5.7 L Dodge Hemi Performance question

I bought a used 2004 Dodge shortbed 1500 SLT w/the 5.7L hemi with 100,000 miles on it. VERY clean truck. Not abused (that I can tell) at all.

Now I love the truck, and it’s primary duty will be plowing. I need to tow once in a while too.

It does great for plowing, but any truck is powerful when you put it in low range. On mountain hills though, or just trying to pass or something, it’s horrible. My V6 Pathfinder has more zip.

The Hemi is rated at 345hp and 375ft lbs of toque. I expected it to do great for towing or mountain passes.

It has stock wheels (20") and the tires are just a little taller than stock (65s instead of 60s). I can’t imagine the 1/2 inch of so diameter taller tires would make that much difference.

I can’t find a power curve for this engine. I’m thinking that I may need to just run the engine faster? It doesn’t seem to make any power until about 5000 rpm. But, I thought that Hemi’s are supposed to have a pretty broad power curve. Is that so?
I’d be interested to hear from anyone familiar with this engine, and what they thought about it.

FWIW, here’s what purports to be a power curve from an early Hemi (from a Jeep forum): http://www.jeepforum.com/forum/attachments/f67/130618d1278540244-05-08-5-7l-hemi-torque-hp-curve-hemi-curve.jpg

Are you using the right gas? IIRC the Hemis are 89 octane recommended (but not required) and so if you’re running regular 87 octane the power might be a little off.

Other than that, I got nothing. I had a similar truck with the 4.7L V8 and, well, the Hemi is definitely the one to have.

Thanks for the link. Looks like torque is pretty flat and crosses HP at a little over 5g rpm.

I usually run regular. But yesterday I put premium in it. The only noticeable difference was that the engine ran hotter.

I wonder if the previous owner ‘chipped’ the engine and screwed something up.

They are also just heavy not-even-remotely-aerodynamic trucks. Plus they annoyingly don’t have a front axle disconnect, so there’s always that extra drag. My 4.7L one was also great for grunt work and pulled off the line pretty well, but would bog down like crazy on the highway. Granted you’ve got a 100 more horsepower to play with, but if you’re saying it feels like a V6 Pathfinder I’d say that sounds about right-- mine definitely felt more like 4 cylinder Tacoma on the highway!

Setting aside the engine has 100k miles on it, one can’t ignore the weight of the vehicle. I’m sure you’re pushing close to 5,000 lbs, if not more. W/regard to addressing your preference for additional grunt, and assuming your engine doesn’t suffer from anything other than normal wear and tear, you are probably SOL. I had 345 HP 5.7 in a 2006 Charger and I currently have the 375 HP version in a Challenger. Both were/are good performers, but 1,000+ lbs. of additional weight is a significant factor.

Torque and HP curves always cross at 5,252 rpm.

Speaking of aerodynamics and weight…:slight_smile: I have a Western plow mounted to it now. I will see how it does when I can remove the plow. But still,that’s only about 500 lbs of weight. I mean it is sloooowwww. Slower than my Pathfinder.

Eh. I also have about 200 lbs of winch and bumper on the back. But I’m not sure if this truck will pull ~3000lbs of tractor and trailer over the continental divide. (I did it with my old 92 Pathfinder*). Seems silly with all that engine.

*my previous Pathfinder. I have an 06 now.

. Really? Because of the way HP and Torque are measured? Huh?

So (quick google) your '06 Pathfinder weighs in at about 4,300 pounds and has 270HP whereas your truck is around 5,300 lbs without the add-ons. The power to weight ratio is a tiny bit better on the truck, but park them side by side sometime and see how much more air the truck has to push out of the way (even without the plow!).

With drag forces increasing exponentially with speed, it takes a heck of a lot of power to keep a big full-size truck moving at highway speeds. That’s why they put such ginormous engines in all of them them now, since people expect them to be able to cruise at 80 MPH all day just like a normal car. In terms of towing performance and low-speed acceleration where drag is less of an issue, the truck should outperform your Pathfinder, but yeah, highway performance is always going to be tough for big trucks.

Yes. In fact, as I understand it, it’s more correct to say torque is measured and HP is calculated from torque.

HP = (RPM* TRQ)/5252

Hmm… If the engine is putting out 375 of torque (if), I’m surprised that it struggles to get up to 50 mph on a 6% grade. Even with a plow on it. It’s not pushing THAT much air under 50mph.

I can make it do it with ‘passing’ gear at 5000 rpm. That seems strange to me, and I’m not used to running a V8 at that high of an rpm for long. I know newer engines can and do run at higher rpm, but I’m a bit shy of pushing it to 6000 rpm.

Would 5k rpm with some 6k be needed for this engine?

Not that it maters, but the tach goes up to 8000 rpm. No red-line is indicated on the tach.

Had a 2010 Hemi Challenger, and I never found the powerband either. It was the most disappointing engine I’ve ever had in that regard. All hype in my opinion. The good news is the reliability is pretty darn good. The transmission was excellent (5AT), among the best I’ve ever had. My only complaint was the engine just didn’t deliver the promised performance.

It might be that this engine becomes a classic. The design of the engine is maxed. No room for more more valves in the heads like all the other engines now have. The thing barely squeaked by with the initial emission certification, that’s why it was equipped with dual spark plugs on each cylinder. It’s the end of the line for the hemi I’m afraid.

I have the same pickup; 2004 half ton 4x4, 20" wheels and the 5.7 Hemi engine. I have nothing but praise for the truck and the engine. It has a fairly consistent power across all RPM’s. It’s a big truck and, like all pickups, you’re pushing a brick through the air. My work truck is a government dodge with the 4.7. There is no comparison between the 4.7 and the 5.7.
I maintain the heck out of the Hemi, and put in a performance tune from Superchips http://superchips.com/products/ to increase shift points and towing.
The Hemi has been a great engine for me.

Hmm…

Thanks for all the replys. The engine seems great. Starts at 20 - F no problems ever.

As I think about it, I think it may be the transmission gear controler (or whatever it may be called). The truck is either running a 2k rpm, or 5 k rpm.

Trying to pull up a hill, the engine is luging untill I mash the pedal. Then passing gear, and back to luging.

Forgive me, I havn’t had this on the road too much. It’s my driveway/road plow truck. Thinking about it, it doesn’t seem to have a middle ground. Like 2nd and 3rd gear.

More testing is in order.

One other thing with driving around with the plow on is that not only is it creating more drag by, well, plowing the air instead of letting it pass through and out the engine compartment, it also will cause the engine fan clutch to be engaged all the time due to the lack of airflow through the radiator. That’ll rob a small but potentially noticeable amount of power from the engine.

I wouldn’t generally expect especially a half-ton gas truck to drive normally at speed with a big honkin’ plow on the front. Some plow-less test driving is definitely in order.

Yep, re the fan. Found out I had a bad clutch on the fan right after the plow was put on. It did get hot. Drew heat off the engine with the in cab heat and was ok till I got home. It was a warm drive. :slight_smile: It’s fixed now. I think you or someone else suggested that I had a problem with the clutch on the fan.

I know what you are saying about the plow on the front, and slowing it down. A plow on a truck up here is SOP. I do think that the transmission is not shifting when it should. Heh. I haven’t ‘manualy’ changed gears in an automatic trans since my '62 olds 98. Never had to. I’ll check out the trans and see if it’s doing it’s job. I don’t think so. The more I think about it, I think I only have 1st and 3rd and OD. It’s odd. I’ll see if I can get William (the trucks name) out for a test tomorroe.

I spoke with my brother today, he has the same truck you do with similar mileage. He is real happy with the power. He tows a heavy trailer about 30 ft long and sails right up long hard grades at 65 mph. He says when he stomps on it to pass it scoots. I would get your truck checked out.

Having nothing to do with this discussion, but for the record the 5.7 cylinder heads are not hemispherical. While preferred for intake/exhaust flow/engine output, Chrysler couldn’t get past an emissions issue with a true hemispherical head design. Some reference to the engine/cylinder head as “Semi-Hemi.”

It does sound like the transmission could stand some attention. My '06 SLT mega cab with a 5.7 hemi may not exactly take off like a scalded cat, but it does have some giddyup even after 87,000 miles, and no problem pulling about 7,000 pounds.

With any luck, a fluid and filter change may set things right, or at the very least, make sure it’s got enough fluid. How does it behave if you put it in tow/haul mode?

I would also consider changing the fuel filter