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Old 09-26-2017, 09:27 AM   #2 (permalink)
Ecky
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Join Date: Dec 2011
Location: Vermont
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Gaptooth (retired) - '00 Honda Insight
Team Honda
Gen-1 Insights
90 day: 54.26 mpg (US)

Such Fit - '07 Honda Fit Sport
90 day: 41.27 mpg (US)

Connect - '15 Ford Transit Connect XL
90 day: 23.4 mpg (US)

K-sight - '00 Honda K-sight
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After alternator, battery and equipment efficiency losses, you're probably looking at roughly 2:1 watts in vs watts out. Most aftermarket head units can put out ~50 watts peak, ~20 watts continuous. If we assume 100 watts constant draw at the crank to run the radio, that's about ~15% of 1HP, or maybe 1-2% fuel economy worst-case in most cars.

In my G1 I have a 640w amp and a sub on top of an aftermarket head unit, and generally speaking it disappears into background noise (lol) and I can still hit 90-100mpg blasting the radio. In theory I could be drawing up to 2HP at the crank for maybe a 20% loss in ecnomy, but I'd probably destroy my ears getting anywhere near that. Normal listening volume, even with an amplifier, there's no easily discernible economy loss.
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