How To Read a Dyno Graph

What Is A Dyno?

There are two main types of dynos. A chassis dyno is what most people are familiar with, and it's essentially a treadmill for cars. The vehicle is strapped down and the drive wheels (rear wheels for a Mustang) are placed on large rollers. The operator will then “drive” the car through the gears until they hit the 1:1 gear, which is typically 4th gear on most cars, but would be 5th gear on MT-82 manual transmission-equipped vehicles. Then starting at a lower RPM, the operator would put the pedal to the floor all the way to redline to measure the power output to the wheels of the vehicle.

Engine Dyno

The second type of dyno is what most engine builders and manufacturers use to measure power output: An engine dyno. An engine dyno is when a machine is used to measure power output right off the crankshaft rather than to the tires. The numbers from an engine dyno will be higher than a chassis dyno due to parasitic loss or drivetrain loss of power, which is typically somewhere around 15% depending on the vehicle and other factors. Meaning that if your 2016 Mustang GT is rated at 435 crank horsepower, you’re actually putting about 370 horsepower to the rear wheels. We could dive into the physics behind it, but in simple terms it’s due to the fact that when the power is transferred over a distance (transmission, driveshaft, rear differential, rear axles, etc.), the overall output will be reduced.

Dyno Highlights:

• Used to measure power output of a vehicle, typically for tuning purposes
• Two Main Types: Engine Dyno and Chassis Dyno
• Engine Dyno reads power from the crankshaft
• Chassis Dyno reads power from the wheels
• Chassis Dyno will read roughly 15% lower than an Engine Dyno due to parasitic loss

Let’s Clear The Air...

First off, we’d like to clear up a common misconception when it comes to dyno graphs and dyno numbers. They’re really not 100% realistic. From one dyno to the other, the same exact car with the same exact modifications will not put down the same exact power numbers. There are various reasons for this, but there are just too many differing factors that could change the numbers you’re seeing on the graph.

This inconsistency between recorded power outputs isn't important though, because 99% of the time dynos are used for tuning purposes. Tuners will use a dyno as a tool to measure power output while monitoring engine characteristics through their laptop simultaneously. That way, they know that their tune is safe by watching things like knock sensor levels and air/fuel ratio while checking power output throughout the dyno sheet.

Reading a Dyno Graph

Now that you know the difference between a chassis and engine dyno along with the reason as to why dynos are used, you’re ready to learn how to read this graph.

For this particular example, we’ll use my 2011 Mustang GT. The blue lines are baseline numbers of a completely bone stock car. The red lines are the power and torque numbers with a JLT Cold Air Intake, Off-Road Mid-Pipe, custom welded Resonator Deletes and Ford Performance GT500 Axle-Back exhaust, all tied together with a custom tune on 93-octane from Revolution Automotive on their DynoJet.

To read this with some sort of sense, we’ll start from the left and work our way right. First off, you’ll notice that the vertical axis on the left reads HP numbers while the vertical axis on the right reads ft-lbs of torque. The axis on the bottom can typically read two things; either engine speed (RPM) or vehicle speed. I personally find it more informational to know the engine speed, so I know where in the RPM band my peak torque is.

So, let’s get to it. Below, you’ll find a list of letters which are labeled on the dyno graph above.

L - This would be considered the legend. Blue represents the baseline run and red represents the modified run. The lighter shade of either color is torque, whereas the darker shade will be horsepower.

A - For this particular Mustang, the tuner started the dyno run around 2,250 RPM. This is when the tuner “floored” it in the 1:1 gear and began recording the results.

B1 - This point is the max torque for the baseline dyno run with no modifications - 346 lb/ft @ 4,300 RPM.

B2 - This point is the max torque for the modified dyno run after a tune and modifications - 402 lb/ft @ 4,400 RPM.

C1 - This point is the max horsepower for the baseline dyno run with no modifications - 366 hp @ 6,300 RPM

C2 - This point is the max horsepower for the modified dyno run after a tune and modifications - 426 hp @ 6,600 RPM.

D1 - This point is where the tuner ended the baseline dyno run nearing the factory redline.

D2 - This point is where the tuner ended the modified dyno run with the raised 7,300 RPM redline.

E - This point is 5,252 RPM. Due to the physics equation behind the relation of torque to horsepower, the two curves will always cross at this RPM.

Baseline Peak Numbers vs Mods + Tune Peak Numbers:

Horsepower: 366 @ 6,300 RPM | 426 @ 6,600 RPM

Torque: 346 @ 4,300 RPM | 402 @ 4,400 RPM

For more information on the relation of horsepower to torque and how closely related they actually are, check out our article on Horsepower vs Torque.

First off, you’ll notice that the baseline numbers of a 2011 GT seem low at 366 hp and 346 lb/ft of torque. However, the advertised numbers for this model year were 412 horsepower and 390 lb/ft of torque at the crankshaft. If you factor in parasitic loss, which is around 15%, the numbers aren’t far off from what they should be to the wheels.

Okay, so the first inclination of most people is to focus on the peak numbers. While this is a good way to compare power numbers across different vehicles and modifications, there is a lot of unspoken information you can read in the curve of a dyno graph.

Aside from the obvious power and torque gains throughout the entire graph, you can see through the shape of the torque curve that this is a naturally aspirated car. This is because the torque curve is relatively flat for most of the power band. This means that as you accelerate, you’ll get a smooth, steady feel throughout the rev range.

This is not always the case with forced induction cars, though. You’d be able to tell if this car had a turbo or supercharger based on the shape of the torque curve as well, so be sure to check out our other tech article for more info!

A Quick Note: These are very general guidelines based on most Mustangs. There are various factors that go into the shapes of these curves like camshaft timing and overall engine design, so be sure to research your own personal car further in depth before running it on a dyno.

Wrapping It Up

Now you know the very basics when it comes to reading a dyno graph. It’s important to know what your tuner is handing you after you spend money to get a proper dyno tune to support all your aftermarket modifications. With that said, focusing on things like peak numbers is closed-minded when you have the ability to see the entire graph of how your car performs all the way to redline.

When you’re ready to get further mods to get you to the point where you can get a custom dyno tune, be sure to remember CJ Pony Parts for all your Mustang modification needs!