NHW11 Prius Aeromods. <.29 or Bust

I've been working on these over at ecomodder for a while and thought you all would like to see my progress.

I'm really enjoying this. the Gen 1 is a real looker and takes very well to modding.

This is my to-do list with a good chunk done.

1) Grille block. Done
2) Basjoos headlights and hood. Done
3) Smooth wheel covers. 1/2 Done
4) Front undertray. Done
5) Full undertray.
5) Plexiglas "double rear window".
6) Wheel boattails.
7) A-pillar tape VGs. Done
8) Rear wheel skirts.
9) Front chin air dam. Done
10) "Side Kilts" Done
11) Side trailing edge lips.

 

LOL. Which ones? the Previa's or the Meteor's?

 

Partly the wide angle shot. Partly that some of those crazy body kits are actually based on sound aerodynamics.

Which makes me think of:

Fantastic new video game: Need For Fuel Economy! Whoah. Thrilling! "I just got 1000 points for passing that gas station. Kewl."

 

Were I live I need the ground clearance. I'd put in a height variable pneumatic system If I had tons of cash though.

I do have plans for a full under tray with a diffuser at the back. It's not too bad under there but it could use something from the rear axle to the bumper for sure.

I can't do a mirror delete because it's meant to be my honey's car and she wants them there. I can go to town under the car though and I'm allowed to mod it "as long as it doesn't look weird" So, fair enough, I have some design constraints. Luckily she's into the aero look so rear wheel skirts are OK.

BTW, Domokun rocks!

 

Here is a shot of the car while we were shopping.

I added the wheel deflectors yesterday. They are made from rubber baseboard. I attached them with 3M "automotive acrylic plus attachment tape" 1/2" x .045" And hey, It's NASCAR licenced. Woo hoo. For ultimate ecomod attachment, If ductape is somehow tragically, not available, this is the stuff. It's what is used to attach emblems and plastic body panels. I paid $44 <Ouch!> for 20 yards. You can buy smaller quantities from auto parts stores and body shop/paint suppliers. I got 10 feet of base"board" from the roll ends bin for $5. It's meant to be a consumable.

I calculated the area of the space between the wheels to be about 268 sq. in. and the space under the air dam to be 252 sq. in. I figure that way there is a balance there so less air will be forced to go through the wheel wells. I don't know if it's a sound theory but it's all I have for now. Since the rule of thumb is to have the air dam no lower than the lowest part of the underbody, I'm just including the wheels into that rule. Makes sense to me.

It seems to work. It's certainly not worse. The butt-o-meter is reporting better. Hmmm. Is 10 fans at the end of a carport a wind tunnel?

Speaking of the law... here the minimum ride height is determined by the wheel rim. No part of the car can extend be below the lowest part of the rim with the exception of flexible mud flaps. So I'm good.



Below is a view of the back of the air dam. I plan to close in the underside so it's flush with the hard airdam and run another rubber baseboard on the inside to create a full fairing for the front wheel.



Below is a shot of my coroplast bending technique. Crease the inside then bend inward.

 

It looks pretty radical. By following all the latest aero trends and established theory the little Prius comes out looking like a nascar. People must wonder what I'm doing crawling along at the speed limit?!?!?

I still have to try to figure out the optimum front air dam depth/intake area. It will change when I install the rear "double window" to eliminate the flow separation on the rear window. This should raise the pressure at the rear, reducing the amount being "sucked" under the car. The planned belly pan will also help. It feels rock solid at speed now.

I have a digital vacuum gauge that is accurate to 1/10 psi. I wonder if I can use it to test various mods.

Wind noise is now much stronger at the A-pillars so I think noise is reduced elsewhere.

For the first time I was able to keep 4.1 L/100 all the way from Mission to Bowen. Normally it ends up at around 4.5. Too many variables to be sure though. I have to find a good place for a coast down test and/or a top speed test as you suggest.

 

The only real way short of a trip to a wind tunnel with a big cheque is a coast down test. there is an instructable on it somewhere. From this you can roughly figure your Cd.

I do but since the car is primarily my wife's, they stay. In the following thread by MetroMPG side mirror removal showed a 2.5% improvement.

From:Side mirror drag effect on fuel economy quantified



I should really be testing each mod as I go along but since I don't live near a long flat stretch of highway I have to just stick to proven mods, current trends in aerodynamic cars and my limited understanding of aerodynamics. I'm currently reading The Aerodynamics of Road Vehicles By Hucho.

Apparently the Gen 1 is .29 stock. The Toyota wind tunnel seems to be a little generous but that's all I have to go on at the moment.

 

I don't think that's even a drive in tunnel.

I may have a candidate for roll down testing. I will have to do some baseline runs to see how the resolution/variability is. Going to blow this tank average doing tests though.

 

Just found some tires in a narrower size: 165 70 14 that have a similar rev/mile to the OEM RE91s: Nokian Hakka C van. They have a favourable load rating 89/87S. These will have a reduced profile for lower drag. I'm still looking for info on their RR. Most Nokians are LRR though.

There are two references to tire width and drag in Hucho's book. Both refs show a .01 increase in Cd for every 10mm increase in tire width.