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Rebuild Magnum 5.9 or Swap Hemi 5.7 (Gen III)

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1999 Dodge Durango SLT 4x4 5.9 Magnum
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Discussion Starter · #1 ·
Disclaimer:

I would prefer the 6.4 or even 6.1 Hemi but, they're more than I would like to spend on this project.


Competitors:

Rebuild current Magnum 5.9
I would have to build it up to keep-up with the modern Hemi's out there plus, I'll be towing long distances. I not only want the power but, I need it as well. (I suffer from a lead foot.)

VS.

Swap with a Hemi 5.7 (Gen III)
I would have to bore it out because I simply cannot go down in displacement, it goes against my religion.


Budget:

$5,000. I'm okay with refurbished parts. At the end of the day, I still need money left to pay for the stuff to tow. I'd hate to spend all my money on the engine & have nothing to tow.


My specific applications for my 99' Durango 4x4:

35% around a semi-urban city with some suburbs on the outskirts of the city
20% towing my 2,800 lb car to the track
10% out to the desert to shoot the dunes
10% up to snowy mountains for snowboarding
10% bad weather
(10% maybe tow a speed boat someday too)
5% other road trips


Long-Term Consideration:

150k miles @ $5/gal:
Magnum 5.9 avg. 11.5 mpg = $65k
Hemi 5.7 avg. 18.5 mpg = $40k
(City mpg ➕ Hwy mpg ➗ 2 = Avg. mpg)
That makes the Hemi $25k cheaper than the Magnum, in gas, after 150k miles! (…. if it lasts)

Aluminum is not as durable as iron.

Hemi would be more complex & expensive to repair.

Hemi parts may be easier to find, maybe even more-so as the years pass.
 

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'79 Macho 360 Magnum, Comp 480 cam, Hughes springs, 650 Thunder AVS, Pertronix Flamethrower ignition
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8,400 Posts
5G will go further in your 5.9 that you already have than in a 5.7 that you still have to buy with that 5G, in my opinion. I'm sure if you are mindful of your driving habits while towing with your 5.9 that you can improve your fuel mileage like coasting more often and rolling out of hole less aggressively.
 
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if you already have the 5.9 I think you'll be best suited with rebuilding that over the hassles of a Hemi swap. If not, first I think your mpg estimate with a Hemi is a bit high - I'd wager the mpg delta between the two engines will be much less.

$5k isn't that big of a budget for any engine rebuild especially if 'bumping it up' will be involved, but I think yer much more likely to stay within/close to that budget with a 5.9 build.

Honestly...a fresh 360 rebuild with good ignition system will probably be more than enough for your intentions. You may not win all the races you're planning...but meh - not sure that's a reasonable intention with that low of a budget. Otherwise, while I'm not an expert in either department, a stroker kit and aluminum heads (and everything that goes with a 'custom' build) will probably help a lot towards the hot rod side of your project.

- Sam
 

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'79 Macho 360 Magnum, Comp 480 cam, Hughes springs, 650 Thunder AVS, Pertronix Flamethrower ignition
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8,400 Posts
I have a few friends that have 500 and 600 horsepower naturally aspirated 360's. One has a Magnum and the other two guys have the LA. Of course they have more than $5,000 dollars into them.
 
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...cool n all, but are those 'truck/towing' engines, or 'race' engines? Unlikely either are $5k engines tho?
 
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'79 Macho 360 Magnum, Comp 480 cam, Hughes springs, 650 Thunder AVS, Pertronix Flamethrower ignition
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8,400 Posts
Lol, I added that later that those guys have more than $5,000 into their engines. A lot more. Their engines are race engines and not truck engines. I just mentioned the horsepower numbers as reference to being able to get lots of power from a Magnum if ever desired.
 

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OP, your lead foot is going to eat away at that optimistic hemi mpg. The savings are about low-rpm cruising so it does the cylinder cut-out thing.

I read/hear a bunch about cam and lifter issues on the hemi's. Plus you have a extra work of making the electronics run the newer engine.
 
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For what it's worth, my '18 2500 5.7L with 4.10s gets 10-12 MPG. If you drive a lot of flat highway with a 1500 and airplane gears you might see 16 MPG.
 

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For what it's worth, my '18 2500 5.7L with 4.10s gets 10-12 MPG. If you drive a lot of flat highway with a 1500 and airplane gears you might see 16 MPG.
My 2019 challenger rt with the 5.7 was at a steady 10-11 mpg with 3.73 gears, I liked the gas pedal a lot. I feel like the bone stock 5.7 is quicker than a mildly beefed up 5.9 but that’s just me. 5.9 for reliability and cheaper to mod is what I’d go with, especially since you have one.
 

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1999 Dodge Durango SLT 4x4 5.9 Magnum
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Discussion Starter · #10 ·
Thank you so much guys. Not bothering with the Hemi swap kinda feels like a big headache avoided. Now I've got some direction with this project.

I appreciate the input on my budget & mods. I might have to be flexible with the budget, and cool my jets with getting it all souped up.

Maybe just intake, headers, & exhaust (gonna straight pipe it, I miss having a v8 & don't mind being more than a little on the loud side. Current Holley Redhot glasspack sounds nice but, I feel the Magnum could sound better.)

I'd loooove to really build 'er up but, I also have a car that I've been dying to get on the track. So, the more I spend on the Durango, the less track time I get.


Sam, thanks for the input on the ignition system. I would not have thought of that. I don't know very much about ignition systems beyond that shiny MSD logo you see on some engines. Ignition coils which confuse me.

So, ignition, heads & stroker kit to beef it up a bit but, not go too crazy? I guess cams too? Gotta love a lumpy v8!

How much should I budget for +-?
 

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1999 Dodge Durango SLT 4x4 5.9 Magnum
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Discussion Starter · #11 ·
OP, your lead foot is going to eat away at that optimistic hemi mpg. The savings are about low-rpm cruising so it does the cylinder cut-out thing.

I read/hear a bunch about cam and lifter issues on the hemi's. Plus you have a extra work of making the electronics run the newer engine.

Aaaaah, the cylinder cut-out thing, THAT's why. Gotcha. Thanks for the input on my lead foot & electronics. Yea, I guess my lead foot will kill those mpgs, & I have been fearing the idea of the labor involved in making the electrical systems communicate, like what you see on those car customization shows.

Yea, I've heard/read something about Hemis having some issues, I just never fact checked them or read in detail what the problems really were. Are those cam/lifter issues what causes the Hemi tapping sound I've read about?
 

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It's really hard to beat the new tech.
If I was going the small block route... I'd go with the new.
Yes, some 5.7's have had issues with the complicated valve train.
But I'm pretty sure that's been blown out of proportion. Mostly guys who let them idle for prolong periods of time thing.
Who does that? There's a video out there saying all those lifter ticks are actually common exhaust leaks on the 5.7. Our Durango has that issue right now. Covered under warranty. I thought for sure it was an lifter issue.
It would definitely be more money converting over to the new tech. So there's that against you. You can't just throw one under the hood.
If I were to do this... I would keep the MDS. 4 cylinders for cruising is awesome.
We love that feature in our 2009 Challenger 5.7 and our 2017 Durango 5.7.
I'm amazed at the fuel mileage we get out of those cars on long trips.
We can drive all day long in our Durango on one tank of gas.
 

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Thank you so much guys. Not bothering with the Hemi swap kinda feels like a big headache avoided. Now I've got some direction with this project.

I appreciate the input on my budget & mods. I might have to be flexible with the budget, and cool my jets with getting it all souped up.

Maybe just intake, headers, & exhaust (gonna straight pipe it, I miss having a v8 & don't mind being more than a little on the loud side. Current Holley Redhot glasspack sounds nice but, I feel the Magnum could sound better.)

I'd loooove to really build 'er up but, I also have a car that I've been dying to get on the track. So, the more I spend on the Durango, the less track time I get.


Sam, thanks for the input on the ignition system. I would not have thought of that. I don't know very much about ignition systems beyond that shiny MSD logo you see on some engines. Ignition coils which confuse me.

So, ignition, heads & stroker kit to beef it up a bit but, not go too crazy? I guess cams too? Gotta love a lumpy v8!

How much should I budget for +-?
My personal opinion on headers after having them, stay away from them lol. I’ve burnt myself, they’ll melt all plastic around them, and eat through plug wires if they aren’t strung up. I’d keep the exhaust manifolds and straight pipe it, true duals if possible. That’ll be just as good in my opinion. My Ramcharger has the manifolds with some flow master mufflers, no cats. She’s loud enough on true duals.
 

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Yea, I've heard/read something about Hemis having some issues, I just never fact checked them or read in detail what the problems really were. Are those cam/lifter issues what causes the Hemi tapping sound I've read about?
The particular youtube vid I'm looking for doesn't seem to be around anymore. The point was made the cam is very high in the block and oiling isn't ideal. Possible solution being to drive it harder vs lazy idling; to get more oil supply/movement.

Anyway... I think keeping your 5.9, since it is a magnum, is worth sticking with.
 
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