Ryland is right. It is the principle of it. My friend said that it could not be done. And I am the kind of person that if you tell me that I can not do something I will go to the end of the world trying to do it. I will order a EV switch this morning. I am also going to try a block heater.
Does anyone think that blocking off the upper grill hurt anything? Temp around here is down to about 80 to 90 degrees.
The reason for the areo mods is because it is the easiest and it seems to be helping.

Hi Billy, I bet you can't convince the world to get along and to take better care of the planet and each other. :)

The channel between the side skirts keeps the air turbulence coming off the back of the front wheel confined to that channel so it doesn't interfere with the smooth air flow going under the car between the left and right wheels.

On the wheel spoilers, I don't understand your description "bring them down and turning them inward to make less flat area".

As far as boatttail proportions, if you go to my photowebsite( https://smg.photobucket.com/albums/v4...Honda%20Civic/ ) you will find line drawings of the Questair Venture. Take the shape of its tailcone and paste them onto the back of a photo of a Prius, then work out your boattail dimensions based on the known demensions of the Prius. The only change you might make from the Venture tailcone shape would be to slightly reduce the curve of the underside of the tailcone to account for ground effect.

I'll bet skinny tires would be far simpler and a more effective first step to lower the Cdx compared to skirts. With skinny tires on already, I'd doubt if adding skirts would help much at all - and they's suck in the winter or if they sped up the rust process in northerm climes. Who would chip in $20 for wind tunnel tests? ;-)

I would think that the rolling resistance of narrower tires of the same overall height would make the overall drag that much better if I could use my experience as a heavy long distance road cyclist who really values rolling efficiency - just not at the expense of flats.

If I had a Prius that would be a modification that I'd do, but I might wear out the originals first unless for some reason I wanted super high mileage numbers right off the bat. With the mileage that even a poorly driven Prius driver gets, there isn't much gas to be saved but the driving technique has to get extremely complicated so I'm not sure how much I'd do rather than smart coasting as much for the brakes, and not driving too fast. I frequently have other people in with my and being focused on the nth mpg doesn't make for very good company unless you both share the passion. My SWMBO doesn't care, but will drive the most efficient vehicle. She wants the vehicle to do the energy management, not her. Still, she really appreciative when I put skinnier better rolling tires on her mountain bike. She was way faster.

what size rims does the prius have? if they are 14" then the tires from a honda insite would fit, and give you a 5% increase at least, they are 165/65-14" I'm pretty sure.

[QUOTE=basjoos;70480]The channel between the side skirts keeps the air turbulence coming off the back of the front wheel confined to that channel so it doesn't interfere with the smooth air flow going under the car between the left and right wheels. QUOTE]

To further expound, the rounded nose on my car gives me mostly laminar air flow under the car, so the paired side skirts serve to confine the front wheel turbulence to the channel between the skirts. The dust trail left behind me when driving on a gravel road reduced considerably after I installed the side skirts.

Of course, with a front air dam, you're creating a large pocket of turbulent air behind the dam that covers most of the underside of the car. You'd need to delete the dam and install a smooth underbelly to get the laminar flow.

Are you talking Prius-specific info about adding skirts? Can you point me to what you have read?

What is (quantify) "very, very little"?

fuel economy forum
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Old MPG wisdom
 

In the old days, I read a story about a guy who claimed he got 75 MPG out of a Triumph sports car by
1. coasting between full power runs up to 40-50 MPH or so, and
2. "mohawked" his tyres by cutting away all but the middle inch of tread
(and inflating them like crazy.

That's crazy, but sounds plausible. P&G can add quite a bit and I bet he had very little rolling resistance with the mohawked scheme, though I wonder how long each tire lasted.

I hate driving in traffic, it's too hard to go slow during a commute between lights and coast down enough to be effective and a light at every block is very hard to time.

As was stated, if you're below 45MPH I'd first look at lowering your rolling resistance. I'm not sure about the Prius (with the regen braking and such) but normally if you jack up a car and spin a wheel you want it to keep spinning for quite a while. If it doesn't eliminate the brake drag and maybe consider new wheel bearings.

Next get skinnier or low rolling resistance specific tires, or at least overinflate the ones you have, that should help quite a bit.

Next, I'm not sure how you would drive with the EV switch, but the point is that you get to control when the engine is running and recharging, so you can prevent it coming on at a light only to idle and barely charge the system. I'd assume you'd want to tie it into P&G. That is, cruising down to a light you flick the switch and know that you're not using any gas while coasting or while sitting at the red light. When accelerating away from the light you'll be using the gas engine most efficiently, so turn it on then and let it charge the car then.