Depends on the context, and also I don't make any claims for product tests that I haven't personally done
![Wink :wink:](./images/smilies/icon_wink.gif)
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On some cars like the 350Z the intake plenum is so poorly designed that the amount of air being fed to each cylinder is different by as much as %10. The spacer for that car allows more volume and more even airflow in the plenum and does no doubt give more power.