i love reading these posts. they inspire me to continue chipping away at my car's aero issues.
i pulled a hubcap off the car tonight and brought it inside to mull over how best to streamline it (cover it fully or just cover the holes). and i worked on my permanent set of side skirts this afternoon as well.
what's up with photobucket? how come your pics disappeared?
The aero mods resulted in no noticable change at low speeds (below 35mph), but significant changes above 60mph. The increase in drag that I normally start to notice as I get above 65mph is greatly reduced and when I let out the clutch and coast, the speed takes much longer to come down than it used to. The decrease in drag has given me the effect of a horsepower boost at highway speeds and I can now pull hills in 5th at 65mph that I used to have to shift down to 4th to maintain speed on. Wind noise is greatly reduced and road noise is somewhat reduced. All in all, it was a great return on about $50 in parts and most of a day's worth of work on the car. It resulted in an mpg boost at interstate speeds from 44mpg to 62mpg and the mpg's for local driving went from the 54mpg typical for this time of year up into the upper 60's (hopefully into the 70's with some more tweaking and warmer weather). If the car companies were serious about improving mileage, you think they could do this treatment to the new cars they sell.
I just can't wait to start my own undertray. This seems like almost an obvious thing to do to vehicles. The general public just doesn't realize that it can hurt economy of a vehicle. Maybe it is because they can't see it normally.
How many mounting points did you have on the undertray?
__________________ Current Stable
GasSaver: 2000 Honda Insight Silverstone w/AC 65+mpg
Track Terror: 2002 Honda S2000 Gran Prix White- lots of mods - 28mpg
Beater: 1988 Honda Civic DX Hatback - Stripped - 30mpg
RIP: 1996 Honda Civic LX 42mpg - you will be missed
On the Civic hatch, the exhaust runs down the center tunnel and then cuts over to the right side of the car by the rear wheel. I ran Coroplast down the left side from under the front bumper to the rear of the car, spanning from the the plastic curb at the side of the vehicle (where the lift points are) to the frame at the edge of the center tunnel. On the right side, the Coroplast ran from under the front bumper to just ahead of where the exhaust pipe curves to the right side of the vehicle. Then I spanned the tunnel with roof flashing. I drilled and tapped for 8-32 screws (used screw and fender washer) about every 14" or wherever I could find a suitable attachment point if the frame wasn't available over the the entire span. I ran white duct tape over the seams and screw heads and ran metal foil tape over the seams by the roof flashing. The hardest part was bridging the area under the gas tank, since I obviously couldn't drill into any of the metal there and the exhaust ran through the linkages of the right rear wheel which limited where I could use Coroplast over there. In the engine compartment there is a fairly large opening on either side opening into the front wheel well where the drive shafts attach to the front wheels, so I used these for the radiator air exhausts. Since I took these pics, I've had to open up the grill block some more, so I now have a single center 4" x 4" opening and the smaller opening on the right side. The taped-over opening is for the AC radiator and I'll open it if I need it when it gets hot enough to require use of the AC. Once I determine how much radiator opening I need, I'll replace this grill block with one that I can manually adjust the openings of from inside the car. Look at Krousdb's undertray installation on the Del Sol Aerodynamics thread for additional pointers as I used his installation as a referance when installing my own underbody panels.
(2) 4'x8' sheets of 4mm thick corrugated plastic (Coroplast)
(1) 20"x 10' roll of aluminum roof flashing
(1) box of 8-32x 3/4" panhead screws
(1) box 3/4" fender washers
(1) roll of white duct tape
(1) roll of heat resistant foil tape
(4) 14' pizza pans (for flat hub caps)
(2) tubes of caulk
Enough jack stands or blocks to suspend your car high enough to work under with all 4 wheels removed (be careful!).
Drill and tap for 8-32 threads
Box cutter for cutting Coroplast
Tin snips for cutting flashing