Blowing Up the Mould

No more Mr. Stingray. 

All images: Author’s collection

As the Corvette became a more serious proposition after the commercially successful but softer by the year C3 Stingray, its publicity material followed suit…

When introduced for the 1968 model year, the voluptuous Corvette Stingray did not meet with the universal praise from the press that GM had hoped for. Of course, the C3 had big shoes to fill after its much loved predecessor, but embarrassing initial quality glitches as well as a perceived of loss of focus as far as the sportscar aspect was concerned did not help its plight either.

The buying public thought otherwise however, and as the seventies unfolded sales of the C3 actually went up year-on-year culminating in its best sales performance (for this particular model) in 1979. Nevertheless, those responsible for all things Corvette within Chevrolet division decided to change course for the next generation.

Designer Jerry Palmer had worked on facelifts of the C3 and was now tasked with styling the future Corvette. Chief engineer for the C4 project was Dave McLellan, successor of the famous Zora Arkus-Duntov. Palmer was a sports car aficionado and not exactly to the liking of some of his superiors at GM; often commuted to his job in his Ferrari 308GTB, an interesting connection to the Corvettes he worked on professionally being that his 308 was one of the rare early vetroresina fiberglass bodied examples.

Several experiments with mid-engined Corvette prototypes notwithstanding, the brief remained a front-engined V8 two-seater as before but without the superfluous styling gimmicks of C3 and with handling and braking characteristics to rival the best Europe had to offer.

All new from floor to roof, except initially at least the engine, the new Corvette that ultimately emerged still displayed the traditional Corvette styling cues its customers expected but in a sharper, lighter and more compact (9 inches shorter, 2 inches wider and a wheelbase shorn by 2 inches) package. The new so called Doug Nash 4+3 manual transmission, a four-speed manual with an automatic overdrive on the top three gears, was an interesting concept but did not earn a lot of fan mail during its existence due to its baulky gear linkage and some durability issues.

Contrary to previous ‘Vettes, the body panels of the C4 were not made from regular fiberglass but out of sheet moulding composite (SMC) plastics. Underneath the new skin the old body on frame construction was also relegated to the past, replaced by a uniframe. This is different from a true unibody/monocoque in the sense that only the door posts, windshield frame, the frame overhead behind the seats and the rear portion of the floor pan were welded into one assembly.

The front and rear five-link independent suspension featured transversely positioned composite material leaf springs, and the C4 Corvette was fitted with unidirectional tyres especially developed for this car by Goodyear. Vented disc brakes on all four wheels provided the stopping power.

Freerk Schaafsma, a Dutch-born engineer on the C4 development team, was one of the major contributors to the new underpinnings and in a Car and Driver report noted: “I was born and raised in Europe, and I know that a car doesn’t necessarily have to be like a European machine in order to be good“. He and his colleagues openly admitted however that the Porsche 928 was the data point on which a great deal of C4 development centred. “When we compared our car against the Porsche, I can tell you there were a lot of good feelings at Chevrolet” Schaafsma concluded.

By Corvette standards the 205 hp delivered by the carryover L83 engine with throttle body crossfire injection appeared rather tame, although it is important to keep in mind that US-specification versions of the Porsche 911 Carrera and Ferrari 308GTB QV had 207 and 233 hp at their disposal respectively, so the power deficit was not as large as one might think.

As the C4 Corvette neared its planned introduction, several quality issues with parts suppliers and logistical hiccups in the factory were the cause of an unusual occurrence: there would be no 1983 model year Corvettes. Instead, GM started the 1984 model year early. On January 3, 1983 the first 1984 Corvette rolled off the production line – it would not be until march of 1983 before the first cars were delivered to customers. During this unusually long model year well over 50,000 Corvettes would be sold, evidence that the new direction for America’s only sportscar had been accepted by the buying public.

The motoring press had mostly positive things to report about the new Corvette- roadholding was excellent and handling confidence-inspiring which made it easy to drive fast. To quote (translated) the normally not very US car-friendly German car magazine Auto Motor und Sport: “lightning quick yet very benign“.

The styling also drew many positive remarks. Testers were less happy with the harsh ride which, especially with the optional F51 suspension was a bit too much on anything other than a billiard table-smooth surface. The gearbox was deemed baulky and many scribes would have preferred analogue instrumentation over the complex digital instrument panel.

Tron called, they asked for their movie set back.

Over the course of its life the C4 Corvette benefited from continuous development; the suspension settings were softened slightly in 1985, and in the same year a new L98 V8 with electronic injection and 230 hp replaced the old L83. A significant event for traditionalists was the return of the Corvette convertible for 1986 after an absence of 11 years, the suspension settings were augmented once again for 1988 and the year after a ZF six-speed manual transmission replaced the 4+3 gearbox.

The big thing for the 1990 model year was of course the introduction of the mighty ZR-1 with its all-aluminium 390 hp 32-valve quad OHC V8 engineered by Lotus, the company having become part of the GM portfolio in 1986. This engine, known as the LT5 and manufactured not at GM but by Mercury Marine propelled the Corvette ZR-1 straight into supercar territory with a maximum velocity of 175 mph and a 0-60 time of just under five seconds. Over six model years 6939 ZR-1s were produced, and only available domestically. Another welcome change for 1990 was a remodelled dashboard, still partly digital but ergonomics and legibility were much improved.

An in hindsight perhaps unwise decision was a 1991 external facelift whereby the regular Corvettes now received the same rear end styling as the ZR-1 with square taillights; this change diluted the exclusivity of the ZR-1 as to most eyes all Corvettes now appeared virtually identical.

A more powerful 300 hp LT1 V8 powered the 1992 Corvette, again moving the standard car closer to the ZR-1. The year was cause for celebration at Chevrolet as the one-millionth Corvette was built.
As the end of the C4’s run neared, modifications were fewer but for its last season, 1996, an optional 330 hp LT4 engine became available.

To commemorate the final year of the C4 two special editions were offered: the Grand Sport and the Collector Edition. The Grand Sport was inspired by the original item of 1963 and available only in dark blue metallic with a white stripe (which made it resemble a Dodge Viper GTS to some), special black wheels and two bright red hash marks on the driver’s side front wing. A limited edition of just 1000 were made.

The Collector Edition had a paint job similar to the 1982 version that concluded the C3’s production run, painted Sebring silver and of course featuring special badging; 5412 were produced at a premium of US $1,250 over a standard Corvette.

The C4 set the Chevrolet Corvette firmly on a course towards becoming an alternative to be reckoned with by the international (read European) establishment and although it was just the first step on that journey, consecutive generations have remained true to this missive.

Early brochures for the Corvette C1 and C2, easily the most valuable now, were nothing exciting from a production values standpoint- often just simple folders and if they were stapled brochures they did not have many pages. The C3 Corvette continued this trend, but from the first brochure for the C4 model on (and just about every Corvette catalogue ever since) this changed radically.

Luxurious items, often in a matching envelope, they offered multiple high-quality paper pages and contained a wealth of detailed information; sometimes even with actual upholstery samples and paint chips.

For the C4 generation, the 1996 brochure is arguably the nicest with its arty cover, but every catalogue has its attractions as the theme changed almost yearly. The 1991 ZR-1 catalogue with its stiff carton slipcase is a very rare owner’s brochure presented to buyers who had placed an order for a ZR-1, so that item was never to be found in any showroom and is thus not easy to locate. The regular C4 brochures however can still be found for reasonable prices if one exercises some patience and shops around.

Author: brrrruno

Car brochure collector, Thai food lover, not a morning person before my first cup of coffee

14 thoughts on “Blowing Up the Mould”

  1. Good morning, Bruno. What a great read to start this workweek. I had no idea a man who has the same first name as I do was responsible for the chassis. I met a friend yesterday and our talk let us to the C4 Corvette, which was an unlikely topic.

    The brochures of the C4 are lovely too. I kind of want a Corvette now and I am wondering how much of this really is a coincidence?

    1. As Dame Edna might say, “Spooky….” I think, Freerk, that you should start looking for one now!

    2. Hello Freerk,
      Hmmm…. although I more or less expected you to react to the fact that a namesake was involved in the car’s development, that you also discussed the C4 with a friend yesterday is…indeed interesting, especially if you are among those who don’t believe in coincidence. I have never owned nor driven a C4 (I did try out a C5 many years ago and came away pretty impressed) I am afraid I can’t give you any advice either way on pursuing ownership of one, but think you could do a whole lot worse from a styling/performance/price mix perspective.

    3. I think you are right, Bruno. Not looking for a replacement for my E92 as yet, but the Corvette is on my radar now 🙂

  2. The ownership demographic of 70s/80s/90s US “sports” and “muscle” cars with their large displacement and very weedy engines in the UK is such that on seeing one I have an immediate and very strong reaction; they seem to be almost exclusively run by very strange men who wear cowboy hats and go to meets dressed up in some sort of weird Americana outfit.

    It’d be like BMW/Mercedes/VW owners going to meets dressed in lederhosen and listening to oompah bands.

    1. Hi David,
      I see what you mean; as a one time owner of a 1964 Lincoln Continental sedan I was also struck by the fact that most attendants at classic US car gatherings seemed to be stuck in some kind of “Elvis lives, yeee-haaa!!” parallel universe, garnished with the odd confederate flag and a generous smattering of tattoos of varying levels of size and scariness. Almost without exception, the ones I talked with were actually quite pleasant people, proving one should always try not to judge a book by its cover.
      However, neither me nor my car really seemed to “fit in” although the Continental certainly got its fair share of attention and compliments. Unfortunately no Americana meet ever had a “Mad Men” section where at least my car if not my own person would enjoy a more fitting environment 🙂

    2. I have visited may editons of the Saturday Night Cruise in The Hague and I see your point, David. I have to say that like Bruno I don’t fit in, but I never had a single bad experience with the people there.

  3. Good morning Bruno and thanks for featuring my favourite generation of Corvette today. The C4 really became a serious proposition in 1990 with the ZR-1. Of course, the British motoring press remained a bit sniffy about it because it wasn’t mid-engined and the Corvette continued, in the UK at least, to be regarded as the four-wheeled equivalent of Harley-Davidson motorcycles, a visible symptom of an ongoing mid-life crisis!

    (Apologies to any Corvette or Harley-Davidson owners out there whom I have cruelly stereotyped. I am a 60 year-old owner of a Porsche Boxster, so am in no position to throw stones inside this particular greenhouse!)

    1. Oh, that was by no means just a British peculiarity.
      In Germoney, the prejudices were quite similar. The majority of the readers of these car magazines, as well as presumably some journalists, did not even know that the Corvette had been a pretty good basis for successful racing cars for decades.

      However, the somewhat cheap feel of the interior, as well as the bling-bling electronic instruments used on the C4, did not help in acquiring a respectable image.
      (Up until the C6, the performance was in the “Supersport” class, but the interior was just in the “OK for an Opel Corsa GT” class. After that it got a bit better inside, provided you were a lover of “Japanese coal mines”).

  4. Ah yes, that LT5 Lotus quad-cam engine. There is a story surrounding that one.

    One of the key dimensions of an engine is the bore spacing. This is the distance from a bore centre-line to that of the next bore. Chevrolet’s small block has a bore centre spacing of 4.4″ (by comparison both Ford small blocks, Windsor and Cleveland, have 4.38″ and the Chrysler LA is 4.46″). All the small block Chevrolets up to and including the present LS run the 4.4″ dimension. That necessarily included the LT5 engine since its cylinder block was originally intended to be machined on the same transfer line as that of the regular push-rod engine.

    GM had a stake in Lotus (their major focus was the active suspension which had been developed there utilising the expertise of Dave Williams). They sought to make use of Lotus ability to quickly undertake and complete development projects. In Lotus’ engines area the was a design/development group headed up by Tony Rudd. The group had already developed a quad-cam four-valve engine intended for a Lotus sports car and also a possible future luxury sedan. Lotus had been promoting variants of the engine around and about for some time. GM took a look at this and considered it might have a good home for it in the Corvette. There were some issues. That engine was way too small. It was only 4.0 litres. It was low on torque. The standard pushrod engine had far superior bottom end torque since it had 5.7 litres. Remember, these were both naturally aspirated engines. Another show stopper was that the 4.0 litre V-8 would need an entirely new line to manufacture since it shared no critical dimensions with the small block Chevrolet. So, GM tasked Tony Rudd to come up with a more suitable design for a quad-cam V-8 engine for Corvette. It needed the bore spacing to be 4.4″. It had to be around 350 cid (5.7 litres) since that was the standard small block capacity at the time (not a good look making the top of line engine substantially smaller than the standard version) and it had to be narrow. This last requirement was vital.

    On the production line the Corvette’s engine was loaded into the car from underneath. The frame rails running along the sides of the engine bay set a maximum width for whatever engine was to be fitted to the car. The regular small block fitted between them with little issue. An issue for quad-cam engines with cylinder banks set at 90-degrees is that they tend to be wide and bulky (it is sometimes said that for a naturally aspirated street drive engine a quad-cam tends not to be as power dense as a push-rod engine). As the Corvette’s frame rails could not be moved any further apart it was necessary to ensure the new LT5 engine could be routinely line fitted between them. This provided a bit of a challenge for Tony Rudd and his colleagues. They succeeded by choosing a tight included valve angle and standing the exhaust valves up a little more than usual.

    Originally the cylinder block was to have been a common casting for the quad-cam and the standard engine. This meant it would have been in cast iron. On the advice of Tony Rudd it was decided the quad-cam ought to be cast in aluminium. This was a major change. There were several downstream effects from this. The biggie was that the bore was reduced. In the regular 350 cid small block the bore was 4″. When using an aluminium casting it was necessary (at that time) to incorporate iron or steel liners or sleeves in the bores in order that the aluminium pistons could reciprocate without galling and picking up on the aluminium parent material of the block. The use of sleeves meant that the bore had to be reduced slightly. It ended up at ~3.9″. This reduced capacity and so in order to get it back up the stroke needed to be increased to compensate (up from ~3.5″ to 3.66″). This had to be done in such as way as to not require the deck height to be increased (that would make the engine wider again, a big no-no) and not to allow the rod-stroke ratio to become too small (that would lead to excessive piston side-thrust with issues of friction and wear). Juggling variables such as gudgeon pin locations (move it higher in the piston, but not so high as to affect the rings), valve lengths, valve-spring installed height and so on allowed all the targets to be achieved. On top of all this there was the emissions* regulations to meet and, of course, changing some of these dimensions did have an effect on that. Not an easy challenge, but one which was successfully met.

    The engine was launched. It was exotic, exactly as GM wanted it to be. It sent a signal to the market, as GM wanted. It hit most of its performance targets. It also turned out to be quite expensive to manufacture. As stated in the original article above, much of it was manufactured by a contractor, Mercury Marine. This was partially as the result of choosing not to use a common cylinder block for the quad-cam and push-rod engines and going with cast aluminium for the quad-cam block.

    There is another string to the story though. There were some engineers who felt that to achieve the performance targets that GM had set for the Corvette’s LT5 engine there was no necessity to go to the exotic quad-cam layout at all. They believed that a careful revision and modification of the cast iron push-rod engine would provide the same performance for far less cost. The Lotus derived quad-cam spurred them to focus efforts on further developing the conventional push-rod 350 cid engine. They knew it was structurally more than strong enough. They were able to match the quad-cam performance quite early on. Before long they surpassed it, although Chevrolet did not bring to market these versions of the engine until after LT5 departed production.

    The efforts of GM’s in-house engineers resulted in the realisation that overhead camshafts are not necessary to achieve performance. Two engine designs resulted from this. First was a new generation small block Chevrolet with reversed flow cooling system and other novel features. Secondly, the all new LS series of small blocks presently in production. Meanwhile the quad-cam LT5 has quietly faded from the scene, forgotten by all except Corvette experts and marque enthusiasts. Fun while it lasted.

    *never underestimate how difficult and vexatious this is. It is one of the major reasons so many makers went to four valve engines…

    .

    1. Hello JT,
      Thank you for providing some extensive background information concerning the LT5 engine- much appreciated!

  5. As jewelery, the LT5 is beautiful, but as propulsion it was doomed to be an evolutionary dead end.

    There’s an old saying that in engineering there are no solutions, only tradeoffs. The art of engineering is making tradeoffs where the upside falls where you usually are, and the downside falls where you are usually aren’t.

    Unfortunately, the LT5 is a case of paying the price without reaping the reward.

    In the case of the pushrod/cam in block, the tradeoff is speed for size. Replacing four cams in the head with one in the block gains enormous weight and volume. The LT1 motor is a tiny thing, the LS series almost unbelievably so (about the same size as a 3.5L VQ35DE). The downside is the additional reciprocating mass of the pushrods puts a ceiling on RPM, and the two valve geometry puts a ceiling on valve curtain area.

    A large V8 has a bore and stroke of around 100mm. A large bore negates much of the flow disadvantage of the two valve design, as the large combustion chamber allows you to simply push the valve down further. A large stroke similarly minimizes the RPM disadvantage of the pushrod engine as you are already limited by piston speed.

    A 1995 C4 ZR1 with the LT5 is 111mph in the 1/4(*), the 1996 GS with the pushrod LT4 is only a tiny bit slower at 108. Dig a little deeper and you find LT4 heads flow 250cfm and the LT5 flows 300, the LT4 redlines at 6300 and the LT5 at 7100 – small gains at a huge price.

    Fast forward ten years and the mighty Mercedes M156 finds itself at a disadvantage to the smaller, lighter GM LS7. Fast forward to today, and here’s a comparison of the GM LT1 to the Ford Coyote – the Coyote is 30% larger in volume.

    (*) These are ‘Murican cars, so we use ‘Murican units. (***)

    (**) https://www.lsxmag.com/news/clash-of-the-titans-gms-gen-v-lt-vs-fords-gen-iii-coyote/

    (***) Strangely for a ‘Murican, the LS isn’t my favorite motor – most of my favorite engines are straight sixes.

    1. All of that makes sense, but what is 100mm? If you said nearly 4 inches… Sorry, couldn’t resist. In general I prefer the metric system, though, but in the case of ‘Murican cars i don’t mind ‘Murican units.

      I’m a straight six guy as well.

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