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Discussion Starter #1
Thought I'd do a quick post about this. I made an under engine aero panel the other day, pretty cheap and easy. My car hasn't had one since I bought it. The panel I made is one piece, almost completely flat, 1/8" thick pvc plastic, covers entire under engine, from edge where front bumper terminates under radiator to that aluminum cross piece that passes just behind the oil pan/in front of engine torque mount.

Drove the car a couple times, the last time a good cruise that I do all the time. I got 6 mpg better than I usually do on my best runs (78 vs. 72). Driving faster yet at high mpg seemed noticeably easier, like I could drive maybe 3-5 mph faster than I usually do over some long stretches, yet getting the same or better readings on the FCD. Much of the time it's a bit tricky to keep the FCD in the 50-75mpg range; this time it was easy, and holding 100 mpg wasn't very difficult, either. I was getting similar results over the whole route, facing various directions, so I don't think wind was a factor here...

On the other hand, it was bit warmer today than over the past few months, maybe 5 degrees. And I'm running premium fuel unlike usual. So these two things might complicate things. I've also been sorta keeping an eye on how the knock sensor behaves on premium fuel vs. regular; interestingly, it seems to be less active on premium, but it took a few trips to actually see that change...

Anyway, just wondering if others have experience, observations, about running with and without the under engine aero panel. Frankly, I'd never think the panel could do that much, but after my drive today I'm starting to wonder...
 

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Discussion Starter #3
Interesting, so that's what they look like. I never really took a close look at the OEM, though I knew it was more than one piece. It would have been nice to have your template. I should have made one first, if not from the OEM panel, then simply by trial and error, fitting in place. I did the trial and error, fitting in place with the plastic sheet I bought. I kind of screwed up in a couple places, nothing big though... I'll take a couple pics tomorrow or something.

BTW, one can make the panel fairly easily, with little cutting, if you start with a 38" X 26" sheet. Those are the major dimensions and all that's needed is a little trimming around corners and such. I bought a sheet that was 40" X 30" and just ended up cutting it to 38" X 26" (it was priced by size, per square foot, cut to size, TAP Plastics). My sheet cost $20... Oh, one thing though: that 38 x 26 doesn't include a lip that fits over the front bumper under hang; including one would have been a bit better. You can see in Blue-Civic-Hybrid's pic how the front edge of the panel has a lip across the front, long tabs that would overlap the front bumper under hang; mine doesn't. So add about 1/2" to that 26" dimension...

Also, I went with PVC, but after working with it and getting the panel fitted and installed, I might have been better off with ABS. The ABS is denser, heavier, yet a bit more rigid, stronger. I thought the PVC would work better because it felt more flexible, more like the existing pieces. But it's perhaps a bit weak. 1/8" ABS might work better, though the PVC might be easier to work with...

Anyway, I'm still interested in hearing whether others have experience, observations about mpg with and without under engine panel...
 

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Discussion Starter #4
Here's a few pics. Not the greatest quality. You can see how the right side of the panel is a little different than the left. The left should be like the right. I made an extra cut in the left that wasn't necessary...






 

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That looks great, I know Jeff did something similar and he was hitting the 90 MPGs in his car. I just changed my EGR valve on my car and now it is so easy to get and hold lean burn, before I was only getting 60-63 MPG for a tank. Now I'm at 455 miles on this tank and easily getting 76 mpg with almost all of it being city driving. The few times I drove on the HWY at 60 MPH it was very easy to hold lean burn at 100 MPG. A good EGR valve makes a huge difference in getting good MPG, now maybe I'll try the panel mod and see what kind of change that makes.
 

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Discussion Starter #6
It's definitely worth the bit of effort, the aero panel is. Like $20 and change for hardware... 1/2 the reason I did it was to keep the engine clean, plus maybe it will stay a bit warmer. The rest is gravy.

I'm usually pretty skeptical when it comes to making changes like this and claims of improvements. But I'm pretty certain it's making a noticeable difference, I mean, just by feel. Once I get up above 40 mph I think I'm maintaining higher speeds more easily, with less throttle... The 6 mpg I noted above is a bit of 'proof', so perhaps it's not totally my butt dyno and placebo...

I'll just have to drive a while with it, over several tanks, and see if there's some mpg numbers to bank on. If one were doing mostly highway driving I'd say the panel is a must-do mod. With half and half driving, I'd venture to say, at this early stage, that a 2-3 mpg improvement isn't unlikely...
 

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Wow! Really, really nice to see this stuff! Without these posts I might not ever have found the older posts to see what the bottom of mine should look like!
The underbody pieces on my '04 are missing, mangled, or recently removed by me 'cause they were just scooping up snow & air. I was just under the front bumper with zip ties trying to hold up the pieces hanging down and make things a bit more aero until it warms up some more here.
The previous owner parked the car on city streets that aren't plowed often. The snow gets all icy and jagged - really tears those rather delicate underbody pieces to shreds over the years.
By next winter I'll be ready! I want the whole engine bay buttoned up pretty well. I'm looking for the cheapest bra/mask I can find right now to help hold some exterior grill blocks in place. (My bumper came to me a bit damaged so I'm happy to cover it up). That and a warm-air intake mod and I'll be ready for whatever Minnesota has coming next winter.
Thanks again for the informative posts & pics!
 

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....Drove the car a couple times, the last time a good cruise that I do all the time. I got 6 mpg better than I usually do on my best runs (78 vs. 72). Driving faster yet at high mpg seemed noticeably easier, like I could drive maybe 3-5 mph faster than I usually do over some long stretches, yet getting the same or better readings on the FCD. Much of the time it's a bit tricky to keep the FCD in the 50-75mpg range; this time it was easy, and holding 100 mpg wasn't very difficult, either. I was getting similar results over the whole route, facing various directions, so I don't think wind was a factor here......
eq1,

Check my signature for information on my Under-Body Panels.

They run the entire length of the car, and took all summer to make, several years ago. There's a similar post with maybe more detail over at EcoModder.

My mileage gain with the entire smooth underside was probably about 5 or so mpg, and it's also much better is snow.

Changing the oil is now 10 times easier than with the stock panels.

Jim.
 

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Know anybody who has spare OEM underbody panels?

I have a 2000 Insight that I bought this summer. It is missing the underbody panels. Do you know of anybody who made their own panels and might want to sell the OEM panels? Thanks.
 

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I have a 2000 Insight that I bought this summer. It is missing the underbody panels. Do you know of anybody who made their own panels and might want to sell the OEM panels? Thanks.
I have some underbody panels. Do you need passenger or drivers side? One more question you just bought an Insight '00 and you've been a member since '03? May be one of the firsts to join IC.NET? :)
 

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Discussion Starter #14 (Edited)
Was browsing the mpg forum and noticed this thread I started about the under engine aero panel, a bit less than a year ago. Changed my oil yesterday so had to take the panel off. Thought I'd update and simply say that the panel is holding up well, basically as good as it was when I installed it... 1/8" PVC.

I mentioned earlier that ABS might've been better, stronger, but regardless, the PVC seems to work fine...

Never really 'checked the numbers' to tell whether I was getting mpg improvements, though. Probably never know for sure... Basically, I think with every little effort, improvement, I make (not that there's many) I just end up driving faster and what-not yet getting the same mpg...

[edit] Here's a quick MPG graph for the last couple years of driving, with my aero panel install noted... Hard to say, but looks like I might've gotten a couple more mpgs out of it. Except for the 3 fill-ups after the aero panel, I started using premium fuel as well. I think the biggest improvement was from installing RE92s rather than 175 Pirelli P4s... Averages based on complete or near-complete fill-ups, my own calculations; white line shows FCD figures for most tanks, tracks pretty closely...
 

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My updated Version (one bolt on the left still missing). The area around the exhaust mainfold/cat is left open because the air that comes in the engine compartment has to go somewhere. If the air can't flow to the underbody it will be pushed to the sides which is not a good thing. In this point I was inspired by an article about front spoiler designs. AutoSpeed - Modifying Under-Car Airflow, Part 1
The paragraph about the Opel Calibra:
In the case of the Calibra, the centre section of the front spoiler was lifted to allow more (yes more!) air to flow under the middle of the car, so making the total flow more parallel with the car’s long axis. This reduced the amount of air being deflected outwards by the front wheels, reducing the size of the wake and so drag.
 

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The material is very easy to work with (2 mm thickness). Unfortunately the car won't be driven the next months. But I'm planning to do something similar to the rear underbody as well.
 

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I used a sheet of clear plastic from the screen of a big projection TV set. It's 3/32" thick. I only had the aluminum panel behind the bumper and the drivers side under engine panel when I bought the car.

The panel I made covers from the front aluminum cross sheet metal back to the normal aluminum cross bar and from the drivers side under engine cover to the right side of the car. I made some cardboard templates to get an idea of what shape the final cover should be.

Using the cardboard template, I laid out the outline on the plastic with a marking pen. By using the clear plastic it was fairly easy to figure out exactly where the mounting screw holes needed to be.

I cut out the shape by using a 1/4" x 20 bolt stuck in a soldering iron as a heated cutting "blade". By placing the bolt so it was vertical with the panel between the head of the bolt and the soldering iron barrel I was able to guide it along and cut the shape out. If you try this make sure you have plenty of ventilation. The fumes from melted plastic can't be good for you.

The plastic will melt and ball up on the rest of the sheet. Once it has cooled off you can use a pair of pliers to carefully chip the melted stuff away. I was able to bend the plastic tab in the front down by using a heat gun to soften the panel where the bend needed to be.

The first cover I made cracked at the rear mounting bolts because the front bumper must flex back and forth when driving at highway speeds. I used the cracked cover as a template for a 2nd one and elongated the rear mounting holes ~1/2" fore and aft so the panel could move. I used two thick vinyl "fender washers" sandwiched between large metal washers with the mounting bolts not clamping the panel very tightly at each rear mounting point. I used long bolts and spacers with a lock nut on top of the aluminum cross piece as the mounting method.

It's been on the car for a year now and still looks fine. Also if you drop a tool or bolt from the top of the engine compartment you can see where it is from under the car. Then use a magnet to slide the bolt around so you can remove it from above. :)

I don't have any before/after mpg comparisons because I put the panel on before I put the car on the road after buying it.
 

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