121 replies to this topic

[3gencivic]

that rear bumpper would be intersting to find out.

i found for the drag strip i did the rear cut out and i belive i cut my times down. i did get my best ever run with it. but hard to say.

i would say the mugen full kit would flow the best. it looks to be a solid front grill adn smoth edges on the car. fenders ete.
dont thing the mirrors are that well for air flow.
the diff wings would be cool to see witch are better the dx or si or mugen
ressesd vs flush headlights
front lip vs no lip

[gkiing]

You may be interested to know that the coefficient of drag of the 1G crx is 0.26, one of the first cars to get below 0.30. I think the audi quattro may have been the first below .3

[crxls]

you guys ever see myth busters when they researched the truck tailgate for MPG? they verified 2 times that the tailgate in the up (closed) position was better for fuel economy than the tailgate being down (open). they also verified that the tailgate being replaced with one of those nets was even better yet for fuel economy. im willing to bet that the rear bumper on the crx is the same deal, holes better than cutout.

[Ron22]

You might want to try this web site
http://www.gassavers.org/forum.php
They would have ideas and I know they would be interested in the results.

[ChrisF-dude]

According to my old book, the 84-85 CRX with recessed headlights had a aerodynamic efficiency of Cd 0.33. If that helps as a baseline.

[cbstdscott]

The rear bumper has been one of my pet projects for some time. I have always thought that it needed some modification and so I did this to mine:



Without the benefit of a wind tunnel, my butt-o-meter tells me that the car is more stable (less buffeting) at high speed. I have been considering the design of a defuser to further smooth the flow under the car, but it is a "back burner" idea right now.

The information about the pickup tailgate makes sense if you are familiar with the concept ot the Gurney Lip. Racer/Builder Dan Gurney discovered that a small lip at nearly a right angle`to the plain of a wing increases the wing's effeciency. The turbulance casued by the small lip "tricks" the air into thinking the wing is larger than it actually is.

Scott

[Vicious]

i'm getting gitty with excitement and i'm not even particapating in the experiment but still anixous for the results

[RexKrazy]

i've thought about a gurney flap. that would be something to add on later if I can't get the rear downforce. It would be a small strip at a right angle along the back of the car. The methology is that the flap creates a stagnation point infront of it making a high pressure region. This could add significant drag also, seeing as you're lowering the pressure behind the car.

.26 is really really low for a CD number. you sure on that? .33 sounds more believable. mine is an 86, so it should be slightly better.

I'm not sure if the pickup truck thing applies to the rear bumper. We actually ran a pickup truck test a few years ago and it indeed did worse with the tailgate down. This is supposedly due to much larger circulation region in the bed w/ the gate down. I'm not sure if they tried a net or not, but that's interesting. In our case there is no steep drop off besides the gas tank, and I don't think that would be a problem unless you pull the bumper all the way off. In any case, sealed will be better. Anyone have any frontal area numbers on the car? It would be nice to have the real number to get an accurate CD. It's not teh easiest thing to measure well.

I like the idea of adding some type of gurney flap....I think i'd have to build a whole new "spoiler" though. Maybe make it a little longer because I'm not sure that the flow will be reattached by that point. might have to make a fairly large flap like the nascar boys to get any effect.

I'm excited too

[shahriar35]

I was always curious with how much a difference it would make w/ a car that has been clayed and waxed compared to one that hasnt been. I mean its the same as idea of a dirty air plane

[RexKrazy]

the cleaner the better :-). however, I'm sure you'd have to be on a giant speedway to see the difference in lap times.

[Maine_Honda_Racer]

That's a pretty neat project - ODU was smart to work out that deal with NASA on the Full Scale Tunnel. Although my CRX wasn't built until after I graduated from Tech, it would have been a tight fit in their measly little 6'x6' Stability Tunnel.

In a related racing note from about twenty years ago, here's my '69 Olds Delta 88 (#77) meeting its fiery end at an Enduro race across the street from Langley:



Good luck with the testing!

Doug

Hey that's Langley Speedway. My cousin sponsors a car down there. I will be down there after my racing season up here with my Monte Carlo!!

Ben K

[RexKrazy]

FYI the wind tunnel to be used is accross the street on Langley Air Force Base.

[gkiing]

Yes .26, Its in the ballade sports crx brochures

[RFL85CRXSI]

Cant wait to see the results of this project!
Now as for the rear bumper cut out, if I remember correctly there was a post about this a while back. Its said that the more you take out of the rear to increase airflow (and with a front lip) the more vaccum is created underneith the rear of the car which inturn helps stability at higher speeds... Now here is my question... This vaccum that is created, wouldnt it inturn cause the car to slow down and increase the engine load?

[85Beater]

Leaving the tailgate up creates a small eddy of airflow inside the bed. The majority of the air simply rolls over this pocket (as anybody who has ridden in the bed of a truck on a cold night can attest). when you lower the tailgate this pocket is removed and the turbulence directly behind the cab increase, which screws your slip stream all the way back. I guess the net would allow the pocket to form, while allowing the pocket to be more stable (much like the hole in the middle of a parachute).

And yes, I am excited about these wind tunnel results, been watching this post for a while and getting more excited by the day.

Interesting about the rear bumper, might have to nab a spare and modify it to see just what your talking about.