Finished the underpan on my VX
 

Spent some time today and fitted a front under pan and covered the center of the car with some 2' wide flashing so the exhaust isn't hanging in the stream of air. This is basically the last step in my VX under pan since I did the sides of the car long ago.

I'll get better pics in the daylight but for now:
What I first installed (view from behind the car)
https://www.imagestation.com/picture/...0/e9449405.jpg

Finished (view from under the drivers side front)
https://www.imagestation.com/picture/...3/e7d98892.jpg

No SuperMID to report solid numbers with, but I should see a 1-2 MPG gain since I drive Highway speeds 90%+ of the time as well as the school season starting again. So far I've noticed better coasting at highway speeds (up to 65MPH)

:thumbup: on the nice work.

That front and mid section now looks like the underside of my car. Now all you need to do is to finish covering the area from the gas tank to the back bumper, including that curved section of the exhaust pipe (the only area open on the underside of my car is the underside of the muffler.

Thanks for the props!

I actually ran the flashing all the way to the rear sway bar in the back of the car, lol. I don't think I'll be doing much more to it this year. The muffler fills the void on the passengers' side and I have the stock VX diffuser in the drivers rear.

The CX didn't have a stock diffuser, just the exposed gas tank, underside of the spare tire well, and back bumper, so I also covered that area of the car with coroplast.

This would be perfect for a how to do write up.

Yeah, it could be good for a how-to... if it weren't for me not taking any pics during the construction, lol.

Basically, it went like this:

Parts -
4'x8' Sheet of Coroplast (from a sign shop, $12)
2'x4' Sheet of Coroplast (free campaign sign)
20"x10' roll of aluminum roof flashing (from Home Depot, $9)
100 small self drilling screws (from hardware store, $4)
100 small washers with rubber lining (from hardware store, $7)
~10ft. of aluminum foil tape (From Home Depot, bought a 50ft. roll, $12)

How I did it:
I split the 4'x8' sheet lengthwise to get two 2'x8' sheets.
Then I removed the factory side skirt plastic retainers and slid the coroplast between the side skirt and the unibody.
Re-installed the plastic retainers securing the coroplast on one side.
Then used the self drilling screws and washers to secure the inner side of the coroplast to the unibody near the exhaust.
Trimmed the length of the two strips near the back of the car.
I then took the 2'x4' piece and screwed and trimmed it to fit the contour of the front underside of the car and to clear the suspension bits.
I cut a slot out of the front piece to clear the exhaust bits.
Then I screwed in the leading edge of the flashing to the front of the underside of the car covering the slot I made in the colorplast.
I secured the opposite end temporarily so I could put in some screws along the length of the flashing.
I covered up the edges of the flashing as well as the edges of the coroplast with the foil tape.
VIOLA! Underpan!

Good stuff. Thanks for sharing.

No problem, Bill. That is what we're all here for, to share and learn.




Jeez, I sound like an afterschool special, lol.

Nice stainless steel exaust !
I'd love to hear some more on your results with the front piece under the engine and transmission.
I just scored some ( 1/16" ? ) aluminum sheetmetal that was being thrown out as garbage. I plan to cover the underside just as you have.

One of my main concerns is that the sheetmetal will rattle and make all sorts of noise. I made and installed an aluminum belly pan just under the engine and transmission on my car. The thong worked fine when driven along, but rattled and buzzed at idle.
I made the first one out of thin flashing akluminum riveted to aluminum cross bracing, so I'm hoping that this thicker stuff I have n0ow will work better.

If you have time, I 'd love to see some more images of your work.

Boy I sure wish I could start paying attention to mods for my car. Well, if when I get the basics taken care of (like getting the car past inspection) I'll know where to go to start work on the underbelly pan and other aero mods.

Nice work TomO!

One advantage of having the underpan is your engine stays a lot cleaner and there's less road noise. Much of the "road noise" is actually wind noise generated under the car.

basjoos - I have noticed that road noise is diminished. Hasn't been long enough to notice if the engine bay stays cleaner, but I'd have to agree that it would since the dirt really has no place to get into the engine bay now except through the radiator opening.

1993CivicVX - The time for your mods shall come soon enough, lol, and thanks.

Nerds Laugh At Me - It's a mild steel exhaust system that I coated with High Temp aluminum content paint, so basically it's a crude form of aluminized steel. I do have a slight rattle where the flashing contacts the exhaust near the 90 bend. I am going to stuff a chunk of fiberglass in between the tube and flashing to stop it. It only rattles at startup and once in a great while at idle. I'm also thinking that I have a great template now to make an all aluminum underpan. but that isn't going to happen unless I come across a 6'x'10 sheet in the garbage, lol.

Nice work Tom. Looks clean.

Hope it helps more than mine did! I suspect it will, because your ride height is significantly lower than the Flea's.

why not just use all aluminum sheets? isn't aluminum lighter than coroplast?

any prius owners did a underbody? if so post pics too!

Thanks!
How much of an increase did yours make again?

I'm only expecting about a 2% maximum increase from mine.

Cost was a big factor in using the Coroplast vs. Aluminum sheet. And to have an aluminum sheet the same thickness of the Coroplast I used, would have been twice the weight and 10 times the cost.

2% in A-B testing, 3 bi-directional runs for each of A&B. :) Speed was 90 km/h I think.

All else being equal (which it's probably not) I still think you'll see better gains because of the lower ride height/higher flow velocity underneath your car.

I still wish I would win a SuperMID!

I still only do tank to tank averages so it'll still be a week to week-and-a-half before I can start to see results of my under pan. I installed it with 100 miles on the tank already too, lol.

Hopefully I can get a 3% increase as the front of my car is also lowered 1.25 inches more than stock. Time will tell.

Awesome writeup.

I just went from a 92 CX to a 95 DX (hatch) that is setup more as a trackday car. It's my beater, since I have a 99 Si for auto-x/trackdays.

Anyway, I just lost about 10mpg in the changeover. I've been a bit of a hypermiler in that I was able to wring a best of 49.x mpg out of my CX (1.5" drop, skinny tires, VX diffuser, Akimoto cone filter).

The new one has a d16z6 swap, DC 4/2/1 header, stainless 2.25" b-pipe, stock axleback exhaust and Ground Control/Koni yellow suspension.

I just added a VX diffuser to the rear end.

I was surprised to see how much of an effect lowering the front end has. At the moment, the front is higher than the rear (former ownder had it jacked up for winter use) Since my suspension is adjustable, I'm going to drop the front an inch for a total of a 1.5" drop.

My question (after all this) is that I have a nice urethane lower lip for the front spoiler that I haven't installed (don't know if I want to attract more attention to the car). Do they actually do something to improve aero (in terms of efficiency) or does it add drag??

Great forum. Looks like I have a lot to learn...

thanks :D

The VX in stock form has the Front Urethane lip. If it's the stock lip then yes, go for it. But lowering the car dos more than just having the lip. If it's an aftermarket lip, what kind is it as some of those lips will add more downforce and drag than the OEM VX lip will.

It's aftermarket.

Here's a crappy cameraphone pic I just took:

https://img406.imageshack.us/img406/2...rontlipub0.jpg

Close to stock, but I can see where it "scoops" air and creates downforce.

With that lip, you could use it if you don't have an OEM one handy. I'd personally block those holes on the sides as it's just letting air hit the front of the tires wich isn't as efficient as it could be.

For all you guys that did the bellypan with self-tapping screws:

How did you take care of, or is there, intrusion into the passenger compartment? I have enough choroplast to do the pan, I also now have a secondary ride so I'll be able to put her out of commision long enough to do the pan (spacing it out over a couple days).

Thanks for any input you can provide.

I think if you go down the center of the car you should be fine as well as intrustion goes. There is also the pinchy space on the sides that doesn't go directly to the cabin. *shrug*

There are reinforcements that run parallel to the exhaust tunnel that I screwed into for attachment points. The screws were no longer than 3/8" and the reinforcement was about 1/2" so there was no intrusion into the passenger cabin. Along the outside edges I used the existing holes from the side skirt attachments to sandwich and secure the coroplast.

Thanks for the quick replies!

I feel much better about doing this mod now - I've got 318k on this chassis (not as much as basjoos, but I might catch up! Well, eventually. :p ) and would like to keep it going.

I just made sure that they intruded in areas that were out of harms way - like under the seats . Also, I took full advantage of the frame and just drilled right into that.
( I hope I did not weaken it in any way . That would have been really dumb.)