Prius aero mods (undertrays, grille block, mirror delete...)

[krousdb]

Note: see also Autospeed article: adding a chin undertray to a 1st gen Prius


This is the 1st gen Prius tray.


I did this about a month ago....


Compare to the Prius undertray in this article: Autospeed article: adding a chin undertray to a 1st gen Prius

At least we are on the same page.

Yesterday I kicked it up a notch.....


Prius Rear Undertray Rear View. The drivers side does come with a tray (diffuser) but the passenger side is open due to the complication of the muffler and exhaust. I used a screw thru the coroplast about 1" long that rests on the muffler to keep a gap between the coroplast and the muffler. From the rear, the white coroplast was quite visible. The green paint was all I had. I also ran out of coroplast. Once I get more I will do something less piecemeal and paint it black. I have yet to go for a drive. Hopefully nothing falls off.

[MetroMPG]

That front undertray looks smooth! Nice work.

Where does the forward edge of the rear tray attach? What's the leading edge position relative to the control arm?

[MetroMPG]

PS - why is your grille not (partially) blocked? Inverter cooling concerns?

[krousdb]

Originally Posted by MetroMPG

That front undertray looks smooth! Nice work.

Where does the forward edge of the rear tray attach? What's the leading edge position relative to the control arm?

I want to call it the rear axle, but that is not a good name for it. The horizontal member between the two rear wheels is heavy gauge steel formed into a "V" cross section the point of the V is facing forward, one leg horizontal and the other sweeping down at a 45 degree angle. This forces any airflow down underneath. Within the V is a torsion bar. The leading edge of the coroplast conveniently rests in the V just under the torsion bar. I used wire ties in three places around the V shaped member. Did that answer your question?

[krousdb]

Originally Posted by MetroMPG

PS - why is your grille not (partially) blocked? Inverter cooling concerns?

Well first of all it's warm down here so keeping the engine warm is not a concern. Last year I did tape up both grilles and monitored the coolant temp. Normally it stabilizes at 185F. With the bottom grill blocked, the coolant temp did not change. With both blocked, the temp would cycle between 205 and 195 because of the fan kicking in. So one or the other is fine, but both is not good.

From an aerodynamic perspective, grille blocking is worth looking into. In fact, I will be heading up north next weekend to do some "research".
I also have one more aero mod in mind. Hopefully in a few weeks I will have something to show.

[MetroMPG]

Thanks, yes I can picture the rear undertray setup.

I wish the Prius had caught on more up here than it did, so I could find one to look at more closely.

The Camry hybrid has been outselling the Prius in Canada - I know 3 people who own them.

[Daox]

Looks good. I like the rear underbody panel very much. Let us know how it works!

[krousdb]

Well first of all, nothing has fallen off or melted, so that is good news. As far as effect on FE, it's hard to say for sure. Comparing today's drive to work with one a week ago which had the same temp and wind direction and speed, I noticed a 2 mpg gain after adding the rear pan and removing the passenger side mirror. But I can't be sure that the gain can be attributed to those changes because 10 days ago I had new tires installed which tanked my FE by 6 mpg. It could be the new tires breaking in.

[krousdb]

Update:
I met with Frank with Hybrideffects.com last Saturday. We used my car to make a mold of a lower grille block. Frank will be making me a fiberglass panel that will fit over the lower opening and hopefully I will have it installed soon. I will post pictures when I get them.

The grille block will have no openings to begin with. If I need more than the upper grille for cooling, then I will use a hole saw to cut a few openings. I will use a rubber plug to close them when I don't need the extra airflow.

I was able to get a 4x8 sheet of black coroplast. It is getting quite pricey now. The first time I bought coroplast, I paid $15. Now it is up to $30. I guess we can blame the ecomodding craze for that.

This weekend I hope to do a complete underbody pan. I also plan on working on a RH mirror delete cover panel and a windshield wiper shield.

A few weeks ago I installed new tires, ContiPremierContact in the OEM 185/65/15 size. These were highly rated by CR for low rolling resistance but they have fallen far short of my expectations. At first, my FE dropped by 10%. After 2000 miles, I still see a 5% reduction. When I put the Integrity's back on, the FE goes back up to the previous levels. When I finally do some tests to determine the effectiveness of all of these mods, I am hoping that the Conti's break in fully and get me back to where the Integrity's were. What would be really great is if I can find someone local with a Prius who could do a few highway runs so that we could do some comparisons. PM me you are willing to participate.

[bestmapman]

Hi,

Is the panel going to be flush with the bumper or inset at the grill? Also, what are you going to make the under pan out of?