So you just added that new tune, and you want to know how much power your truck is putting down, or maybe someone called you out on your 1,000 horsepower claim. If so, there is only one way to find out, putting your rig on the dyno.

We all know the Duramax is a stout motor that can handle some big numbers. Likewise, there are countless discussions on the internet about who makes the best/most powerful truck or how much horsepower will I gain from this mod. While it is easy to estimate (or brag) that your truck is more powerful, a few dyno pulls are the only way to know for sure.

For most auto enthusiasts, a dyno is a dyno, although there are some differences in how they operate. Likewise, there are a few things to keep in mind for Duramax and other diesel truck owners since they are considerably heavier than a typical passenger car. In addition, they can put down more torque than some dynos can handle. Lastly, diesel engines are a different animal altogether, and finding a good shop can be a challenge when it comes to tuning. With that said, let’s jump into the world of Duramax performance, tuning, and dynos.

What Is A Dyno & How Does It Work?

In simple terms, a chassis dynamometer (often referred to as a dyno) is a machine with rollers installed in the ground, although some manufacturers offer portable models. The drive wheels sit over the rollers, and the dyno measures the force applied to them as the vehicle accelerates at wide-open throttle.

As a dyno measures horsepower and torque at the wheels, these numbers will be lower than the factory rating which measures output at the crank. In general, there is about a 15% loss in horsepower and torque through the drivetrain. For example, a stock Duramax LBZ is rated at 360 hp and 650 lb-ft of torque, although the number at the wheels will be around 300 and 550, respectively.

In terms of dynos, there are two types, inertia and loaded. Inertia dynos have free-spinning rollers and do not apply resistance to the drive wheels. If your Duramax has a larger turbo, it may not apply enough force to fully spool it up, and the dyno may show numbers that are lower than the truck is capable of. On the other hand, loaded dynos use an adjustable eddy brake that can apply resistance to the rollers in order to more accurately represent a wide-open throttle pull on the street.

Lastly, there are corrections that are a love or hate thing for some. Essentially, they take into account things like temperature, altitude, and humidity. For example, if you dyno your Duramax at sea level on a 60-degree day at sea level with low humidity, it will put down more power than it would on a hot and humid 90-degree day. Obviously, corrections are imperfect and open to interpretation, although many dyno sheets will include the raw and corrected numbers.

Common Duramax Modifications To Maximize Power

If you are serious about modifying your Duramax and want to keep track of its progress along the way, the first step is to dyno it in stock form. That way, you have a baseline to measure future progress. As for getting more power out of your truck, it comes down to how much you are willing to spend, as Duramax tuning can get expensive real quick, especially if you are looking to push over 500 rwhp.

Up to 150 Additional RWHP ($2,000-$3,000)

By far, a tune is the best bang for the buck, with an increase of 75-100 hp and 150 lb-ft of torque not being unreasonable. Likewise, there are sizable gains to be had from supporting mods like a cold air intake, a free-flowing 4” exhaust, a Y-bridge kit, and larger turbo intake tubing for the LBZ and earlier engines. An aftermarket lift pump is highly recommended as it takes the strain off the common rail pump, and it can be had for less than $1,000.  Of course, there are different modifications needed depending on what year the truck is.  

Over 150 Additional RWHP ($10,000 and up)

Going over an additional 150 rwhp is where things can start to get expensive as this is the limit of many stock components such as the transmission, turbo, and injectors. You can expect to shell out $5,000 for an upgraded transmission and a few thousand more for a bigger turbo and injectors as well.  With more demand on the fuel system, an upgraded injection pump will be needed.  

While the Duramax is a sturdy motor, its limits vary depending on the year. The earlier LB7 and LLY are usually good for around 500-550 rwhp with the LBZ and later being capable of handling 550-600 rwhp before the internals become a liability. Unless you have at least $20,000 to spend on an engine tear-down and transmission upgrade, 500-600 rwhp is usually the stopping point for most Duramax owners.

Finding A Shop With A Duramax Capable Dyno

Without going into the long debate of which dyno gives higher or lower numbers, they are expensive pieces of equipment. They typically cost between $30,000 to $50,000 for the dyno itself, and that does not include installation, accessories, and maintenance. As such, they are usually found in larger tuner shops. In addition, many dynos have horsepower and torque limits, so even if your local Honda speed shop has one, it may not be capable of handling a Duramax that is putting down 700 horsepower/1500 lb-ft torque.

Assuming the dyno can handle the power your rig is putting down, you don’t have to take it to a specialty shop as the process for dynoing gasoline and diesel-powered vehicles is the same. However, if you are interested in getting a custom tune or specific feedback on modifications, then yes it pays to spend some extra money and take it to a shop that specializes in Duramax engines.

If you plan on dynoing your truck after some mods, it is recommended to use the same dyno since there are differences in how some models measure horsepower and torque. Likewise, doing so during the same weather conditions, if possible. In the end, it depends on your goals. Putting your truck on a dyno is the only way to know how much power it is putting down. In addition, it is not very expensive and usually costs around $150 for three pulls. Likewise, many sled pull competitions and diesel drag events typically have dynos available and competitions for the most powerful truck.

How Much Power Can A Duramax Make?

Suffice to say, the deciding factor is your budget and how fast you want to go. There are Duramax motors putting down over 1,000 hp and 2,000 lb-ft of torque, but most of these trucks are used in competitions like drag racing and sled pulls. While some are street-legal, saying they are daily driveable is a bit of a stretch.

Likewise, reaching those levels involves shelling out 10’s of thousands of dollars on custom-built engines with higher flowing heads, beefier cranks, connecting rods, and pistons, to name a few. Not to mention expensive transmission builds, upgraded common rail pumps, bigger injectors, and turbos.

Keeping that in mind, 500-550 rwhp is the stopping point for most Duramax owners as this level offers a good balance of power and reliability. Either way, it is more than enough power to have some fun or surprise an unsuspecting pony car owner. In addition, things like a moderate tune, cold air intake, and exhaust mods will not negatively affect driveability and fuel economy.

If you regularly maintain your Duramax and don’t romp on it daily, you probably won’t notice a difference in the engine’s longevity. While the Allison transmission is quite sturdy, adding an extra 150 horsepower will take its toll over time, especially for the five-speed versions behind the LB7 and LLY. With that said, the harder you drive your truck, the sooner things will break, although a few dyno pulls or quarter-mile passes are generally not going to be an issue.

Do I Need To Dyno My Truck?

Short answer, No.  A dyno is a great tool and is very helpful when trying to optimize the performance with additional modifications made.  But it is just as important for the truck to drive smooth and have good street manners.  It is very common for a truck to have great dyno numbers, but be practically un-drivable on the street.  How a truck performs on the street should be a priority for most as that is how the truck is used.  Towing the boat, camper, etc while still starting up easily in the cold mornings and smooth power delivery.  

Over the last 20 years, the Duramax has earned a reputation for being a motor that responds well to modifications. It has only gotten better with the latest L5P putting down 445 hp and 910 lb-ft of torque. While that is a significant increase over the LB7 and LLY, the older engines are just as capable of putting down some good numbers. Not to mention, being pre-emissions trucks, they are easier to tune and can be had for a fraction of the cost of a new one.

Perhaps this is your first Duramax, or you are just starting down the road of mods and want to get some baseline numbers. Maybe it is about bragging rights among your circle of friends. If so, there is no better way to find out than on a dyno, although choosing one (or a shop) can be a complicated affair. Some may not be able to handle higher horsepower trucks and/or may not have experience with the Duramax or diesel in general.

Merchant Automotive has the gear to help your Duramax make some serious horsepower the right way! Our passion for helping owners build out incredible Duramax trucks started back when our founder and visionary Eric Merchant was cutting his chops at a General Motors dealership. Within a few years, Eric was not only a master mechanic, but was taking his business to another level by helping Duramax enthusiasts build incredible trucks. Today, we’re known as the leading Duramax experts in the country.

If you have a Duramax truck, you’ve landed in the right place.