One Reason Diesel Engines Produce More Torque Than Gas Engine

July 18th, 2017 by

Many people in the truck world know that diesel engines produce more torque than gasoline engines and that is the reason consumers that need a truck for heavy duty towing buy diesel trucks, but a lot of people don’t know why diesel engines produce more torque. So we’re going to explain one reason and compare the differences of a gas engine and a diesel engine and try not to complicate it.

Ram 2500 Heavy Duty Engine

The Ram 2500 is available with a couple engine options, but for this comparison, we are going to compare the two engines that are the most similar in engine displacement — the 6.4-liter V8 HEMI engine and the 6.7-liter Cummins turbo diesel I-6 engine.

6.4L V8 HEMI Engine

Engine Displacement: 6.4L or 392 cubic inches

Bore x Stroke: 4.09 x 3.72 = Bore x Stroke Ratio of 1.099:1 – Oversquare Engine

Power: 410 horsepower 429 lb-ft of torque

Automatic transmission

6.7L Cummins Turbo Diesel I-6 Engine

Engine Displacement: 6.7L or 408 cubic inches

Bore x Stroke: 4.21 x 4.88 = Bore x Stroke Ratio = .86:1 – Undersquare Engine

Power: 370 horsepower and 800 lb-ft of torque

Automatic transmission

Explaining the Numbers

Aside from the fact that gas engines and diesel engines are different because they use different types of fuel, they are also constructed differently, and their different designs gives them different qualities.

The most obvious difference between the two engines is the difference in amount of power each engine makes. Although the 6.7L Cummins Turbo Diesel engine is bigger than the 6.4L V8 HEMI engine, the difference in engine sizes really isn’t too substantial, but there are other engine components that are fairly different and that helps to explain the differences in power and torque.

Horsepower and Torque

There are a few reasons the bigger 6.7L engine doesn’t produce as much horsepower as the smaller 6.4L engine, and there are reasons that the 6.7L engine produces substantially more torque than the 6.4L engine and one of these reasons are the number of cylinders in each engine. The more cylinders an engine has the more air it can ingest, and more air equals more horsepower. Considering that, it makes sense that the smaller 6.4L engine with more cylinders (8) produces more horsepower than the larger 6.7L engine with fewer cylinders (6).

However, when it comes to torque, the differences in amount of torque comes down to the differences of construction of each cylinder, rather than how many cylinders the engine has, and one way to see the construction of a cylinder is by looking at an engine’s bore-to-stroke ratio. The 6.4L engine has a bore-to-stroke ratio of 1.01:1, making it an oversquare engine, which means that the bore (cylinder diameter) is larger than the stroke (piston length). This design allows each cylinder cycle to be completed faster and that results in more air supplied to the engine at a faster rate, which results in higher horsepower.

On the other hand, the 6.7L engine has a bore-to-stroke ratio of .89:1, making it an undersquare engine, which means the bore is smaller than the stroke. In an undersquare engine, the cylinders have a smaller bore, but a longer piston stroke, so it takes a little longer for each cylinder cycle to be completed, so horsepower is not as high, but during the time it takes for the piston to reach the cylinder head, more compression is created, which results in more torque. Additionally, the undersquare design results in less heat loss during the cylinder cycle, which makes it ideal for diesel fuel because it requires higher temperatures to burn, which also makes a diesel engine more fuel efficient.

Torque in Pounds

So what does the difference really mean in a real world application? When the Ram 2500 is equipped with the 6.7L Cummins Turbo Diesel engine and the standard 3.42 axle ratio it has a maximum towing capacity of 17,980 pounds and when the same Ram 2500 is equipped with the 6.4L HEMI V8 engine and its standard axle ratio of 3.73 (slightly larger) the truck has a maximum towing capacity of 13,320 pounds — and that’s a big difference!

There are pros and cons to both types of engines, but what really makes the difference to the buyer is how much do you really have to tow? If you need maximum towing power, than a diesel truck may be what you want. You can view University Dodge Ram’s Ram truck inventory online here, we have an extensive selection of diesel and gasoline trucks.

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