View Single Post
Old 09-26-2017, 08:27 AM   #2 (permalink)
Master EcoModder
Ecky's Avatar
Join Date: Dec 2011
Location: New Zealand
Posts: 4,758

ND Miata - '15 Mazda MX-5 Special Package
90 day: 36.95 mpg (US)
Thanks: 2,642
Thanked 2,340 Times in 1,447 Posts
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.
  Reply With Quote
The Following User Says Thank You to Ecky For This Useful Post:
COcyclist (11-07-2017)