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Which Loses More Power: A Three-Inch Exhaust Or A 2.5 Inch Exhaust? Engine Masters Tests Out The Backpressure Theory On A Chevrolet 454!


Which Loses More Power: A Three-Inch Exhaust Or A 2.5 Inch Exhaust? Engine Masters Tests Out The Backpressure Theory On A Chevrolet 454!

Here’s a fun question that you can use to fire up just about any message board: what does a high-horsepower engine like better: a 3″ exhaust to breath better with, or a 2.5″ exhaust that offers up a bit of back pressure and that opening up the flow of air out of the engine will cause the power to fall off of a cliff faster than Wile E. Coyote when he’s within a lunge of the Road Runner’s tail feathers. Truth is, any four-stroke engine is nothing more than an air pump that is powered by controlled explosions. The better you can get air to flow, the happier the engine will be. To put this whole “back pressure” deal to bed once and for all, Freiburger and Dulcich head back to the dyno room at Westech with a 620-ish horsepower Chevrolet 454 and enough exhaust tubing to plumb the Titanic with to prove once and for all that an engine loves to breathe. How much power will be lost between the mufflers, and more importantly, how much power will disappear with the exhaust system, period? Hit play below to find out!


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14 thoughts on “Which Loses More Power: A Three-Inch Exhaust Or A 2.5 Inch Exhaust? Engine Masters Tests Out The Backpressure Theory On A Chevrolet 454!

  1. Oklxs03

    I know there are limits on the dyno but not having an H or X pipe definatly cost some torque and horsepower. In the real world even that 600 HP motor would sound horrible without some kind of crossover.

    1. 1966longroof

      Exactly what I was thinking. It would have been the perfect time to test both. But then again who knows how much dyno time they are allowed when shooting these videos.

  2. Chevy Hatin' Mad Geordie

    That leader photo looks like he’s using the muffler as a bong to see if the 2,5 inch exhaust gets him as off his tits as a 3 inch one…..

  3. Truckin' Ted

    Crossover? X-pipe? I don’t really care.

    This is still one of the best web shows…………EVER.

  4. Danno

    Ok, so they proved that a 600+ HP, solid roller big block makes more HP and TQ with the larger exhaust system. Not really surprising and likely to make a lot of pussef off neighbors. In the real world how many of our cars are running around on the streets with that kind of engine? I would have liked to have seen the same test done on say an average 350-400 HP small block street engine. I am guessing the results might be quite different. And with happier neighbors.

    1. Will-I-Is

      Danno,
      My car is running around on the streets with that kind of power, but it’s a supercharged sbf. 🙂
      I bet the same results would hold true for a smaller hp engine. If engines make their best hp with open headers and a short torque tube, then it only stands to reason that a larger exhaust would be more beneficial than a smaller exhaust.

  5. jerry z

    It’s amazing how much louder the 3″ is compared to the 2 1/2″ system. I’ll take the 15 hp loss for my driving pleasure.

  6. john t

    I kinda disappointed that with each setup they didn’t fine tune the carb to get optimum power – how much of that loss wasn’t so much the exhaust but the carb running rich?

  7. Ryan Spitz

    These shows are bullshit. Their magazines are in the toilet and they are counting on sensational web shows to carry the day. Danno is right. A better test would have been an average street setup which for most guys with families and budgets is closer to 400 horsepower than 600 horsepower. These type of shows are quick and dirty get it done fluff that provide no real answers for guys like me who have to save up for every part I buy. How about some instrumentation to actually read pressure in the pipes before and after the mufflers.

    1. Will-I-Is

      Ryan Spitz,
      Common sense should tell you that there will be less “pressure” (back pressure) in a larger exhaust system without the need for pressure sensors. IF, they were only testing mufflers then I could see where pressure sensors before and after might do some good, but here they were only testing pipe sizes and whether or not “backpressure” or the lack thereof affect power & torque.
      These guys verified for me that my supercharged engine will produce more power and torque with the larger exhaust.

  8. Wes

    “Truth is, any four-stroke engine is nothing more than an air pump that is powered by controlled explosions.”

    This comment bugs me. Is not an explosion. You actually dont want an explosion. That’s called detonation. What you watch for in a cylinder firing is conflagration. The rate at which the fuel burns.

    1. Will-I-Is

      Wes, I looked it up and an engine’s operation appears to be closer to a “controlled explosion” than it is to a “conflagration”.

      Definitions:
      1. conflagration – a very intense and uncontrolled fire.

      2. controlled explosion – the deliberate detonation of an explosive device or substance under strictly controlled circumstances.

      I think the term you may be looking for is:
      “Burn Rate” – refers to the time required for the air/fuel mixture to burn completely.

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