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Old 06-15-2013, 03:03 PM   #11 (permalink)
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Black and Green - '98 Honda Civic DX Coupe
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FIRST TEST RESULTS: box cavity (inconclusive)

Not surprisingly, there seems to be no measurable benefit or loss to FE from the "rear box cavity" design I tested this morning. This because the benefits would be small and the instruments and my approach to the test probably created too much noise in the "data."

The mod prototype (it's ugly):

I created a box like the one in post #3 above that has a flat decklid spoiler at the top, parallel sides extending downward along the trunk seam to a horizontal bottom midway across the rear bumper. All of it extending about 150mm off the back of the vehicle. Rigid. Stable. Attached with copious amounts of black duct tape. Pics:





Course and conditions:

I picked a 1 mile long hill, uninterrupted by lights and without heavily traffic.

The last "weather underground" report Friday night predicted wind at 2mph out of the SSE at 5am, shifting to 1 mph from the S by 8am. Temps were expected to be 52F at 5am and rising to 59F by 8am. Complete cloud cover throughout the morning.

Method/approach:

I drove the car 10 miles to the site to warm the tires and engine. I arrived at about 6am and was done by 740am, after which I went out for coffee with some friends. I used the Ultra Gauge speed sensor reading instead of the OEM gauge. I got the car to 20 mph or as close as possible--evenly coasting--by the time I crossed a specific crosswalk line on the road at the very top of the hill. Then I coasted, braking at the bottom, ahead of a light that was nearly always red.

I aborted any run where I could not get an consistent coasting speed at or as near as possible to 20.9 by the time I crossed the start line. The ultra gauge, I did not realize, seems precise but it not. Its speed readings jump by increments of about .7mph, which is more than 1% of the top speeds I achieved on the course.

To compensate for the rising temps and the effect they might have my speeds, I started without the box cavity attached for three runs (cooler ambient temps of maybe 52F), did six straight with the box cavity attached (presumably slightly warmer ambient temps) and then three more without the box cavity (during presumably warmest ambient temps of possibly 59F).

Results:

Numbers are speeds in mph at four different points coasting down the hill

A1 (no mod):
20.9 35.7 56.7 58.7 = +37.8
20.9 35.7 56.7 59.3 = +38.4
20.2 35.1 56.0 58.7 = +38.5

B (mod):
20.9 35.7 57.3 59.3 = +38.4
21.6 36.4 57.3 59.3 = +37.7
20.2 35.1 56.7 58.7 = +38.5

20.9 35.7 56.7 59.3 = +38.4
21.6 36.4 56.7 59.3 = +37.7
20.9 35.7 56.7 59.3 = +38.4

A2 (no mod):
21.6 36.4 57.3 59.3 = +37.7
20.9 36.4 57.3 59.3 = +38.4
20.9 35.7 56.7 59.3 = +38.4

Average final speeds: A (59.1) B (59.2)
Average speed change start/finish: A (+38.183mph) B (+38.183mph)

Conclusion:

Obviously, there was no change distinguishable from noise created by imprecision in the testing methods and gauges. The results are equivocal. Starting from a still position and using a GPS device would lessen the "noise." Hussain Ali's study of the box cavity I mentioned above showed a very small benefit, anyway. And a study by Adrian Gaylard et al. has suggested the benefits were smaller for a coupe style body like mine. Ali also suggests that the diffuser and its angle mattered a lot.

Next Steps

Leave this mod idea behind. Do underbody panels, an adjustable angle diffuser, and wheel well skirts next. Get a GPS and do any future testing from a standing position. Maybe I'll redo this test later in the summer. A comparison before and after additional aeromods might be fun.

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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.


Last edited by California98Civic; 07-14-2013 at 08:17 PM.. Reason: To add Gaylard link and "next steps."
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Old 06-26-2013, 10:32 AM   #12 (permalink)
40-60-40 MPH P&G
 
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does your thrush muffler came with the oem routing ? or you did have to weld it or something else?
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Echo-Troll Modding Thread

I know i dont have a very good write-up
no lean-burn? no good gear ratio? p&g is the answer
MPG=1 TIME=0
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Old 06-26-2013, 12:13 PM   #13 (permalink)
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Quote:
Originally Posted by echo-francis View Post
does your thrush muffler came with the oem routing ? or you did have to weld it or something else?
I cut the Bosal (OEM) routing off at the muffler with a hack saw. I then had to hire someone to weld the Thrush to the routing pipe. I wanted the thrush for its weight and more importantly it's smaller size, so that the diffuser I am working on this summer will fit better. The Bosal hangs down into the airstream much more.
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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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Old 06-26-2013, 02:18 PM   #14 (permalink)
40-60-40 MPH P&G
 
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me to its for its weight and smaller size because I want to upgrade my rear belly pan.
but I dont want to spend $$$ to have the job done. I just want to simply install it.
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Best Highway Trip (~36.8 Km): 2.16 LHK (109 MPG (US) )
Best Commute Trip avg (73.8 Km ): 2.33 LHK (101 MPG (US) )
Echo-Troll Modding Thread

I know i dont have a very good write-up
no lean-burn? no good gear ratio? p&g is the answer
MPG=1 TIME=0
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Old 07-05-2013, 10:04 PM   #15 (permalink)
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Black and Green - '98 Honda Civic DX Coupe
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"Maintain" before "mod"

I replaced the hub bearing unit on the driver side, front. Loud cabin noise is gone. And the car coasts WAY better. Seems especially notable at lower speeds, where aero is less of a drag. Psyched to return to modding now.
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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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Old 07-13-2013, 05:27 AM   #16 (permalink)
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Not sure how far along you are on the belly tray. Some tips.

Home.depot sells light aluminum window frames for.mesh window that make a great frameto mount your under tray.

Be sure to leave plenty of.space around your exhaust, or the coroplast will eventually warp. Coroplast will.warp around the engine and tranny too. Maybe use aluminum in this area instead.

I noticed.a 2-3 mpg gain overall with a belly tray.
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Old 07-14-2013, 08:21 PM   #17 (permalink)
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Black and Green - '98 Honda Civic DX Coupe
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This is a great suggestion, thanks. I was at Harbor Freight today looking for tools and trying to learn a little. Be at Home Depot, maybe, tomorrow. I'm just at the point of buying hardware having scoped-out places to insert bolts and a general design plan. I'm possibly gonna use sheet aluminum, even though it costs a bit more (not sure how much more yet, waiting for a quote).

BTW, I posted photos of my "box cavity" prototype in post #11 (above).
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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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Old 07-16-2013, 10:45 PM   #18 (permalink)
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Thanks for this thread. I love the clarity and detail of your posts.

Edit: I agree about the spacing from the exhaust on the under panel. I ended up cutting 12''wide x 24''long around the catalytic converter. It seems to be getting better cooling now as there is some air flow along the exhaust, which I've found is important in warmer weather. I'm sure this has added some turbulence, but it's probably quite minimal since the mpg has been creeping up since I've done it. I think the underbelly is good for a solid 3mpg on my Festy.

Last edited by mikeyjd; 07-16-2013 at 10:53 PM..
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Old 07-17-2013, 06:00 PM   #19 (permalink)
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Quote:
Originally Posted by California98Civic View Post

Tires overinflated (60psi).
I applaud your efforts at improving your fuel economy, but unfortunately you've also created a car that is an extremely dangerous device for you and others around you on the road.

1. Your tire inflation pressures are 15-25psi over the acceptable maximum inflation pressure limit for any 175/50/13 or 175/70/13 tire on the market. That's a blowout waiting to happen. The highest available 175/50/13 or 175/70/13 maximum pressure for any tire of the sort on the market is 44psi, fyi.

2. Your lowered suspension, despite improving your aero-capabilities make it much more likely that if you do end up in a collision, you will not survive unscathed. Your crash-bar height at the front, at the rear, and as far as the side-impact beams are concerned is now significantly lower than that of the vehicles around you. The net result is that if you have a crash, your car will effectively pass partially underneath the other car in the incident, drastically increasing the likelihood of serious injury or fatality for you and your car's other occupants.
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Old 07-17-2013, 08:59 PM   #20 (permalink)
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Quote:
Originally Posted by Vansquish View Post
I applaud your efforts at improving your fuel economy,
Thanks.

Quote:
Originally Posted by Vansquish View Post
but unfortunately you've also created a car that is an extremely dangerous device for you and others around you on the road.
Not true. Although cars are inherently dangerous, mine is not especially so. And I have a perfect driving record. 12-15K miles a year and no problems. No moving violations, no accidents, no demerits of any kind. I think speeders and drinkers, and the sleepy, the texting, the cellphone chatters, and the lane hoppers are the actual menaces on the road, regardless of the qualities of their motor vehicles. And the available evidence supports me. Speed, distraction, intoxication, and reckless driving are the main causes of accidents. IMHO, my "Black and Green" is one of the safest presences on the road. My long driving history with it is my best proof.

Quote:
Originally Posted by Vansquish View Post
1. Your tire inflation pressures are 15-25psi over the acceptable maximum inflation pressure limit for any 175/50/13 or 175/70/13 tire on the market. That's a blowout waiting to happen. The highest available 175/50/13 or 175/70/13 maximum pressure for any tire of the sort on the market is 44psi, fyi.
This has been discussed frequently on this site and you can search those discussions. I don't want to recap them. But the stated tire pressures on sidewalls are not the last word in what the tires are capable of and what is safe.

Quote:
Originally Posted by Vansquish View Post
2. Your lowered suspension, despite improving your aero-capabilities make it much more likely that if you do end up in a collision, you will not survive unscathed. Your crash-bar height at the front, at the rear, and as far as the side-impact beams are concerned is now significantly lower than that of the vehicles around you. The net result is that if you have a crash, your car will effectively pass partially underneath the other car in the incident, drastically increasing the likelihood of serious injury or fatality for you and your car's other occupants.
I have not lowered my suspension. So this comment is simply not about my car.

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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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