2007 Prius aero mod journey

[jamesshaw89]

Oh yea forgot to mention the SG was giving me some 9999 MPG numbers on slight down hill runs at 68mph on the trip to Cinci and the flea market! I could feel the transmission go into neutral and the car glide for a few hundred yards up to maybe 1/2 mile? then the gauge would pop back to 40-200+mpg depending on how much the hill flattened out or went back up hill.

Other than that I can't really tell any difference in smoothness so I'm hoping I'll see something at fill up or on the next couple tanks of gas? When I fill up I do like an extra 10-20 clicks on the pump to try and get the air out/fuel bladder to expand fully and I'll get anywhere from 1/4-1 gallon more in the car but it is tedious and a PITA.

[Cd]

Oh cool ! Thanks for doing the tuft test. I've been wondering for years about the A pillar vortex on that particular car.

The tufts that you had look a little long. I used ones no longer than 3" or so and spaced them so they wouldn't tangle on my test.
I suspect having the tufts any longer causes more flutter than there should be and this can be confused with turbulence in that area.

You can clearly see the A pillar vortex on my car compared to yours :

[jamesshaw89]

hmmm yea my strings are probably 6 inches long? I would have put more but I couldn't feel my fingers any more. I had intended on putting them all the around the car and getting film on both sides.

I see the a pillar swirl on yours...I might need more strings to see the swirl on mine...your mirror being folded in might be doing some of that? I would have tried mine but I taped all over the window and didn't want to rip them off rolling down the window.

This tuft testing is fun...now if I can just get something useful out of it LOL...

Since I still have them all taped on I might try to fashion some front wheel skirts tomorrow if I make any progress on the boat tail? you guys already noted several times the boat tail is the big gain so I should probably focus on that in the few days I have left before the big trip.

[Cd]

No need to make anything fancy for the back of the car. Just tape some yarn to the back window, just below the spoiler, the bumper etc. The more tufts, the better ( but not too much ! )
If you feel like it though, there has been some discussion about the angle of the Prius rear glass not being the 'optimal' angle, so it would be interesting if you added a sort of 'spine' down the center of the car that has tufts. Im on vacation in Canada ( eh ! ) at the moment and can't draw you a good image of what i mean, but imagine a piece of cardboard spine that stands up several inches on the rear glass looking something sort of like this :




You could 'sew' the yarn through the cardboard and this would keep the yarn from twisting around at any odd angles that result from the way the yarn is taped to the car.

BTW, This is an example of overkill that most likely creates drag from the tufts themselves skewing the results :

If you feel like seeing the airflow behing the rear of the car farther back than the surface of the car, you can have the 'spine' attach to a flat section of cardboard and sew tufts in it as well. ( Basically a sheet of cardboard attached to the back of the car and oriented vertically. )

[COcyclist]

Originally Posted by jamesshaw89

I took the front air damn off after driving to Cincinnati and back and not seeing much of an improvement followed by a coast down test on a local hill I went from 40-56 on Friday without the damn, skirt or wheel covers! but today I went 40-53 with the dam/skirt/wheel covers and 40-52 without the dam but with the skirt/wheel covers. I was getting pretty annoyed after not going faster but maybe today I had a head wind and Friday I had a tail wind? I had driven the car for 20 minutes to make sure everything was warmed up...

Coast down tests are very difficult to do accurately. Done on different days they are almost worthless. Wind speed, direction, temperature, atmospheric pressure, temperature and humidity can all effect your results. Keep trying, eventually you will see what works.

[Tupelo]

Thanks for sharing your work! I've bookmarked your post with the tuft testing videos for future reference.

Something to keep in mind on the Prius is that the lowest quarter of the radiator is devoted to cooling the inverter. Some air is probably still getting to it since you haven't blocked the top grill, but I don't know if this would be adequate. I don't know what the inverter's cooling requirements are either, but I've read that it's an expensive part to replace if it fails.

[Daox]

I've had my Prius' lower grill blocked off for years and I have a PHEV kit so I operate in EV mode a lot more than the normal Prius. It hasn't been a problem.

[MetroMPG]

Thanks for posting the tuft testing videos.

I was interested in the flow behind the rear wheels. Aero junkies have been wondering for years why Toyota didn't put on OEM rear skirts, as Honda did on the 1st generation Insight.



With your skirts, you clearly had attached (though somewhat turbulent) flow aft of the skirt, on the side of the bumper cover. It would have been interesting to compare to what's goes on back there without a skirt.

[ausias]

To see wind condition on test i use this web page:
History : Weather Underground
And I do test on the same road on both directions.

I think tuft testing without wheel covers, and rear skirts will be very interesting.
I also think the tuft are too long and vibrations is greater than real.
You could get better accuracy going faster (because higher drag resistance contribution to fuel consumption) at cruise speed, Reset SG when you get that speed and write the value when you have to slow, drive in the way returnig to start, reset SG when you get cruise speed and also write the mean values when you slow down. Does 40-56 (¿us mpg?) mean instant fuel consumption?, but how much fuel did you burn in how many milles?
In my car 6.2% aero improvement means 5% less fuel consumption at 75 mph. cd=0.325 to 0.30x, because crr=0.0095.
My top speed increase 2.6% (+5km/h) but mine has not the prius speed limit. But the aero top speed is relative to air in the movement axis of the car, so if you get top speed measuring movemnt relative to ground yoo need to measure top speed going back your first attempt and calculate mean of two. A wind of 10 mph will add you +10 (-7.5% cd apparent reduction in my car) in one direction and -10 in the opposite (+8.8% cd apparent reduction if tire rolling resistance neglected).
So its hard to meet accuracy on low speeds if you have low rr tires and low cd on road conditions.
Cruise control near top speed will be the best measure. (pocket Autobahn or airport needed for scientifical reasons).
I post you some semi-empirical number with my car as example:
(attached excel)

[F8L]

I think this is really cool and I am thankful that you are so thoroughly documenting your progress but I have a couple questions regarding your use of the word neutral.

In a couple of posts you mention going into neutral and being able to coast further. I assume you do not mean physically shifting into neutral right? I want this to be clear for other Prius owners so they do not think that putting the car in neutral will increase gas mileage. The best method to increase gas mileage and increase coasting distance is to enter a glide or warp stealth mode.

In neutral the best you can hope for is approx. 300mpg because fuel cutoff doesn't happen in neutral. In warp stealth you can achieve infinite mpg (9999mpg on SG2) albeit with a little HV battery use.

I am pretty sure you know this but others who may be lurking may not.