1989 CRX aero mods
 

The winter of '09- '10 I started looking into how the NASCAR and F1 guys were using Computational Fluid Dynamics in their designs. After studying alot of computer generated model airflow analysis and real time wind tunnel test pictures, it started to become obvious how the air moves around things. An air dam forces the air to go around or over the vehicle. An air dam with a forward facing splitter creates a more concentrated area of recirculating air to form just behind it under the front end creating more down force. I believe it does this two ways, first by creating a lower pressure area and second by catching the air in front and above the splitter. As the speed increases, the mass of air, in that area just ahead of and above increases, exponentially. By properly designing the splitter and dam to transfer the load to the chassis, you now have down force without the drag of a wing. I never tested my design with the forward facing splitter because my operating speed range is right at the bottom of where air pressure begins to increase fuel consumption. Double the speed, air pressure increases 4 times and fuel consumption increases pretty linear with air pressure change. Although the design does increase down force because you can feel the cars handling behavior change after you hit 80 mph. My next post will include a simple materials list for those interested and I will need to get out and shoot some new pictures, as I seem to have lost all of the ones I had, including the ones with the boat tail that really did nothing but draw attention. Yes, the first test run with it, earned me a ticket because the license plate was covered up.

I'm a bit confused. You're road racing or what?

1989 CRX aero mods
 

Sorry, no I am not racing. I used data generated by the guys who are racing to come up with my design. It is on the shade tree side but works great all the same. I will post pictures as soon as it warms up a little. -8* this a.m.

Increased downforce is increased drag. Not what you want for hypermiling.

moorecomp,
Yes and no, any movement through the atmosphere causes drag. Managing it is the key. As far as hypermiling goes, would you agree that the best milage you can get with the least effort is what we are all trying to attain?
C

True, but moorecomp has a point. If the vehicle does not need any more downforce, I wouldn't go out of my way to add more. Many sports cars have high drag coefficients as a result of the downforce produced/ required to run 180+ mph. There has been a few discussions about front splitters, I would argue that it is more efficient to redirect the air around the vehicle, than to have it apply force and push down on the splitter. Anytime you have the car push the air, you're adding drag.

Yep, as long as you're driving the speed limit there should be no reason to add downforce. Most road cars will naturally produce some lift but it's nowhere near enough to become a problem unless you're out on Bonneville (or looking for a $400 speeding ticket).

1989 CRX aero mods
 

I'm in total agreement. I believe that with the way I caused the air to go around the car, that it both reduces air getting under, creating lift and creates down force at speed. I am going to attempt to post photos of the car with the boat tail and with the other mods.

Cool, I'd love to see pictures.

coyoteX - I understand you're having trouble posting pics.

Describe the problem here and I or someone will help you out.

Also FYI, see: http://ecomodder.com/forum/showthrea...der-18279.html

OK, I finally figured out how to put photos in an album. You can go there to see the Tadpole. These cars were so well designed they are tough to improve on. The boat tail really did nothing but draw unwanted attention with no real world benefits. The original grille block installed did reduce excess air from building up under the car and improved handling in cross winds though. The new nose and diffuser under the rear, made a very noticeable difference in handling, in all wind and speed conditions. The exhaust system has been streamlined, mainly by removing the rear low hanging muffler and installing a dual tube glasspack inline behind the cat. When you look in the rear wheel well, on this body style Honda, you will notice that the rear bumper cover is open to catch air at the bottom. I made little close outs from ABS to fill that void. All newer cars have air strakes to create turbulence in front of the tires. The leading edge of the front tires create as much or more drag than the mirrors do. I made strakes out of ABS for front and rear tires. I removed the rear because the angle I made in them kicked the air sideways too much. This was noted by driving close to a grocery bag and it moved violently sideways as the rear tire passed. Watching light snow dust in the mirrors also helps visualize the air movement as you are driving. Without the rear tire strakes this no longer happens. When I drive like most people fuel consumption seems to be close to the EPA. When I drive consciously, I can see around 17% improvement. With the aero mods there is up to another 10% improvement over that. Its mostly in how we use the right foot.

The original grille block left a slot about 1 1/2" wide just below the bumper. The new nose only has the opening you see below the license plate. I designed it to function sort of like a NACA duct. There is a piece just inside the opening that directs the air upward toward the radiator. The floor of that opening starts at the narrow part and deepens as it widens. I have climbed Wolf Creek Pass in 95* summer heat and had no issue with engine temperature. The diffuser under the rear starts at the rear suspension framework, ending at the bumper cover and opens up 5" and widens 7" toward the rear. The key to diffusers working is that they have to see the ground between the fences on the sides. This separates and smooths the air flow as it controls its expansion out the rear.

We usually use "tadpole" to describe three wheeled vehicles with a single wheel in back.

http://ecomodder.com/forum/member-co...7-img-3790.jpg

http://ecomodder.com/forum/member-co...-100-0443a.jpg

Did you tuft the boat tail to make sure it works? As a former boat tail owner, I have a hard time believing a tail that long (even if just on the top and without wheel skirts) wouldn't show.

Hucho would suggest an approximately 3 degree angle on the diffuser [for a liftback body style] and it looks like you're pretty close (it's hard to tell in the photos). Good craftsmanship, too!

Oh, and I like your front end work. Looks very industrial!
http://ecomodder.com/forum/member-co...6-img-3793.jpg

Now I understand why! The bottom angle on that tail is crazy. It's so steep, it may even have formed a pair of energy-sucking counter-rotating vortices that increased drag enough to cancel any benefit of the top/side taper.

How did you make the Tail, and how did you attach it to the car?

Sven7, with the tail on from the side it had a tadpole look, besides my grandson likes the name. I try to be effective with whats available. Never have cared what other people think about what my car looks like. The main aluminum plate, that attaches at the license plate mount and to the suspension frame underneath was free. There is a piece of 1x1x1/8" aluminum angle bridging the corners of the bumper cover and center plate. The cover is 1/8" haircell ABS. The diffuser is just formed with haircell ABS. Total cost maybe $100. It works what can I say.
MetroMPG, you are absolutely correct, it did create 2 counter rotating vertices behind the car. The length from the tip of the tail, over the top to front bumper was very close to the length under the bottom. It also made using the hatch useless, so I took it off and went a different direction. By focusing on the front and bottom, visually to most people, it is not noticeable.
sheepdog44, I used drywall bullnose corner bead, it makes a nice smooth rounded edge, its cheap, light weight, strong and easy to rivet. The panels were made out of coroplast. I attached it to the bottom of the bumper cover and the the side of the body just inside where the rear hatch closes. The hatch opened and closed fine, its just that you had to reach over the side to get anything in or out of the car. Sorry, No build pictures. I did that like 3 years ago.

Whats important with front air dams? The farthest point forward has to be the lowest point on the car.

The car really is a blast to drive, especially on raods like HWY 550 north out of Durango, "the million dollar road". With those skinny tires it drifts very controllable if I push it. I put drilled/slotted rotors on and can easily over power the tires on hard stops. It don't go uphill fast but I don't have to use my brakes much coming down, HAHA. Thats the trade off for fuel economy.

Thanks for the interest guys

That's an interesting picture. I too have a crx and was wondering what exactly u did to achieve the 70mpg run? I have some mods done and the best I got was 56mpg.

What CRX model do you have, Si, DX or HF? The differentials make all the difference in the world. What are your RPM's at 60 mph? The best gauge you can add to any car to help in learning how to use your right foot is a vacuum gauge. The larger the better. Slight adjustments in throttle position can make huge fluctuations in vacuum. Learn to read the terrain ahead, adjust the throttle before you get there, let off the throttle and accelerate. I think my best tank was 84 mpg.

I have a hf. Rpms are ~1750 @60. So the only mods u have done are the grill block, rear defuser, and tire splats? That's really exceptional for just the stuff u have I would like to try and replicate that mpg if I could. Eventually I am going to be making an under belly pan and grill block with wheel covers as well.

Wouldn't it help MPG if you took off the mud flaps

What mudflaps? If you mean the ones in front of the rear tires, those are likely improving MPG as the act as tire spats to direct air around the spinning rear tires, instead of allowing the air to go straight into them.

ultimx, Does your crx have the shift light? If it does it is a 49 states Fed edition. Good start!!! your car does not need a bellypan. Look underneath from the rear. Does your car have A/C? If it does and you want to keep it that limits what can be done with a grille block. Getting your exhaust system all in a straight line is a good simple start. Then you can do a diffuser in the rear where the muffler is now. Oh yeah, I picked up almost 5 mpg with the skinny Sumitomo HTRT4 tires.

No but I have the transmission. Yeah I saw your album and might do the same thing but full rear enclosure. No ac so I'm good. What size wheels do you have? Idk if I can find this tires. I was looking for the LRR tires but didn't see any in the size I had.

I had 175/70R13's and went with the recommended, P165/70R13, Sumitomo HTR T4's and averaged almost 5 mpg better. These are LRR tires and they work pretty good in rain and snow. With all of the variables in real world driving, I don't think the full rear fairing is practical. If you are headed to Bonneville, then absolutely, you will need it. I still say, start with installing a vacuum gauge and learn how to use your right foot. I believe a few years ago, a guy entered one of these cars in a mileage event and averaged 108 mpg. That was on a closed course, fuel economy event, probably 45 mph top speeds, not the real world. Mirrors, passenger seat, spare tire and any unnecessary weight were removed. I believe he taped all body gaps and rolled window down to get in and out. Oh, he did make his own version of a nose that was quite a bit larger than mine. It reminded me of a cow pusher on the front of an old train.

Aren't the stock tires larger than that? I do plan on installing a vac gauge. I'm pretty good at staying in constant pressure but this should help visualize everything. You are right on the milage but it wasn't closed course. Lol I do remember that article cause I plan on doing something similar

im very intrigued. i was planning to do a similar rear diffuser for my 4 door. i like the nose. its not too noticeable on the crx. any pics of the rear diffuser and rear tire spats up close?

ultimx, This is the stock tire size for the HF. As for the VAC gauge, it's not constant pressure but the highest vacuum under any load condition that matters. You will see that conditions constantly change. On long hills I try to keep at least 2" of vacuum. On reasonably level terrain, I try to average 8" or better. Remember, I'm at 6000-7000 ft. elevation most of the time.
slownungly, What photos I have of the diffuser are in the Tadpole album. Basically, it's a 3 sided tapered box, that attaches at the rear, of the rear suspension, near the control arm pivots and at the bottom of the bumper cover. The front tire spats are more important than the rear ones. The leading edge of the front tires create as much drag as the mirrors do. Turbulence from everything else going on under the car minimize the need for the rear tire spats. Look under all newer cars at the body protrusions in front of the tires to get the idea. The side view of the car with my foot in the picture is the best profile shot. Note the thin flaps ahead of the front tires. Those create turbulence in front of the tire. I removed the ones you see in front of the back tires because they were to large and not really needed anyway. I also removed the small fins on the rear corners of the trunk lid. On new cars, the tire spats have a curb shape and are very short. You want to create a concentrated area of turbulence that will flow at the tire, so that it does not attach to the tire. Turbulence will set you free. Remember the divots on the cover of a golf ball.

Ok so you want a spat in the front to direct the air at the tire and not around it? I took your advise and looked at a 2007 Toyota yaris I inspected this morning. It had front and rear spats but the front is only a small one while the rear is a little longer, I'll include pics.

And in regards to the rear diffuser why did you make it that box shape instead of a full pan? Does it direct the air out better that way?

Here's the yaris spats.
http://i1050.photobucket.com/albums/...ps25aac3ac.jpg
http://i1050.photobucket.com/albums/...psd2e411b9.jpg

slownugly, Look at the diffusers under F1 cars to get an idea of how small they can be and still be very effective. The important aspects are; fences on the sides, roof has to face the ground, angle of the roof 3*-5*. If you can find wind tunnel tests, it's amazing how the diffuser under the bottom changes the air flow over the wing on top. Belly pan vs. no pan, are you headed to Bonneville? Get a vacuum gauge and learn to use your right foot first.

Haha no bonneville. I'm about to start doing aero mods on my civic and I'm debating which routes to go. I like the mods you have done because they are subtle and barely noticeable and that's what I'm after. No crazy boatail or anything. I researched diffusers and learned their effect on f1 cars. I'm a mechanic and diagnostician by trade so I'm very in tune with how the car runs. It's a lean burn engine and I monitor it via afr gauge. I should have a vaccum gauge but that will come shortly. However, I'm a total noob at aero modifications so I'm just looking for a game plan

Do you have pictures of what your talking about?

I am running an AFR gauge also, it lets you know what the computer is seeing in the exhaust. The Vacuum gauge watches the intake side. The AFR gauge watches the exhaust side. Being a Tech, you know the Intake Event is the most critical. Read some of Bisimotos stuff, the Honda single cam master. When climbing hills, I try to keep the AFR pulsing with the best possible Vacuum. Usually only 1"-2", on the Vacuum gauge. When the AFR pegs out rich, that's unburned fuel out the tailpipe. Letting off the throttle, ever so slightly, gets it pulsing again. On downhills, If you crack the throttle, you can actually pull more vacuum and see no pulse or very low AFR reading. I use a ScanGauge II on my '01 Tacoma and it's cool to watch the MPG go to 9999. When you get the technique down, you can actually let off the throttle slightly as you are cresting hills, watch the Vacuun actually increase and be accelerating at the same time. This is completely contrary to how most people drive.
As far as good engine mods, a 4-2-1 header is necessary, so the exhaust pulses hit the main pipe in sequence. As far as exhaust back pressure and harmonics, I did the math and Honda already has that taken care of. A full exhaust, header to tailpipe tip the stock size would be ideal, but you won't be able to come up with a small tube header. It's not a problem though, because as long as you go back to the stock pipe size behind the header, you regain exhaust speed. Big tubes are only good for astronomical RPM's, racing only. No good in the real world. Hey, you can always sell it to Ricky Racer.
Good luck Dude.

Yea I need most help on the uphill part. I use dfco a lot. I can read that on my afr because it pegs lean. I know exactly what you mean with the cresting a hill thing. Right before I hit the highest spot I drop into lean burn and that pulls me over the hill. Good advise on the afr uphills. I need a good medium on uphills where it's enough engine load to maintain speed but not so much that it drops my mileage.

It' a good thing we don't have to go uphill both ways!!!!
ultimx asked about pictures and I don't know how to get to the album with my cars pictures, can you assist? I think he wanted to see pictures of the rear diffuser.

I created a photobucket account and use that. I take a pic and send it to the account. The. From there you copy the link and paste it on the post you want the picture. Very easy if you have a smartphone. I have photobucket on an app so it's very simple

DCFO is a way to slow down while using no fuel, but coasting without slowing down (engine on or engine off) is even more efficient in the long term. Unless you are actually coming to a stop, or have a downhill stretch that is so long that even if you crest the hill at 5 MPH you still get too fast.

-soD

That's what is great about the Vx transmission. ( hf transmission too) the final drive keeps the rpms so low if the hill is steep enough I can use dfco and gain speed without touching the throttle or using eoc. Or shifting to neutral. If the hill causes a decrease in speed I blip the throttle a little to get back up to speed and continue dfco.

It's all about averages and weighing them out. I could shift to neutral and go 5 miles at 20:1 afr. Or I could dfco 4 miles at 99.99 mpg and 1 mile accelerating at 14.7afr. Or eoc for 5 miles. Eoc obviously most effective but I'm wanting to prove hybrid mileage from this car without hybrid techniques (shutting engine off)or expensive battery packs. I'll save the eoc for my last goal

I was referring to the f1 cars underside. Iv looked for the. A while ago and didn't come up with anything.

ultimx, Just google F1 race car diffuser images and click on the images 100's of them come up.

Awesome thanks! Any more modifications in the future for the crx?