1989 CRX aero mods

[coyoteX]

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.

[coyoteX]

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.

[Sven7]

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





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!

[MetroMPG]

the boat tail that really did nothing but draw attention

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.

[sheepdog 44]

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

[coyoteX]

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

[ultimx]

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.

[coyoteX]

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.

[ultimx]

Originally Posted by coyoteX

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.

[RandomFact314]

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