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jamesshaw89 02-15-2012 09:46 PM

2007 Prius aero mod journey
Hi all,

I've been lurking on the forums for a couple years and am just now starting to implement some mods on my Prius. I google'd "signs" and called around until I found 4x8 1/4" coroplast in black for $20 a sheet so I picked up 2 sheets this afternoon.

Mod #1 turned from a grill block into a front air dam. I cut and taped some cardboard into the front bumper and guesstimated an 11" piece would be a good start so I cut (2) 11" pieces with the ribs running from top to bottom so it would bend around the front bumper. I unbolted the license plate and used windex to make sure the bumper was clean for the black duct tape to stick to it. I tried to use a heat gun to get the coroplast hot enough to smoothly bend but it still buckled at the sharp part of the bumper curve. I put the 2 small triangle pieces in the center of the air dam to keep it from bending until I can make a more substantial support later this week.

Other than with the Scan Gauge and driving the same route using cruise control I don't have any good testing methods yet but...

Car was able to reach mid 180's coolant temp @ 55mph where it normally only makes it to 170's and sometimes only 160's.

Trip to school is usually 58mpg and today I got 68 but the temp was 56 vs 30's normally so the extra 20 degrees ambient could have done most of that. my best ever on that trip is 78mpg using no heat and no lights @70 degrees, today I had the heater on 2 and my driving lights still set on 55.

Trip home is almost always 54mpg lights and heat on same as tonight cruise set at 55...pulled in the driveway at 58mpg and it was misting rain the whole trip home.

Net gain? with it being warmer today I have no idea.

Wheel skirts(front and rear), belly pan and possibly a boat tail are the mods I'm shooting to get done and tested in the next 8-9 days. I'm going to be making an 1,000 mile round trip next weekend so I'm hoping to really get a good trip average.

So far my normal long highway trip average is right at 52mpg with cruise set at 58mph in 55mph and 68mph in 65mph zones.

OK more tomorrow after I make the rear wheel skirts.

sendler 02-15-2012 09:58 PM

I'll be interested to see if the air dam helps or hurts you. Clean air passing under a car is not a bad thing depending on how well it exits the rear.

basjoos 02-16-2012 08:22 AM


Originally Posted by sendler (Post 287182)
I'll be interested to see if the air dam helps or hurts you. Clean air passing under a car is not a bad thing depending on how well it exits the rear.

To keep a clean airflow passing under the car so you don't need to use an airdam, you'll need to meet several criteria. You need to have a low stagnation point on the nose to divert most of the air over and to the sides of the car so the air passing under the car isn't being compressed between the car and road and exiting to the sides of the car between the wheels. This compression and air exiting to the sides creates drag and unsafe amounts of lift at higher speeds. Also need totally smooth underpanels and you need to exhaust the radiator air someplace other than underneath the car. On the Aerocivic, the radiator air is exhausted into the front wheel wells and into the right rear wheel well. Then the front air splitter/front wheel skirt/double side skirt/rear wheel skirt/rear mini-boattail creates a "pontoon" around the wheels on each side that channels the air passing under the car, keeping it smoothly flowing straight back and exiting the car under the boattail.

jamesshaw89 02-16-2012 01:58 PM

Foam floor mat for side skirt troughs between the wheels like aerocivics? I've been looking for a suitable material and I think this will work really good?

Picked up a pizza pan from Walmart for $3.50 but it seems really heavy compared to the aluminum ones I found at Gordon Food Services who have aluminum ones for $5.50.

Also picked up 4 packs of small stainless round head wood screws to attach the pizza pans to the trim rings $1.18 a pack of 5 screws

I'm going by the recycling place tomorrow to see if I can find some aluminum angle pieces before I pay $5-6 for them at lowes

Also thanks to this forum I discovered coasting in neutral today and it works wayyyyyyyyy better than trying to feather the gas pedal. I'll be checking this out more for sure.

jamesshaw89 02-17-2012 08:35 AM

Thanks for the heads up on the front air dam guys. I'm going to revise it to stop level with the belly of the car as well as be parallel with the ground. Using an 11" piece when curved and angled bows up in the middle. After I get that sorted out I want to figure out some kind of air splitter for the front tires and boat tail for the rear tires.

I cut the coroplast to make the side skirts last night I just need to go by lowes and get 1x6 pine board to put between the wheels to attach it to. The 4 inch wide board seemed too narrow as the tread part of the tire is about 6"

I can't believe how good this thing coasts in neutral and so far 3 out of 4 times the motor doesn't start up at 41 mph like it does if your in drive and feathering the gas.

Is there a way other than neutral to have the motor not start up at 41 mph?

I need to look up coast down testing today and use my garmin 305 gps watch I use for running to gather the distance and timing data.

Cd 02-17-2012 09:00 AM

So what do you have planned at the rear of the car ?

As you know, most of a cars drag exists at the rear of the vehicle.

The area around your mirrors has a good amount amount of drag. If not replaced with cameras, replacing the mirrors with something smaller than stock might help.

Smooth wheel covers can also be made and fastened right to the trim ring on the stock wheels. If you dont like the look, you could even use clear plastic sheeting.

By the looks of it, Toyota did a pretty good job of keeping the wheels flush with the body. If you attached smooth wheel covers, you might get the same results as a full wheel skirt, but without the 'odd' looks.

The wheel gaps are small compared to some cars, but you can still add flexible rubber sheeting around this area to seal the gap even more.

sendler 02-17-2012 09:28 AM


Originally Posted by basjoos (Post 287261)
To keep a clean airflow passing under the car so you don't need to use an airdam, you'll need to meet several criteria.

Aren't Prius already very clean underneath?

Cd 02-17-2012 09:34 AM


Originally Posted by sendler (Post 287516)
Aren't Prius already very clean underneath?

My thought exactly. ;)
The airdam most likely just adds frontal area.

A few panels underneath can still make it even better though, and i agree with Basjoos about the pontoons.

I have to wonder about the added frontal area they ( pontoons ) have in crosswinds though, but thats a thread i'll create all by itself.

jamesshaw89 02-17-2012 10:52 AM

I just read up on the coast down testing and I don't know how feasible that is is going to be to do...

Maybe the ABA testing or round trip route done on the same day might be better? since the temperature change makes such a huge difference in the Prius mileage I'm not sure the best way to test anything?

Is there a good way to test mods on a Prius? Like you guys are pointing out I would hate to have one mod help and another mod hinder but not know which one did what?

Front air dam angle...Keeping the same angle as above the bumper to "throw/push" the air above the car seems like what I would want to do right? having a flat plate from the bumper down seems like it it would be pushing the air instead of cutting through it?

Belly pan...I looked under there a couple weeks ago and there are a lot of plates already under the car but I did see a few places that looked like they could be cleaned up some. There is a big trough where the exhaust goes that should benefit from from aluminum sheet or maybe aluminum screen as I saw someone use.

Boat tail...I have pondered several options which all have to be removable as my wife will be driving this car full time here shortly and she really does care what it looks like when she is driving will however be our long trip car so I can put mods on, take them off for them. So far I've pondered using a plate of blue sheet foam cut to the shape of the back end and using expanding foam to take up the space between the foam and the car's rear bumper/hatch. I was thinking of wrapping the rear of the car with plastic wrap to protect it from the foam and should make the boat tail mounting point a nice molded fit...from there though I am wondering how to figure the angles. The lights and license plate I was thinking of using extension lines to LED's that will work the same as the factory tail lights. I'm not sure how long the thing would be yet either, I would like to take it all the way to a sharp point but how long would that make it?

How do you guys draw your arc for the rear boat tail angle for the top, bottom and sides? do you make like a giant compass with a piece of string to draw the arc or ???

Rear view mirrors...I picked up some small 2"x2" stick on adjustable rear view mirror things from wal mart but they are kind of too small to be useful...I did see another one this week that is probably 4"x4" which I could stick inside the car and remove one/both the rear view mirrors. I tried folding them in but backing into a parking place was about impossible even using the back up camera...

Wheel covers...I couldn't figure any way to put plastic sheet on the wheels? I started putting the pizza pans on last night but my stainless screws were just a little too short so I need to get some more today.

Man I wish I knew a good way to test each of the mods on this car to see if they are helping or hindering...what about coasting down a hill starting from a set speed in neutral and checking for a velocity at different places/the bottom?

Daox 02-17-2012 11:21 AM

Nice job with things so far!

This is a good read:

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