Why More Boost Doesn't Always Mean More Power

Why Do Two Engines With The Same Displacement & Same Boost Make Different Horsepower?

40w ago

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If two engines have the same boost, and the same displacement, why does one make more power than the other? The answer is complex, but ultimately it comes down to how much air (specifically oxygen) can you get inside an engine's cylinders. The more air you have, the more oxygen you have, thus you can inject more fuel and produce more power. But manifold pressure is only one measurement that will determine how much oxygen you'll have within your combustion chamber.

Temperature and humidity also play a role on the engine's performance. You need to look at manifold density, instead of simply boost, to really know how much air the engine is getting. Not to mention ignition timing, air/fuel ratios, and the efficiencies of the turbos you are using. This video will break it all down from beginning to end!

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Comments (5)

  • Microscopic hole is going to have the smallest flow even if you have 1000 psi pushing air through it. Huge hole is going to flow tons even with 1 psi behind it. Therefore engines with better flow characteristics (porting and matching) and larger openings (valves, throttle body, intake manifold, cam lob size and duration ex) will get more air to the cylinders without the need of excessive boost levels. And that's just airflow. Then you have how the EFI system mixes fuel and air, how well the engines stops pre ignition / knocking, how much timing you can add, and how much heat the engine can take.

      9 months ago
  • Avogadro constant, a useful comparison.

    Can you talk in SI units instead of these funny, old and outdated imperial ones.

      9 months ago
    • Yes, a mole is the SI unit for amount of substance. One mole has 60200000000000000000000 molecules in it, no matter what those molecules are - hence it is a constant.

        9 months ago
  • My naturally aspirated engine is dramatically effected by air quality.

      9 months ago
  • Great video and superb explanation!

    I've been watching for many years now and have even designed some R/C cars using your videos.

      9 months ago
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