What next?
 

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.

EV switch, totally. Not sure how much it would help, but it would just be super duper cool...

p&g or fas?? are you doing these already? whats your comute like? is it all city or more highway?

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! ;-)

Perfect for the EV button!

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?

Why are you doing a bucnch of aero if you dont break 45mph? the best person to ask how to get a priui to 100mpg would be yosi becuse he has done it it think.

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.

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"?

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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.