Advertising Power Gains as a Percentage

We’ve recently been asked why we display our power gains as a percentage rather than actual horsepower and torque values.  The most straightforward answer is – simplicity.  There are many variables when it comes to obtaining a power figure.  Things like tire pressure, dynamometer brand, type, and model, how a car is strapped down, the weather, and more can all impact the final measurement of power.  A change in any of these variables can swing power figures by a significant amount on a car that has remained, otherwise, exactly the same.

In order to arrive at a percentage gain, we take the average of three pulls before and after a change.  Whether this change be a small tweak to the tune, changing out a hard part, or experimenting with dyno setup you will likely see a change, or delta in the output.  We then take that change and calculate it into a percentage gained or lost from the initial value.  As an example (seen in the video):  we take three dyno pulls of a completely stock car and average them.  Next, we install our Big SF Intake and flash that car with the appropriate map file.  After that, three more dyno pulls are made from which we calculate an average.  We can next take the delta from the two averages and divide it into the original power numbers to arrive at our percentage gain.  It’s as simple as that!

If you’re looking for a bit more clarity when it comes to dyno results, check out our recent COBB Blog article titled Interpreting Dyno Results.

Samuel Latham on December 11, 2016 says:

2012 Impreza wrx
93 Oct
SF Intake COBB
Stock Exhaust


    Marshall on December 12, 2016 says:

    Hey Samuel,

    The only part that is not compatible with our current OTS Map offering is the 3-port EBCS. If you want to utilize that part, a custom tune would be required. Alternatively, using the factory boost control solenoid would allow you to use our Stage2+SF OTS map.


Nolan La Course on June 5, 2018 says:

So how does the access port itself increase the power?

    Adam Hill
    Adam Hill on June 5, 2018 says:

    Hi Nolan,

    That is a question that could have a super long answer, but click the link below for a video will cover the basics. If you are new to tuning, I’d recommend watching the entire series. Let me know if you have any other questions.


Chris Eseltine on November 15, 2019 says:

How much power would a 2017 Sti get with a invidia catless divorced downpipe ,invidia cutback,unequal headers n up pipe ,and a Cobb cai
The car runs like a flat out monster I have raced cars that do 12s in 1/4 mile n beat them.?

    Adam Hill
    Adam Hill on November 18, 2019 says:

    Hi Chris,

    With those modifications, you will need a custom tune on a 2017 STI along with fuel system upgrades. So the power will vary significantly. Also, we do not recommend or support a catless downpipe. Our high-flow catted downpipes are rated at around 500whp, so they are more than enough to handle most street driven builds.