1989 Chevy Celebrity 4 door - kammback ideas
 

Attached are some ideas I have been thinking about for the Celebrity, which is currently parked for the winter season. Obviously they are arranged from hardest to easiest.

The section over the trunk lid needs to be hinged so it folds away from the window, so I can open the trunk, I have attachment ideas. So anything more than the trunk lid part will need to a 2-piece deal. My bumper is heavy chromed steel with several attachment holes (for a VR body kit that was offered from the factory) so I can attach something lightweight with little worry. Lighting is not a concern, I can add lights and rewire with no problems.

Any thoughts or comments as to if any of these would be better? Or if there is anything different that would probably be better to try?

I think the first shape is the only one likely to help much - the others seem prone to separation, especially if any smoothing is done up front. Perhaps you can make a single large shape and hinge it at the roof, so that it can lift up along with the trunk lid. Or, it could replace the trunk lid completely.

ideas
 

I agree with Bicycle Bob,and would choose the top for greatest drag reduction.----------------- The bottom image might be a compromise and with that,I would include a rear spoiler angling up and to the rear to intersect the teardrop template line.Can't be steeper than 30-degrees from horizon or drag starts to go up again.--------------------- Since the two central images fall below the teardrop line,they would as Bob has mentioned,be in separated flow and of no benefit.-------------------------- If the length issue scares you,remember,you can chop it off vertically wherever you like.Just know that the length is what is buying the drag reduction.

If going with the first design, it will look more like the fast back montecarlo's of the 90's.

Anyhow, you can make it as a three piece spoiler. The side pieces, made of metal or plastic and attached directly to the rear quarter panel and roof. The middle piece made of plexi glass and attached to the roof and the side pieces. Wouldn't look to bad and if you hinged the mounting point at the roof and attached it to the trunk with a single pillar at the edge of the trunk, you could still open you trunk and use it. All you would need to add are some pieces of velcro to keep it attached to the side pieces while driving.

Thanks guys for the input. I was even wondering if I even had the teardrop in the right place.

I read somewhere about the best cutoff point being at 50% of the overall section or it increases drag. So I take it that means the height of the straight part of the cutoff should be 50% of the total height of the car. If so then I could cut #1 shorter. Is there any truth to that, or is longer really better? I just took it back to a straight part of about 8" high or so, enough for lights and a license plate.

Also, if I ended up going with just a trunk piece, it sounds like it would be best to still follow the teardrop. Which would be easier so when I add the back piece, it will still follow the teardrop.

I am not going to drill into the body, even though it would make the design a little friendlier. The trunk would have rails that clamp to the trunk lid edges, and a windowed shell that snaps over it, probably with spring pins or something that can be used without tools. Whether or not it would hinge would depend on the geometry. Then the back piece would bolt to the holes in the bumper, and probably to the anchor holes for the taillights as well.

I owned a Chev Celebrity Kamm back!
called it a Chev Citation hatchback.

Yeah the Citation was basically just a Celebrity hatchback. 98% same underpinnings. Different nose clip, different back end, different dash. But you could bolt in a Celebrity dash if you wanted, all the bolt holes lined up. I thought once about getting a Citation and making it a Celebrity hatchback, or even cooler, getting a Phoenix and making a 6000 SE hatchback.

50 %
 

Wagonman,when they discuss 50%,they're talking about cutting the body off when it has tapered ( top and sides )to 50% of the vehicles frontal area,wherever that occurs.At that point the car would have a drag coefficient on the order of 0.21,if everything else was properly shaped.

I had a couple hours today and it was nice out so I got started on the kammback frame. The angle is pretty close to the teardrop I drew in earlier, plus the measurements on the car were pretty close too, to the nearest inch. The back bar ended up 6 1/2" high instead of 6", I will probably go back and lower it to 6". The long strip is just a piece of flat bar laying there to show the angle. Does it seem like a decent angle, or do think I should make it shallower or steeper?

I plan to finish the kammback by welding a full frame of the 1/8" x 5/8" flat bar that I can get in abundance from the scrap pile at work. This will make it light and rigid.

I was tossing around window ideas, and for starters I plan to stretch a heavy shower curtain liner over it, held on by retainers of the same flat bar. I bought one at Walmart for $6 and they are decently transparent. I may do lexan later on if this ends up working well, and if I have more to spend, they cut the engineering dept to 4 day weeks because things have been slow.

Nice to see this moving ahead!

Do you happen to know if you have attached flow on the end of your trunk lid? (I'm guessing you may not, based on the rear glass being so vertical - so separation happens at roof height.)

If you don't, you stand to gain nicely from the kammback.

Thanks metrompg. We have had a few nice days this year. Every other day it just wants to stay 30F all day and rain/snow/wind, but nicer weather has gotta show up sooner or later. I had to go downstate yesterday so I took off the bars after taking the pic. Gotta go back tomorrow, then I'll be home for almost 2 weeks again.

About the flow, azraelswrd was kind enough to do this for me back in the flow illustrator thread.

http://ecomodder.com/forum/44755-post49.html

Which makes me think that the flow over the trunk is really not that bad, and the most benefit would be a stub tail that starts at the end of the trunk, sorta like #2 in my original sketches. It certainly would be a lot easier to make.

But I'm not so sure about the accuracy of the flow illustrator, especially when everyone said that the angle from the top of the back window to the tip of the trunk looks too steep for attached flow. I would think the people here (who are going to have first hand experience) would give better advice.

2D model of a 3D world.
Look at the curved sides of the rear window.
http://ecomodder.com/forum/attachmen...7&d=1240594513
There must be flow from the sides which will combine with flow across the roof and I'd guess (complete guess - not amateur let alone an expert) disrupt what looks like a more or less static bubble in flow illustrator.

Might be worth tuft testing with and without simple side fins and possibly a small truck deck lid extension.
http://ecomodder.com/forum/attachmen...9&d=1240724264

The kammback wouldn't necessarily have to be hinged.
It could be mounded on rails.
Slide it back to open truck.

Testdrive raises some valid points. I'd also be reluctant to conclude anything from the flow illustrator demo because for another thing, the free stream flow seems to be entering from above instead of straight ahead, flowing downward at an angle top left to bottom right. Not sure why. But that would mess things up too.

To confirm, all you need is a single row of tufts taped across the last 4 or 5 inches of the trunk, and some way (or someone, if your mirror doesn't show it and you don't have a vid cam) to watch them from inside while you drive. If they're streaming back, you've got attachment. If they're swirling around randomly, you don't, and your Kammback is going to help even more.

Today after work I did a tuft test. I removed the kamm base rods, then taped on 7 pieces of white yarn along the last 5 inches of the trunk lid. I could just barely see them out my rearview mirror so I took the wife with me about a mile down the road and back. Both there and back, the strands were wagging back and forth like a dog's tail.

So after we got back I got to do more on the kammback for a few hours. The pics show what I accomplished till I could not see anymore. I ended up just leaving the back bar at 6 1/2" high, it should still be a lot better than the current airflow. It is just tack welded but it is pretty rigid so far and is nice and light, weighs maybe 10 lbs. The only thing I might change is knock out the frontmost diagonal braces and replace them with pieces bent at the top so it more closely follows the c-pillar.

I am actually thinking more and more about leaving the extensions on the back and completing the boattail, that's why I haven't cut them off yet. It measures about 2 feet, which is just about the same as another sketch I drew (just a little bit shorter version of the one posted by testdrive). The bottom of my steel bumper has holes that I can use to bolt some angle iron to support the back end, and I can hinge it there. (I really would rather just hinge it on the rearmost anchor bolt rather than try to make it slide.) Over the 2 ft boattail the width of the car would taper in to meet the bars that currently extend out, which comes out to about 15 degrees per side.

Hope the weather stays decent, I want to keep working on this.

Nice work. Keep it up. :thumbup:

Here is tonight's progress. The bottom beams will be angle iron from a scrapped bed frame. I just have them as wood right now because wood is a lot easier to make adjustments to. They are bolted to the bumper the same as the angle iron will be. There are actually 7 holes in the bottom of the bumper so I can attach some triangular bracing down there. The angle in the top view is a bit steep where the boards are, so I will probably make the back end of the frame a little wider at the bottom.

Then my welder quit working. :mad: The fan runs, the wire feeds, there is continuity through the gun and wire, but it just won't arc. Hope to have it fixed really soon.

The transition from the sides of the car to the sides of the tail appear to be quite abrupt.
I wonder if this wouldn't be an instance of less is more?

At trunk lid level, the transitions are very gradual. Down at the bottom the car is a little wider, plus the tail does not go back as far at the bottom. So the angle of the boards does make for a more abrupt transition than I would like at the bottom. That was what I was saying about widening the tail at the bottom where the boards are. It's not nearly as bad as it looks in the pics, the bottom looks very abrupt in some pics because the boards go up as well as inward. But the bottom is still more abrupt than I would like at the moment.

Also once I can weld again, it will have more triangular side bracing that comes close to the taillights and the bracing will be a bit convex to better match the car profile. Same with the short bars that go from the trunk lid to the back bar, they are currently straight but will be convex a bit when done. They are actually not attached at the trunk lid end, that is where my welder quit. Gotta have lots of triangular bracing to keep it light and rigid.

Hopefully this is what you are referring to. With a smoother transition, does it look like it should be beneficial so far?

My eyes weren't processing that and I managed to skim over the "widening the bottom" part. Sounds like you'll do fine once the welder is up and running again. Hope that turns out to be a cheap an easy fix.

I've wanted to see someone put a boattail or partial boattail on a sedan for a while. Good luck! It's looking great so far.

Wow, that looks great. How are you planning on covering it all up?

For the top part I am currently thinking of using a heavy transparent shower curtain liner, stretched over it and held down by retainers made of flat bar. I bought one for $6 at Walmart, and they seem to be at least as transparent as a convertible top window. Shoud be good for starters. If it works out well and if we get back on 40 hours at work, I would probably try lexan. The flat bar I can get for free from the scrap pile at work. I want to keep this as economical as possible. For the sides, I am thinking of either coroplast, aluminum sheet (I have a roll I picked up from a garbage pile once), or steel sheet from a dryer skin (which I might just do since I can weld it to the frame and add to the rigidity).

I have this idea for the rear. Same as I did for a trailer I made a long time ago. The lights are 4 1/2" round trailer/truck lights. The license bezel with backup lights is from a Celebrity (or other a-body) wagon.

http://www.angelfire.com/mi4/wagonma...house/BACK.JPG

Got the welder going again tonight. I didn't get to do much except strike a couple arcs, since it was starting to thunderstorm, but it seems like a stronger arc than when it was working before. It ended up being a whole slew of problems, not sure if they all happened at once or if it was cumulative, but I am thinking the latter. Out of 8 diodes, 5 were bad (3 dead and 2 shorted). The optocoupler and a resistor were burned up. 1 burned trace on the circuit board, a couple other melted solder joints. The diodes themselves were going to cost around $100, but after enough digging I found another brand with the same specs, and total cost with shipping was under $40. That includes a spare optocoupler and 2 spare diodes.

The board was a piece of cake to repair, after soldering 3 mpguinos.

This is a downstate weekend, so I should be able to get going again on the kammback/boattail early next week.

Got a little more done. 2 or 3 nights ago is the dark pic, then it stormed for awhile, then the light pic is before it got dark tonight. It is very rigid and still really light. I trimmed the trunk rods and added bumper supports (still need to brace to the hole in the center of the bumper). Bumper supports are scrap bedframe rails from the neighborhood piles. Only framing left on the shell is to make a piece each side to better follow the rear glass of the car, and to finish the bottom of the back part. Then I get to skin it and add taillights. I picked up 3 scrap water heaters in neighborhood piles so I should have enough skin for it. I also tried on the shower curtain liner, it fits like it was made for it and even without stretching it I can see halfway decent out the back. I am really hoping to have something that works by next Thursday so I can try it out going downstate.

I am really not fond of how this camera distorts the image. Most of my pics make the tail look twisted off to one side of the car, and make the rear transition look really sharp. It is not sharp, right now it is even less than the 15 degrees that I started with.

Kammback
 

The form looks dead on! I think,once it's skinned and you get a tank on it,you'll be smiling at the gas station.

The frame is finally all welded. It is totally sturdy, I push on it and it moves the car as a whole. Bumper supports are braced to a center hole in the bumper. If tomorrow is nice, I will start skinning it. I think I am going to skin it as shown in the photochop, with a panel at the front part that will follow the window better than any piece of flat bar I can form.

Sunday's progress. Got to work on it all day. Looks hideous now, but should look a lot better with a coat of burgundy Rustoleum.

Now just need 3 things. Paint, lights/license plate, and to attach the shower curtain liner which is just laying there in the pics. Still hoping to have it done by Thursday.

That is amazing but please get rid of those mudflaps.

Highway mileage gains??
 

:thumbup:Kudos for your well thought out work on a sedan Kammback. I am sure many of us are hoping you can log some good fuel mileage data over the long weekend. Do you have similar highway mileage data that you can compare to, with trip conditions as close as possible to your new data? I am eager to see if you notice a significant, measurable increase in fuel mileage at highway speeds with the partial boattail.

Also, I couldn't quite tell from the pictures if the clear top part is still hinged to allow access to the trunk.

I think we might learn more from some quick coastdown tests than MPG figures (unless you're planning some A-B-A with your MPGuino... don't let me discourage you!)

I haven't stopped by this thread for a while - wow, you've done a lot!

It's probably going to be another week before I finish it. First I need to sharpen my drillbits to attach the shower liner. And it's been too windy to paint it. Then since I am still cut back on hours, I wanted to find a deal on tallights. I found some on ebay, for about $1 a piece including shipping and they are supposed to be here next Thursday.

The clear part does not hinge. The whole thing hinges at the back of the framework that comes off the bottom of the bumper. I have a pic at home I can post. It still bolts to the rods on the trunk so it is not going to flip up or anything when driving.

Not sure about the coastdown tests. Michigan has these whipping winds that never quit and change direction a lot. Plus the roads are beat up. So it is nearly impossible to get a consistent coastdown test anywhere. I'd be better off just seeing how my mpg is with the guino on a given trip where I know about what I should be getting based on weather, temperature, and wind.

Finally it is pretty much done. Yesterday I cut the taillight holes and painted it and wired the lights. Today it rained for awhile then later I stretched the shower liner over it and attached the license plate. Then I ziptied a piece of coroplast into the bottom of it so it doesn't catch air from below.

I still have to add backup lights, but the wiring is done. I am going to somehow fit in these new driving lights I have had laying around for awhile.

Also from the pics I see my taillights do not have reflective lenses, so I need to add some reflectors or reflective tape.

Also need to add a license plate light. But it's going to be probably the end of June before I drive it at night again, so I can get those things done whenever.

I'm pretty pleased with how it has turned out.

Monday I go back to work, so let's see how it affects my mileage.

I WANT FE RESULTS!!!

I CAN'T WAIT!

:thumbup:

Wooohoo, looks great!

From a distance the round tail lights make it look almost like a Corvette.:) I'm surprised how smooth the shower curtain turned out, do you think it will stretch loose in hot sun?

I can't wait to see your results either.:thumbup:

Hard to tell right now if it helped FE. 30F and wind and rain all morning, plus I had to drop 2 kids in 2 different places on the way. The way home should give a better indication if it is helping.

Have not seen much sun this year so I'll have to wait and see if the curtain heats up and stretches. It was about 40F when I installed it, had to lay boards on it to keep it from blowing away. (Where's that global warming anyway, it's June and I am still running the woodstove.) I stretched it pretty good on there and used a screw and washer at least every 3" with the rough side of the washer down.

A coworker happened to be following me part of the way this morning and he said it looked like a Corvette or Delorean, till I turned the corner then he knew who it was. I was actually shooting for the tail end to look like my old trailer in the pic, which I made to look like a semitrailer, but then I realized I didn't have another license/backup bezel. Now I see it does look kinda cool, like a vette.

One thing I noticed this morning is the curtain was all fogged up so I had to use my mirrors. Another thing is I am getting reflections from the inside of the framework and back of the car which makes it harder to see. GM solved this issue with the windshield of the APV vans with black carpet on the dash, so I may look for some black carpet and fill the area.

This is something I have been thinking of trying rather than the shower curtain, and is cheaper than plexi or lexan. But for now, I want to keep it as cheap as possible since I don't have much money to spare.

One Step Ahead Baby - Clear Banister Guard Kit

Well so far it is tough to measure, but it appears to have given me about a 5% improvement in FE.

Going downstate last time I had a headwind both ways (entire way south, then the wind shifted north for most of the ride home). I got 38.3 there and 39.5 back.

Last time before that I went into a south headwind downstate I got around 36.5 there then about 42.5 coming back in the tailwind.

The last few days it has actually warmed up, 70F in the sun for part of the day. I got 35.5 one day home from work, never topped 35 before except maybe once. Got 34.5 this morning after sitting all weekend and it was about 40F. Coming home today should do well. I am likely getting a small improvement here too, not much but better than nothing. The wind changes so much it varies but it seems like I am doing a little better overall. In woodsy spots with no wind I am getting about 5 instant mpg better. I think the cold weather has trumped most aero gains, but now it is warmer hopefully I will see more.

The shower liner has stretched a little in the middle, it did almost right away then no more. It has a tad bit of flop at anything below 20 mph, then above that it stays solidly pulled out. So either there is vacuum back there, or it is like the bernoulli effect where the fast moving air across it keeps the pressure low and keeps it taut.

Going downstate last time I got a LOT of looks on the freeway, like probably 3 out of 4 passengers turned around and stared after passing me. Maybe I need a little advertising like an ecomodder.com logo on the back and average mpg.

FE
 

Wagonman,I struggled through an entire winter with the bellypan on the T-100.Nothing I could do would produce results until the spring,when temps finally eased.I like to think you'll have the same experience with the Celebrity.------------- I'm so impressed with what you've done,I've had two photos of your car printed in landscape,one for my permanent home reference and one copy to keep in the cab of the truck to show people who ask about what I'm doing.You'll be traveling with me in September when I do the trailer test.I think folks will get a big kick out of what you've done.Congratulations in advance for your expected higher mpg,I look forward to your updates,Phil.

Its pretty funny the amount of attention that 'tails get. I keep seeing other people acting strange when they see my car.

Is there any way to bring the tail end of the vehicle to a point like the trailing edge of a teardrop?

point
 

If you've seen the template from Darin's Project: making a permanent Metro Kammback,you'll see the length necessary to completely eliminate profile ( pressure) drag.Not very practical for daily driving.--------- The trailer project I'm targeting for September will be a way for me to investigate a "full" tail.Since we expect "length" with a trailer it's not a "hardship." By making the trailer a "boattail",it provides a safe way to investigate the inherent gains possible by a full tail.---------------- Since I like to camp anyway,by extending the length,I get a full boattail and a place to "live" out on the open road.The moveable gap-fillers between the truck and trailer face provide a complete flow support surface,from the T-100's nose,to a point 12-feet behind the truck.------------ The wake will be reduced from 29 square feet,to about 1.5 square-feet,to accomodate the rear license plate and taillight pods.Profile drag will be virtually eliminated.They'll be a little skin-friction penalty and increased rolling-resistance from the trailer and its axle/wheels/tires.I got 50-mpg pulling a trailer behind the CRX and it was nowhere as streamlined as what I'll achieve with the "Viking" hull-based unit.From the equations,the rig might see 40-mpg HWY,and 36-mpg Interstate.No telling 'til it's over,hence the premise of the project.