2018 Ram 2500 6.4 Hemi Horsepower Rated vs Real Power

The 2018 Ram 2500 with the 6.4L Hemi V8 is rated at 410 horsepower at 5,600 rpm and 429 lb-ft of torque at 4,000 rpm. That figure comes straight from Ram’s official specifications, and it makes the 6.4L the most powerful gas engine available in the 2500 lineup that year.

But a crank-rated spec sheet number and what actually reaches the wheels are two different things. Here’s what that 410 hp figure actually means once the 6.4L Hemi is turning under load, how it compares to the 5.7L Hemi and 6.7L Cummins, and what owners report once the truck is loaded up and moving.

2018 Ram 2500 6.4L Hemi Rated Horsepower and Torque

Ram’s official 2018 Ram 2500 Heavy Duty specifications confirm the following figures for the 6.4L Hemi V8:

The 6.4L is a naturally aspirated V8 with hemispherical combustion chambers, the same basic architecture as the smaller 5.7L Hemi but with more displacement and revised internals to handle heavy-duty use. It also includes Multi-Displacement System (MDS), which shuts down four of the eight cylinders under light load to save fuel.

One detail matters specifically for the 2018 model year: the 6.4L Hemi in the 2018 Ram 2500 pairs exclusively with the 66RFE 6-speed automatic transmission, according to Ram’s official 2018 Heavy Duty specifications. Ram did not move the 6.4L to the newer 8-speed automatic until later model years, so shift behavior and power delivery on a 2018 truck feel different from a 2020-plus 2500.

For the complete breakdown of every trim-level spec on this truck, see the full 2018 Ram 2500 6.4 Hemi specs guide.

Those are the numbers on paper. What a dyno actually measures is a different story.

Rated Horsepower vs Real World Dyno Numbers

The 410 hp figure Ram publishes is a SAE-corrected crank rating, measured at the engine itself before power passes through the transmission, transfer case, and driveline. Rear-wheel horsepower, what a dyno actually records, is always lower.

For a 4×4 automatic truck like the 2500, drivetrain loss commonly runs 15 to 30 percent depending on the dyno type, correction standard, and drivetrain condition. Owners on the RamForumZ community have posted dyno sheets that illustrate just how wide that range can get. One thread documented a stock 6.4L Hemi 2500 dyno run showing under 300 rear-wheel horsepower and 293 lb-ft of torque.

That single dyno sheet is not an official rating and results vary by dyno brand, correction factor, and vehicle condition. It illustrates the gap between spec-sheet horsepower and what actually reaches the pavement, rather than serving as a fixed benchmark.

What MDS Does to Power Delivery

Multi-Displacement System (MDS) shuts down four cylinders during light-throttle cruising to improve fuel economy. Under acceleration or towing load, the system reactivates all eight cylinders, and the transition happens quickly enough that most drivers do not notice it.

The practical effect is that the 6.4L Hemi runs as a 4-cylinder engine at highway cruise and a full V8 the moment the truck needs power, which is why the rated 410 hp only shows up under load rather than at a steady cruise.

Understanding that gap matters most when comparing the 6.4L against the other two engines Ram offers in the 2500.

6.4L Hemi vs 5.7L Hemi vs 6.7L Cummins Horsepower Compared

Horsepower alone does not decide which 2018 Ram 2500 engine feels strongest. Torque output and where it peaks on the RPM band matter just as much, especially towing.

All three figures come from Ram’s official 2018 Heavy Duty specifications.

The 6.4L Hemi produces the most horsepower of the three engines, but the 6.7L Cummins nearly doubles its torque and delivers that torque at a much lower RPM. That is why the diesel pulls a heavy trailer with less throttle input even though its horsepower number is lower on paper. The 6.4L Hemi, by contrast, needs higher RPM to reach its peak output, which gives it a quicker, more responsive feel in daily driving and lighter towing.

For year-specific towing numbers across the Ram lineup, see the Ram towing capacity chart by year.

Horsepower numbers only matter in context of what the engine is actually doing on the road.

What 410 Horsepower Feels Like Towing and Driving

Owners on RamForumZ report real-world highway fuel economy for the 2018 2500 6.4L Hemi in the 14 to 17 mpg range at 70 mph, with some drivers seeing brief spikes near 21 mpg under ideal conditions like a tailwind or a downhill grade. Most drivers landed closer to the 14 to 17 mpg range in mixed conditions.

Under towing load, the 66RFE transmission shifts more frequently than the later 8-speed automatic used in newer Ram HD trucks, which some owners describe as the transmission hunting for the right gear on grades. That behavior is normal for the 2018 powertrain pairing and does not indicate a mechanical problem on its own.

For a full breakdown of real-world fuel economy across driving conditions, see the 2018 Ram 2500 6.4 Hemi MPG guide.

That real-world context is exactly why the rated horsepower number is only half the picture.

Common Questions About the 2018 Ram 2500 6.4 Hemi Horsepower

How much horsepower does a 2018 Ram 2500 6.4 Hemi have?

The 2018 Ram 2500 with the 6.4L Hemi V8 is rated at 410 horsepower at 5,600 rpm. This figure comes from Ram’s official heavy-duty specifications and applies to the naturally aspirated 6.4L V8 across trims.

What is the torque rating of the 2018 Ram 2500 6.4L Hemi?

The 6.4L Hemi produces 429 lb-ft of torque at 4,000 rpm. That torque peak sits at the same RPM as the smaller 5.7L Hemi, just with a higher output.

Is the 6.4 Hemi more powerful than the 5.7 Hemi?

Yes. The 6.4L Hemi makes 27 more horsepower and 29 more lb-ft of torque than the 5.7L Hemi in the 2018 Ram 2500 lineup. The extra displacement accounts for most of that gain.

Does the 6.4 Hemi make more horsepower than the 6.7 Cummins?

Yes, the 6.4L Hemi’s 410 hp beats the 6.7L Cummins’ 370 hp on paper. The Cummins makes up for it with nearly double the torque, which matters more for heavy towing.

What transmission comes with the 2018 Ram 2500 6.4L Hemi?

The 2018 Ram 2500 pairs the 6.4L Hemi exclusively with the 66RFE 6-speed automatic transmission. Ram did not introduce the 8-speed automatic option for this engine until later model years.

The Real Story Behind the 6.4 Hemi Horsepower Number

The 2018 Ram 2500 6.4L Hemi is rated at 410 horsepower and 429 lb-ft of torque, and that number holds up as the strongest gas engine Ram offered that year. What it does not show is the real-world gap between crank-rated and wheel-measured power, or how MDS and the 66RFE transmission shape the way that power actually shows up on the road.

Owners cross-shopping the 6.4L against the 6.7L Cummins should weigh horsepower against torque delivery, not horsepower alone. If daily driving and light-to-moderate towing are the priority, the 6.4L Hemi’s power band delivers a responsive feel. For sustained heavy towing, the torque advantage of the diesel changes the equation.

Truck owners dealing with unrelated 6.4L Hemi issues can also check the common 6.4 Hemi problems guide for known trouble spots on this engine.