O.K. I'm up to 70+ mpg's I have added disc racing hub caps and a front air dam. I was looking under the car tonight only see a little area that can be covered on the body pan. It's too hot to block the grill. So, what can I do to up my mpg's even more? I want to reach 100 mpg's. What effect will a EV switch have? I am still working on the rear wheel skits but, everthing that I have read says that it will not help or help very, very little. So, what is next? I have a case of beer riding on making 100 mpg's.
Lets see, where do I start. You could install a SMOOTH underbody pan, the one under the Prius is extremely corrugated with small (and not so small) gaps and seams everywhere. Like most other cars, the Prius exhausts its radiator air out the bottom of the engine compartment where it adds drag and turbulence under the car. Search back through the threads and find those photos of the underside of a Ferrari that someone posted on this site last year if you want to see what a truly smooth underpan should look like (and it doesn't exhaust its radiator air under the car). I exhaust most of the radiator air in my Civic out through the front wheel wells and the remainder through the tunnel that the exhaust system runs through sandwiched between the original underside of the car and the underbody pan that I installed (where the air flow cools the exhaust pipes and cat). If you install a complete smooth underpan, you won't need a front air dam (I don't have an air dam on my Civic).
A grill block (I run a grill block year around on my Civic in summer temps up to 105 F so far with no overheating problems with my current design). The amount of grill blocking is something that you would have to figure out for your particular vehicle. One possibility is an active grill that opens or closes either manually or under the control of a thermostat on the radiator. That upper grill opening on the Prius is totally is totally unneeded and is purely a concession to the styling department that gets depressed if they can't put some semblance of a traditional grill on the front of the car.
Wheel well covers front and rear. The front covers are more complicated to install since they need to allow for wheel turning. There are been several approaches to this problem covered on this site.
Rear wheel spoilers (the Prius already has them for the front wheels. If you want, you could bring them down a little closer to the ground than Toyota dared to for increased drag reduction (and also increased risk of striking ground objects). Toyota had to be very conservative in the height of their wheel spoilers for obvious reasons, but you don't have to be.
Side skirts - I have 2 on each side that run from the back of the front wheels to the front of the rear wheel spoiler. The inner side skirt is even with the inside tire edge, the outer side skirt is even with the outer tire edge.
And the biggie, a boattail. You could mount the boattail on the back of your hatch so it would flip up with the hatch when you opened the hatch like the front door on a Lockheed C-5 cargo plane. It looks like it would be fairly easy to install a boattail on the Prius since the rear slope of its roofline has already eliminated a lot of the total car's height by the time you reach the back of the car where the bottail would attach. Look at the tailcone of a Questair Venture kitplane to get the right shape for the boattail.
Gap sealing - go over the car carefully with clear caulk to fill in and smooth out the various gaps and seams in the bodywork of the car to get rid of all of the little imperfections that create turbulence as the air passes over and around your car.
Interior rear view mirrors or small video cameras to replace the large, drag producing external rear view mirrors. This also quiets the interior since the external rear view mirrors make a lot of wind noise.
Replace (or install over) the flat front windshield with a custom curved one to eliminate those sharp corners on the "A" pillars that create the drag inducing "A" pillar vortex. Look at the front windshields of aircraft such as the Cirrus to get an idea of the amount of curving required.
My commute is all city. Nothing over 45mph. I will start working on the under pan. Now let me understand the side skirts. You have 2 side skits on each side? So, your have a channel between the two. How does having 2 help? I was working on the wheel spoilers tonight. I was thinking about bring them down and turning them inward to make less flat area. How far out should them boattail be? Should I also bring something up from the bottom as well?
Wow! How much does beer cost there? It could cost you thousands of dollars and hours and hours of time getting the mileage up, imagine if you started doing powerpack mods!!! Yikes... anyway, and so we have all this time and money going into this lofty quest just for a case a beer? Hrmmm? Sounds more like you're a hypermiler looking for an excuse to go 100 mpg! ;-)
Could you get 155/75R16s anywhere? That would be a perfect tire height match. There isn't much room for rear or front skirts. Narrower tires might help, especially with slightly more offset wheels to bring the wheels in the full 3cm / 1"¼.
Maybe you should pester Michelin for something like this from the various Prius forums and clubs. HCH owners and the others too...
The key thing would be super HRR - maybe a smaller company like Hankook might want to recognize other forms of highly competitive performance tires and get their name out there?
I would think that at 45mph with a city commute you should be able to improve your mileage just by paying close attention to your mpg read out.
I would add wheel skirts, if you pay attention to a vehicle while it's driving in the rain, the wheel wells have large clouds of air/rain being pushed out from the vehicle and this has a simaler affect as if the vehicle was that much larger, and that is part of why wheel skrits are so affective.
I would also check in to doing something like a plug in toping off of the vehicle starting battery so that the engine isn't putting any work in to keeping it charged, and if you have the time/money, look in to adding a solar or plug in charger for the hybrid battery pack as well.
I think this sounds like a great way to get a case of beer, it's the principle of it, and if person you have the bet with looses, the fact that a 100mpg vehicle is possible will stick with them.