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Old 05-06-2018, 11:36 AM   #128 (permalink)
Cyborg ECU
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Join Date: Mar 2011
Location: Coastal Southern California
Posts: 5,233

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 59.78 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
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Originally Posted by mpg_numbers_guy View Post
... How would a tail extension possibly hurt FE? since it isn't modifying the airflow but rather just extending it out.

MetroMPG's was an 8th gen with the more aerodynamic rear end. I know the 7th gen's isn't bad, per se, but it doesn't seem perfect...and I'm at loss where to go from here to hit 50 mpg lol. I'm hitting 50 mpg on some trips, but my tank is still just over 45 mpg per the Torque app.
I see you are right it was an 8th Gen Civic. But it was the sedan, not the coupe. Anyway, it is not that the boat-tail would hurt, necessarily, but mostly that the benefit might be disappointingly slight for all the work. Getting it right is difficult because the shape involves compound curves that can deal with flow coming from below, sides, and top. If the angles and curves are not right you get less benefit or none. So it needs a lot of thought and patience.

You have the auto, so the engine off coasting thing is out. But looking at your car's page, there are other tactics and mods available still, I think, that are easier to design so as to capture a known benefit. HYPERMILING: turning the car off at stoplights, and using engine braking to slow the car when approaching a stop. Engine braking will trigger deceleration fuel cut-off and you will coast to about 1600 RPMs without burning fuel. MODS: undertray (AKA "bellypan") with diffuser, electric block heater to shorten warm-up time, weight reduction especially if you drive in urban suburban places, larger wheel/tire diameter for taller gearing, LRR tires, turning the car off at stoplights, eliminating power steering or putting it on an underdrive pully, putting alternator on an on/off switch and getting a deep cycle battery to charge from the grid... and then the more ambitious, such as an electric water pump.

See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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