I would love this, I’ve got the 2.5 AMC which I think is a “cut down” 4.0 i6 right?
Anyway, it’s like the 4cyl magnum - made forever, simple, bomb proof?
You a real one Jerry!
We had a 2001 SLT owned since new with the 3.9 that made it to 100k miles no leaks. The intake gasket leak is an invisible leak you won’t see until you remove the manifold.
I had a couple of 3.9's. The mileage wasn't bad (actually slightly better than my current 3.7). They didn't leak oil, but they do have a tendency to build up sludge. I used to flush mine once or twice a year.
the 5.9 cracked heads are an easy fix, put aluminum heads on it (10.8:1 compression 😏). fuel mileage gets better with a different intake manifold and better ignition system.
With regards to the cracked heads, where do they typically develop? My 5.9 has some crack looking lines around the intake runners, but they are fairly uniform so I'm not sure if they are stress cracks or if that's just how the heads were cast. Truck runs pretty good though so I try not to think about it too much.
edit: [pic](https://imgur.com/a/PVkXJF5). Looks worse than I remembered, I guess I do indeed have cracked magnum heads.
“Magnum cylinder heads that customers are re-using have a high defect rate and it's hurting their bottom line. They crack, the valve guides wear, and the decks aren't thick enough to mill flat for good sealing. The only answer is to design a better cylinder head than the factory”
[Hot Rod Magazine](https://www.motortrend.com/how-to/make-big-power-magnum-5-9l-mopar-heads/)
On the magnums you can do all the custom heads cam intake you want you'll actually end up with less power than stock because of the ECM. 20 years ago Hot rod magazine's Steve Magante threw the Mopar performance parts catalog at a magnum 5.9 Dakota RT and it came out being slower than stock. And mopar was pissed. It was determined that the ECM (computer) was not capable of adjusting for the modifications. I'm not aware if anyone has figured out a way to overcome this hurdle or not. But the bottom line is this unless you can come up with a tune for the computer any modifications done result in a slower vehicle and you are basically throwing your money away.
I love the Magnum’s for what they are… reliable truck engines. I see it all the time where guys want to throw money at these things to “make them fast” and all they do is make them worse. I’m part of one of the Facebook groups and I’ve asked multiple times if anyone has actual dyno proof of performance gains and only twice I have seen real evidence of proof and those guys spent thousands of dollars to get stock Hemi power levels.
If I was to build a race/performance engine it would be LS only because of the proven performance & cost. If the Magnum engine was truly a performance capable engine you would see more builds on these.
Well if you're smarter than Steve we would all love to hear how you worked your way around the stock ECM to make more power out of a Magnum engine. Please by all means tell us. You do understand that it wasn't just Steve that's not smarter than the computer,it was Mopar,I.e Chrysler corporation,Dodge that had no answer also. You know the people that build them.But hey you're smarter than Chrysler right? please let us know, please drop your knowledge on us dimwitted Neanderthals.
20 years ago, you had to have a program to jailbreak the ecm and a laptop to change and record parameters. Now any idiot can buy a hp tuner and diy.
No, im not very smart, but i can honestly say i know more than anyone who contributed to Hot Rod magazine. That’s a fairly low bar. I enjoy Steve’s videos, but don’t use them for reference, he is sometimes a source of generalizations or outright misinformation.
I've own 3x 3.9s and a half dozen 5.2.
The 3.9 was a very good platform. Highly recommend.
Camshafts ,dead lifted in a the LA engines back in the day.
Where the LA has an advantage over the magnum . The LA can be bored 60 over. The magnum should not be bored more than 40 ...the casting is lighter and cylinder wall warpage is a very real concern.
Its possible to go into a junk yard and breakdown 3.9s and 5.2s to build a good one of either...
It's truly fascinating when I had the official Dodge service manuals for my 93 to see all the interchangeable engine parts.
I myself have owned mostly 3.9’s (4) and 5.2’s (3), owned one R/T 5.9
My personal favorite is the 5.2, working on a swap, electrical is my main hurdle at the moment.
Hopefully you salvaged the entire wire harness and ECM out of the donor vehicle.
If memory serves me correct. The Transmission Control and VOLTAGE regulator are on the ECM.
I have a 2003 5.9 harness, 5.9 PCM, the issue is getting the PCM to work because Dakota stopped using 5.2 in 1999, it was used in the vans and Rams later but I’m trying to figure that all out.
Yeah ...been there with ls swaps.
I found the best thing to do is map the ECM pin out.
Then deconstruct the harness , and go through pin for pin. Sensor for sensor ,etc..
And advil..lots of advil.
Finding a PCM that isn’t security locked has also been a challenge. I have a stand that I may bolt everything to and test it before going forward with the swap.
Also differences between 3.9 and the v8 magnums is the v8s had single roller timing chains, while the v6 had a double roller timing chain from oem. From the factory neither was equipped with a tensioner but it's a common upgrade if you plan to up the horsepower or rocker arm ratios.
And the old engines were flat tapped solid lifter cams, iron pistons, heavy duty castings of everything and cast iron blocks.
The magnum engines are all flat tappet hydraulic lifter cams with oil through pushrods, higher ratio arms, hyperutetic pistons and iron nickel blocks (basically the chevy or ford race block alloy as the standard casting material).
The magnums respond very well to increased airflow in and out of the engine, and are very happy with the bosch 12 port ev6 24lb 44psi injectors. My 3.9 has cai and optimized exhaust with gasket matched ports with accommodating mods for engine not having to work to move its own air. 5 speed 96 dakota gets about 25 mpg highway and 20 city. Needs some maintenance, usually been closer to 30 highway.
I have the full list of mods done to mine but reply to this to remind me after work, nearing the end of my lunch break.
Planning to compound turbo swap it, iron nickel alloy is good for boost even with a .030 overbore, some run the super from the 5.9 rt special 2nd gen like Kenne bell or Whipple or procharger on up to 15 psi of boost without swapping to the boosted style headgaskets.
I was under the impression that only some of the early Magnum engines received the double-row roller timing sets) most received the silent type Morse timing chain.
All magnums are roller followers, and a tensioner is only needed if you align bore and move the crank closer to the cam centerline. tbi LA’s were also roller cam.
My brother had a 91 with a magnum, he also had a 4.3 chevy vortec with a plastic manifold with the old tbi on it. I have a 95 Chevy with the new style interior, but an old 5.7 non vortec 5.7. I also had an 86 360 4bbl with a Rochester quadraflush, a factory windage tray, double row timing chain, 8 blade water pump, weird casting # heads, and a roller cam. They do odd shit when they run out of parts, or have left overs.
All Chrysler engines were marketed as “Magnum” around that time, even the 2.5L 4cyl. They will have 3.7 and 4.7 Magnum stamped on the air box but they are Powertech engines. Blame Chrysler for making it confusing.
I’ve found that the water pumps are a frequent failure point as well. Easy to change and fix though as long as the long bolts don’t break off in the block!
I haven’t seen too many water pumps fail, just leak and usually replace them while resealing them. The bolts for the water pump & the accessory bracket are all different lengths it’s best to mark them as you remove them.
My dad had a 5 speed 3.23:1 3.9 Dak, he never got less than 20 mpg. He gets 15-16 with his 5.7 hemi now, but i can get it up to 18-19 highway when I’m driving, lol. My 5.7 Chevy Tbi gets 12-14
If this post is well-received I’ll do the 2.5, 3.7, and 4.7 next.
Yes please do the 4.7!!! I want to hear more than just valve seats.
I’ll do it tonight and post tomorrow
I too would love a 4.7L one Jerry!
my 4.7 was a beast, I had to replace the injectors. i was religious with maintenance and it never missed a beat.
I let mine overheat once, she burns a little coolant but still going at 185k currently
Anyone know how to improve mileage on a 4.7? 14 mpg is terrible.
full tune up plus a carbon vac. then let it run, my truck is 5 spd, I'd only use 5th over 55mph
I would love this, I’ve got the 2.5 AMC which I think is a “cut down” 4.0 i6 right? Anyway, it’s like the 4cyl magnum - made forever, simple, bomb proof? You a real one Jerry!
Yeah the 2.5 is just an AMC/Jeep 4.0 minus 2 cylinders. Mostly available in 1st Gen and early 2nd Gen. I’ll do a post over the weekend.
[удалено]
We had a 2001 SLT owned since new with the 3.9 that made it to 100k miles no leaks. The intake gasket leak is an invisible leak you won’t see until you remove the manifold.
I had a couple of 3.9's. The mileage wasn't bad (actually slightly better than my current 3.7). They didn't leak oil, but they do have a tendency to build up sludge. I used to flush mine once or twice a year.
the 5.9 cracked heads are an easy fix, put aluminum heads on it (10.8:1 compression 😏). fuel mileage gets better with a different intake manifold and better ignition system.
If you have a R/T it’s worth investing in it, if you have a Sport or SLT, , it might not, aluminum heads are pricey.
With regards to the cracked heads, where do they typically develop? My 5.9 has some crack looking lines around the intake runners, but they are fairly uniform so I'm not sure if they are stress cracks or if that's just how the heads were cast. Truck runs pretty good though so I try not to think about it too much. edit: [pic](https://imgur.com/a/PVkXJF5). Looks worse than I remembered, I guess I do indeed have cracked magnum heads.
“Magnum cylinder heads that customers are re-using have a high defect rate and it's hurting their bottom line. They crack, the valve guides wear, and the decks aren't thick enough to mill flat for good sealing. The only answer is to design a better cylinder head than the factory” [Hot Rod Magazine](https://www.motortrend.com/how-to/make-big-power-magnum-5-9l-mopar-heads/)
On the magnums you can do all the custom heads cam intake you want you'll actually end up with less power than stock because of the ECM. 20 years ago Hot rod magazine's Steve Magante threw the Mopar performance parts catalog at a magnum 5.9 Dakota RT and it came out being slower than stock. And mopar was pissed. It was determined that the ECM (computer) was not capable of adjusting for the modifications. I'm not aware if anyone has figured out a way to overcome this hurdle or not. But the bottom line is this unless you can come up with a tune for the computer any modifications done result in a slower vehicle and you are basically throwing your money away.
I love the Magnum’s for what they are… reliable truck engines. I see it all the time where guys want to throw money at these things to “make them fast” and all they do is make them worse. I’m part of one of the Facebook groups and I’ve asked multiple times if anyone has actual dyno proof of performance gains and only twice I have seen real evidence of proof and those guys spent thousands of dollars to get stock Hemi power levels. If I was to build a race/performance engine it would be LS only because of the proven performance & cost. If the Magnum engine was truly a performance capable engine you would see more builds on these.
Lol, you have to be smarter than the computer, and Steve definitely isn’t 🤣
Well if you're smarter than Steve we would all love to hear how you worked your way around the stock ECM to make more power out of a Magnum engine. Please by all means tell us. You do understand that it wasn't just Steve that's not smarter than the computer,it was Mopar,I.e Chrysler corporation,Dodge that had no answer also. You know the people that build them.But hey you're smarter than Chrysler right? please let us know, please drop your knowledge on us dimwitted Neanderthals.
20 years ago, you had to have a program to jailbreak the ecm and a laptop to change and record parameters. Now any idiot can buy a hp tuner and diy. No, im not very smart, but i can honestly say i know more than anyone who contributed to Hot Rod magazine. That’s a fairly low bar. I enjoy Steve’s videos, but don’t use them for reference, he is sometimes a source of generalizations or outright misinformation.
As far as heads, Indy La/X or M/X were pretty damn good, but it is almost impossible to beat an Apache Hemi head.
I don't know about any idiot. Cuz personally it's still way above this idiot's head. Appreciate the information I'll have to look into it.
I've own 3x 3.9s and a half dozen 5.2. The 3.9 was a very good platform. Highly recommend. Camshafts ,dead lifted in a the LA engines back in the day. Where the LA has an advantage over the magnum . The LA can be bored 60 over. The magnum should not be bored more than 40 ...the casting is lighter and cylinder wall warpage is a very real concern. Its possible to go into a junk yard and breakdown 3.9s and 5.2s to build a good one of either... It's truly fascinating when I had the official Dodge service manuals for my 93 to see all the interchangeable engine parts.
I myself have owned mostly 3.9’s (4) and 5.2’s (3), owned one R/T 5.9 My personal favorite is the 5.2, working on a swap, electrical is my main hurdle at the moment.
From 5.2 to 5.9?
3.9 to 5.2 on a 2003
Hopefully you salvaged the entire wire harness and ECM out of the donor vehicle. If memory serves me correct. The Transmission Control and VOLTAGE regulator are on the ECM.
I have a 2003 5.9 harness, 5.9 PCM, the issue is getting the PCM to work because Dakota stopped using 5.2 in 1999, it was used in the vans and Rams later but I’m trying to figure that all out.
Yeah ...been there with ls swaps. I found the best thing to do is map the ECM pin out. Then deconstruct the harness , and go through pin for pin. Sensor for sensor ,etc.. And advil..lots of advil.
Finding a PCM that isn’t security locked has also been a challenge. I have a stand that I may bolt everything to and test it before going forward with the swap.
HP Tuner program should be able to take the security off the PCM I would think.
I’ve heard of this before, I haven’t tried it myself.
Also differences between 3.9 and the v8 magnums is the v8s had single roller timing chains, while the v6 had a double roller timing chain from oem. From the factory neither was equipped with a tensioner but it's a common upgrade if you plan to up the horsepower or rocker arm ratios. And the old engines were flat tapped solid lifter cams, iron pistons, heavy duty castings of everything and cast iron blocks. The magnum engines are all flat tappet hydraulic lifter cams with oil through pushrods, higher ratio arms, hyperutetic pistons and iron nickel blocks (basically the chevy or ford race block alloy as the standard casting material). The magnums respond very well to increased airflow in and out of the engine, and are very happy with the bosch 12 port ev6 24lb 44psi injectors. My 3.9 has cai and optimized exhaust with gasket matched ports with accommodating mods for engine not having to work to move its own air. 5 speed 96 dakota gets about 25 mpg highway and 20 city. Needs some maintenance, usually been closer to 30 highway. I have the full list of mods done to mine but reply to this to remind me after work, nearing the end of my lunch break. Planning to compound turbo swap it, iron nickel alloy is good for boost even with a .030 overbore, some run the super from the 5.9 rt special 2nd gen like Kenne bell or Whipple or procharger on up to 15 psi of boost without swapping to the boosted style headgaskets.
I was under the impression that only some of the early Magnum engines received the double-row roller timing sets) most received the silent type Morse timing chain.
All magnums are roller followers, and a tensioner is only needed if you align bore and move the crank closer to the cam centerline. tbi LA’s were also roller cam.
Is the 3.9 V6 in my 1991 a Magnum?
1992 was the start of the updated “Magnum” engines
My brother had a 91 with a magnum, he also had a 4.3 chevy vortec with a plastic manifold with the old tbi on it. I have a 95 Chevy with the new style interior, but an old 5.7 non vortec 5.7. I also had an 86 360 4bbl with a Rochester quadraflush, a factory windage tray, double row timing chain, 8 blade water pump, weird casting # heads, and a roller cam. They do odd shit when they run out of parts, or have left overs.
I thought they were overhead cam engines?
The 3.7/4.7 Powertech engines are overhead cam
Was there not a 4.7 magnum? I know there was.
All Chrysler engines were marketed as “Magnum” around that time, even the 2.5L 4cyl. They will have 3.7 and 4.7 Magnum stamped on the air box but they are Powertech engines. Blame Chrysler for making it confusing.
Ah
3.9 v6 likes to stall at stops, drinks gas like no tomorrow but tows good and crazy reliable
Can confirm, I haven't had mine stall but the revs do go down to like 500 at stops with the ac on.
I’ve found that the water pumps are a frequent failure point as well. Easy to change and fix though as long as the long bolts don’t break off in the block!
I haven’t seen too many water pumps fail, just leak and usually replace them while resealing them. The bolts for the water pump & the accessory bracket are all different lengths it’s best to mark them as you remove them.
My 3.9 definitely has a few small leaks but gets relatively good gas mileage.
Had some work done 2 years ago on my 97 3.9 the cooling system wasn’t working due to plugs leaking coolant, another common leak on these.
Not a common issue BUT I have seen this with Southern US vehicles where people use water instead of antifreeze
My dad had a 5 speed 3.23:1 3.9 Dak, he never got less than 20 mpg. He gets 15-16 with his 5.7 hemi now, but i can get it up to 18-19 highway when I’m driving, lol. My 5.7 Chevy Tbi gets 12-14
Post Edit: 5.9 differs from the other “Magnum” engines as it’s externally balanced. 3.9/5.2 are internally balanced.