Hey, just wanting some input on this matchup. Currently own the 5.9L magnum, and not very impressed gas mileage, so ive been doing some research. Recently read that the 5.7L hemi averages 18 mpg highway? Also read the 5.9 magnum only putting out 245 hp and the hemi 345hp? Hoping to get this clarified, and maybe get some input on the gas mileage you guys are getting running the hemi engine. Ive just done a full tune up, rotor, cap, wires, plugs, new k&N filter, 3" exhaust and im lucky to squeze 11.5 mpg on the highway.

If this confirms my fears, really regretting buying the truck i did, and ill probably be looking to sell and upgrade to a 04 with the hemi before spend any more on upgrades. Thanks!

 

Yep, I've had a 5.9 in a '98 RCSB 4x4 and have a Hemi in an '04 QCSB 4x4 and stock the Hemi yields about 100 more HP and gets about 25% better gas mileage.

I was lucky to see double digit MPGs after I lifted the '98 and stuck 35s on, probably about 8-9 in town and might could nip 12 on trips IF I kept it to around 65 mph. The Ram with a heavier QC and lifted with 35s gets about 12 around town and I can hit 16 on trips at or around the 70 mph speed limit. I had hit the low 18s with it on a couple trips when it was still stock. '06+ guys with the MDS version of the Hemi regularly report 20 mpgs highway.

As far as power goes, I've modded the Hemi up quite a bit, probably a little less than 100 extra HP at the crank, whereas I only did the lift and a true dual exhaust on the 5.9. The Hemi, even stock was WAY more powerful from the mid to upper RPM band, but I think they are pretty even down low. I actually think, stock engine to stock engine, the 5.9 might have a slight extreme low end torque advantage, but by about 2000 rpm up, it's all Hemi.

So, I pretty much concur with what you've heard.

 

As for 18 mpg AVERAGE? Sorry, not likely.

 

Yep, my 08 QC with 3.92 gears gets between 20 and 23mpg on the highway. It is averaging about 18.5 at the moment in mixed driving with a 93 octane tune and the MDS turned off.
It is rated 13city/17hwy I think. When it was stock (no tune and MDS on) It did about the same. On flat highways, I have seen 23mpg @ 65mph.

 

I think something's wrong with my truck then. On my recent trip from Tampa to home (about 250-275 miles) I was only getting 15-16 mpg, regarded I was doing 80 and I had all my crap coming home from college. But about a year ago doing the same trip and a trip to the Keys I was getting 18-20 easy. Any thoughts? I dont think that speed and MAYBE 200-300 extra pounds would rob me of 4-5 mpg. Sorry for the thread hijack btw.

 

18 average highway stock. That's do-able, Mike. Hell my pig weighs 7000 lbs. and has 35s and I can hit 16 on trips from Fla. up to the farm and back.


Can you say: T U N E - U P? and clean the throttle body...

 

I was gonna clean the TB after I got the lift installed lol.

 

The 360 is an excellent truck engine, as that is what it was designed to be, a heavy vehicle small block. When the 318 crapped in my 72 Charger (the oil pump failed, but it DID still run) I replaced it with a slightly built 360, lotsa fun then. The 5.7 has the same stroke, smaller bores but way better cylinder heads.

 

Oh, I would agree. The Magnum 5.9 has been around since basically the late '60s when it came out as the LA360 engine. An engine doesn't stay in production for over 30 years if it's a poor design. BUT technology has come a long way and the Hemi takes advantage of it and puts out a good bit more HP while getting a good bit better fuel economy.

The 360 is a tank, I personally know people with well over 200,000 miles on that engine...

 

Not to hijack but my step-father had 56X,XXX on his 95 RCSB 4x4 2500 360. Still ran like a champ