Dream Prius (aerodynamic mod exercise for 2nd gen.)

[SVOboy]

You could consider removing the blades and making a smaller shroud for just the arms themselves (assuming prius wipers are like mine).

[MetroMPG]

I'm with basjoos - undertray is also an important target. I know someone with a 2nd gen Prius who recently added a front tray and saw results from it, which he's still confirming by collecting more data.

I went to the local Toyota dealer this week with the specific intention of looking at the car's underbits - I think there's room for improvement in the rear floor area. (Unfortunately, they didn't have any on the lot or in the showroom for me to see.)

Also: I'd highly recommend playing with cardboard or coroplast & duct tape as a way of prototyping what you have in mind.

Lastly, I'd start at the rear rather than the front, for maximum gains first.

[donee]

Hi All,

I am another Prius owner. I am not so sure the hood extensition to cover the front wiper blades will be that effective. When a leaf or other bit of fluff goes up over the hood and windshield of the Prius its on a boundary layer only 1/4 inch thick. The leaf moves along very quickly over hood, There is no discernable slow down as it goes over the gap between the hood and windshield. Its unlike any car I have driven before. A wool tuft test might be in order to confirm this.

Even so, I changed the front blades to the Bosch ICON blades, which have a smaller profile than stock, and even lower than some of the other blade spring type blades. And with the winter we are having that was a good move for other reasons. These blades are sitting below the hood line projected to the windshield.

In other cars, one can use that hood extension to help change the air direction up the much more vertical windshield, well in front of the windshield. With the Prius, that change in angle is quite small. Indeed, one needs to runs with air recirculate off / with fan much more often to pull air from that point for sufficient defrosting.

There is also very little gap between the hood and the plastic bits to slide a piece of plastic under. So, it would probably need to be mounted to the top of the hood.


The other aero mod I have done to my car is adding 10 mil flashing to the stock Prius wheel rings to make a flush hub cap. The wheels are concave, so the flush hub cap was doable. The wheel rings snap into the a groove in the wheels. So far they have held up well in the heavy snow driving.

Oh, and I am running 3/4's grill block using insulation tubing. Which is a common Prius trick.

[MetroMPG]

Hi donee - welcome.

Certainly of all the items on bestmapman's original list, the front wiper delete would have the smallest impact.

Do you happen to have a picture of your trim ring mod? I'd like to see it.

[donee]

Hi Metro,

Here is a link to it over on Prius Chat ... http://priuschat.com/forums/prius-mo...rim-rings.html

Which describes how I made them. Here is a picture:

[Big Dave]

The front wiper delete is not one of the things I'd do. It would be of little benefit and who wants a car that's afraid of the rain.

The rest of it looks doable and should be effective, although a Prius has a pretty low Cd as is.

Easy way to accomplish it.

Loan car to basjoos.
Introduce him to a good custom body man
Add money
Get car away from basjoos after project completion


Actually, almost any car would benefit from this approach. I am somewhat baffled as to why the VW TDI guys don't do stuff like this.

[MetroMPG]

Big Dave: I think the reason they may not is because they figure "we already get good enough mileage." Sort of like being satisfied that "a Prius has a pretty low Cd as is."

I'd love to see a Prius owner in particular do this, and then quantify the results. It would do wonders for raising the profile of aerodynamics in auto design and aeromodding as a DIY option.

Anything that opens people's eyes to the aerodynamic garbage the automakers are producing (in general) is good, in my opinion.

[donee]

Hi All,

Well, the reason I want to improve the Cd of the Prius, besides what I posted on PC, is that Excell, Hobbit et al have found what they call SHM, or Super Highway Mode. With a stock Prius, the car can hold this up to about 50 mph. At these speeds, in SHM, the Prius is getting 60 to 75 mpg demonstrated. With reduction in drag force, maybe SHM can be used at 62 to 64 mph (which is the max engine un-fired, still rotating speed) and is what the dictates of the proletariat on Chicagoland freeways pretty much force as a minimum crusing speed. Besides, I can't Drive 55.

There is a discussion on here about having to switch out one's final drive to gain the fuel economy performance lower drag would imply. Well, the Prius kinda does this automatically with its eCVT. There is a video on Google Video from Usbseawolf that shows this action at highway speed. And its quite noticable in a Prius too, when one drives in humid, not-wet overcast days versus driving in dry, sunny (heavy air) days.

[donee]

Hi Big Dave and MetroMPG,

There is a guy named Ernie Rogers who has modified his TDI Beetle. And claims to gain much improvement at highway speed. And after been in a Beetle recently at 45 mph, I can sure believe what he has done will have some effect. The roar of sheer vorticies to the outside of the car, right about the rear passenger head level is horrendous.

Of course diesels do not have throttles. So, while without gearing changes, there is no pumping loss improvement. The part throttle performance of diesels is very good, however. And when one lifts up on the accellerator, less fuel is injected. When less force is needed to push the car, its an imediate response that less fuel need be injected to keep the engine at the speed.

Reducing the pumping losses is probably why the diesel CVT Partnership for a Next Generation Vehicles (PNGV) were up around 70 to 80 EPA mpg. They could reduce fuel injection quantity, besides the number of times a second that quantity was injected.

[MetroMPG]

Originally Posted by donee

There is a discussion on here about having to switch out one's final drive to gain the fuel economy performance lower drag would imply.

You'll have to excuse the tendency here to talk with the assumed starting point of an otto cycle engine & fixed gear (usually manual) transmission. (I'm happy to see a growing contingent of diesel members, and more than a couple of hybrid owners also considering DIY options.)

But your point about diesels not suffering from the part throttle, light load losses to the same extent as regular fixed gear otto engines makes Big Dave's question that much more relevant. Ernie took a New Beetle from its horrid starting Cd to something closer to "average"; what would be even more interesting would be seeing someone start with an "average" Golf TDI, for example, and make it much better than average.

The fact that the Prius, with its smart transmission, can avoid the BSFC problem fixed gear otto cycle engines encounter from lessening aero loads makes the prospect of aeromodding a Prius that much more interesting.