Civic hatchback aerodynamics

[molecule]

high priority thread...
it should almost be a sticky...
even without pics
i could see this rounding up over 50% of available mpg gains on my car
i found some good stuff in my garage too
ICING
and a sheet of thin/clear plexi

[Compaq888]

Originally Posted by SVOboy

Damn, 62 mpg at 75 mph, that's ridonkulous.

DAMN!! :JAWDROP:

[The Toecutter]

you should try to calculate your Cd using the coast down method, after figuring our your rolling resistance and such. I'd be interested in knowing.

I suspect you got your Cd down to around .21-.23 to get those MPG figures.

I'm also trying to figure out a way to mimic the effects of the caulking without a car looking like a rolling sicence project. I'm thinking of using bondo to do it, only smoothing it out. A razor could cut those seems just as well. Done right, you could no doubt paint over such a smooth surface and it would look real slick, as if it came like that from the factory...

[Matt Timion]

Originally Posted by The Toecutter

you should try to calculate your Cd using the coast down method, after figuring our your rolling resistance and such. I'd be interested in knowing.

I suspect you got your Cd down to around .21-.23 to get those MPG figures.

I'm also trying to figure out a way to mimic the effects of the caulking without a car looking like a rolling sicence project. I'm thinking of using bondo to do it, only smoothing it out. A razor could cut those seems just as well. Done right, you could no doubt paint over such a smooth surface and it would look real slick, as if it came like that from the factory...

I've been wanting to do the same thing. Perhaps it's also possible to sand down the caulk once it has dried.

[basjoos]

I'm not familiar with the coast down method for Cd calculation, how do you do it?

[MetroMPG]

Originally Posted by basjoos

I'm not familiar with the coast down method for Cd calculation, how do you do it?

there's a technique described in the last post in this thread:
http://www.gassavers.org/forum_topic/weight_reduction.html

i haven't tried it. can't say for sure how well it works.

basjoos - again i have to say i'm impressed with the numbers you've achieved. 62 @ 75 is astonishing.

to compare...from another thread...

Originally Posted by metrompg

a simple scangauge trial i did yesterday - MPG at increasing speed intervals, flat road, no wind, warm (60 ish), cruise control, top gear:

69 mpg (US) @ 65 km/h (40.4 mph)
62 mpg (US) @ 75 km/h (46.6 mph)
55 mpg (US) @ 85 km/h (52.8 mph)

i could only get 62 mpg when going nearly 30 mph slower!

sure, there's probably a temperature difference between your recent driving conditions and my observations, but wow! i think i'd be lucky to get 62 mpg in the low 50 mph range when it actually gets hot here!

[tomauto]

I just dont see how more heat could help mpg.

Also, I have a question about the thermostat modication (170 to 192 degree mod) Where does all the mpg improvement come from?

From what I can see, the only way you are gaining anything is from the electric fan not being used as much but crap, why wouldn't you just have the alternator turn on while your coasting?

I totally dont see a point to the warm air intake. Maybe it is because I live further south. Maybe I am wrong, but doesn't heat hinder any performance? (speed or economy for that matter)

[SVOboy]

I just dont see how more heat could help mpg.

Hot air = less dense = less gas = more throttle opening = same gas but less friction = less gas overall.

Also, I have a question about the thermostat modication (170 to 192 degree mod) Where does all the mpg improvement come from?

Warmer engines are more efficient. Plus honda ecus pull 3% fuel when you hit 195 on ECTs compared to 180.

I totally dont see a point to the warm air intake. Maybe it is because I live further south. Maybe I am wrong, but doesn't heat hinder any performance? (speed or economy for that matter)

It hinders speed, but not economy. OBD2 might be different than obd0/obd1 hondas, but Rick (rh77) saw good increases with a WAI on his obd2 integra.

[MetroMPG]

Originally Posted by tomauto

I just dont see how more heat could help mpg.

other warm ambient benefits:

- less time in open loop (less time spent warming up)
- less tire rolling resistance
- reduced aero drag (less dense air)
- reduced losses to lubricants which are more viscous when cold (bearings, engine oil, transaxle fluid, etc)
- higher tire pressure (if you last filled it when cooler)
- and more i can't rhyme off the top of my head at the moment.

[basjoos]

That is the one nice thing about southern summers. Although they may not be the most comfortable for the driver, those hot and humid conditions give the best FE. When I was getting that 62mpg@75mph, the ambient temp was around 85F with high RH, since a stalled warm front was sitting over the area.