"Лучше запаситесь пивом и чипсами, потому что это будет долгий рассказ. С точки зрения производства я не уверен, что мы когда-либо раньше работали над столь интересной группой машин для DLC. Создавая каждую из них, мы получали настоящее наслаждение, и просто здорово видеть, как огромное количество людей получают удовольствие от их вождения."
Porsche Carrera GT
Just a great car; all the bits of it are in a great balance. Research for this one proved particularly productive as there is a strong and open community of owners at Rennlist who love to talk about their cars and share experiences.
The engine is that famous V10 which began life with intention to race in the 3.5L era of Formula 1. It was shelved for a bit before being brought back for the aborted LMP900 project, and eventually grew to the 5.7L variant used here. The owner's manual includes a nice dyno plot of the engine's full range which matches up well with independent dyno data and served as our main reference point. It makes a smooth 600hp with plenty of torque from 5500rpm right up to the limiter at 8400rpm. Feedback from owners is that it's just a perfect example of a naturally aspirated engine to drive once you get the hang of starting off with the aggressive clutch and virtually no flywheel. (2005 model year updates added some software anti-stall auto-throttle to help get the car rolling) Power goes through a 6-speed manual and clutch-pack LSD to the rear wheels. Ratios spaced in nice progressive steps that increase speed by about 30mph in each gear; combined with the fat torque curve, it feels like you always have a good gear to use and the whole thing is working with you.
Aero claims for the car are modest with CdA=0.72 and a useful downforce of 400kgf @ 330kmh, with both values being backed up well by Sport Auto wind tunnel tests. Aero balance is actually slightly forward of where you would expect on a road car, but still in a nice position given the car's weight distribution and heritage of being set up by Porsche factory race drivers of the era.
Suspension is a very simple double wishbone design with coilovers on inboard rockers. Very similar setup to the Enzo from that same supercar era. Rocker-pushrod design appears to work out to a motion ratio of 1:1 (Suspension tuning being one of the few things not discussed at length on rennlist, aside from how to lift the car for daily use on rough roads) and good photos of one car being worked on show 90N/mm springs at both ends. Those wheel rates, the 1455kg DIN weight & 60% rear weight, and a typical Arnao-Porsche damper setup work out to a very nice chassis balance.
The car did originally have a strong reputation for oversteer as it rolled out from the factory - both in general cornering and lift-off oversteer. It has an adjustable rear anti-roll bar, and their test drivers liked it in the firmest position. Randy Pobst had a good article about it during his time as a Porsche factory driver and pins it on their test drivers all having strong karting background. A bunch of kids who grew up winning races by adopting a ‘pitch sideways and catch’ driving style; heavy emphasis on oversteer in the baseline setup. Porsche eventually changed to shipping cars with the rear bar in the middle of three settings, and pretty much every owner has moved to the softest setting for 'very slight' understeer and increased confidence in the car. Our setups default there too.
It is very quick. In testing on Trofeo R tires, I'm lapping the Ring in around 7:15 (Jussi turned a 7:07, the speed demon). Given that we're modeling newer, better tires, and the official lap done back in 2004 was a 7:28, we appear to be right on target for performance.
Porsche 935/78 "Moby Dick"
While the real thing was an awesomely big job of hacking the rulebook to make the car lower, longer, and more powerful, for us it works out to a fairly mild mod of our existing 935/77. That chopping of the chassis to lower the entire car plus new bodywork front and rear made the car significantly more efficient. Wind tunnel data from the time shows 10% less drag and 50% more downforce compared to the 935/77, though 97% of that downforce is applied to the rear axle; not exactly great for cornering speed, but does wonders for high speed stability and that was the whole purpose of this car. The real secret weapon here was the new four-valve, 3.2L engine with water-cooled heads (code 935/71). While not a huge power advantage on paper over the 3.2L 2-valve 930/80 unit we have in the 935/77 and 935/80 models - 750hp @ 8200rpm vs 740hp @ 7800rpm, both at 1.4bar boost - it can pull right up to 9000rpm and maximum boost of 1.7bar puts it well over 800hp for qualifying. The broader power band plus the improved aero mean it will gets up over 365km/h on the Mulsanne straight while feeling perfectly stable going flat through the kink. It may burn through fuel in a flash, but it's happy cruising around those old tracks at high speed all day long.
Porsche 911 Carrera RSR 2.8
Huge credit to the old Paul Frère books which just go into ridiculous on every racing model from the 1970s and were an invaluable resource putting this together..
The 2.8L flat-6 is good for 308hp @ 8000rpm and drives the rear through a type 915 5-speed. There's a big set of alternate race ratios, but the engine is smooth enough that you won't often feel the need to adjust things per track. The standard ZF limited slip differential could be set for 40% or 80% lock; 40% feels good on ours as a baseline (6 clutches, 50° ramps).
RSR race models were stripped down to 900kg for a neat 40/60 weight distribution. This was the time when wind tunnels were just starting to see use in developing race cars, and the 911 proved particularly terrible at the beginning with upwards of 300lb lift happening at the rear axle in the initial tests. The duck tail addition helped balance that and cut about 75% of the rear lift, but still left significant lift overall. Numerous other tweaks just didn't work very well, resulting in a car with downforce on the front end and lift at the rear, until the 'Mary Stuart' setup which actually made useful downforce at both ends of the car for only a small drag penalty. We've gone with that kind of configuration for our aero model as it just drives the best of the bunch.
Suggested suspension setup for the RSR was effectively identical to the street RS models, with zero camber at the front, -1° at the rear, a touch of rear toe, torsion bars of 18.8mm diameter at the front and 23mm at the rear with 18mm anti-roll bars at both ends. Stiffness numbers make this look soft, but the car is so light that it all works out in the end. It does get faster if you make it lower and stiffer, but the relationship between stiffness and difficulty is quite direct on this car. Dampers are very similar to Bilstein valving spec for the real thing - 100/220 on the front and 160/210 on the rear. Brakes for the RSR came straight off of the 917 prototypes; more than adequate for the job!
I'm loving driving this thing. It's easy to see why they are so popular for vintage racing; the balance of power and grip is great, and the steering feel works perfectly with the chassis balance to glide through corners with the rear end hung out. Top speed isn't especially high at around 250km/h, but the lightness and handling make it a good match for the old Camaro and Ferrari 365. Multi-class at Le Mans with this will be great fun; 911 giving all it's got for 250km/h on the Mulsanne while the 917 and 512M blast by doing closer to 390km/h!
I've never seen so much detailed documentation on a 45 year-old car before; made putting this together very easy. Nice dyno plots, full gearbox/differential specs for various circuits, multiple wind tunnel and track aero tests in various configurations and an array of ride heights, complete chassis blueprints for suspension geometry, corner weights, fuel usage, etc. etc. etc. Amazing stuff in these old Frère books.
Engine for these 1971 cars was the 4.9L version of Porsche's flat-12 making an even 600hp @ 8400rpm and 415lb-ft @ 6500rpm. Unusual engine as it was essentially two regular 911 boxer 6-cylinders joined together in the middle; the length of such an arrangement meaning that power had to be taken from the middle of the crankshaft to help control vibrations and the gears used to achieve this essentially making for a 32:31 overdrive. Also note that while these are traditional 'air-cooled' Porsches, there is a radiator at the front you can damage which will cause some trouble. They ran an 80cm-wide oil cooler up there, and the 917K variants even going so far as to carry a 55L (no, that's no a typo) oil tank to help regulate engine temperature over the endurance races.
That engine drives the rear through the same type-917 gearbox we have later in the 936/77 (minus the power take-off overdrive) and was run as either a 4- or 5-speed unit depending on the track and model type (K models usually going 4-speed, LH 5-speed). Same internals, but they would just block off 5th gear and select ratios to suit a given track with only four gears; an easy thing to do as the power band is quite wide and the engine doesn't need to be up at the top of its range for best performance. Standard differential was a ZF with 75% locking (8 clutches, 40° ramps) and preload. Track tests were done with 25% locking and steady state handling improved slightly, but sudden throttle lifting would then cause the car to instantly spin out.
K models tended to be lighter, even needing ballast to get up to the 800kg minimum, and roughly a 63.5% rear weight bias.
Suspension design is nothing too special and typical of the time: double wishbones up front, radius rods plus inverted lower wishbone at the rear. This is another area with great documentation for camber and toe changes w.r.t. suspension motion, which where is a fair amount of both. Matching that in our model and using real setup values from the period all works out to make good sense; they often ran zero, or even positive, camber at the rear and quite a lot of toe-in at both ends. The camber helps agility at low speed while the toe-in stabilizes, and it all cancels out at high speed under aero load such that the rear tires stand perfectly upright when you are over 200mph, which is good for endurance of the tire carcass. Progressive springs/geometry were used in the design, complicating matters, but some track aero tests provide spring compression for a known aero load so working out typical average rates for the suspension stiffness was easy and drove well from the start on those numbers. The blueprints plus old setup sheets also helped to work out wheel rate for typical anti-roll bar sizes used. Easy stuff and all just works when we put it on the car.
Like the 911 Carrera 2.8 RSR, this was the very beginning of the wind tunnel era and it helped them make one slippery car. Downforce levels are nothing astounding, but useful and well-balanced for high speed stability. Drag levels are astonishingly low at around 400lb for the 917K, making it good for over 350km/h while feeling perfectly comfortable through the Mulsanne kink flat out. Overall a very easy drive at just about any track with great stability and tons of grip from the giant, 14.5" wide rear tires. Feels like they would be good for cruising around at race pace all day long, which is what they were designed to do.
It's like the 917's flyweight sibling and was a surprise highlight of the group for me. Same chassis frame design, same suspension geometry, same width tires, same basic layout of flat engine mounted in the middle driving through a 5-speed gearbox to ZF differential at the rear. Differences largely boiled down to the engine, aero concept, and materials selection.
The engine was an evolution of Porsche's flat-8 design, going from 2.2L and 270hp in the 1966 910 models to the 3.0L unit here good for a quoted 350hp @ 8500rpm though the best examples were making upward of 370hp. Not nearly the power levels of F1-derived units it competed against in the Group 6 P3.0 class (you will have moments begging the car for a little more top speed) but it was reliable, had a strong power band from 6600-8700rpm and, most importantly, was very lightweight. The 5-speed gearbox and differential bore a lot of similarity to the 906, 907, and 910 before it (and even the Carrera RSR) with the ZF 80% lock differential being commonly used; default setup on ours uses the 40% lock configuration as it's a bit easier to approach for a starting point.
Rules of the day very clearly put an advantage to the S5.0 class cars at long races on fast tracks like Daytona, Sebring, Le Mans, and Spa. As the 917 was already doing well there, this allowed Porsche to give clear focus on making the 908/03 a tool specifically for winning at the twistier tracks where the absence of a minimum weight could be put to good use - particularly the Nordschleife and Targa Florio. Aerodynamically, this meant cutting off the roof to save weight with spyder bodywork and a short tail design. Lots of iteration and wind tunnel testing from the 908/02 to 908/03 models resulted in a car that made a nice amount of useful downforce (around 450lb @ 150mph) with a useful balance (around 60% rear) without too much sensitivity to ride height changes, and all for only 10-15% more drag than the 917K design (40-50% more than the 917LH).
Then there was extensive use of magnesium, aluminum, and titanium through the chassis to cut weight as expense of reliability, knowing that the car would be used more for 1000km races rather than 24hr endurance fests. All-aluminum chassis frame weighed in at only 35kg, titanium usage throughout the suspension, magnesium in the gearbox and brakes trimmed weight further. A clever use of epoxy around foam core even resulted in an entire bodyshell for a mass of only 12kg. They even experimented with chome-plated beryllium brake rotors for a further 30lb weight savings, but the wear characteristics of these were sub-optimal. In the end, they had a car which tipped the scales at only 545kg - on average between 100-140kg lighter than any other 3.0L prototype - with a near-ideal weight balance of 55% rear.
So you've got a prototype sport racer as light as an F1 car of the era with just as much rubber and more usable downforce. A bit down on power, comparatively, but it more than compensates for it with the aero grip and nimble handling. One of these broke the 1969 F1 Nordschleife record in 1971 on the way to a 1-2-3 finish in the 1000km race. (granted, F1 retook the record later that year by over 20s) On our modern Nordschleife track, I'm comfortably lapping near 7-minutes flat in this. The 917K feels fat and lumbering by contrast (at all of 800kg!) and is about 10s per lap slower. The situation reverses, of course, going to Le Mans where the 917 can use its power advantage and pull a 15s lead per lap. There are a bunch of tracks in between those two where they come out just about equal - like Oulton Park - and they should make for some great multiplayer competition.
2017 Porsche 991 RSR
What started as a variant of the 991 GT3 R has ended up with quite a different feel thanks to the increased front weight distribution and completely different suspension concept.
The engine begins with the same 4.0L base as the GT3 car, but they must work some serious magic on it for the LM GTE spec RSR. Same layout and capacity with smaller restrictors - 2x31.5mm vs. 2x40mm - and it makes more power than the GT3 car at 520hp. Best guess is the thing would be close to 700hp if run unrestricted...which, IMHO, the FIA/ACO should allow since these are all more like prototypes than GT cars anyway. Still revs to 9400rpm like the GT3, but the smaller restrictor mean power drops off earlier and it is best between 8000rpm and the shift point of 8500rpm. Steering light LEDs reflect this.
Gearbox is your typical 6-speed sequential with a nice array of ratios to select from. Differential is clutch & plate type with the usual Porsche locking values of 45% power / 65% coast. An option for the RSR is to use a viscous pack instead of clutch preload; personally I prefer the steadiness of clutch preload so that is how it's set up by default.
Suspension on the RSR deviates totally from the GT3 R, which must stay close to the original road car. The RSR goes double wishbone front and rear, and our reference material gave good enough data to draw up a new model to reflect what they've done here plus some baseline suspension setup info. Steering feel from the new design is nice but it's definitely a big step away from your ordinary 911. Where the GT3 is more forgiving and does a great job at planting the rear end, this one is more tuned for prototype-like sharpness and carving into high speed corners. It's a bit more 'pro' to drive and quite a bit faster over a lap as the reward.
Then there's the big feature of this car: moving the engine ahead of the rear axle to a mid-engine layout. Nobody will share hard numbers on such a sensitive topic, but our best estimations show this moves the weight distribution forward 4% to about 55.5% rear and reduces the moment of inertia by about 10% in yaw. Makes the car more nimble and does good things for cornering performance with the tire sizes used on these cars.
First tests have it running 15 lap stints at Le Mans with a best time of 3:57 and Long Beach in the mid-1:16s. Pretty close to the real world targets as those will come down with setup work and a better driver. A nice addition to our LM GTE class.
Can-Am was so badass. Minimal rules, maximum speed and creativity. Minimum weight? Nah, we don't need that. Maximum engine size? Nah, don't need that either, and use turbos too, if you like. Just have two seats, enclosed bodywork, and 'reasonable' safety to the design.
Porsche sorta got into Can-Am by accident. They had entered a 908 because of convenience (there happened to be a shared weekend with the 6-hour Watkins Glen race) and did well, but were too far down on power to compete for a win. Further experiments with a spyder version of the 917K (near double the power of 908) were also insufficient on power. The car looked like a good base and the series a good challenge, plus they could use the additional North American exposure. Solution: Turbocharging it out the wazoo.
The engine in our model starts as the 917K base but with compression ratio lowered significantly to 6.4:1 and two giant turbos from a diesel truck strapped on, producing in the neighborhood of 1.3-1.5bar boost. At the 1.3bar race boost level, this makes for a 5.0L flat-12 outputting over 1000hp @ 7800rpm and 1000Nm torque in a range from 5000-7000rpm. Tighten some screws in the wastegate (this was early turbocharging, everything was mechanical) for some extra boost and you get north of 1250hp. The cooling system struggles to keep up with this for anything more than short bursts, so it was common for drivers to back off on the boost during races to save the engine.
Gearbox was an evolution of the 917 unit, strengthened to handle all the extra torque and reduced to 4 speeds. The differential was also a casualty of the design change. Tests using a spool on the 917K were positive for high speed stability and it removes another part which can break under the massive stress, so all the Can-Am 917s used a locked, spool differential.
Aero development in the wind tunnel continued, and with all that extra power, drag could be afforded for the sake of downforce production. Late versions of the 917/10 tested at around 1100lbf @ 150mph for downforce with a 75% rear balance and roughly 1.7:1 lift:drag efficiency. The car would make its own weight in downforce at around 180mph. Impressive numbers for the time! All of the downforce led to some suspension design changes so to reduce camber change with the travel which was inevitable under load at high speeds, plus adding back some anti-dive and anti-squat to the geometry to handle the braking and acceleration loads. Minor differences from the 917K or even 908/03, though. Old testing/race notes give some suspension stiffness targets they used; it ran very stiff at the rear to hold up almost a ton of downforce on the rear axle.
The chassis went through various lightening and strengthening phases, some even using a magnesium chassis frame that brought total weight below 800kg (1200hp to move only 800kg!) while the most successful/reliable cars from Penske weighed in at 820 and 837kg with 65% on the rear axle. To last through 200-mile races without refuelling, the cars could hold 325L of fuel in tanks either side of the cockpit. With driver weight and full fuel load, weight distribution moves forward to 59.5% rear.
Tires were big...really big. Rears are a full 17" wide tread. Think of it this way: the car is about 217cm wide and the rear tires combine for 110cm of that. The driving dynamics are very much dominated by the rear end and getting that power down. All that rubber plus a spool on the axle makes it push at low speed unless you run a very aggressive suspension setup with soft front and stiff rear. Downforce adds with speed and it is balanced enough to the rear that it also adds some understeer for the sake of planting the rear tires when the boost is on (with low rear wing settings and qualifying boost, it will spin the tires up through 150mph). Despite the tendency to understeeer, it is easy to rotate because there is always so much power on tap to help. Be ready to use the brakes a lot. It accelerates so fast that you are approaching most turns 40-50mph faster than any other car of the era. It has good enough cornering grip, but the key to performance is getting into and out of the corners like the rocket it is. Use that power and it is faster than an F1 car of the time.
Also, it does little wheelies on a hard launch. Raise the revs to build boost, dump the clutch, and this happens. This one is huge fun.
Jussi: Initial test at Nords put me at 6:32 and classic Le Mans at 2:55. That first value is as fast or faster than modern GT3s can handle Nords and almost half a minute quicker than I managed in the 917K, and the second is 20 seconds quicker than the 917 managed in 1971. Which was already 10 seconds quicker than the Ford Mk IV managed in 1967. Ludicrous machine.
Porsche 959 S
The supercar way ahead of its time.
Engine for this one was a detuned, 2.85L version of the 962 Group C race engine and one of the great cases of underrating power output. Quoted spec is only 450hp @ 6500rpm and 500Nm @ 5500rpm, all arriving thanks to boost pressures in the range of 1.9-2.1bar absolute. A fairly modest output for the top speed which was independently tested many times in the 197-200mph range. The owner’s manual includes a ‘dyno plot’ and our first tests with an engine matching that plus the right amount of aero drag (a very slippery claim of Cd=0.31) resulted in a top speed of only 175mph. It wasn't until adding ~70hp with a much fatter power band that the straight line performance numbers begin to make sense. I'd guess the real 959s were all producing more like 600Nm and 520hp, with over 500hp in a range from 6000rpm right up to the 7600rpm rev limit. Beefy.
Gearbox is a 6-speed manual, though it is is technically only labeled a 5-speed in the car with an additional gear for off-road. '1st' is quite short and is labeled 'G' for 'terrain' use. For most circuit driving, it does work best to think of 2nd as the lowest gear in slow corners and 1st/G only for rolling out of the pits or off the starting line.
Suspension differs from your typical 911 in that it uses a basic double-wishbone configuration. Each corner had a pair of coilovers and these could be actively adjusted for both damping rate and ride height in the Komfort model. The 959S Sport model bypassed that for stiffer springs and fixed damping to save weight.
The AWD system in this car was remarkable for the time. Rather than a center differential, it has a set of electronically-controlled clutches connecting the driveshaft to the front differential. The computers take into account static and dynamic weight distribution, wheel slip and surface grip, plus a number of other factors and send between 20-40% of the torque to the front axle. (alternatively, the driver can fully lock those clutches for off-road/low-grip use. Center spool option in game does this.) To make this work, the front tires are sized 1% bigger than the rears so that there is always some degree of slip at the central clutch to enable the variable torque transfer. We mimic this in game with a set of centrifugal clutches with the right range of torque holding capacity in the middle of the car. Altogether great for acceleration and high-speed stability, but the drawback of this is that there was always 20-40% of the engine torque being used to drive the front wheels forward; meaning some of the front tires' lateral grip capacity was compromised and the car generally understeers on power. Road tests from when the car was new point out this tendency to power understeer and that the rear end only really steps out via aggressive trail braking, after which is can easily be brought back in line by using power to pull the car straight. The fastest approach to most corners on a paved circuit is to be tidy on the entry and position the car to get back on power rapidly just past the apex.
The car's aerodynamics were focused heavily on drag reduction to get those high top speeds. Porsche marketed the design as being "zero lift". That's a great accomplishment considering the 911's reputation for lift-induced handling issues, but zero lift also means zero downforce. Combined with the car's hefty mass (Sport model over 1530kg in independent tests) and narrow tires (only 235-wide front and 255 at the rear), the 'supercar' performance on this one mostly comes via the fantastic engine and its ability to pull so strongly out of corners to a big top speed.
The cornering speed deficit hold it back from being truly supercar-fast on a dry circuit. Comparison tests of a 959 Komfort against the Ferrari F40 at Fiorano put the F40 at somewhere between a 6-10s per lap advantage...and that’s a short lap. In game, our 959S is roughly a 7:40 car at the Nordschleife. Not slow, for sure, but a ways off other iconic supercars which had more focus put on speed through curvy sections of track. Still, the car was a remarkable technical achievement, has wonderful handling manner on track, and is great fun to turn laps in even if it's not going to be setting any world records. Take it to the RX tracks too; it is a great match for that type of driving.
Jussi: Side note: The same basic system was later used for cars like the Nissan Skyline GT-R (and the current GT-R), Lamborghini Huracan and a ton of other cars, and the modern Haldex system is essentially a reversed version of this system (front-wheel drive with an electronic clutch to transmit power to the rear when necessary). Definitely ahead of its time.