McLaren 675 LT Spider review - manic limits

Last year when the Powerball lottery hit one billion dollars, I sat down that night and spec’d out a dream car online. It just happened to be a McLaren 675LT Spider in the same blue color as the one I was able to review. There’s something about a Spider, in this case a hardtop convertible that has a strong appeal even when you have to protect yourself from the sun. This one is truly two cars in one, and as I discovered, more than just because of looks or catching a breeze.

This 675LT Spider is the owner’s fourth McLaren. He had good experiences with the 12C’s he owned and his P1 that I reviewed is somewhat famous, especially among Motor Trend readers. Being a fan of carbon tub (passenger compartment) convertibles, partly because the minor weight penalty for the roof coming off, the 675 LT is still a track oriented machine, said more so than their Ferrari 458 Speciale. Comparing to the 12C, which the 675 LT is an evolution of, the engine, engine tuning, transmission, and braking are all noticeably different and improved.

Also inevitable is a comparison to the wild McLaren P1. Leagues quicker with 903hp with better throttle response due to the hybrid system, the lighter 675 LT has a quicker turn-in and more grip. Of course the question of weight comes up. The owner’s experience is McLaren’s stated weights are spot-on, his P1 weighing 3300lbs, giving him no reason to doubt the 3,016 lbs stated by McLaren for the 675 LT Spider. This is a very light car by modern standards, especially combined with the output of the 3.8 liter twin turbo V-8 of 666hp. To put that into performance numbers, what has been reported in the quarter mile is low-mid 10s in the mid-upper 130mph range. Put it another way, if the NHRA observed it exceeding 135mph, McLaren could request a letter from the NHRA that that the observed vehicle was banned unless a safety cage was installed….

Acceleration is manic with a rush towards redline that makes your stomach go light and nearly instantly exceeds the speed limit with a mechanical roar properly placed behind you. A hard acceleration upshift cracks like a gunshot. The lateral grip available approaches the “No way!” internal meter in incredulity, the fully bolstered seat keeping occupants in place. The hydraulically controlled suspension has hardly any body roll and braking is just ridiculous, requiring checking for traffic behind you before hammering the pedal for a non-nose dive, torso-leaves-the-seat extreme deceleration.

The suspension, in all McLarens, widely considered superbly riding with the hydraulic system replacing the anti-roll bars.  In the 3^rd mode, called track, is incredibly stiff. We hit some visible bumps and they were definitely felt, but not heard at all. No crash, creak, thunk, nothing. It was weird and amazing not hearing the vehicle reaction, only feeling it. 

Entering the car, a button under the edge of the door engages the scissor lift opening very smoothly. It’s not a wide opening so enter butt first, then swing in the legs with knees bent.  Pulling down the door requires very even effort from the top to bottom, an obvious attention to detail and superior design. The seat is very snug yet instead of feeling pinched, you settle and seemingly mold to it. It’s another example of one that I never adjusted once sitting in it, whether in height, back angle, bottom angle, etc.

 In one of the videos during the top opening/closing process, the hardtop can observed storing neatly into a carpet lined box behind the passenger compartment in front of the engine bay. Driving with the top down at highway speeds was extremely pleasant, wearing a brimmed hat wasn’t an issue. The rear window also goes down, and the owner says this allows for more engine noise in the cabin when the top is up, which can be a treat.

It’s a different vehicle with the top up. The tire and road noise, thwacks from the pavement and gravel hitting the wheel wells are all heard. With the top down none of that is heard as if it all goes away. The hardtop may be the ultimate track weapon and seeing one with a roof scoop was way cool, but the Spider has got to be so much better off the track and more variety in experience provided.

Front trunk space is quite impressive, more than enough for a weekend. The owner said he likes the sound system and that it’s quite good. Another improvement reported versus past models is the infotainment system works much better than past units. 

Negatives that I observed are few and far between. Getting in and out is rather difficult. And the engine cover/hood isn’t easily removed and doesn’t have an option to simply press or pull a release and lift it open. Those were my observations but the first wouldn’t stop me and the second is just to show it off. Despite all his track time, the lack of a limited slip differential has never been a problem. It’s not driven in inclement weather, uneven surface transitions are taken slowly and with the front axle lift system activated so slippage there isn’t noticed. Maybe exiting turn 11 at Mazda Raceway Laguna Seca might exploit the open differential but a mid-engine weight distribution and wide, extremely sticky tires also make up for an open differential  When I asked the owner what negatives there were, he had an uncharacteristically long pause, which was the answer right there. This car is spectacular.

McLaren has brought to market a blazingly quick, extremely light super sports machine that is a borderline hypercar yet lighter and more powerful than both the Ford GT and Ferrari 488 GTB. With an MSRP of $372,600, versus the supposedly quicker lapping Ford GT, it is lighter, makes more power, probably was easier to obtain, and is a convertible that isn’t too cramped for two occupants. The styling is stunning with the top down and surprisingly the owner doesn’t have any photos with the top up, nor did I take any.  Yet with the top down, it is a very livable hyper-exotic car with looks and performance to match. Now the even more powerful McLaren 720S has hit the market, presenting still another choice. And I still play the lottery. 

The complete picture album is on my San Jose Cars Examiner Facebook page:

Comparison of the Ferrari 458 to a Porsche 911 Twin Turbo S and McLaren 12C

Guest author Jwp98 from Illinois shared his experience on 6speedonline.com with three great, extremely fast sports cars. Below are his thoughts after logging several thousand miles on each car. These were sequential experiences, not in the garage all at once.

Visual appeal: 12C
The 12C just does not have a bad angle. The 458 does have some bad angles (mostly solved by the Speciale) but it has some inspiring angles too. The 991 versus 997 loses something, I'm afraid. The rear is so bland and fat, without even the pretense of a diffuser or a big wing to distract and intimidate. The front is improved and side view reveals a handsome, albeit less classic, smoother rake. Quartering away is just gorgeous over those muscular hips. I look over my shoulder when I walk away, like it was the only car on earth. Well, enough of the aesthetic stuff and on to the marginally less subjective.

Exhaust note: 12C (yes really)
Taking a 458 through an overpass at redline is smile inducing. I grew up on V8 Camaros and tractor pulls, not F1 metallic rasp, but I'm still smiling. The broken glass crackle on downshift is even better, and less likely to get police attention.

The 12C is underrated for this obligatory application, but more commonly when you are putting around in town you can hear the turbines lovely chu-chu-chuff, an unpredictable animal noise from right behind your head. It'd be hard to overemphasize this constantly pleasant event.

The 458 at "town" speeds has a flatulent ricer sound when the valves open at low rpm (2500 I think). Fail.

The 991TT has a new, surprisingly brassy baritone that the 997TT totally lacked. I'm not aware of a wastegate in any VTG system but turbine noises are always there on lift, and are entertaining without sounding artificial or intrusive. On overrun there is a predictable, out-of-character, deep crackle. Maybe it's piped in somehow. I don't like it at all. Oddly I much preferred the lively low splutter of the 997TT. More organic, softer. One might have to roll up the windows or even drive on snow to hear it, but wow do I miss it. Nostalgia for cars past.

Acceleration: 991TTS
Incredibly 550 hp is a knife to gunfight these days. Those numbers were offered at entry level by Ferrari and Lamborghini 4-5 years ago. Domestics too are seeing 600-700 hp stock, with a warranty and a bargain sticker. The lighter 12C will destroy anything at it's price point and above once it grips. Nonetheless, despite it's weight, I'm giving the 991TT the powertrain blue ribbon. It has minimal lag, rewarding gearing, smart auto modes, and sick torque. It's the nuclear roller skate you can take anywhere.

Fun: 458
Tough call. The 458 and 991 turbo are both very responsive. The 458 is quick as a video game. Most city driving is between 20 and 50 mph, for me anyway. The 12C is not geared for enjoyment at those speeds. Torque to the wheels is more important than torque at the shaft, and the 991TT is a genius at torque management. What the Porsche lacks in thrill it partly recovers in accessibility. One does not
have to fret about dragging the snout or parking 1/2 mile from gawkers.

Reliability: 991TTS
So far the Porsche takes it. Definitely not McLaren. modern Ferraris are fine IMO, if you enjoy jokes about Italian culture (no offense intended) and can tolerate a few electronic gremlins.

Tech: 911 TTS
Despite the ground-breaking use of active hydraulic suspension and carbon fiber tub on the 12C. All told, the 991TT offers a LOT of tech, most of it quiet and interesting to read about, with no need to learn or fear the action of differential couplings and computer sampling rates. Just drive as fast as you dare. It's efficient too, not that it really matters, but why embrace low-tech and waste? The small fuel tank  makes it seem to guzzle, but it does not. The start stop mode on the 991 I have tried once. If the digital gauge tells true, oil pressure comes up too slowly at take off. I know there's a microlayer of lube waiting there, but no. Just no. Fortunately it defaults to off. The keyless start on the 991 is embarrassing however. Lexus had push button start in 2005. Corvette had heads up display in the 90s I think. Are you there Porsche? It's me, clock radio. Sorry, couldn't resist.

Track potential:
I don't plan on tracking the car and am in no position to instruct on rear engine dynamics. The 991 turbo with ECU, exhaust, and sticky tires should be a force. Perhaps THE force, depending on the track.

Luxury: 991TTS
No contest. I don't have to tell anyone here about practicality either. This is the only supercar my wife wants to drive, and has single handedly made me a sunroof fan. Good audio but the seating position may not be as good as the 997.

Value and depreciation: 458
Porsche for great value, Ferrari for slow depreciation.

Safety: 991TTS
Not very exciting to discuss but if the car does not have confident brakes, grip, and headlights, this is a fun killer, if not a man killer. Bearing witness, lots of turbos are daily drivers (mine is not). Porsche is the clear winner here, and has been for years. Visibility/seating position matters too when you're threading 18-wheelers in the rain.

Handling: 458
Twitchy, quick, alive, if not the grippiest on stock tire options. Porsche is strong here though. It's nimble and doesn't feel like a heavyweight. Easy to place, as they say. The 4-wheel steering is not so noticeable to me, except in parking lots and torque vectoring, is just as innocuous.

The Ferrari steers so jittery, snappy and the rear steps out on a whim. The 12C offers more feedback.

The Porsche's steering is a little, well, different. The extent of wind effect and tram lining are disturbing. Happily there is less of the creepy rear end twitch than in the 997. It's less telepathic than its peers and not as light in the nose of course. It's not the "snap out of your hand" wiggle of previous gen cars. But it's not really numb either. There is just something odd. Almost as if the less I consciously steer the better line it delivers. It likes inputs of pressure, not motion. That kind of feel flatters neither my driving nor the 911 pedigree. But, as I read reviews of the 918 and its competitors, no one is talking about feedback. Reviewers use vague words like "rewarding", "precise" or even "heavy", which sounds an awful lot like "numb", interesting. Whether it's the electric motor impact I don't know, I've read there is no difference between the 991TT and the 991 GT3 except software (and AWD). The new steering will take some getting used to. I am wondering about the impact of a yet to be announced software flash and different tires.

Transmission: 2014 Porsche, 2012 Ferrari, 2013 McLaren
One wants consistent creep with predictable light throttle response on the street. On the track, lighting speed without chassis jump or power interruption. All can deliver the latter, durability being the unknown. All are also viscous dual clutch packs. Graziano may have supply similar hardware for the mid engine cars, but the software is quite different. This has been extensively debated elsewhere. I suspect some combination of durability and versatility was ultimately sought compromise, in other words. My McLaren’s 1-2 shift was needlessly choppy. It also allowed a lot of slip before hooking up. Not good when you’re trying to feel for traction or get out of someone’s way on the 8 lane rush home. Mode control does goes to McLaren for not using silly words like “race” and for logically and completely divorcing drivetrain and suspension settings.

Perhaps its unfair to compare different years and software iterations, particularly to the 458. Of the three the Porsche feels most like an automatic yet not soft. Interestingly it has some clatter, some gear slack you can hear when I assume bits are turning at equal rates more or less, or disengaged, with no load. Not annoying like reported in the GTR but more a throwback to light flywheel manuals. The crisp bark on upshift goes to Ferrari, referencing the exhaust note mentioned earlier. Sounds like something unique and violent is happening in there, to wow onlookers, to propel you forward, and harness the inertia of those between- gear RPMs.

Comfort: McLaren 12C
Once you're in. I'm not a fan of NVH, especially that whump of air the 911 sends into your skull on crossing an expansion joint. Any tech to get rid of it is worth an investment. The 12C suspension is almost as good as they say, but not like a sedan. It's doors are a huge PIA though. I'm 6 feet
tall and reasonably flexible. And imagine a pregnant women shoehorning in then the door failing to close, or making wind noise all day. Yup, it happened.

The Ferrari was versatile enough for short trips but I don't recommend driving it 400 miles with a hangover. The 991 ride is not much better than a 997. I've deflated tires, changed modes, considered the speeds and road surfaces, considered the deceptive softness of the seats. It is harsh. I'm reporting here as one who logged many road miles in 997 GT3 and GT2 cars. Noise level is high too, but such is life in the big league and part of the experience. Until it's not, and then we admit it sucked.

Summary: I'm happily sticking with my Turbo S for the foreseeable future. Even getting a child seat. The three cars above aren't perhaps direct market competitors but I hope these notes are useful to anyone shopping or thinking of a change. I should mention I'm not brand loyal and have low confidence in any company to build and support a reliable super sports car using cutting edge tech. It is apparently too tall an order. I'd love to be proved wrong. If I had to give money to one of the big manufacturers in the future it would probably be Ferrari. But again, this hypothetical car isn't a daily driver. So far, have all been delights in one way or another. You get your money's worth, particularly in the preowned 12C and turbo markets.

The Goodwood Festival of Speed is the pinnacle of automotive events

The Goodwill Festival of Speed, held this past June 27th through the 29th, 2014, is best described as a Concours D’elegance worthy car collection, an airshow, an international car show, a rally race, an exotic car show, a racing motorcycle show and demonstration, a hot rod show, a motocross exhibition, an off road driving experience centered on a hill climb time trial event disguised as a huge outdoor festival and bucket list to-do deep in the English countryside.

To properly take it all in, plan on attending all three days and bring charged back-up batteries and extra memory cards for your devices. Ideally a laptop to store it all nightly if you're appetite for speed is ravenous. If it isn't, it will be.

The Hill Climb is the central event that the rest of the show follows on either side of the track. The course is 1.6 miles long so plan on walking, a lot. Some nasty blind and off-camber turns greet really fast straights below the main house and well up into the countryside. You name it, it’s on the track, running loud and fast. Or in the case of the Rolls Royce and surprisingly the Pagani Huayra, just fast. More on the cars later.

Surprisingly the escorted return trip down the hill can be equally entertaining with burnouts or even an occasional donut and better photo opportunities. A video camera is the best bet along with easy editing and still photo capture.

Only a true fan would make the long trek to the top of the hill to see the Rally portion in the trees The drawback to the provided shade is not being able to see the military jet(s) performing their fly-bys and stunts. The course jump does provide good action provided its a with a quicker car for more air time. If you make the trek, the good part is it is a fairly short downhill walk to the last main straight with a beer booth, big screen, grandstand and great vantage points seated or in the grass. If you want to get more dusty than the rally, the off road riding experience and dirt course nearby provide fun action, including being a passenger if you pay the fee.

Further down is where everything else is gathered. In the main house courtyard was Maserati, celebrating 100 years in a display of sensual curves of carbon fiber and sex appeal. At the entrance vying for most provocative yet functional shape of the event, the commemorative images on the MC12 race car edged it over the McLaren F1 GTR long tail racer. Both had an awesome shrieking exhaust note. A V12 engine will be someday be regarded as a fine musical instrument as well as an awesome powerplant in future generations. Never mind preserving the manual, don't lose the V8, 10 and 12!

The well received Maserati Alfieri concept was the centerpiece of the display that was so good that the poles for the canopy cover were an annoyance, even if blocking a minute viewing angle. And achingly made of near-obtainium was the Gran Turismo MC with seemingly bespoke carbon fiber accents. It is perhaps the sexiest used car under $100k.

Just outside, the famous yearly sculpture appeasing the car gods raced into the sky confirming the heavenly blessing for three days of speed and sun. One could watch another big screen here or just lie in the grass and absorb the vibe of octane fueled mania. More and larger grandstands across the track lead to multi-level auto manufacturer displays rivaling those at major auto shows. The Nissan Gran Turismo concept, a Jaguar F-Type R cutaway and the Toyota LeMans hybrid racecar were just a fraction of the standouts that could easily take hours to explore.

Taking a bridge back over the track leads to a concours worthy rare care display, small but exquisite in execution. Yet if the names Clarkson or Schmee mean anything to you, a series of tents housing the modern greats ups the ante. Two LaFerraris, a Porsche 918 and McLaren P1 sit among nearly ignored greats like the McLaren 650S, Ferrari F12, a 458 Speciale, Nissan GT-R Nismo (which later ate hay)
and an obviously different sounding GT-R Nurburgring non-stock “record” car. The Pagani Hyuara also stood out but taking the most outrageous award went to the Koeneggsegg One:1 with its aerospace sculpture rear wing, extreme bodywork and carbon fiber wheels.

McLaren had a large plot with the P1 and the unveiling of the 650S GT3 as stage highlights. Also on display were the 650S and the 650S Spyder. Fittingly nearby was the race car paddock has something for everyone from historic racers, NASCAR, LeMans, F1, FIA, etc. Further on was the largest food court with lots of benches and the motocross stunt area. The nearby vendor tent area had some
superfine products, art and automotive luxuries. The world’s fastest car, the Bloodhound SSC had a large display as well.

A building near the starting line, that was long and non-descript but very open had smaller manufacturer displays but also some real gems. The sultry Mercedes AMG Vision Gran Turismo was showing it’s risqué curves. Nearby another Ferrari 458 Speciale in its display sat neglected at times. The redesigned 2015 Ford Mustang GT has great lines, finally modern and sophisticated. A surprise
appearance Lexus RC-F sport coupe with a carbon fiber hood was another treat.

But the reason it is all here is the Hill Climb. Whether standing at the start for some burnouts by the F1 cars along with shrieking starts, roaring V8s and screaming V12s, it is a spectacle to behold. Historic NASCAR racers, the supercars and the outrageous modern F1, FIA GT and LeMans racers and much more displayed showing what speed is all about. All day for 3 days and is a glorious sensory overload with over 300 cars and bikes making the run to the top. The fly-by moments desperately caught on film due to their sheer speed and close access allowed by the hay barriers were unforgettable. The announcers and interviews were excellent, either on the PA system or by an available earpiece radio.

The only complaint was when an interview was occurring the announcer would miss a particular car, so trying to get a shot of some really special super cars was particularly difficult when it would zoom by at over 100mph seemingly unannounced.

Not only were the cars spectacular, the riders and drivers included Derek Bell, Kenny Brack, Jensen Button, Emerson Fittipaldi, Dario Franchitti, Lewis Hamilton, Damon Hill, Sebastien Loeb, Kimi Raikkonen, Richard Petty, Freddie Spencer, Jackie Stewart , Al Unser Sr. and Michael Waltrip. This year the fastest time of the Hill Climb this year was 44.6 seconds set by Sebastien Leob in the Peugeot 208 T16 Pikes Peak car.

The Goodwood Festival of Speed is a must-see for all automotive enthusiasts and race fans around the world. Attending a car show leaves one yearning to see the cars in action as they are designed while at a race it is difficult to see them up close and personal. At Goodwood, you can do both while attending arguably the single premier automotive event in the world.

Check out the 150 picture photo album here:
https://www.facebook.com/media/set/?set=a.523455664425816.1073741837.378354382269279&type=1&l=443e268197

Design flaw in the new McLaren MP4-12C?

There is a disturbing trend in the automotive world of eliminating the limited slip differential (LSD). Manufacturers are promoting alternatives with fancy names, but none of them do what an LSD can do and this can be an issue. If you're spinning, you're not accelerating. This can be a big, big problem on the street and on the track for reasons I'll explain.

According to Road & Track Magazine, Nov. 2009 issue, the upcoming McLaren MP4-12C doesn't have one! This car has every ingredient to make it one of the greatest sports cars on the road except for the potential penalty of lacking an LSD. This is could be a major compromise from a company that is renowned worldwide for it's engineering expertise and racing pedigree. Multiple championships in Formula 1 and at the worlds fastest production car for 7 years are their best known accomplishments to the public.

The MP4-12C is their first entirely designed in-house street car that will compete head-to-head against the upcoming Ferrari 458 Italia and F430, Porsche GT2, the Lexus LFA and the Lamborghini LP560. Pinnacles in modern sports car design with lightweight materials and horsepower levels in the mid-500 range for extreme performance and race bred technology for the street and for the track. Ferrari in particular emphasizes their E-diff for 32% better longitudinal acceleration vs. the F430 and 1.25 second improvement in lap times at their Fiorano track. Read more about it here. The Porsche is a rear-engine design and the Lamborghini is all-wheel drive, both of which aid traction.

Other greats like various BMWs and Porsches also have this "deficiency" as well, but not their flagship or higher performance models. The BMW 335i series vs. the M3 is an example of the more sport orient ed model having a limited slip differential. Due to owner feedback (complaints), the Dodge and Chrysler SRT-8 models finally received LSDs in their 4th model year. One could surmise several specific makes and models always have LSDs. Corvettes come to mind. How about Ferraris? It's a safe assumption, one would think.

With an "open" differential, both wheels apply engine power to the ground and even can lay down twin black strips of rubber when there is a loss of adhesion or overpowering the tires. However, when one becomes "unloaded" due to less traction and starts to spin, the power isn't transferred to the other wheel which means the rate of acceleration doesn't increase. This causes headaches on the street, the racetrack and the dragstrip.

Most annoyingly daily driving can be compromised. Uneven surfaces encountered pulling out of a parking lot or driveway onto a road when the rear tire (or front tires for front wheel drive vehicles) slips and the manufacturer promoted traction control kicks in. Begin accelerating and if aggressively programmed, the engine power could be reduced besides just the rear brake being applied. A real pain in the ass. A little extra brake wear over time and now you're maintaining your speed or slowing down when you should be accelerating. Try it when a vehicle is headed your way and you "thought" you had enough time... That is why many drive with Traction Control partially off. I'll control my throttle, thank you very much.

How about in rain and snow? Drive over or start on a slippery patch and you just sit and spin, the wheel with traction never getting the available power transferred. Apply more gas and you spin faster. Great. At the dragstrip it's the same thing. Get "out of the groove" with one tire and the other doesn't pick up the slack. For those that run higher traction tires such as drag radials at the dragstrip, the uneven distribution of the power from one side vs. the other can break a rear differential or half-shaft at some point.

Where all these exotic cars are meant to be is on the race track and the potential oversight of the McLaren means in tighter turns, the inside wheel can spin and power isn't then applied to the outside wheel of the turn, meaning a slower corner exit. Spinning is neither winning nor accelerating.

There has to be a good reason why the McLaren doesn't have an LSD so I contacted them with that question. The MP4-12C has multiple systems that they call the Proactive Chassis Control system that McLaren feels eliminates the need for the LSD.

The system consists of adjustable roll control for precise body lean control during high lateral acceleration cornering and it decouples for a better ride when in a straight line. The shocks are interconnected via hydraulics and adjust depending upon conditions and driver preferences. Finally it has a system called Brake Steer which brakes the inside rear wheel when braking into a corner and if spinning when accelerating out of a turn. Obviously brake steer is controlled via electronics and McLaren feels this eliminates the need for the more mechanically complex and heavier LSD. In other words, optimize chassis control and steering and the power delivery takes care of itself.

Granted there are some innovative weight savings with the MP4-12C such as the 175lb carbon MonoCell tub. Interestingly, aluminum brake hubs are used but not carbon ceramic rotors. Also the body panels are not carbon fiber either. Couldn't the weight of the LSD be offset in more traditional areas? I wonder if an LSD would actually be larger, compromising the design with the mid-engine and transmission placement. Perhaps it would have meant additional width, length or even height to the components, raising the center of gravity?

The drawback of a limited slip differential, besides extra cost, complexity or weight (as I roll my eyes) is potential snap oversteer which means when then the wheel with traction "hooks up" suddenly from excess power, it could cause the car to fishtail. That is something you could catch on Youtube. The "open" differential is quite predictable since the power isn't being transferred to the other side. The other disadvantage, and it's quite minor, according to the SRT Engineers the constant transfer of power can cause a ever-so-slightly decrease in acceleration. The benefits far outweigh the costs.

Adding an LSD is a common upgrade among owners of many performance-oriented cars via aftermarket parts. Can it be done with a rear transaxle, dual clutch transmission in a mid-engine car? Doubtful. There are reports of a planned hardtop convertible version of the MP4-12C that would be a first for a mid-engine car. Could this be a business decision to keep the components lower in the chassis, forgo the LSD and accommodate the folding top design? Also a higher performance is supposedly planned and perhaps this model will be "properly" equipped.

The reason many manufacturers leave out a limited slip differential is because of cost savings, pure and simple. Less mechanical parts means less cost. If it was a size and packaging issue that meant raising the center of gravity, extending the wheelbase, or something else radical, will it mean the McLaren, while wildly fast and capable will still be left behind by the competition?

2/8/2017 Edit:  Car and Driver published an article comparing an electronic torque vectoring differential vs. a standard limited slip differential in the Lexus RC-F in October 2015. They didn't bother with the obviously slower brake torque vectoring open differential. The e-diff car was quicker around the track and higher skidpad results. www.caranddriver.com/features/whats-the-diff-we-put-torque-vectoring-to-the-test-feature

6/1/2019 Edit: Being that the cars are fair weather driven, with rear weight bias, the open differential seems to work for McLaren with the selective brake bias (braking one rear wheel) used for quicker turn-in. This may cause excessive wear on the brake pads, but that isn't the concern. Meanwhile the E-diff continues to be the preferred equipment among other manufacturers.

Having driven over 150,000 miles in a '06 Charger SRT-8 6.1 and a BMW 335d, both with 425lb ft. torque (when stock), I can attest that open differentials suck. That's why owners screamed for an LSD and Dodge later added it as standard equipment.
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Got a question about cars you would like answered? Want to know about performance, racing, modifying, shopping, makes, models, events, etc? Ask me here: AskRobAboutCars@gmail.com and I'll do my best to answer your question and publish it here on Examiner.com!