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Will I Gain More Horsepower With An Exhaust System?

After-market exhaust systems are almost always less restrictive than factory exhaust systems. However, that doesn’t mean that adding an after-market exhaust will always result in more power. Depending upon your vehicle and the system you choose, an after-market exhaust can add as much as 50 horsepower or as little as 2 or 3 horsepower. Here’s how you can figure out what to expect:

Don’t Focus On Horsepower Only

How to calculate horsepower

Horsepower is calculated by multiplying torque by RPM. Therefore, if a new exhaust system adds just 10 lb-ft of torque at 5,000 RPM, that will result in a horsepower increase of 9.5 hp. While that might sound like a solid horsepower gain, an extra 10 lb-ft of torque at 5,000 RPM usually doesn’t do you a whole lot of good in day-to-day driving. After all, how many of us run our engines at 5,000 RPM on a constant basis?

Throw Exhaust System Manufacturer Estimates Out the Window

Because horsepower is a function of RPM, it’s very easy to show big horsepower gains on paper. Diesel trucks are a great example – because they generate gobs of torque anyways, adding an extra 35 lb-ft of torque at 3,300 RPM results in a gain of 23hp. This number may seem impressive, but an extra 35 lb-ft of torque at 3,300 RPM isn’t that useful to your typical diesel truck owner. It’s a good increase to be sure, but it’s not usable power.

The other reason that you shouldn’t put a lot of stock in manufacturer estimates is that dyno results are fairly easy to manipulate. When a vehicle is tested on a dyno, there can be significant variations from test to test without any change to the engine. If a manufacturer takes their worst run from their “before” tests and their best from “after” tests, they can show a really big gain that’s mostly due to normal variations between runs.

In other words, exhaust system performance estimates are always very generous. If the kit from Flowmaster supposedly adds 8 hp and the kit from Magnaflow supposedly adds 13 hp (or vice versa), chances are good that both perform pretty close to the same.

The Most You Can Gain is 2-5%

If you want to know how much power you can expect to gain from adding an exhaust system to your car, assume that your engine will get 2-5% more powerful. More specifically, large engines like a big 6.0L V8 typically see about a 2%-3% horsepower increase. Smaller engines, like a 1.8L 4-cylinder, typically see a 3-5% horsepower increase.

Exhaust systems add power when combined with air intakes and programmers

HOWEVER, exhaust systems have a multiplying effect if you combine them with other add-ons. The exhaust system by itself won’t add a lot of power, but combined with an air intake and a performance chip or power programmer you could see a significant increase in performance. You’ll also see a slight increase in fuel economy (assuming you keep your foot out of it, of course).

Remember That The Intangibles Have A Value

Adding an after-market exhaust system to your vehicle isn’t just about adding some more horsepower or improving fuel economy. You’ll enjoy a sportier exhaust note, better throttle response, and hopefully driving will be just a little more fun.

Considering how inexpensive an after-market muffler is, it’s a nice way to customize your vehicle on a budget. The icing on the cake is slightly more power and improved fuel economy.

16 Comments Post a comment
  1. Mike Murdoch
    Feb 22 2012

    honest grass roots, readable and not over the top techo tripe, well done

    • Jason
      Feb 22 2012


  2. Randy
    Apr 19 2012

    How much are those programmers?

  3. justin
    Aug 1 2012

    if im runnin an after market muffler which is a flowmaster should i install a high performance intake also?

    • Jason
      Aug 2 2012

      justin – There’s definitely an advantage in upgrading both your exhaust and your intake, and I would recommend both. Even if you just add a performance air filter.

  4. Sylvain
    Apr 30 2013


    Thanks for your article :)

    Any idea about the gain with the combo you suggest?

    You said 2-5% only the exhaust so I guess around 10 with the combo?

    Thank you

    • Jason
      Apr 30 2013

      Depends on the engine. As a general rule, the combination of a programmer, exhaust, and air intake can add at least 20hp. The compromise is that your vehicle will be louder and that most after-market tunes require you to run premium fuel.

  5. Bob albertson
    Oct 21 2014


    I have a 1977 Chrysler Cordoba with the LA 360 4bbl making a factory 170 HP. I will be putting a pair of chrome shorty headers along with an X-,Pipe 3″ dual exhaust system with a pair of high flow performance mufflers. I will also be replacing the factory cats with after market high flow cats.

    Can you give an idea of an approximate increase in HP and TOURQE?

    I will also be installing a new set of iridium plugs and synthetic motor oil. Also I will be putting in an electronic HGH performance ignition system with the factory air cleaner with a K&N air filter.

    With these changes I given, what kin of HP gain can I expect? The only other upgrade I plan on a bit later, will be a high performance intake manifold with a rebuilt factory Carter thermoquad carburetor. And what type of HP gain from the new t intake give me?


    Bob Albertson

    • Jason
      Oct 21 2014

      Bob – No idea. A 360 can easily make 300hp, and with massaging could jump up to 400hp…but this is an old car with what is (I’m assuming) an original motor. You could very easily stress the motor.

      My advice is to get with the local classic performance shop, ask for some quotes on things, and see what you can learn. You also may find that there’s a rebuild kit for your 360 that boosts power, with new cams, upgraded internals, etc. Good luck.

  6. Akthar
    Nov 3 2014

    I have a Dodge Charger 100th year anniversary edition. It has 370 Hp. BY how much will the Hp increase if I add a varex exhaust system ?? I read earlier that if I install Magnaflow exhaust system, I could gain a min of 20hp. Is that true?? Your explanation will be highly appreciated.

  7. Moe
    Jan 17 2015

    Ok so hi guys I just bought a 2015 Corolla s 1.8L. Now Its a good reliable car. I’m just trying to gain more hp. And I wanna do that without stressing the engine. I’m just think about getting a exhaust system, intake, and a computer chip. Any suggestions.?? To how how much hp I can gain with that?? Will it affect my engine too much?? It only comes with 132hp. Which is not enough lol. Plz suggest and advise on what should I do.

    • Jason
      Mar 3 2015

      Moe – I wouldn’t try anything radical with the newest Corolla, at least not until the after-market releases some parts specifically designed for this vehicle. I’d say you need to wait 12-18 months to see what comes out (if anything).

      • Edgar Rodriguez
        Jun 3 2015

        I put a flowmaster muffler to my 2015 corolla and it feels more powerful at running but I do not feel a big diference on takeoff which is what I Don’t like about this car I am going to buy a K&N Typhoon intake specifically made for this type (model) of car I will post what I get

  8. Jun 26 2015

    Howdy! I could have sworn I’ve been to this website before but after checking through some
    of the post I realized it’s new to me. Anyways, I’m definitely glad
    I found it and I’ll be bookmarking and checking back often!

  9. girish
    Jun 30 2015

    i got 04 hyundai tiburon GT model. recently i installed cold air intake & it sounds gr8 & take off quick. i’m planning to add G-Force chip & cat- back exhaust system. any idea how much HP it gonna make after installing chip & exhaust in combo? thanks


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