Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post

Istas · 06-07-2009, 09:14 AM

Greetings everybody.

I just made a 2900 mile trip out to visit friends in Montana. I've been here a few weeks, and I'm here for a few more. While websurfing I stumbled across the Ecomodder forum, and it got me thinking about all that gas I'll be using on the way home. So I read lots and lots of posts until I got an idea of what I'd be capable of, and comfortable with, doing.

My initial question: if I can get a bit over 30 mpg on the highway without any modifications at all, is it out of the question to expect a 10 mpg improvement from some modest aero mods?

Car is a FWD Subaru Legacy sedan. It turns 18 in October (of 2009). The good news is that I (mostly) don't care how it looks at this point (as you can tell by the pop-riveted sheet metal patches in five places that, at the time, saved me $200 in replacement fenders and who knows how much bodyshop payments).

The bad news is it's 17 years old (so no OBDII). The engine's got some wear on it (though not as much as could be, at about 189k miles), it's an automatic transmission, the speedometer sticks and it has no cruise control.

So, please let me show off my progress so far (modest as it will be; no full boat-tails in the near future, and even if I had a manual, engine-off pulse-and-glide is more effort than I feel like spending while driving).

Here's Car in as good an "original" picture as I can find.

Go pop-rivets! I've had a comment from someone that it reminded them of something from Mad Max.

My first thought was, what's the easiest and most reversible mod I could do? After reading plenty of threads on this forum, I decided on a door mirror delete. PA apparently also has that "at least one mirror that can see behind the car" law, so I went for it.

You can see the mirrors are pretty big. Using two different calculation methods, I found that each mirror has a frontal area of about 40 square inches. Folding them in (which the stock mirrors do, glad Subaru realized they're huge) reduces that to about 16 square inches. Good, but not as good as it can be.

Removing the mirrors entirely reduces the frontal area of Car by 3%. Three. Percent. That brings the CdA from 6.81 to 6.61, and that's assuming no reduction in drag.

Here's a comparison pic of my three mirroring options.

They came out very easily, and I'm able to put them back in whenever I want. (which is good for A-B-A testing that will come; also, I believe I need to put them back to pass inspection)

I bent up some sheet metal (to keep with the theme, of course), and with a couple of bolts, nuts and washers, there were no more exposed holes. Also, due to the way I angled the metal in some areas (and folded the edge over in others), there's not a sharp corner to be felt, even when the door's open.

(I won't bother showing a picture of the driver's side here, as it's just a mirror image of this one. Get it? Mirror image? *cheesy grin*)

So what next? Thinking about it, I decided on the mod that would be the easiest (in my opinion) to do while having the least chance of degrading performance, something sure-fire that at the very least would not hurt anything. Rear wheel skirts.

Following the example of several people on this forum, I went with the aluminum bar support at the bottom.

I kept at least an inch of clearance from the tires, figuring that a little too much clearance would be better than too little.

(by the way, don't make the same mistake I did, figuring that steel bars would be stronger for the same dimension of bar, and cost a bit less; I returned them because it was far too difficult to work with)

After I had the support bar and brackets in, I used a piece of cardboard to get a rough outline of the fenders, then traced that onto the galvanized sheet metal I so love and cut them out with tin snips.

For each one, I folded over a bit at the bottom for the smooth, non-dangerous edge (using channel-lock pliers to get to 90 degrees, a flathead screwdriver to get it to an acute angle, then a hammer to get it flat), and drilled the holes in the support bar.

I lined up the slightly oversized sheet metal where I wanted it, leaving about half an inch overlap around the whole curve, then marked where to drill the two center holes in the sheet metal with a pencil while an assistant held it in place for me. Drilled those two holes, then used washers, bolts and nuts to fasten it to the support bar in just those two places.

I then used the pliers to bend the edge of the metal 90 degrees to fit the curve, going an inch at a time, bending then checking the fit, unbending and rebending when necessary, and trimming the little bit I needed to with the tin snips.

I took the skirt off, further folded and hammered the whole edge, put it back in place with the two bolts, marked where to drill the two top holes and the remaining front hole on the support bar, got them drilled, then put the fender securely in place and drilled the final, rear hole that goes into the plastic bumper at the bottom.

I'm happy with how they turned out. As with the mirrors, there's not a sharp edge to be felt. They sit right inside the edge of the fenders, and they're quite sturdy, no wobble at all.

The bottom of each skirt undulates a little, and the trailing curve at the bottom is a little severe for aero, but on the whole it has to be doing more good than harm, I think.

06-07-2009, 09:14 AM	#1 (permalink)
Istas is not covered in bees. Join Date: May 2009 Location: Seeley Lake, Montana, USA Posts: 207 Honda - '05 Honda Accord EX 90 day: 27.16 mpg (US) Insight - '00 Honda Insight w A/C 90 day: 66.55 mpg (US) Thanks: 53 Thanked 51 Times in 26 Posts	Is 42mpg too low a goal? Greetings everybody. I just made a 2900 mile trip out to visit friends in Montana. I've been here a few weeks, and I'm here for a few more. While websurfing I stumbled across the Ecomodder forum, and it got me thinking about all that gas I'll be using on the way home. So I read lots and lots of posts until I got an idea of what I'd be capable of, and comfortable with, doing. My initial question: if I can get a bit over 30 mpg on the highway without any modifications at all, is it out of the question to expect a 10 mpg improvement from some modest aero mods? Car is a FWD Subaru Legacy sedan. It turns 18 in October (of 2009). The good news is that I (mostly) don't care how it looks at this point (as you can tell by the pop-riveted sheet metal patches in five places that, at the time, saved me $200 in replacement fenders and who knows how much bodyshop payments). The bad news is it's 17 years old (so no OBDII). The engine's got some wear on it (though not as much as could be, at about 189k miles), it's an automatic transmission, the speedometer sticks and it has no cruise control. So, please let me show off my progress so far (modest as it will be; no full boat-tails in the near future, and even if I had a manual, engine-off pulse-and-glide is more effort than I feel like spending while driving). Here's Car in as good an "original" picture as I can find. Go pop-rivets! I've had a comment from someone that it reminded them of something from Mad Max. My first thought was, what's the easiest and most reversible mod I could do? After reading plenty of threads on this forum, I decided on a door mirror delete. PA apparently also has that "at least one mirror that can see behind the car" law, so I went for it. You can see the mirrors are pretty big. Using two different calculation methods, I found that each mirror has a frontal area of about 40 square inches. Folding them in (which the stock mirrors do, glad Subaru realized they're huge) reduces that to about 16 square inches. Good, but not as good as it can be. Removing the mirrors entirely reduces the frontal area of Car by 3%. Three. Percent. That brings the CdA from 6.81 to 6.61, and that's assuming no reduction in drag. Here's a comparison pic of my three mirroring options. They came out very easily, and I'm able to put them back in whenever I want. (which is good for A-B-A testing that will come; also, I believe I need to put them back to pass inspection) I bent up some sheet metal (to keep with the theme, of course), and with a couple of bolts, nuts and washers, there were no more exposed holes. Also, due to the way I angled the metal in some areas (and folded the edge over in others), there's not a sharp corner to be felt, even when the door's open. (I won't bother showing a picture of the driver's side here, as it's just a mirror image of this one. Get it? Mirror image? cheesy grin) So what next? Thinking about it, I decided on the mod that would be the easiest (in my opinion) to do while having the least chance of degrading performance, something sure-fire that at the very least would not hurt anything. Rear wheel skirts. Following the example of several people on this forum, I went with the aluminum bar support at the bottom. I kept at least an inch of clearance from the tires, figuring that a little too much clearance would be better than too little. (by the way, don't make the same mistake I did, figuring that steel bars would be stronger for the same dimension of bar, and cost a bit less; I returned them because it was far too difficult to work with) After I had the support bar and brackets in, I used a piece of cardboard to get a rough outline of the fenders, then traced that onto the galvanized sheet metal I so love and cut them out with tin snips. For each one, I folded over a bit at the bottom for the smooth, non-dangerous edge (using channel-lock pliers to get to 90 degrees, a flathead screwdriver to get it to an acute angle, then a hammer to get it flat), and drilled the holes in the support bar. I lined up the slightly oversized sheet metal where I wanted it, leaving about half an inch overlap around the whole curve, then marked where to drill the two center holes in the sheet metal with a pencil while an assistant held it in place for me. Drilled those two holes, then used washers, bolts and nuts to fasten it to the support bar in just those two places. I then used the pliers to bend the edge of the metal 90 degrees to fit the curve, going an inch at a time, bending then checking the fit, unbending and rebending when necessary, and trimming the little bit I needed to with the tin snips. I took the skirt off, further folded and hammered the whole edge, put it back in place with the two bolts, marked where to drill the two top holes and the remaining front hole on the support bar, got them drilled, then put the fender securely in place and drilled the final, rear hole that goes into the plastic bumper at the bottom. I'm happy with how they turned out. As with the mirrors, there's not a sharp edge to be felt. They sit right inside the edge of the fenders, and they're quite sturdy, no wobble at all. The bottom of each skirt undulates a little, and the trailing curve at the bottom is a little severe for aero, but on the whole it has to be doing more good than harm, I think. Last edited by Istas; 06-07-2009 at 09:25 AM..