The Shelby American (Fall 2021)

was getting too hot. All this in spite of a large number of apertures which should have supplied them with more than enough air. We discovered that what was happening was that—due to design changes that had been made over a period of time probably without reference to the original specifica- tions—practically all of the duct-work was at a ‘stall’ condition,” i.e., no air was moving in the ducts. The GT has two pairs of air inlets at the rear; one right behind the door and another higher up and farther back, beside the rear window. Origi- nally, the upper ducts were supposed to admit air for the carburetors and the side ducts were to pick up air for the rear brakes. Remington decided to split off both pairs. The inboard side of the upper ducts now goes to the carbs, the outboard side goes to the rear brakes. The lower halves of the side ducts now direct air to the exhaust system, the right upper half feeds air to the transmission oil cooler, and the upper left leads to the engine oil cooler (both coolers are Shelby additions). Engine compartment air was origi- nally picked up at grilles in front of the windshield and ducted through the doors. Ford found out that the grilles were in a near-zero pressure area and put a small louvered grille over the engine compartment behind the rear window. Remington enlarged the louvers by about 100%. At the front, not enough air was get- ting to the brakes or through the radi- ator. Relatively minor alterations sufficed to get air to the brakes, but the radiator was a Gordian knot. Ford Advanced Vehicles had been convinced that a dry-sump lubrication system was necessary. Remington didn’t think so. It required a separate oil tank, overflow tank, oil radiator, oil lines and 15 quarts of oil to be circulated by a second, power-consuming scavenger pump—all of which added unwanted weight. Moreover, the oil tank and ra- diator were up in the already-crowded nose. “We congested the whole front end of the car,” apologized Lunn; “in future approaches we’ll allow more space.” Remington couldn’t wait. He gam- bled on a conventional wet sump for the Cooper-Ford “King Cobras” and it had worked well enough. The distance from the crank centerline to the ground was the same as the Ford GT, so out went the dry sump system. This left more front aperture available for the air flow to the radiator, and al- lowed the exit flow to be cleaned up. Adding a small spoiler on the forward lip of the air exit on top of the hood dropped the water temperature 40°. “We now have a condition where the engine runs excessively cool,” reported Miles. “This happy state of affairs means that we can redesign the nose cutting down on the air flow through the radiator and thus improve the top speed of the car with no increase in horsepower.” Lunn’s group is already at work on a new nose that is longer and lower. It will make its first ap- pearance at LeMans, June 19. The next problem was weight. Close to 60 lbs. had been saved by abandon- ing the dry sump, but the car was still overweight. Ready to go, less fuel, it had never weighed less than 2200 lbs. The design target had been 1800 lbs. Originally, the GT40 used the alu- minum block, pushrod Indy engine, but this was discontinued when the “production line” started making the 4-cam Indy engine. The GT40 is now powered by the stock 289 cu. in. 385- h.p. cast-iron Cobra engine—just like the ones in the Daytona Coupes except for the 1-inch shallower oil pan and a smaller diameter 3-plate clutch. The minimum allowable weight for a GT prototype of this engine size is 2035 lbs., so only 100 or so more pounds can be saved from the Shelby cars before they have to start ballasting. Although there has been talk of welding up a chassis center-section out of aluminum sheet (which would save about 100 lbs.), the first approach will probably be to lighten the fiber- glass body parts. The present nose and tail sections are, “typical European fiberglass,” according to Miles. “What we need are some body sections laid up using fiberglass linen in very thin sections, which will give the rigidity and strength we need—without the weight.” The Borrani center-lock wire wheels have already been scrapped. “The wire wheels were originally fitted in the be- lief that you would get some air flow through the wheels, which would re- sult in the brakes running cooler. This is a fallacy; you don’t get any air flow through wire wheels when they’re spinning—they are just like a solid disc,” said Miles. Specifications were drawn up for magnesium wheels and sent to Ted Halibrand. He couldn’t have the mag wheels ready for Day- tona, so the GTs ran with cast alu- minum wheels. Mag wheels will be on the cars at Sebring and after. The mag wheels were not only stronger and lighter, but also gave Remington the opportunity to increase the rim width from six inches in front and eight in the rear to eight in the front and nine-and-a-half in the rear. Nobody was very comfortable with the Dunlop R6 tires and they were re- placed by Goodyear Indy tires. The wider rim necessitated widening the rear body section about two inches, in- creasing the spare tire area and re- working some of the chassis paneling near the forward end of the pannier gas tanks in the door sills to get enough steering lock. So, finally, to the brakes. Part of the problem was solved with improved ducting and by the mag wheels (which tend to draw heat away from the discs). At Daytona, the “g” loads on the banking were so high that the wheels were pressed up into the wheel wells and squashed the end of the duct; this will be remedied by Sebring. Kelsey- Hayes, which works very closely with Ford on disc brakes, made up a set of radially-ventilated discs from Mee- hanite for Shelby American. These were put on the cars for practice at Daytona and the drivers were ecstatic about the way they worked...until the discs cracked. Remington said that Kelsey-Hayes would make the next set of vented discs from high nickel con- tent cast iron. “The vented disc,” said Miles, “is definitely the answer.” Final touches to the car before Day- tona included replacing the four Ben- dix fuel pumps with three Stewart-Warner adjustable pumps, The SHELBY AMERICAN Fall 2021 58