When you scrutinize the dyno graphs we post alongside the ECU tunes in our catalog, you might notice an interesting phenomenon: the actual maximum power often doesn’t match the manufacturer’s claims listed in the car’s documents. Take, for instance, the Lifan X60 with a 1.8L gasoline engine. In stock form, one unit of this model showed a peak of 120 horsepower on the dyno, while the official spec sheet states 128 horsepower.
Where did the missing 8 horsepower go? Was it a poorly performed dyno test? Or maybe the car manufacturers are lying to us? Let’s consider another case. The VW Passat 1.8 TSI. The spec sheet claims 160 horsepower, but the dyno shows 164 horsepower. Extra, unaccounted-for horsepower as a bonus? Let’s dig into this.
The types of dynos
First, a mini-overview of the types of dynos, how power measurements are taken, how we do it, and the nuances you need to consider when performing a test.
So, a dynamometer (dyno) is a device used to measure an engine’s power output. There are various ways to measure power output, with two of the most common methods being inertial and load-based. These methods involve placing the car on a roller dyno, where the car’s wheels turn the rollers. Given the constant moment of inertia of the rollers, the speed at which they turn, and the time taken to accelerate, a computer program calculates the torque and power at the wheels. Engine power (i.e., power at the flywheel) can also be calculated by converting the wheel power using a function that factors in parameters and coefficients such as the gear ratio and transmission losses.
You might now be wondering, what maximum power is indicated in the car’s documents? Is it at the flywheel or the wheels? The answer: the maximum power listed in the documents is at the flywheel, not the wheels. According to standards, this should be determined on a special engine dyno. An engine dyno is a unique type of dynamometer where the engine runs independently from the car, either with or without auxiliary equipment (depending on the test standard). The engine is connected only to the fuel supply, exhaust system, and necessary electronic components. Many people compare this type of test to lab conditions, which is a fair analogy. The data obtained about power and torque (including maximum values) are the most accurate.
How do we determine maximum power? How is power measured during chip tuning? Obviously, no one will remove the engine each time to get the most precise numbers. Therefore, for most cars with a maximum power of up to 300 horsepower, the inertial method on a roller dyno is used. This is the method we personally use, as it is ideal for “everyday” cars. Moreover, the error margin in converting wheel power to flywheel power with this method is very small.
For cars over 300 horsepower, load-based roller dynos are typically used. These are equipped with eddy current brakes, which allow for creating the necessary load for accurate measurements of high-performance cars.
There are also less common methods like hub dyno testing, where the car is not placed with its wheels on the rollers, but the wheels are removed and special adapters are attached to the hubs for the hub dyno. This method has its pros and cons, but that’s not the focus of this article.
Okay, we’ve sorted out the measurement methods and noted that not all of them are equally accurate. Let’s move on.
Power is not measured!
The next thing to understand is that on a dyno, power is not measured but “recorded.” We deliberately avoid using the word “measure” to prevent confusion. In fact, using the phrase “measure power” is less accurate than saying “record power.” The dyno “records” horsepower, rather than calculating it through some super-intelligent method. This is a crucial distinction. Think about the etymology of the word “record.” To record means to capture it here and now, under the current conditions, with the current state of the engine, the transmission installed, the wheel radius, the engine oil, and so on. To “record horsepower” means to capture it here and now. Tomorrow, you could refuel with a different gasoline and get entirely different results.
You need to understand that many external factors affect the recording. This includes compression, which varies in different parts of the world because it directly depends on air characteristics. Thus, even under identical conditions, the maximum power recorded from an engine can vary in different locations (or in the same location at different times).
If you think about it, determining engine power is an extremely multidimensional task. It’s like a mathematical function with hundreds (if not thousands) of parameters. If you approximate or ignore some parameters, significantly reducing the function’s dimensionality, you will get deviations. And that’s what we see.
To partially minimize such deviations and for standardization, experts have developed standardized measurement methods (from ISO, SAE, DIN, and other standardization institutes). There are ready-made normative requirements for conducting tests, formulas, and coefficients for normalizing recorded values, and so on.
Also, note that we haven’t even mentioned that horsepower can be metric, mechanical, or even electrical, each with different power values in watts. We haven’t mentioned the auxiliary equipment of the engine, which significantly affects power output. We haven’t covered transmission losses. We haven’t discussed that engine power can be Net (including auxiliary equipment and aggregates) or Gross (excluding them). Depending on the standards of different countries, which regularly change, the car’s documents can list different power values, either Net or Gross (and the difference between them can be quite substantial).
For all these reasons, horsepower is a very relative value. As is the maximum horsepower output of a car’s engine. Marketers use these figures to sell cars. Consumers use these figures to choose cars. Yet, in reality, these figures mean very little. No one will tell you how they were obtained. And certainly not how accurate these figures are.
Of course, we need a reference point, which is why the maximum engine power figure exists in a car’s specs. That’s why it’s listed in the documents. But don’t take it as an exact, unchanging value. It’s not like a byte of information on your computer, which can always be interpreted unambiguously. It’s not like the time on a clock, which will be the same within a single time zone, whether you’re in Moscow or Syktyvkar. It’s not like the compression ratio in an engine—an absolute value that, unlike maximum power, is the same whether in your garage or on the moon.
So, when you see that the stock maximum power on a dyno graph in our tune catalog doesn’t match the official specs, don’t take this information critically. In fact, on the graph, this information doesn’t matter at all. What matters is the difference between stock and tuned. And even then, only if the tests were performed under identical conditions: the same temperature/density/humidity of the air, the same fuel, the same oil in the engine and transmission, the same car, the same dyno, and so on.
By the way, using a dyno also requires intelligence. Many car owners want to get on the dyno to measure their car’s maximum power. If you’ve read this article carefully, you should understand how nonsensical and unimportant these figures are. A dyno is a tool, not a toy for joyrides. Its sole purpose is to show the final difference between “before” and “after” an ECU tune. The effectiveness of the tune is evaluated by this delta across the entire operating range of the engine. That’s the essence of testing when developing modified tunes.