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Old 07-30-2020, 12:26 AM   #281 (permalink)
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Originally Posted by veloman View Post
I'm starting to mod my gen 3 and wondering what these plastic things are in front of the front wheels? Looks like unnecessary drag.
Pretty sure they lower drag by tripping the air before it hits the rotating tire.

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Old 07-30-2020, 01:47 PM   #282 (permalink)
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I guess it's been a while since I've updated anything here. Addressing previous posts in reverse order:

-Don't remove the air dams in front of the wheels; they exist to reduce wheel drag.

-I never formally tested the cargo box, but did take it to the Green Grand Prix in 2018 (and on to NYC, after which I decided to remove it--parking, maneuvering, and reduction in rear visibility with it on was a bear). It was good for 62.8 mpg at the competition and returned 55.3 mpg on the trip to New York and back.

-I did test the air curtain ducts, both with coast downs and fuel economy over a section of road. The first version of the front ducts increased drag about a third as much as rolling all the windows down, but adding the rear ducts to it reduced drag so that there was no change from no ducts at all. The front ducts also noticeably and negatively impacted stability--the front end felt "squirrelly" in crosswinds, passing truck wakes, etc.

So, I removed the first version and made a second version. These are larger, covering more of the wheel arch, have strakes inside to guide airflow, and are horizontal. I reduced the outlet width to 12mm from 15mm, so exiting air is ~2.5x as fast as inlet.


Air curtain ducts. First version, left. Second version, right.

Coast down tests with the front ducts on and off (with rear ducts on for both) were inconclusive--there was just too much variability to measure a small effect. So I went out on a calm night on US 45 and measured fuel economy over a 3-mile section north and south, 6 runs in each configuration. Front ducts alone showed 0.29% decrease in fuel economy at 55 mph (70.1 mpg average base/69.9 mpg front ducts), but adding the rear ducts showed 1.28% improvement in fuel economy over no ducts at all (70.1 mpg base/71.0 mpg front and rear ducts); it appears the efficiency improvement is attributable to the rear ducts or some synergistic effect between rear and front. Further, the car is extremely stable with the new front ducts, which is reason enough to keep them on.


Black tape indicates attachment flanges of original ducts.

-Another recent project: I noticed in Toyota's press package for the 2016 Prius a reference to the "fresh air intake" to improve fuel economy and a valve setup to switch to engine bay air if the intake tube gets clogged with snow or debris. I had thought the intake was not routed to the outside of the car after looking at it at an auto show, so I looked more closely at the parts catalog and it does indeed take in air via a tube that goes over the radiator to the high-pressure, ambient-temperature air at the front of the car.


#10 in this image.

Curious, I looked at my pictures of the Honda Insight and Hyundai Ioniq, and they appear to do the same. So I decided to experiment with reducing intake air temperature by taking in fresh air. Using the Scangauge, I measured IAT on the highway with no tube attached to the airbox (12-15 F degrees above ambient), a tube run to the stock intake location behind the passenger headlight (11-12 F degrees above ambient), and then fabricated an intake using a NACA duct (6-8 F degrees above ambient). The NACA duct was necessary for its good pressure recovery, since the structure of the front end of the 3rd generation Prius didn't allow me to run a tube anywhere in the high pressure zone on the face of the car.



I included a secondary intake tube by using a 2" PVC elbow with a 1 1/2" T that's open to the engine bay. This is similar to the intake box setup of the Dodge Challenger SRT Hellcat, which has a headlight intake tube feeding directly to the box and a bottom open to the fenderwell as a secondary intake source. At higher speeds, there's enough pressure at the inlet to feed outside air to the airbox, but if that ever gets clogged with snow or debris and the pressure drops below engine bay pressure, the intake will draw bay air instead. Also, the 1 1/2" pipe points down as the main intake tube goes up about a foot to clear the radiator subframe, allowing for water drainage and using gravity to prevent water and debris reaching the airbox. I tested it this week in a series of Midwest downpours and it functioned as intended--no misfires, no codes, filter and airbox completely dry afterward.

-610 mi camping trip this week, taking a mix of interstates and US highways to the northwest part of the state and back, returned an indicated 61.0 mpg on the display.


At Mississippi Palisades State Park, Savanna, IL.
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Old 07-30-2020, 03:12 PM   #283 (permalink)
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Quote:
Originally Posted by eco_generator View Post
Pretty sure they lower drag by tripping the air before it hits the rotating tire.
Hmm, well I think it could be significantly improved as it's just a piece of vertical plastic. I will attach a larger, rounded tire spat to it.

Another area I see as an easy, no negative mod is the sides of the black grill. Only the center of the grill is open. So I'm thinking of rounding those side areas to help the air move past easier. Maybe some sheet aluminum with expanding foam underneath.

Cool thread. I am working on reading it all.
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Old 07-30-2020, 04:31 PM   #284 (permalink)
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Hmm, well I think it could be significantly improved as it's just a piece of vertical plastic. I will attach a larger, rounded tire spat to it.
Production vehicles tend to be more conservative than all-out racers.
Quote:
Another area I see as an easy, no negative mod is the sides of the black grill. Only the center of the grill is open. So I'm thinking of rounding those side areas to help the air move past easier.
A bellmouth. Are you thinking internal or external?
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Old 07-30-2020, 04:44 PM   #285 (permalink)
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Originally Posted by freebeard View Post
Production vehicles tend to be more conservative than all-out racers.

A bellmouth. Are you thinking internal or external?
Here's a very crude mock up I just did.
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Old 07-31-2020, 04:43 AM   #286 (permalink)
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Are you planning on covering that lower lip spoiler? Any concerns about stability?
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Old 07-31-2020, 10:38 AM   #287 (permalink)
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what are these

Quote:
Originally Posted by veloman View Post
I'm starting to mod my gen 3 and wondering what these plastic things are in front of the front wheels? Looks like unnecessary drag.
As eco generator commented, they trip the flow.
The face of the tire is descending vertically, at the same velocity of the vehicle's forward motion, and the air, essentially acts like it's striking a waterfall.
The hour-glass body void, for wheel-flop cannot support airflow. It's a pretty serious mutilation.
The 'taco' fairings ( as Goro Tamai of MIT refers to them) help cause the air to deflect away from the face of the tires, as well as 'jump' the hollow void of the wheelhouse, then re-attach to the underside, once beyond the void. It's not as clean as streamlining the wheels and suspension, but it's way out ahead of nothing.
The solution is demonstrated with the Cd 0.189 VW XL1 and it's 'canoe' fairings. With very tight clearances, these types of fairings can reduce the total wheel drag contribution by 70% or so. The Cambridge University CUER eco racer demonstrates an ideal a example of the technology. Cd 0.11!
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Old 07-31-2020, 04:09 PM   #288 (permalink)
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Really am curious and interested in the air intake modification to get more flow and volume could you elaborate and show more images Thanks
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Old 08-01-2020, 11:48 AM   #289 (permalink)
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Quote:
Originally Posted by TexasCotton View Post
Vman 455
Really am curious and interested in the air intake modification to get more flow and volume could you elaborate and show more images Thanks
I used a Butler duct, BBP-7024, with a 2.5" outlet and neoprene hose from Pegasus Racing:





2" PVC for the section behind the headlight:



With an elbow at the end and more 2.5" hose to attach to the duct (this is version 1, with no 1 1/2" T):





The stock intake hose was 2" or so. Note that no matter what hose size you use you won't get more air volume; the volume of air sucked in by the engine is a function of cylinder displacement, and the volume flow rate through the intake is a function of displacement and engine rpm. But you can change the pressure drop through the intake hose by using larger tubing/fewer bends/larger radius bends/higher inlet pressure (I wasn't really concerned with this, so I didn't bother measuring pressure across the intake, instead measuring IAT just to verify that it's getting fresh air, i.e. that inlet pressure is higher than engine bay pressure since it's open to both. Julian Edgar has several articles on Autospeed about this however, if you're interested). This does affect intake temperature and, related to that, mass flow rate.

Note also that I had the space to route this only because I removed the windshield washer system two years ago; otherwise, that occupies the space behind the passenger headlight.
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Old 08-01-2020, 12:20 PM   #290 (permalink)
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The air intake mod is interesting. What about water/moisture entering when it's raining?

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