbh the 3.8L was pretty good in the minivans, drove a couple of those (2001 and 2003) and they had good power and reliability. Idk what happened when they put them in Wranglers, maybe the extra weight and terrible aero was too much for them to overcome... Might have had too tall of gearing as well, idk. I'd consider swapping one of those in a hotrod if I really wanted to use a Mopar V-6.

There's no question it was a slug with the hardtop on. But with the top and doors off, it was pretty snappy.

 

[YY1]

I don't recall any vibrations in any of the fleet that I drove.
The worst mechanical things about the 4.3 powered fleet were-
The s-10's had terrible ABS systems. Worst case was pavement change from asphalt to gravel with light brake application.
Pedal would go to floor and sometimes ABS would kick in. NOT a comforting feeling.
The astro's had a pronounced lag between accelerator application and rear axle engagement.
I'm surprised we didn't rip the rear ends out on a regular basis.

 

[volaredon]

I lost count how many ball joints I did back in the day on s10s especially 4wd ones and idler arms (each van had 2 of them) on the Astro's.
Then onto the alignment, the Astros didn't suck to do as bad as the ford aeroflops....

 

[HankRearden]

I lost count how many ball joints I did back in the day on s10s especially 4wd ones and idler arms (each van had 2 of them) on the Astro's.
Then onto the alignment, the Astros didn't suck to do as bad as the ford aeroflops....

Agreef. Also working commission,I loved Ford f trucks and Rangers. Many weeks their junk twin flopping I beam suspensions were the difference between paying the rent or living in my toolbox.
Gm w body rear disc brakes literally started a fist fight over who got the job once.
Not the only time I got in a fist fight at work but the only time it was for a job.
I miss the 90's and working with real men

 

[YY1]

We had one aerostar in the fleet.
It was severely underpowered compared to the astros, but it was considerably more comfortable.
The foot room in the astros was literally equivalent to a milk crate. (I measured both).
...and the seating position put your knee above the bottom of the window line.

 

[MV8]

Everything is a compromise. If the donor for the light build included a perfectly fine 3.9 and plenty of hood clearance or no hood, I'd use it but leave room in front for the smoother running v8. I'd don't like the height (for hood clearance) or vibes that come with any big v6, L4, or L5, to try to address with balance shafts. A 3.9 magnum would be a beast in a miata.

 

[YY1]

Was anything special done to the Prowler 3.9s?

 

[toolmanmike]

@dart64gt put a 3.9 in a 66 Dart wagon. It looks right at home in there.

 

[DumpsterFire]

weird. I worked on and drove a bunch of them in dakotas and my experience was not nearly as positive.

I even bought a couple first gen dakotas with less than 100k miles and blown up 3.9's. Both broken connecting rods.
Maybe Ive just never seen a good one.

I think they were much better made in the magnum years. I'm beating hard on a v6 dakota and doing a lot of towing it shouldn't be doing. Dumbest thing so far was snatching a dart parts car out of the blue ridge mountains. Heaviest thing so far is pulling my diplomat home. It keeps highway speed no problem.

 

[HankRearden]

@dart64gt put a 3.9 in a 66 Dart wagon. It looks right at home in there.

View attachment 1716359743

View attachment 1716359744

View attachment 1716359747

Looks like a nice fit

 

[DumpsterFire]

Everything is a compromise. If the donor for the light build included a perfectly fine 3.9 and plenty of hood clearance or no hood, I'd use it but leave room in front for the smoother running v8. I'd don't like the height (for hood clearance) or vibes that come with any big v6, L4, or L5, to try to address with balance shafts. A 3.9 magnum would be a beast in a miata.

On stuff like that it's hard to not go ahead and do a v8 if you're doing all that work. I only have a v6 beacuse it's already in the truck and was cheap. Don't see much reason to seek out a v6 magnum. If I blow up mine I'm probably just throwing a 318 in

 

[MOPARMAGA]

3.9 Magnum isn't a bad running engine until the seats crack which isn't as common (from the heads I've seen)as V8 heads. or the plenum gasket poops out.
Typical Magnum stuff.

 

[MOPARMAGA]

If I was going to do a v6 it would be a 3.5 from late 90s and or the later 3.5 early 2000s.
98 intrepid with a 3.5 would make a 5.0 gt mustang owner reconsider their hotrod stop light to stoplight.
I have no idea how one would make it rear wheel drive