(first posted 6/27/2014) Over Father’s Day weekend, I flew up to Denver and drove a 1968 Mustang High Country Special up to Steamboat Springs, Colorado for the Rocky Mountain Mustang Roundup (I’ll have more on that car and the drive up in a later post). While the show has a decided Mustang focus, other Ford powered vehicles are welcome at the show, including this 1984 Capri RS Turbo. This car is the Mercury equivalent to the 1984/85 Ford Mustang GT Turbo, a car the enthusiast world has almost completely forgotten.
If the Mustang GT Turbo is a forgotten car, this Capri is even more obscure. Not only is the RS Turbo version a rare option on the Capri, but thirty years out, the Fox bodied Capri has faded into the mists of time. Looking at the lines of this car, it’s clear why many folks mistake this Mercury coupe as “just another Mustang.” Trust me, I owned a 1982 Capri RS twenty years ago, and witnessed this model confusion first hand. But speaking as a former owner, this car is extremely original, right down to the Michelin TRX wheels. All in all, it’s a great subject for today’s post!
In the early eighties, turbo badges weren’t really all that rare on Fox bodies. Starting in 1979, a carbureted turbo four cylinder was offered in the Mustang Cobra and Capri RS. In addition, in 1980 this engine briefly appeared in the Fairmont Futura coupe. Rated at 130 horsepower, it offered a peak horsepower rating close to the 1980 4.2 liter (255 cubic inch) small block, but supplied far less torque. Placing the carburetor above the turbo inlet led to major drivability issues, especially during cold starts. While Ford needed economical engines to make their Corporate Average Fuel Economy (CAFE) numbers, the carbureted turbo four wasn’t ready for prime time and Ford dropped it in 1981 (although some sites say Ford built a few in 1982 for the Canadian market).
In 1983, Ford brought out a much improved 2.3 liter turbo (this picture is from our featured car). This new engine used multi-point fuel injection, and made a respectable 145-150 horsepower. Ford developed the engine for its new “euro-style” Thunderbird, but decided to offer it in the Mustang GT and Capri RS, thinking that greater sales volume would help amortize the development costs. However, due to decreased oil prices in the early eighties, the demand for high cost, high technology, high power, economical engines dropped off (if the demand was ever there), and Ford’s production capacity for this engine exceeded the sales numbers.
Nowadays, these turbo powered cars are rarely spotted on the street. I’ve been looking to capture pictures of a 1983-84 Mustang GT Turbo for the past two years, and have yet to spot one. In fact, at the Las Vegas Anniversary celebration, I looked all day and didn’t find a single turbo GT among the several thousand Mustangs (although there were two or three Mustang SVOs).
Speaking of the SVO, most people assume these ’83-’84 turbo cars use SVO technology. Looking at this head-on shot of our Capri RS, it should be obvious the inspiration is far more GT than SVO. The center mounted hood scoop, quad headlights, and Marchal Fog Lights all came out of the GT parts bin. Overall, the look matches Ford’s brute power playbook, and shares none of the SVO’s aerodynamic styling elements. In addition, this turbo four lacked the intercooler used in the SVO, and fell short of the SVO’s 175 horsepower rating.
For further proof of the GT linage, check out those four bolt TRX wheels. These wheels arrived on the scene in 1979, and while they were on their way out in 1984, they were definitely a GT option. In contrast, the SVO chassis came with unique 16″ wheels mounting Goodyear Eagles, used the five bolt wheel pattern from the Mark VII, and included disc brakes out back. This car used the GT’s four bolt pattern, with mounted drum brakes on the rear axle. There’s nothing wrong with this approach, but it takes more than a turbo engine to make a car into an SVO.
The 1983 Capri included a new backlight and tail light panel. When the Fox bodies came out, I liked the Capri’s flared fenders, but felt the front and rear clips were far too close to the Mustang. This new tail helped differentiate the ’83 Capri, but Ford dropped the Capri three years later. I guess the changes proved to be too little, too late. Also, check out that lip at the bottom of the window glass- If that’s intended to be a spoiler, it’s probably the smallest air dam ever mounted on a pony car!
The Capri interior also suffered from Ford’s cloning stamp. I’ve owned a couple of early Fox bodies, and outside of the steering wheel badge, I don’t see a single element here that’s unique to the Capri. I suppose the detailing on the instrument panel fascia or the door panel may qualify, but everything else screams “Mustang.” The Fox body interior was nice enough for the time, but Ford should have added something to justify that step up to a Mercury.
In closing, let’s check out this rare “RS Turbo” badge. The internet doesn’t provide much information on these cars, and as is often the case, provides conflicting information from site to site. Some sites indicate all ’84 Capri Turbo’s came in this dark grey paint color using the bright orange and red accent stripes you see here. Mercury may also have called these cars the “Charcoal Capri.”
At this point, I’m not too sure- I know Ford offered the Mustang GT Turbo in several colors, so perhaps the Charcoal Capri was a special package. Regardless of the paint and trim packages offered in 1983, I’m confident this little turbo hatch deserves a place here at Curbside Classics!
Related reading: Michelin TRX wheels/tires
Now THIS IS A REAL TREAT the Mercury Capry! After all those Mustangs… Thanks for posting 🙂
I have an 84 Mercury Capri RS Turbo for sale if you know of anyone wanting one to restore.
Do u still have and where u located?
I do still have the car, I’m located in Sparta N.C. If you are interested email or call me. comet_066 @ yahoo.com. 336-928-0385
This is a predecessor of the SVO. The SVO evolved from it, not the other way around. Incidentally, the best way to get a Fox Mustang is to buy an SVO that someone squirreled away when it was nearly new, thinking that someday it would be worth fixing and collecting. Then, rip out that silly lump and put in a nice 302. SVOs change hands in collector condition for a fraction of the value of a decent GT, but they have much better chassis, brake and interior components. All they need is a good engine, and you have the car Ford should have built.
“All they need is a good engine, and you have the car Ford should have built.”
The SVO was expensive though. Nobody would have paid that huge premium for the same 5.0 in the GT. And the handling suffers greatly with the v8, even if you have all the upgrades. That defeats the purpose of the SVO.
From what I’ve seen, the resale today between the GT and SVO is pretty similar. Personally, the SVO is too specialized for me to consider owning one. With a little added boost it is quite an engine. Rough, sure, but it’s a Mustang so who cares?
With a little help from Car and Driver’s archived reviews, I found that the ’84 SVO weighed 3,102 lbs and the ’85 GT weighed 3,167 lbs. Part of the SVO’s mass is its higher equipment level, but the engine isn’t that much lighter than the 302, which was always one of the lightest V8s, comparable to some British fours. If someone were building an ideal Fox today, aluminum heads would open up the potential for an SV8 that handles better than a stock SVO.
Agreed. Most of the SVOs handling capabilities over a GT or LX 5.0 are from the substantial suspension and braking improvements fitted to them. The weight difference between a 2.3 Turbo and a 5.0 alone really doesn’t amount to much, the 5.0 is light for a V8 in the same way the 2.3 is heavy for an inline 4, add a turbo to the mix and it’s even heavier.
I wouldn’t V8 swap an SVO though, that’s just blasphemy in my book.
I stand corrected. I owned both a normally aspirated 2.3 and a 5.0 GT, and the 2.3 felt a lot better through the twisties than the GT despite the limitations of the weaker suspension and smaller tires. I didn’t realize the SVO was so heavy. Even the front/rear weight bias isn’t as far off as I thought, within a percent.
Yeah just go to the Ford UK parts bin and get a Cossie, that will blow V8s out of the water.and bolt right in
This brings back a flood of memories. A year later, I was in the quest for my first new car. The turbo was not on my radar at all. I test drove a TBird Turbo Coupe and hated (make that HATED) the drivetrain. Dammit, there was no reason that a Red Blooded American Male should have to settle for a rough, peaky, torqueless four when the same company makes a silky smooth yet powerful torquemonster V8.
I test drove a Capri 5.0 but vividly recall that the Mercury salesman was much better suited to selling Grand Marquis and Town Cars than anything high performance. That dash looks like the one in the Mustang GT that I tested. It was my least favorite feature of the car, and reminded me of every dash in every FoMoCo product since about 1972.
I bought the VW GTI, but still wonder if I should have bought the black Mustang. Owning a Capri would have been a long nightmare of having to try to explain to people what it was. Oh yes, this is a fabulous, fabulous find. I had forgotten that the Turbo version of this car ever existed.
Many a time I wished I had a 5.0 HO under the hood of my Turbo Coupe, especially in traffic with four aboard and the AC on. 🙁 But on the open road, the turbo four worked reasonably well enough.
I had an ’84 GT in charcoal, the dash looked OK in that. The gray and black on red doesn’t really work though.
Neat looking Mercury, but sure does look like a Mustang. I really like the front view especially the old school license plate and the missing “I” is just another detail.
If I owned one I would be seriously temped to switch them around to read CRAPI.
My friends grandfather had a cheapo 4 banger 79-80 Capri that we nicknamed the CRAPI.
Get the Aussie ragtop and that is the CORRECT spelling.
I liked this generation of Capri, and thought that the bubble back window distinguished the car from the Mustang. It was what the car needed.
The bubble back window had originally appeared on the Mercury LN7, but car was discontinued, and Ford appropriated that styling treatment for the heavily revised EXP. The Capri died around the time the revamped EXP appeared.
Capris weren’t a common sight when new. Undoubtedly a big reason, as jpcavanaugh noted, was that the dealers weren’t too enthusiastic about selling them. It didn’t help that Lincoln-Mercury, by the early 1980s, wasn’t exactly synonymous with sporty cars of any size or style.
I’ve never seen one of these in the metal,unlike the equivalent Mustang.
You would expect Capri sales to be down by the time the new hatch came around due to the sales aging for this type of car, Mustang included. The ratio of Capris to Mustangs in ’79 was pretty typical Mercury to Ford IIRC, but after ’83 Capri sales just stopped. I blame that almost entirely on the bubble hatch, it looked terrible with the car’s sharp edges and tall body. The ungainly proportions were made all the more apparent when compared to the strikingly beautiful Z28 which had become the new hot pony car.
Agreed. I have always thought that bubble hatch was ugly. Almost as ugly as the notchback. The GT Hatch is where it was at.
My first new car was an 81 Capri Black Magic. Basically, a Capri RS with gold accents everywhere. It had the 255 V8. Brother got an identical one but with a V6. His had all the bells and whistles (and T-Tops). The Capri/Mustang comparison was always part of the conversation. There was just no brand identity.
I first laid sight on the bubble back attached to an LN7 and thought they looked very nice. Then, I saw the same thing applied to the publicity shots of the new ’83 Capri and thought, never again!
Come to think of it, 83 was a bit of a “corner” for Mercury. They came out with that wierd horizontal rear window on the Cougar to differentiate it from the T-Bird. It was almost like they were trying to chase customers off.
The 1983-1988 Cougar was quite successful. Even Ford reportedly didn’t expect it to sell as well as it did.
The 1983-88 Cougar and Thunderbird are the perfect example of how to successfully differentiate two vehicles that share the same basic body and sell in the same market segment. People who didn’t like the Cougar did like the Thunderbird, and vice versa.
+1 (though I’m biased)
Mercury did an excellent job of differentiating themselves from Fords in the 80s, the Sable instantly comes to mind as well. Compared to the 70s where 2/3rds of the Ford/Mercury lineup shared the same exact 1972 Montego Bodyshell, Mercury in 1983 seemed damn near autonomous.
Also, in addition to my fondness for the Cougar roofline, I think the Mustang notch roofline was much more attractive as well. The hatchbacks never looked right without a spoiler, (which helped to visually flatten out the deck more so than do anything fancy with air flow) and I think that’s the big part of the reason the Bubbleback on the 83 Capri doesn’t work so well.
Funny, today in traffic I saw about an 84-86 vintage Cougar with whites and wires, it still looked in pretty good shape, I was able to stare at the blocky roofline for a few minutes, I always thought the were odd looking, but not bad, down here in the SOFLA, almost 90% of that vintage Cougar received some sort of dealer add on glop top “Caliente” package-with the Caliente in gold of course…..which made them into pretty hideous pseudo pimp mobiles for old ladies, some even got continental kits too.
Autonomous? I wouldn’t go that far, in 1983, most of the Mercurys were still pimped out Fords, true that the Cougar was a little different on the outside, but the interiors were pretty much the same, same for the Fox Marquis and LTD and Crown Vic and GrandMa, as well as the Lynx, LN7 and the Capri, though I was impressed when the 1986 Sable came out and it was SO different from it’s Ford counter part, different sheetmetal and a different DASH, wow, that was a big one for Mercury, which usually had the same Ford dash with extra wood silver gauges, I thought maybe Ford had really decided to up Mercury’s game.
But it was all a blip in the radar.
I just mean autonomous comparatively speaking to previous and succeeding Mercury eras, not nearly as autonomous as GM brands in their heyday, but by Ford standards pretty good. They had some legitimate distinctiveness for one of the few times in the brands life and the 83 Cougar was really the start of that, followed by the Topaz (in sedan form) and then the Sable.
The bubbleback Capri I’d argue could be a sort of successful attempt to make it distinct from the Mustang too. The problem IMO was that the damage was done, if the Capri came like it was in 1983 from the start in 1979 it probably would have made more of an impression as a “Capri” rather than just a Mercury Mustang. It wasn’t distinct enough from the start and when it got distinct it came off as a half assed appendage tacked on to the same old body.
I owned an ’84 Capri like this (same gunmetal gray color) but with the 3.8 V6. Actually, it was an excellent car with its 140 h.p./240 lbs. ft. of torque. It was a surprisingly quiet and refined tourer that didn’t kill me with insurance premiums. I was told the bubbleback was the largest piece of glass (certainly the heaviest) ever put on a car.
I had a 85 Capri. It came with a 4 banger but I quickly improved on that. It’s surprising how a 351 wakes a car that light up.
I always liked the look of these TRX wheels, although they weren’t in use for long. For any company other than Ford, selling these cars with expensive and rapidly obsolete tires in a size nobody else made would have qualified as a dirty trick to play on the customers.
I liked the look of these with the exception of the bubble back. The front end always looked better to me than the equivalent Mustang.
Regarding the metric system, it’s amazing that metric tires sizes have flopped. But we got liters for motors, etc.
You would think anything with a turbo would go over big in a mountain state. Knew a guy that used to race flathead Ford Jalopies. He told me that Ford sold a higher compression engine (head was only difference) for the rocky mountain states. He was running heads he found in Denver. My BS meter wasn’t fully developed yet (1959) but never caught him in a lie(of course no google at the time) so I believe him.
EFI did a lot to erase the normal drivability difference but the turbo would certainly help liven your life in the thin air.
I have actually driven one of these, at a sports car club track day at Pacific Raceways SE of Seattle. 120mph tops in the straightaway, and IIRC the power didn’t really come on until 4K rpm. I spun out downshifting into 2nd going into turn 3a, and the car’s owner spun out in turn 5a-b while I was a passenger (fortunately caused no crashes or car damage in either case).
The car’s owner had the suspension completely set up for autocrossing, and a few years later had transplanted a built 460/C6 9″ ford rear end drivetrain into it (along with 5-bolt front hubs). I got to ride shotgun for an autocross event and watched the G-meter suction-cupped onto the windshield in front of me read 1.24G while I ripped the handle right off of the door!
This Capri was a handsome Fox variant. Different enough on the outside to justify its existence.
I was suspicious of any domestic four at the time, Ford in particular, worse yet in a traditional rear drive car, and a turbo, yikes!
I thought that the Ford 2.3 four-cylinder from these years was reliable. It just wasn’t particularly refined, even in standard form, although given that GM was still offering the Iron Duke, that was hardly a cardinal sin in those days. Or is my belief mistaken?
As noted, I was Suspicious of any domestic four at the time. Virtually nothing in the past would suggest that a turbo 4 Ford would have been anything but mediocre, if not outright bad. This could have turned out to be the engine that pushed the Japanese back into the ocean, but I never would have bought it in 1984.
A while back we had what may be an even rarer Mercury in our service department, a 21k mile ’83 Cougar XR7 Turbo. First one I’d ever seen.
You know this post is a coincidence as at a stop light I saw a 79-86 Capri in Laurel Maryland today while driving home from work. it was all black with dual pipes driven by a middle aged woman. Now Capri’s are rare around here(though there is a guy with a souped up one in nearby Savage MD) but what made this interesting was it was a convertible. Now I could have sworn that the only Fox Capri’s made were hatchbacks and that the Mustang was the only convertible and chalked it up to somebody putting a Capri front clip on a Mustang convertible. However when I got home and googled it, I discovered that ASC/McLaren teamed up and made a bunch of Capri Convertibles and that one I saw most likely was one of them. Sadly I did not get to take a pic but if it is rolling around Laurel, I will spot it again and take its picture
http://www.ascmclaren.org/WhatIsAnAscMcLaren.html
Wow, I just learned something today, by way of following the TRX wheel links. Never knew they were an oddball size/configuration but I do remember liking the design on those cars.
I remember the Capris. Never liked the bubble back, it just looks….bloated. But other than that, the bodystyle is cool looking. I always did prefer the ‘4 eye’ look to the foxy body mustangs to the bland aero facelifted ones from ’87-up.
I have mentioned on this site before that I owned one of the original 1980 Mercury Capri Turbo RS models. Mine had the Recaros and the TRX suspension and the four speed manual. To say the car was badly engineered is something of an understatement. In late 1984 we were looking for a replacement for our 1977 Olds Delta 88 Holiday and was hoping to find something smaller and good on fuel. My wife and I both had somewhat long commutes, but not having children yet, we didn’t need the space and thought a smaller car would do.
I was willing to try another turbo Ford after sampling my friends 1983 Thunderbird Turbo, it was a great car. In the even lighter Capri body, it would have been a pretty darn good performer. But, there were none to be found in all of Northeast Ohio or Northwestern Pennsylvania at that time; if I wanted a regular 4 cylinder or V8 RS Capri, no problem.
I waited until the spring of 1985, at which point I think the turbo RS was cancelled. We ended up buying one of the last 4 speed V8 Capri RSs (IIRC, they went to 5 speeds early in 1985 production). Unfortunately for me, we got one good year out of the 1985, by early 1987 the car was nothing but trouble…
I’ve never seen one of these cars in the flesh, but (oddly) wouldn’t mind having one now. Of course, in my MM garage, there would be a whole bevy of mid-80’s domestic muscle cars… But one of these would be reaaaaallly cool!
The car looks like it is original rather than restored (a new alternator perhaps?), and is in amazing condition. Presumably stored for a long time and low mileage?
It is a restoration (the owner had a photo album showing the before and after pictures), but as the TRX wheels indicate, he worked hard to maintain originality.
Wow, that is a lot off effort in refurbishing or reproducing hens teeth parts, decals etc
the fox mustangs always made me think, what if GM had dropped the F body at the height of the gas panic and then pony/muscle cars came back? would they have rebodied the V8 Monza and called it a Camaro?
I still love my little Black Beauty…sitting sadly under a tarp in my driveway… A great little 1983 5-speed V-8 Capri RS. I had to put her up a couple of years ago because I couldn’t find a reasonable way to replace her very expensive rubber. Now, she just breaks my heart every time I peek under the cover. Bubble-back and vague shifter included, I loved driving that car!
My favorite story about her was I had just finished re-building her old-school 4-barrel Holly, and went over to the local Ford/Mercury dealership parts place to pick up a set of the funky pre-heats that came off the manifold…anyway, I walk into the place and ask the guy behind the counter for the weird Robby the Robot arm looking sleeves, he asks me the year, make, model … Engine size questions… I answer … He proceeds to tell me they didn’t make that car with a V-8, and if I had the car there, he would show me how to (count my spark plugs) to figure out how many cylinders my car had. I bit my tongue, refrained from punching him in the face, and put up my best good girly girly face, handed him my keys, lead him out to where I was parked…and watched his jaw drop after he popped her hood. Then I simply turned to his growling @$$ and asked him if I could have the parts I asked for NOW?
Put some aftermarket wheels and tires on it.
Hmmmm…thought I did respond to this… Didn’t have the money then…and now six+ years later it has left me with more of an overhaul than I have the time or money for…
Everything looks better in gray with orange stripes. Get a buddy with the same model in orange with gray stripes and pretend to be Tyco slot cars! The living room rug will cushion any rollovers.
Okay, probably shouldn’t post before I’ve had any coffee. 🙂
HA! I know all about those tyco slot cars! I have a handful of the Tyco 4 eyed mustangs…A few nice color schemes, but some are VERY wonky. Honestly, I cant say Im a huge fan of charcoal grey as a main color for a car at all. For wheels, or for a grille or even a lower stripe, its ok. My gripe with these is the hogged out front fenders that just look awful….
LOL! Love it. Wait, are those Michelin TRX radials?
how fast would a 150-shot naws make the capri 5.0?
I have a 1984 White Capri RS that has sat in a heated garage since 1989, inspection sticker on wind shield says 11/89. I don’t see myself ever driving it, maybe sell for the right price. Anyone interested email me for pictures and details. Located in NE PA And by the way, it has a 150 HP NOS system on it, full bottle never cracked once.
Could you send me some pictures or particulars of the car?
I came across this article today, probably a year late, but do you still have a Capri to sell? My e-mail is sellis1012@sbcglobal.net. I am in Dayton, Oh.
Steve
I bought an 84 Capri RS turbo in 85. Toasted the turbo 4 within a year, swapped in a bored/stroked 331 v8 and ran 12.9’s @105 in the 1/4. Those were the days. If i had known how rare they were, I might have kept it stock.
Please advise
Send me an email address and I can send more pictures
Notice 11/89 inspection sticker, 45,000 miles on body, less than 200 on motor, trans, rear, brakes, bushings, etc
Interior still smells like it did when it was new
NOS system never tried yet, just licensed it as an antique, did 11.66 1/4 on street tires, will get into the 10’s on giggle gas no problem
Hasn’t seen a drop of water not even to wash it for 25 years!!
Clearer pic of NOS setup. Super Power Shot plate system, with purge valve, RPM switch, adjustable fuel reg, safety switches, bottle heater with pressure control and interior NOS pressure gauge, remote bottle valve, the works, just have to finish wiring it all
Thank you. bad time to be looking at a car.
This is my 79 Capri RS Turbo 4 speed.
It’s a 62k mile one owner all original survivor.
I wonder how many like this exist?
Please advise
“thinking that greater sales volume would help amortize the development costs. However, due to decreased oil prices in the early eighties, the demand for high cost, high technology, high power, economical engines dropped off (if the demand was ever there), and Ford’s production capacity for this engine exceeded the sales numbers.”
Now how many times have the best laid automotive plans gone awry?
Especially in the early 80s, more than they went right.
I often think, what if they developed tuned port injection in 1978 instead of the Oldsmobile Diesel? There were a few costly dead-ends during that time.
Not that I’m one to defend GM’s decisions very frequently, but could it be that microprocessors weren’t cheap enough yet to mass-market the sorts of engine management systems that gave us peak-car from the nineties through the first decade of the twenty-first century? Diesels of the day used mechanical injection pumps, so they didn’t really have any engine management.
D and K Jetronic debuted years before, and are pretty primitive as compared to closed-loop Lambda controlled systems that came later, but they still offered power and drivability improvements compared to carburetors. Beetles and Opels had Jetronic before 1976. Don’t forget that they had homegrown fuel injection on 76 Sevilles, and the 368 had fuel injection before (and with) the 4-6-8 system. If GM could’ve integrated port fuel injection across the board by 1980, even if it was constant-flow and basic, everything sure would’ve been different. Had they spent the Oldsmobile Diesel development money on scaling Jetronic type systems, it would’ve been better spent. Hindsight being 20/20 and all that. Remember, it would’ve continued to scale up, you could go from constant flow to batch fired, to sequential without having to change the engine hardware or manifold. The Olds Diesel was a pure dead end.
I don’t think that the results of any of the Cadillac fuel injection systems were satisfactory, and even after VW moved to Pennsylvania they still couldn’t maintain price competitiveness with fuel injection. Opel was briefly fuel injected right up until GM decided they were too expensive for purpose and started rebadging Isuzus. Look at the premium BMW had to charge for the tii in 1974, and at how ordinary the Bosch-injected and expensive 320i was in performance. It was the way forward, but it just wasn’t a real panacea before electronic monitoring of inputs and outputs.
GM did do port EFI for the 500 in Eldos and it did use Bosch licensed injectors. It was a very expensive option, I want to say it was $500. Of course since it was a option that price had a high profit margin so it probably cost them $125 per car over the 4bbl. It did nothing for the rated HP and it was not a real help in driveability either. Like many of the other attempts at optional fuel injection once they were a few years old many of the cars were converted to a carb to cure the driveability issues.
However GM kept with it and in fact leapfrogged everyone with the Cadillac Digital Fuel Injection and then their TBI system brought the most advanced system in the market to the masses.
@Dave Skinner That small spoiler at the trailing edge of the hatchback glass is just that, it cleans up the airflow and deters it from curling under the tail panel/bumper and creating lift. They are much more prevalent on current designs that have convex/sloping/fastback rear glass.
In late 1978 while considering the purchase of the then new Mustang, I chatted with a young guy who had a turbo Capri parked at a grocery store where I was shopping. As his Capri was an early build there was an issue with the turbo in his car. And I also recall the early turbo engines had valve train problems. He disconnected the turbo in frustration.
I bought my Mustang Cobra in July of 1979. My car was built in May and I had no problems with the turbo engine or the car. My only gripe was the poor fuel consumption. Around 20 mpg, Imperial gallons on the highway. The small gas tank didn’t help either. I did not consider buying a Capri as I was put off by the squarish look of the car.