OK Lots of ideas. First some of these ideas are only useful if you are a good DIY type of guy for some serious hacks.
I am good at the AERO stuff so thats where my ideas will roam with. Skirt everything. Is it UNIBODY or Body On Frame? The following ideas will really only work well with Body on Frame so I will assume its that.
First thing is do you want LOOKS or Performance? I would start by gutting the interior. remove all panels and replace with Lycra Skins. Won't look like crap but won't have the nice lines of molded panels will dump 50-60 pounds easy. Remove carpets add single layer of rino lining. Again not pretty but should drop another 30 pounds Headliner too delete but its REALLY light I would prefer to keep it or your gonna really roast in the summer. Full size Spare? replace with donut. My commute is long I would never go spareless.
Jack? if its a hydro replace with a porsche aluminum jack another 10-15 pounds saved.
Remove ALL seats except the drivers seat. If your good at this and the dimensions permit this get some Minivan captains chairs. you know the Fold and Go removable seats? GET the floor MOUNTS as well. Remove the guts in your car and add those mounts you got from the minivan. NOW you can add fold and go removable seats to your car. Only have the number of seats you NEED in the car stow the rest in the garage. On some cars removing the seats is a LOT of mass!
You can have some SERIOUS fun with the front clip of the car. Remove the bumper. Install some "extensions out the front for support (aluminum) and start gluing on the Blue Foam from Home depot and get that sawzall and sander out. HAVE FUN. Remember you want the shape of the nose of an airliner NOT a jet. Highspeed needs SHARP while "any" speed your will ever see in that car is aerodynamically very slow. At slow speeds the bulbous but smooth front is LOWER drag than a sharp pointy front.
Once you got a nice shape Fiberglass it and your done. Paint to suit. If you wanted to you could also REMOVE the foam from the inside just leaving the fiberglass shell. In fact if you did this carefully you could REUSE that foam in case you ever needed to make another bumper.
Have you tried virtually SEALING the engine compartment? how hot does it get? whats the highest ambient temp where you can keep the engine temps safe?
you want to skin under the engine and seal the front completely. Ever see the skin of the SR-71 Blackbird? longitudinal ridges? add something like that in aluminum to the roof and run your coolant to the roof. Now you have the entire surface area of your roof for air cooling. Add in some peltier cooling and you JUST might be able to keep that engine cool with almost no external air flow. I have NOT tried this yet but you might be able to reverse peltier and use the HEAT of your engine to generate electricity to power the second peltier to cool your coolant. Not sure if that will work would not be efficient but any cooling with the otherwise wasted energy of your engine is bonus.
Delete the door handles and "smooth" the parasite drag points of your windows. Door Frames Windshield Frames. Delete passenger wiper Make driver wiper removable. Don't forget aero shell caps for the stubs.
Delete the antennae and install an internal antennae inside the windshield. Not as effective but your probably listening to MP3's anyway. Don't forget to fiber and fill the antennae mount locations.
Aeroshell both wheels. Banjoss (sp?) came up with an ingenious method to solve the front wheel turning issue that I am definitely going to have fun with!
Boat Tailing the rear is not good enough. REMOVE your hatch all together. Goto the junk yard. Get another hatch. GUT it. make it so its an empty flimsy frame. use the sawzall with gusto here :-) remember this is the junkyard spare nothing to lose!
Add some support struts out the back and have at it with the blue foam again. Cut a rough shape so you reduce how much blue foam you need. Finalize your boat tail shape. Make it aerodynamically seamless with the rest of the car.
Before starting with this I would create an aluminum frame to attack to your "gutted Frame" (in the end your going to get rid of as much of that original frame as you can in fact there is only 3 peices you want left. the 2 hinge mounts and the "lock" point at the bottom. Everything else you want eventually gone.
Mold release the entire thing and fiberglass the crap out of it. IF you can afford it go with a hybrid carbon kevlar weave instead of the fiberglass. Will be much more rigid and lighter by a LOT.
YOU COULD cut out and add a window. Me personally? leave it and add a camera at the rear top of the car. LCD rear view mirror. Same thing with the side view mirrors. Delete replace with cameras to LCD's on the dash.
Windows are important but how bout the rear door windows? do you really need them? if not SKIN them to remove that parasite drag. If you do not even need to see out them you can carbon them and remove the windows all together.
Mold in LED lighting for everything except the headlights. ADD LED lights to the headlight housings. There are times when you do NOT physically need headlights to see with but need them so OTHERS can see you (tunnels constructions when raining even (some states wipers on means HL's must be on) In those cases the LED's will be more than enough to meet the safety and legal requirements without the amp drain of the full head lamps.
Consider downgrading to some older headlamps where they are dimmer. on these the high beams are about as bright as todays NORMAL position lights. So when its unusually bright out your fine and when its really dark you turn on the highbeams. now your no brighter than you were before and can still see just fine. This is probably not worth the effort though so unless its easy drop it.
I have no idea if this is possible but its something I plan to try. Retrofitting something like an AC Compressor pully to the alternator. I am not sure "how" this clutch it engaged or disengaged. if its electrical perfect. Now you can HAVE an alternator but virtually erase its load when not needed by disengaging the clutch and it will stop spinning all together.
Replace all hard fans with electric fans. I have seem some mention electric water pump. Did not know this was possible. DO THAT too. I would consider DUAL pumps with some high tempt valves so you have a backup simply by flipping the valves and flipping a switch. With Y's you might not even need the valves just turn one off and the other on.
SOME engines can "move" water without a pump at all just not very well. in the winter you might even be able to turn it off but not likely if you seal up that engine compartment good enough.
Consider making your accessories "plug in" ie a few extra batteries and "plug in" at home. sure your now using power from the grid to run your accessories but THAT power is a lot cheaper and cleaner than the power your alternator would consume.
Was your car available with all wheel drive? if so consider getting the AWD rear axle and attaching an electric motor forklift style to it. A simple relay full power on off (IE no controller) use this to "assist" the ICE during acceleration to offset some of the otherwise LOW FE you would get during acceleration of hill climbing. If its powerful enough you might even be able to FAS to a stop and not even start up the gas engine until you have reached the limit of your EV motors speed capacity. Even if thats just 20mph thats 0-20mph that you had your ICE OFF !!
If your commute only includes a few full stops this might be doable with a very modest battery pack. I am working on trying to do this with my voyager.
I was also considering an "aerobrake" on the roof of my van. A rather sizable one even. If there is a tail wind I would "extend" this aerobrake and and steel some energy from the wind pushing me. While the gain is TINY over the lifetime of the car it would easily pay for itself as it would be very cheap to build if you can DIY well. Make it out of carbon so its nice and light. One way to do this is a WIND meter on the car. when the AIRSPEED is faster than your actually speed IE the wind is blowing from behind faster than you are driving then the aerobrake will ADD energy to your drive. Once your ground speed is equal to or greater than the tailwind you stow the aerobrake.
Not sure how much the gain would be but it might also be worth deploying as a big rig passes you. IE lets those eddy currents off the rear of the truck PUSH you a little more. The more aero your car the less benefit you will see from drafting.
This is getting a bit complex and is even beyond what I can build but its an idea. I am thinking side skirts that ALMOST touch the ground but that ride on tracks so they can move up and down. Hard linking these skirts to your suspension. So as your suspension compresses the skirts "rise up" an equal amount so they never "hit" the ground when you dip etc.. I have no idea if they can be rigged without a fast enough reaction time to void impacting the ground but assuredly this would let you get them CLOSER to the ground than you than you otherwise could.
Also do the same thing when you "boat tail" the rear ends of your tires into the aeroshell.
Remember always LIGHT WEIGHT. you do not want the added mass of an aeromod to eat up your FE gains with increased mass.
I would LOVE to skin the bottom of a car but am unsure how to deal with the hot exhaust? Suggestions? even if you aluminum skin it would not this now TRAPPED heat pose a significant fire hazzard to the now sealed underside of your car? Might be worth modding the car so its all skinned EXCEPT the tail pipe. Have a pipe bender make you a NEW set of exhaust pipes (if possible with your car ride height) so there are as few if not NO bends in the pipe as possible. IE straight back onces it enters the airstream to the rear of the car. Consider more expensive OVAL tubing so its FLATTER. Also weld an aluminum AEROSHELL to the front and rear of the muffler and cat so they are more aerodynamic.
So imagine remove your exhaust system. SKINNING the bottom of the car and now reinstalling your exhaust system on the outside of this skin. The Skin could be carbon mostly and aluminum anywhere withing 8 inches of the exhaust system.
if you can get the muffler and cat close enough you can merge them aerodynamically.
Here is a quickie drawing I made to describe this
http://www.nerys.com/stuff/aeromod1.gif
The other area of trouble will be the suspension. if your spring over your ok if your Independent A arm its going to be harder. You can either skin ignoring the a arms and AEROSHELL the a arms independently OR make your skin include enough volumetric space to accommodate the full travel of the A Arms. You will want some Drain holes at low points in the skin so you an pop then open now and then to make sure no water is gathering in there. That adds mass and promotes rust :-)
Find some aluminum rims. The fancy spider ones are a good choice since there a lot less metal in then so there lighter. Then skin them with a disc of carbon. Light & Aerodynamic. Steelies are usually heavier than aluminum rims but NOT always.
Go with LRR tires and get the skinniest ones you can safely use on the car. IF your car is torquey and you never see the mountains IE relatively flat terrain consider upping the diameter just a tiny bit. I gained 2+ mpg in my jeep doing this when I added the 31" mudders but they SLAUGHTER me when I go to the mountains :-) (yes I corrected for the equivalent gearing change in the larger tires IE I used the GPS to determine miles driven and adjusted the odometer accordingly. Mines needed almost a 10% change. IE it reports I go 10% less than I actually do. so when I go 10 miles my odo thinks I only went 9 miles.
This is good for steady state driving I am NOT sure how this will work with Hypermiling techniques it might make it worse. I am brand spanking new too hypermiling.
OK car itself. Power Steering? can you change this to manual? how big are you? even just changing the steering wheel (if this is pre airbag) to a 15" wheel may make it totally usable with the PS disabled.
Do they have ELECTRIC brake boosters? Would be nice if you can reduce the pulley belt accessory count to ONE the clutched alternator (not worth removing all together for safety reasons)
Smaller fuel tank? if your MPG is good going from a 20 gallon tank to a 10 gallon tank will make your car over 60 pounds lighter when full not counting the lighter fuel tank.
If you do exhaust work consider upgrading the exhaust system. The upgrades that increase power also usually increase Fuel Economy as well.
Also as someone on the first page said depending on luck and your skill level install a SMALLER engine might reap massive rewards especially if you lighten and aero mod the car enough!
IF your car is Body on Frame REMOVE each body part one at a time and consider making a carbon/fiberglass COPY of it!! Even keeping the parts that bolt and cutting away the parts you see from outside (the skin) to replace with carbon could dramatically reduce mass! this is a LOT of work and a LOT of carbon. but you could do ONE panel at a time. Bit by bit as funds permit.
Its almost 4 am here thats enough for now. I will see if I come up with any more later
Chris Taylor
Levittown PA USA