Suzi has been a great car. Small cross sectional area, lower Cd than the hatch (.32 vs .34), taller gearing, and a "larger" 4 cylinder engine (1.3 L). Suzi does great and has consistently returned me 50 mpg in the summer if I try. I have done some aerodynamic modifications to her, so I did a coast down test to see if the work had helped.
LIST OF MODIFICATIONS
AeroSpike drivers side mirror
I don't think this helps at all, but boy does it get the questions going! It is actually really solid, and from the calculations I have done (on paper) it is about as effective as what I had originally. This one may get remade eventually, but people seem to like it just like it is.
Folded passengers side mirror
1/2 grill block (leaving the radiator side 100% open). Not too pretty, and not 100% smooth, but it works. This is blocking the half of the grill that the AC condenser would be on, but with no AC, it really doesn't matter. The radiator remains 100% open, and the lower block attempts to seal off and direct air flow toward the radiator.
Windshield wiper block
This one also isn't the prettiest. I think the gains from this one are relatively small, but it gets people to ask questions, so I will keep it (or make a better one). Right now it is coroplast and is held up by scrap 2x4 pieces. Since the picture was taken, I have trimmed it to the point where I can lift the driver's side wiper when cleaning the windshield.
Smooth undertray beneath the engine compartment and trunk (none in middle of car). Made out of coroplast (used campaign signs [like everything else]) and sheet metal (old light fixtrues). The sheet metal is used to cover the exhaust.
Front Window Suction Generators
These pieces of coroplast prevent air from trying to enter/exit the top of the window. The result is suction being created at the front of the window where there is a natural low pressure area. I think I will make another set that is considerably larger (allowing ~4-6 inches of roll down) and see if I can get the suction increased.
I had done a coast down test once before the aero mods(single coast down in a single direction) and determined my Cd,Crr to be 0.304,0.0147. On my trip to Wisconsin (where I got 48.4mpg@61.7mph) I did another coast down, again single coast down in a single direction. This time the Cd,Crr come out to be 0.265,0.160. Between the two tests I went from bald tires to new tires, which may explain the small discrepency on that number. I know the results are not rock solid, but even if it's close, the mods are a HUGE improvement. It puts Suzi in the sub 0.28 category! It puts me close to the Cd of my wife's "new" Prius II (Cd 0.26)! The biggest difference I noticed when adding the bellypan/wiper block/grill block was the difference in cabin noise at 70 mph. My wife and I could hold a conversation! I have been thinking for quite some time about building a partial kamm back (which I saw someone on here do and call it the "uglyback", but before I do, maybe some real coast down tests would nail down what I have now, and the uglyback effectiveness could be quantified with more certainty.