Aero aids on an xB.
 

Having gotten as far as I'm going to get in the near future with driving changes, I'm looking at further ways to up the mpg on Box.

I'd rather not drastically alter the exterior of the vehicle at the moment, plus there isn't much short of a boattail/kammback that is going to help this shape significantly.

So I'm looking at ways to improve the underside. An oddly the most logical place to start looks to be at the back. The rear bumper is pretty low, and looks like a giant airbrake from underneath

https://farm3.static.flickr.com/2254/...9497e79ba6.jpg
https://farm3.static.flickr.com/2103/...ff0b06c819.jpg
https://farm4.static.flickr.com/3215/...4ee111a382.jpg

In addition to the general unareo shapes under their, that entire lower section of the bumper does absolutely nothing but stick down into the airflow. Optimally I'd just remove it, but the xB looks very odd with it missing. So I'm thinking about using some aluminum or chloroplast to make a underbody panel that goes from just behind the rear suspension and down to meet the rear bumper lower edge.

My big concern is whether the long expanse from where it is attached near the suspension to where it attaches near the bumper will end up flexing or bowing in excessively. Also I'm not sure about water/dirt/etc collecting on top of the underbody panel.

Any suggestions or ideas?

For your bumper, what about a "roll pan", which commonly replaces bumpers on lowered pickup trucks?
https://www.bionicdodge.com/1995%20Da...an%20Right.JPG
Obviously there would be custom fabbing involved...

JanGeo is getting damn fine FE out of his xB, might want to see what he's doing...

I think your right about the belly pan, but the back? I wonder...

https://www.fuelly.com/attachments/fo...9e9b44d108.jpg

After looking at some FE sites aimed at big boxy trucks, this looks like one of the simplest approaches. Think of the red lines as 4 plexiglass panels that attach along the edge of the hatch... it does give a bit of a kamm-type drop, but it's main purpose seems to be to separate the low pressure area from the back of the vehicle. On your Scion it looks like it might be pretty easy to implement, and it might look darn cool too.

just a thought.

How about bumper vents ?
https://www.joeheckracing.com/image/p...leen05rear.jpg

Something like this? :
https://www.streetstyler.com/LipPics/xbrl.gif

After months of slacking, I finally got around to doing some areo mods to Box.

First up was a new front lip spoiler made from a garage door seal. It is only about 1" tall, but the front is low enough I didn't want more (the bottom of the bumper already has a fair amount of scrapes & gouges).

https://farm4.static.flickr.com/3147/...4c34990377.jpg
https://farm4.static.flickr.com/3168/...dbefd41bb4.jpg

Next was the big project, as I mentioned at the beginning of this thread, the space under the rear cargo area & bumper is really aerodynamically messy. So armed with some black chloroplast, aluminum flashing & some screws & zip-ties I set about fixing that. I did it over two days, with probably about 4-5 hours in it all total, maybe less. ignore the splashes, I drove through a muddy parking lot between the first & second sessions of working on it.

Overall shot:
https://farm4.static.flickr.com/3134/...63f4a052c5.jpg

From the left side:
https://farm4.static.flickr.com/3076/...2848d8bbd9.jpg

From Right side:
https://farm4.static.flickr.com/3228/...a50237307c.jpg

The front edge is tucked above the gas tank, and zip-tied in place. I was very careful to not put and new holes in the body of the car where they might rust. So everything is attached by zip-ties, or screws into the plastic bumper.

Detail of Right wheelwell and around muffler:
https://farm4.static.flickr.com/3238/...e9f743cb30.jpg

I pondered enclosing the muffler, but didn't have a good way to do it and not end up worrying about excessive heat buildup.

Detail of Left wheelwell:
https://farm4.static.flickr.com/3065/...0e894dba2d.jpg

From above:
https://farm4.static.flickr.com/3238/...9e58205fde.jpg

The little bit of flashing is the only part visible from outside. If you kneel or squat down you can just make out some of the edge of the black chloroplast at the edges of the bumper.

I've driven a bit with it on, and aside from one part of the flashing where the tailpipe passes through touching & rattling it works great. Ironically I don't know what it is doing for my MPG as I've loaned my Scangauge to a friend and won't get it back for a day or two.

looks good keep us posted on the results

Wow! Great work there.

You could put VGs on top/sides, or a spoiler to cut the airflow clean. You could also use the box as mentionned, idea patented by some university (google) for trucks, but might not apply here since the Xb is shorter than a rig.
If you can attach them, air dams for the rear wheels. Grill block in front, maybe even shape the nose angle of the Xb to help the airflow to stay closer to the body above.

Improbcat - have you seen any improvements from this mod? I have been thinking about doing the same thing.

Alan

Nothing dramatic, my most recent tank was just shy of 38mpg. Unfortunately my mpg have been steadily dropping because my O2 sensors are overdue for replacement and I don't have the $250 for them. So this put me back where I was a bit back, but I'm probably not seeing as much as I could have. I will admit to being a bit disappointed that it wasn't more impressive.

My next addition (after the O2 sensors) will be a front belly pan, and blocking off the parts of the lower grills not directly in front of the radiator.

Do replacing the o2 sensors make that much of a difference? I know I had one of the 02 sensors on The Beast replaced because it was bad and throwing a code, but I left the other one alone. That was right after I got the truck. So one of the sensors is almost 4 years old and has ~40,000 miles on it, and the other is probably 10 years old with 152,000 miles. The truck just passed emissions a couple of months ago. I haven't given it much thought because I really haven't noticed anyone saying they were replacing an o2 sensor for FE unless they were talking about upgrading to a heated o2 sensor.

-Jay

Hey how did I miss this thread for so long . . . been working like crazy lately. Improbcat nice work on the rear belly pan - I was really concerned about the air flow in or out of the rear fenders - them being so open to the big space where a trunk should have been under the rear . . . could put a full spare tire in that space or a bigger gas tank! Be interested in how you make out with the FE after that covering.

I did 48mpg to home today and 55mpg coming back - this after my run out to Cape Cod on Tuesday this past week where I got 44mpg going out at highway speed (about 1-2mpg more than usual) and 49.0mpg coming back on a slower Route 6 with a lot of stops. It seems that the Racing Disks help FE at lower speed (40mph) a lot more than at higher speeds (65mph) probably because the air flows right over them at higher speeds.

I think you have inspired me to add the Foam Board center rear belly pan on mine next chance I get into the garage so I can see if it affects FE.

I think it is time for the Irridium plug install too!

Not trying to hijack thread but....

JanGeo what are you doing to get those numbers from your xB? I am lucky to get 33mpg out of mine....

When you install the iridiums how are you going to gap them?

- Alan

Got a link for them?

Hey Alan

You xB guys should be a member of ScionLife.com - plenty of good info there on all sorts of things. The gap on the Irridium plugs for best performance (FE) is pretty big 0.044" if you get the EIX-11 they are already gapped bigger than the standard small gap of 0.032". Of course I got the standard ones so I will have to pry them open - maybe installing them later this week . . . finally!

Most of my high mileage is typical hypermiling technique but some of it is the Synlube that I added after gentle engine break in at 3700 miles (now at 22080) which provides better lubrication and no oil changes . . . plus 40-42psi in the tires and 3-4 oz of acetone in the gas every 10 gallons. The Racing Disks seem to help a little too.

Get a Scangauge and back off the gas sooner and you too can get great mileage but I think a lot of it is the lube in the engine, power steering and tranny running the Synlube. I get high 30's going up hills on the highway and typically cruize at 65mph in the low to mid 40 mpg.

My box has over 105K on it, and still has the original O2 sensors. The one front of the cat is my primary concern as the replacement interval is 100K or less and while I haven't been throwing codes, the engine is not running as well as it could. I've also been getting some carbon on my plugs, which indicates it is running a bit rich, and since the O2 sensor is a vital part of that I figure replacing it is a good way to start.
If your car is running well don't worry about the O2 sensors, but since mine isn't I'm looking for likely causes.

Its running fine, but I still think I should be getting somewhat better mileage than I actually am. I checked and it appears I can replace all the o2 sensors on the truck for under $100. I've also been thinking about plug wires. I can't remember if those were replaced when I bought the truck or not. I know the cap & rotor were replaced, and I saw that someone had put some cheap copper plugs in it so I replaced the plugs with some OEM Platinums. Later on this week I'm coming up on some time off, I may just replace the o2 sensors and rig up my HAI.

-Jay

Did you buy that garage door seal? At Lowe's I noticed it was $15 for a pretty long strip, which is steep for a piece of rubber.

Also, I cannot find Coroplast anywhere that's not an online store.

get a phone book and look up sign shops. most will sell you a sheet of coroplast. I got a white sheet 4ft x 8ft and it was 20 bucks.

check around there are usually a few sign shops in a given area.

Thanks, I was looking for sign shops. They will probably wonder what I need Coroplast for... Haha.

My "mods" are:
tape on the lower grille, synthetic tranny and engine oil, and Konig Daylite wheels that save me 32lbs total, plus look sexy!

I drive an automatic like a newbie though!



As far as spark plugs: Do the Denso Iridiums really help a lot?

I think I paid $7-8 for a 9ft foam rubber seal, plus I had to buy two rolls of heavy-duty double-sided tape.

I got my through a buddy who works at a sign shop. It was free as it was cut-offs from a larger project.

As for the plugs, they will mostly give you greater durability over the stock xB plugs, so you don't have to change them every 30K miles. You might get a tiny power & MPG boost, but don't expect anything dramatic.


Oh, I finally changed the front O2 sensor & re-gapped my plugs to .044. On a ~70mile drive where I had previously gotten 42mpg (on the scangauge) *at best*, I managed to average 47.5mpg without trying nearly as hard. So I am inclinded to beleive that with the O2 sensor making the engine run better I'm truly seeing the benefit of the undertray. As of now the scanguage says I'm at 38.5mpg for the tank (and only the last ~70mi is with the new sensor), but I'll see when I fill up as the SG tends to be optimistic.

Alright. Thanks! I hope the tape sticks in all weather conditions! :p

By and large it is sticking ok, the only problem spots have been the slight "kickup" towards the center of the bumper on each side, and the very back edge near the tire.

The "kickup" may only be because it poured rain right after I installed it and water got in between before the adhesive on the tape had set. At the back edge the lip on the bumper for the tape to stick to is small and the seal gets pelted with water & dirt from the tire. I'm goign to peel some of the tape off and re-stick it, and add a few screws to reinforce it when I get the chance. But it is staying pretty well thus far.

Did you replace both o2 sensors? or did you just replace the front one? I ask because I have been told the rear one lasts longer. Not sure why.

I just installed NGK iridiums gapped at .044 and the car idles much better. I have not run through a full tank yet but I am interested to see if it helped.

Guess I need to get a scangauge soon so I can see what is going on between fill ups.

Or some clamps or something could work. That little indent is an issue, hmm?

Just the front one for right now. The rear one tends to last longer since the exhaust has been treated by the cat by then and is cleaner.

They are a pretty sweet piece of kit.

Well my tanks since the addition of the undertray & lip have not shown any improvement. If anything they seem to have gone down slightly.

I'm wondering if the front lip is to blame. There is a plastic piece under the bumper that acts a bit like a front belly pan, and I'm wondering if blocking that with the lip is actually worsening air flow there.

I think I'm going to pull off the lip and try that for a tank or two, then maybe try a smoother front belly pan & possibly a partial grille block.

yes take off the lip. Those are there it the underside airflow sucks, but your airflow is good so it is just hampering you.

When doing the measures, have you guys calibrated the ScanGauge? Mine was way off optimistic (>10%).

Else use it to compare before/after mods, and not for absolute MPG readings. Don't adjust it until you have results without the lip.

If the lip lowers MPGs, then maybe just put a dam in front of the wheels to deflect air from them without adding frontal area (since drag = Cd x surface).

Now that the undertray/lip will almost be tested, maybe you can start looking above for spoiler impact on MPG.

I use the scanguage for a rough idea of my mpg while driving, but figure my mpg per tank the old fashioned way. I fill up at a lot of different gas stations so due to the variance in pumps I can't ever get the SG dialed in 100%.

it might help if you were to remove that lower section of the rear bump and have your undercarriage pan on an angle up to help reduce the wake behind the vehicle.

would vgs around the tail end of the car help the aerodynamics?

That would look really silly!

The rear aero is a mystery to me, its just flat on top.

it will reduce 4-5in of wake behind the car...

if anything i would think the vgs might look a little weird looking, but the rear aerodynamics is no mystery, there isnt any. :p

So does the air shoot straight off the back or spin down or something?

A rear undertray should certainly help, I have the materials, just need the time now.

Good work on the underbody and lip!

Did you ever get around to blocking your grill?
With mine I just used a piece of garden edging, cut to fit and ziptied in place. I will try and get some pictures. (probably took about 5 minutes to do) I wanted something that would be easy to remove, just in case.

Basically, if you WD40 the plastic after you install it it ends up looking really shiny and for me, similar to my stock paint. It really isn't noticable at all, and as long as you use black zip ties noone will notice them either. (I only used one at each corner)

If I were you I would also look into some different wheels. The scion steelies, from what I have read, weigh in around 22lbs. While the Scion Spiral wheels that I have are around 14, and the 7 spokes are said to be about 16 or so. You can find the stock alloy wheels on ebay all day long for $150 for the set. While a lot of people on Scionlife.com and Clubxb.com like to run the steelies with "Beauty rings". Or if there are any "Honda-tuners" in your area, they like steelies for track use. (so it shouldn't be a problem selling them)

I eventually plan to install Enkei RPF1 wheels, which weigh 9lbs each.

I feel like the XB is just a lost hope as far as aerodynamics go and I try to make up for this by never driving over 60mph unless someone else is in the car. (usually on vacations) I was a little more of an overzealous hypermiler whenever I had my "VX Civic".

I really don't expect the XB to get anywhere near 58MPG average and I am completely happy with it getting 38mpg consistently and 42 on those random "good tanks"

Although, I have random thoughts almost daily of ripping the A/C, belts, Alternator, radio out of the car; installing a solar roof and a charger outlet to charge a row of Deep cycle batteries that would be installed in the trunk; lining the underbody with Coroplast and aluminum; removing my mirrors, windshield wipers; blocking off the front bumper completely; removing the spoiler and lining the entire rear of the car with VGs and or Airtabs; removing the carpet, carpet padding and rear seats; gutting the dash; removing the metal bumper supports in the front and rear; and replacing the roof and all windows on the car with plexiglass.

But then I drive the evil thoughts out of my head and realize that everything just might be OK, and if I work hard enough, maybe I can afford a Tesla Roadster one day.

Either way, good work!

the vgs will help spin the air down into the wake of the vehicle

I see. I wonder what would be good to make them out of?
They wouldn't be too noticeable on top of the 'box. ;)

plastic:) im sure it would be easier to just buy a set. unfortunately im drawing a blank as to which thread they were in.

Geesh I've never heard of these things.
Here we go!
Anybody try these?

https://www.manufacturersdepot.com/SP...1180622063.jsp

https://www.gassavers.org/showthread.php?t=6178
https://www.gassavers.org/showthread.php?t=1482