The Car is the Star
GT40 - Where Sheer Power Met Reliability
The car that won the 1966 Le Mans, not only for Ford, but for America. Employing the world’s finest minds and talent, Henry II set out to crush Ferrari and he did so, badly, with a 1-2-3 finish. These are the specs, nuances, development and overall history of chassis P/1046.
The design of the GT40 Mk. II was carefully constructed after hours and hours of purposeful attention to lightweighting, strengthening and aerodynamics. It wasn’t until the ‘60s that aerodynamics was truly studied in race cars eclipsing 150-200 MPH. Enzo Ferrari had the mindset that if a car couldn't go faster, it needed more horsepower. Ford engineers knew both horsepower and aerodynamics win races.
Ford came up with their early GT design in Dearborn by looking at what the competition was doing. Formula One cars of the day were well constructed and employed lots of technology, but were fuel tanks on wheels. It wasn’t until 1962 when Lotus designed the first monocoque chassis with the model 29. The Lotus 29 was a rear engine 4.2L Ford powered 370 hp V8 in an aluminum monocoque designed chassis that had Girling disc brakes, a 4-speed transmission, 6- and 7-inch tires and weighed only 1,170 pounds. The car, as advanced as it was, had absolutely no "aerodynamics" or active & passive safety considerations in it's design.
Considered to be technologically advanced for its day, modern Ford engineers tested a 1969 Le Mans winner from their museum when they decided to resurrect the classic ‘60s GT40 as a limited-production high-end sports car. What they discovered in their high-tech wind tunnel was that the GT40 had, in the words of Ford aerodynamicist Kent Harrison, “an incredible amount of front-end lift.”
It wasn’t until the ‘60s that aerodynamics was truly studied in race cars eclipsing 150-200 MPH.
| CID - | 427 |
| Bore x Stroke - | 4.2346 x 3.784 |
| Connecting Rod Length - | 6.488 |
| Horsepower @ rpm - | 485 @ 6200-6400 |
| Torque @ rpm - | 474.5 @ 3200-3600 |
| Compression Ratio - | 10.5:1 |
| Carburetion BBL - | 1 x 4-bbl |
| Carburetor - | Modified Holley 780 cfm |
| Lifters - | Mechanical |
| Rocker Arm Ratio - | 1.76:1 |
| Valve Lift (in/ex) - | 0.527/0.527 |
| Valve head Dia (in/ex) - | 2.060/1.625 |
| Cylinder Head Material - | Aluminum |
| Cam Specs (in/ex/overlap) - | 342/324/96 |
The Powertrain
Thousands of hours of testing were completed before engine number AX316-1-41 was built built and fitted into chassis P/1046. It was Ford’s 427 FE 90-degree OHV V8 engine pulled from the Ford Galaxie (used in NASCAR at the time). There were a few reasons why Roy Lunn, the godfather of the GT40, opted for the powerplant. After unsuccessful campaigns with the 255ci and 289ci engines, the logical next step was to throw in a big block, but that presented major design concerns.
Engineers were concerned about ground clearance, cooling, intake and exhaust clearances, oil capacity, fuel handling, durability and driveability. However, in the end as you may know, all the hours spent testing and fitting paid off. One reason due to having access to a dynamometer. Without this, real world testing may have been almost obsolete. Ford didn’t have access to the track, so the dynamometer helped Ford simulate a 24-hour run of the Le Mans circuit. This allowed Ford engineers to test the engine and driveline units and simulate the on-course throttle, clutch and shift patterns of the company’s race engines. Thus, in addition to the larger engine and more reliable engine, Ford used forward-thinking and technology to dethrone the prancing horse.
Outsmarting the Competition: The Dynamometer
Ford didn’t have access to the track, so the dynamometer helped Ford simulate a 24-hour run of the Le Mans circuit.
The Interior
Chris Amon was quoted as saying, "The interior was quite comfortable, as much as a race car can be, compared to other race cars I have driven.”
- Instrumentation:
- 7000 RPG Tach
- Oil Temp
- Water Temp
- Fuel Pressure
- Ammeter
- Gearbox
- Warning lights:
- Differential Oil Pressure
- Engine Oil Pressure
- Right Hand Drive
- Perforated seating to keep drivers cool
Height
The name “GT40” is derived from its concept name of “GT” coupled with a roof height of only 40”.
Nose
Data from wind tunnel testing of the Mk II cars lead to the nose of the Mk II-A vehicle being shortened by nine inches saving 19 lbs. in weight. The revised nose also made the car more aerodynamic.
The nose created 14.1 sq. ft. of frontal area and helped create the 0.39 drag coefficient and 5.50 drag area.
Tires
As told by Chris Amon, "We were the only car that started on Firestone; the rest of the Fords were on Goodyear. Bruce and I found very quickly that the Firestones were either chunking or losing their treads. Two or three pit stops early in the race and we got ourselves way behind. The decision was made to switch our car to Goodyear. This was a bit tricky because Bruce and I were contracted by Firestone - you can imagine that Firestone wasn’t too impressed by this. After we switched, Bruce said to me, 'We've got nothing to lose. Let's drive the doors off it, and by next morning, we were actually in the lead."
The tires used were Goodyear “A” competition tires.
The front tires were 9.75 -15 or approximately 250/60/15.
The rear tires were 12.8 - 15 or approximately 325/60/16.
Construction
The Mk IIs were created from a semi-monocoque construction made of .024 in. (0.61 mm) steel. Hinged front and rear panel sections and doors are of reinforced fiber glass. The design leads to increased strength and reduced weight. Roy Lunn and the group decided that the main structure would be a semi-monocoque steel construction utilizing the roof skin section as a stressed member.
Approximately 240 separate panels were used in its construction utilizing the roof skin section as a stressed member and conventional welding techniques of the day were used. Abby Panels in Coventry was contracted to build the first two prototypes and over time built all the GT40 chassis.
Component testing was completed by the end of November 1963 and the next several months were spent in detailing and procuring items for the first prototype builds. On March 16, 1964, Abby Panels delivered to FAV the first chassis, and the car was completely assembled in only 16 days.
Colors
Chris Amon said the color for P/1046 was chosen by Carroll Shelby. Given that both McLaren and Amon were native New Zealanders, the color black pays tribute to the national rugby team of New Zealand, the All Blacks. As well, the “Silver Fern” was added to the side of the car. The Silver Fern is a national symbol of New Zealand representing the leaf of the New Zealand fern.
Gurney Bump
As the 6’2” driver, Dan Gurney, was too tall to fit into a standard GT40, bodyworkers added a roof protrusion, called the Gurney Bump, to allow extra headroom.
Rally Stickers
Entry stickers from the 2003 and 2013 Goodwood Festival of Speed, showing P/1046 had road time in its later life. These stickers will not adorn the vehicle in its post-restoration state.
Air Scoops
We the heavier design of the Mk II, the brakes became a major concern. The original MK I used solid 1/2" rotors and were replaced with 3/4" ventilated rotors. They were 11.56 inches in diameter. The original Girling CR and BR calipers were modified to accommodate the new vented rotors. New molded asbestos brake linings were also used.
The front brakes with the new shortened body work on the Mk II-A, as compared with the long nose prototype cars, had a more direct air stream path. The air flow at the rear of the vehicle is more turbulent and generally at a lower pressure. The engine and trans assembly also presented some limitations as far as ducting. The side body air scoops on the rear quarter (weaker air stream) had a splitter and provided air to the carburetor and the rear brakes. This combined with external periscope-like air scoops mounted on the rear deck (first used at Sebring '66 - see photo) was positioned into the high velocity air stream and provided reduced rotor surface temperatures and reduced brake fluid temps (also critical).
The lower rear quarter air scoops provided additional cooling air to the high efficiency engine oil cooler (L) and the transmission oil cooler (R). The two front NACA air-scoops provided air to the cockpit for improved driver comfort. The rear deck center mounted vent (first used at Daytona '66) (see photo) provided additional air for engine and exhaust cooling. The hood opening was primarily to vent air.
Brake Discs
The Mk II cars designed in part with Shelby featured quick change ventilated brake discs, which helped the brakes stay cool and perform well across a broader temperature spectrum. The system included a flip-down retainer that made removal of the brake caliper, and thus pads, quick and easy with crew members losing any pieces. See Chapter IV in the “Legend of Le Mans” series in the Documentary section of this site for an in-depth explanation.
Rear Spoiler
The rear 5” spoiler was added by Shelby as part of several aerodynamic changes aimed to stabilize the car at high speeds. Chris Amon said the car felt so stable at speed on the Mulsanne Straight he could drive with one hand.
Rear Fiberglass
According to Mark Allin of Rare Drive, the shop restoring chassis P/1046, the rear fiberglass is original. Mark came at this conclusion by closely examining historical photographs, seeing where items were attached and then checking to see if P/1046's holes were still there/lined up. Onlookers can also see where the luggage boxes melted a square-shaped hole in the fiberglass from the heat of the car during the race and there's also an extra rubber flap in the wheel wells that are unique to this car.
Exhaust
The exhaust of a GT40 Mk II is aptly named “bundle of snakes” and is the originator of this type of exhaust specific to 90-degree flat-plane V8 engines.
These beautiful works of art built by English and American craftsmen displays where two tubes from each bank of the V-8 are crossed over the engine to collect in 4-1 collectors with opposing tubes. What was the purpose of these tangled spaghetti-like devices? Most modern V8s have what is known as 90-degree cranks (aka crucified cranks, bent cranks, cross-plane cranks) wherein the cylinder firing order is such that two cylinders on each bank fire consecutively as opposed to alternating banks. The purpose of the 90-degree crank is to minimize vibrations inherent to “flat-plane” cranks.
Suspension
The GT40 Mk II cars utilized independent with unequal length A-arms, coil springs, tube shocks (Koni) and anti-roll bar up front.
The rear was independent and comprised of trailing arms, unequal length lateral arms, coil springs, tube shocks (Koni) and an anti-roll bar.
Interesting to note is that Mark Allin of Rare Drive has the date curated by Shelby-American and Ford as to the alignment specs and even tire pressure used for competition.
The Block
The 427-cubic-inch Wedge V8 became known as one of the most powerful and dependable high production power plants. The engine's history dates back to 1958 when Ford introduced 332 and 352ci engines. In 1960, a 352 high performance engine was introduced followed by a 390ci engine in 1961. The high performance version of the 390 brought up the displacement to 427.
The production 427 included some special features, such as, high compression cylinder head, aluminum intake manifold, high-RPM camshaft, solid valve-lifters, and heavy-duty valve springs. It also had impact-extruded pistons and special connecting rods for high strength and superior resistance to heat and stress.
The proving grounds for the engine was NASCAR, debuting in 1963 the 427 powered Ford to several championships.
In 1967, a Ford Mk IV powered by a 7.0L V8 like the Mk II, driven by Mario Andretti and Denny Hulme, held the fastest average speed record until it was broken decades later in 2010.
Dry Sump Lubrication
The Mk II-A had a new oil scavenge system due to ground clearance requirements and chassis interferences. To reduce weight, the front is sand cast aluminum and the oil pan is sand cast magnesium. The system is capable of delivering 20.5 gpm at 70 PSI, enough to satisfy lubrication requirements at 7000 RPM.
Fabricated Tubular Header System
A main priority of the GT40 was extracting as much horsepower from the engine. Ford engineers had a lot of experience with extracting horsepower from the 427 in the NASCAR vehicles. Various designs were tested on the dynamometer and the final design of 32" length and 2.25" diameter headers proved to obtain optimum power at high RPM (6000-7000 range). It is interesting to note, the severe bends in the design had little or no effect on horsepower. One challenge was to maintain consistent cross-sectional areas in the hand fabrication. The design took two tubes from each cylinder bank of the 427 and crossed over the engine to collect in 4-to-1 collectors of opposing tubes. This was known as 180 degree headers. This design proved to be effective based on the 'production' engine design that used a 90-degree crankshaft. The purpose of the 90-degree crank is to minimize vibrations that is more acceptable for a passenger car engine. This design resulted in being nicknamed the “bundle of snakes”.
Ford Kar Kraft T-44 Transaxle
The T-44 transaxle was designed and built by Ford's Transmission and Chassis Division. The primary challenge was to transfer the 475 lb-ft. of torque to the driving wheels. The design uses a multi-piece case that was sand cast from magnesium alloy. Power was transferred from the engine to the T-44 transaxle via two dry-plate 10-inch long clutch discs, housed in the flywheel.
The KK T-44 transaxle assembly proved very reliable and withstood the thousands of shifts needed to win the 24 hour race.
