Motorcycle enthusiasts often ask why dyno charts vary between shops, manufacturers, and tuning centers. The confusion usually arises from charts and data shared across social media and online forums. Unfortunately, these comparisons often lack context, making it difficult to interpret the information correctly. Many times, the charts are compared without considering crucial factors, such as differences in test standards, procedures, and hardware configurations. To help clarify, this article will explore the variances between dyno’s, dyno charts, and tuning shops so you can make more informed comparisons.
Understanding Inertia Dynos and Relative Factors
An inertia dyno, such as a Dynojet chassis dyno, operates based on the laws of physics. These laws remain constant, so the dyno itself experiences minimal test variance. However, the outcome can still vary greatly due to external factors. The conditions, the bike being tested, the hardware, and the dyno cell design all influence results. These variables are relative, meaning they change in relation to each other.
Even when testing on the same dyno model, small differences in conditions or procedures can lead to different readings. Additionally, tuning plays a significant role. A comprehensive, accurate tune can make all the difference, and the tuner’s skill level is crucial.
Key Factors That Affect Dyno Results
Environmental Conditions
Air conditions in the dyno cell, such as temperature, humidity, and barometric pressure, significantly impact power output. Since these factors can change hour by hour, it’s essential to compare charts using the same correction factor. This factor standardizes the data, not the engine output, which prevents misleading comparisons.
Tuning Quality and Methodology
A reliable tune requires more than just a peak power number. Carefully examine the entire curve:
- Is the curve smooth or abrupt?
- Are there any dips or anomalies?
- Was the tuner skilled with your specific product and engine configuration?
Gear Selection
The gear used during testing affects the numbers. On a Harley-Davidson, testing in 5th or 6th gear is ideal since these gears are closest to a 1:1 ratio. Testing in lower gears can result in lower power numbers due to gear reduction losses.
Air Exchange and Cooling
Proper air exchange in the dyno cell is critical. Insufficient airflow can cause the engine to breathe its own exhaust, reducing output. Controlled airflow and temperature ensure consistent results. It’s also important to monitor carbon monoxide (CO) levels in the room.
Engine Temperature
Testing at the optimal engine temperature is crucial. Both the Air/Fuel mixture and spark temp correction vary based on engine temperature, affecting power output. Proper dyno cooling fan placement ensures that intake air temperature stays consistent. Engines perform better with cool, fresh air.
Fuel, Oil, and Lubricants
The grade of gasoline, oil, and lubricants impacts output. For instance, the viscosity and temperature of these fluids matter. Overfilled fluids can reduce performance, so maintaining optimal levels is essential.
Tire, Wheel, and Driveline Factors
The weight and size of tires and wheels influence power readings. Heavier components reduce output. For example, OEM wheels on some Harley-Davidson models are heavier, often resulting in 2-3% lower dyno numbers. Aftermarket transmissions, chain drive conversions, and soft sticky tires can also lower output.
Serviceability
Well-maintained components ensure accurate results. Factors like air filter condition, injector flow, fuel pressure, drive belt tension, clutch slip, and tire pressure all contribute to power output.
Human Bias
The tuner’s intentions can skew results. If a tuner has a bias, they may deliberately influence the outcome. It’s crucial to work with someone genuinely invested in your bike’s success. Avoid shops that make excuses or draw conclusions before tuning.
Understanding Dyno Correction Factors
When evaluating engine performance, it’s essential to understand the role of dyno correction factors as well. These factors adjust test results to account for varying environmental conditions that influence engine output. To understand the various correction factors, SAE and STD, please read this article.
Why Consistency Matters
All these factors demonstrate why variances between dyno’s, dyno charts, and tuning shops exist. Consistency is key when testing, and it’s crucial to control the variables within your reach. Even slight changes can alter results, so eliminating inconsistencies is essential.
Ultimately, exceptional tuning and components deliver the best performance. The most reputable tuning and engine shops follow a methodical approach, ensuring reliable and accurate results every time. Understanding these variances allows you to make informed decisions and achieve optimal performance for your motorcycle.
If you have any other questions, feel free to reach out to our team here at Fuel Moto for more clarification.