How to Read A Dyno Graph
What is a Dyno Graph?
When tuning vehicles and testing certain performance parts, most engineers and manufacturers will test the improvement on the engine by testing its performance through a dynamometer.
A dynamometer is used to measure the power output of a vehicle. Tuners will run an initial pull with the vehicle in its initial state, and after installing a certain engine performance part, they'll run a second pull to test the difference in engine power and torque.
When Dyno testing, a dyno operator will monitor engine characteristics through their laptop while operating the engine. By doing this, they can guarantee that external conditions are consistent between pulls by watching things like knock sensor levels, intake air temperature, barometric pressure, and air/fuel ratio while checking power output throughout the dyno sheet.
There are two different methods associated with measuring power output: Engine Dynos and Chassis Dynos. An Engine Dyno reads power directly through the crankshaft (or flywheel).
A Chassis Dyno, on the other hand, reads power from the power output by the rear wheels on a drive roller(a treadmill-like platform) or hub connection and is what most people are familiar with. When performing a Chassis Dyno, the vehicle experiences parasitic loss which is the power that is naturally lost as energy passes through the gearbox, transmission, differential, etc. The results are discussed as wheel horse power or WHP, and Wheel torque, normally just described as lb-ft with a note that the value is at the wheels.
Dundon Motorsports has what is called a hub dyno. We chose a hub dyno for its accuracy, safety and repeatability. A hub dyno requires you to take the wheels off the car and the dyno is bolted directly to the hub (where the wheel is bolted) to ensure the results are not influenced by tire size, tire pressure and there is no possibility of slippage (where the tire and roller loose contact at higher horsepower levels). It’s also much safer and doesn’t require any straps to hold the vehicle down, but does require a knowledge of the gear ratios of the transmission (they must be entered, so you can get results in any gear not the 1:1 gear ratios that are prevalent for roller dynos). Some examples of popular hub dyno’s are Dynapack (what Dundon has) and Mainline.
Breaking Down the Dyno Chart
On the X-axis, you'll find the Engine Speed measured in revolutions per minute (Engine RPM). The Engine RPM measures how many times the engine's crankshaft makes a full rotation every minute (and also how many times the piston moves up and down in the cylinder
On the Y-axis, you'll find Engine Power measured in terms of horsepower (hp). Horsepower is the measure of work done, and is the metric used when determining how much power the vehicle is capable of producing. Going back to physics class power is the amount of force done per unit time.
Dyno Graph Curves
When performing a dyno pull, tuners test for two separate variables: power and torque and are represented on the graph and "curves" or the lines on the graph.
The Torque Curve can be recognized by its fairly consistent shape almost a straight line across the graph. It primarily climbs dramatically as the dyno operator takes the vehicle to 100% throttle, sometimes almost at a perfect 90-degree angle, and then quickly plateaus off with minimal climb or drop from beginning to end.
The Power Curve can be recognized by its shape as well. Typically it will climb steadily at a 45-degree angle as the power steadily climbs at higher RPMs.
Rev Range & Redline
You'll notice on the Dyno Graph that the lines that appear on the graph don't begin at 0 RPM but in the middle of the graph. Where these lines begin and end is called the Rev Range (also referred to as RPM Range).
The tuner will initially start "driving" the car on the rollers or hubs to get to the 1:1 gear ratio (typically 4th gear). The Rev Range begins when the tuner, in the 1:1 gear and with the engine already turning, takes the engine to 100% throttle"floors" the engine and starts the tune.
He will keep the engine at 100% throttle floored until just below he hits the Redline which is the maximum amount of torque the engine can produce without overheating and damaging the engine the maximum rev limit of the engine.. Once the Redline is hit, the tuner lets off the accelerator and the Rev Range is decided. When you see the lines drop off on a dyno graph, that means that the tuner has hit that redline.
The Powerband is similar to the Rev Range in the fact that is a range on the graph. But instead of the start and end being between the moment of "flooring" and hitting the Redline, the Powerband is the range on the graph between Peak Torque and Peak Power.
Peak Torque is typically found at the moment on the graph when the Torque Curve (the line that tracks torque throughout the Rev Range) climbs up and breaks into a flat curve.
Understanding The Results
A dyno sheet without a baseline is meaningless. Every dyno will read differently. Every operator will generate data in a different way, so beware dyno results or numbers without baselines and always ask if conditions were consistent between the before and after.
Let’s look at an example of a dyno sheet.
Example of a Dyno Graph
This dyno graph comes from our 2020 Speedster Street Headers and Lifetime Loud Muffler Package. We will be looking at the two curves, Torque Curve and Power Curve, individually. Some dynos split these curves into two separate sheets while others keep them on the same sheet.
The first dyno you see here is the Torque Curve. As we mentioned earlier, Torque graphs can be recognized by their usual shape of a steep incline followed by a plateau. This shape is due to the fact that internal combustion engines are not 100% volumetrically efficient (this is a topic for another day). Peak torque happen where the engine is at peak efficiency.
On this graph, the rpms used to quantify the results is between 2250 RPM and 8500 RPM. The baseline test is the green line while the purple line is the test ran with our Street Header and Lifetime Loud Muffler exhaust added to the vehicle.
Looking at the results, an additional 47.20 lb-ft of torque was created at 4310 RPM once the part was added, and peak torque occurred at 6000 RPM of 325 lb-ft. Further torque increases continue from peak torque all the way to about 8600rpm.
Torque gains are the thing you can feel when driving a car. Torque is what makes you say “Whoa, this car has a lot of power, it really throws me back in the seat when accelerating” a lot of drivers refer to the feeling of the car having “grunt” or has “raw power”.
The second Dyno we’re looking at is the Power Curve. The Power Curve can be easily recognized by its usual shape of climbing at a 45-degree angle until tapering off.
Since this graph comes from the same pulls as the previous sheet, the Rev Range is the same of 2250 RPM and 8500 RPM. Looking at the results, an additional 19.22 horsepower (HP) was created at 7718 RPM once the part was added, and peak power occurred at 8500 RPM of 470 HP.
Power, is defined as how much Work the vehicle is actually able to produce. Whereas torque is the force created to get the vehicle moving, Power is that force applied over time (Work). So if we can keep the engine efficient (more torque) at higher rpm’s we will have a higher amount of horsepower. The mathematical formula for horsepower is based on torque, HP = (torque in ft lbs x rpm)/5252. The derivation of this is beyond this post but if you’re interested contact us and we’ll put another blog together for the nerdier bunch (like us!) to help you understand these concepts better. The higher the horsepower, the more the car can push against the increasing frictional resistances that come with speed (drag from the air, friction from the tires, etc…) and the higher the top speed.
Now we have to analyze the two graphs to understand the story behind the data.
We would naturally conclude that the 2020 Speedster Street Headers and Lifetime Loud Muffler Package is designed to create more power to get the Porsche at its top speeds faster.
More torque from the engine accelerates the car quicker and gives you the potential to hit your peak power numbers faster, in which the slight boost in horsepower is added bonus.
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