Grand designs 1971

They say trouble comes in threes. Indy fought off two intrusions, but not the third. By Keith Howard

By 1970, Indy traditionalists had had their fill of foreign interlopers. First Cooper and then Lotus had eclipsed the front-engined roadster. Then Lotus pushed 4WD and turbine power, and almost won. As the '70s began, Indy diehards may have thought upheaval was past: rear engines were now the norm; 4WD and turbines had been outlawed. But in 1970 McLaren built its first Indycar, the M15. It was a toe-dipping exercise and relatively conservative, but one feature presaged the revolution McLaren would initiate the following year.

Wings separate from the body were banned by USAC, so designers tried to generate downforce via the car's body or with upswept engine covers. But with the M15, McLaren went a step further by forming the engine cover into a wing. It wasn't large and, being immediately behind the roll-over bar, wasn't fully effective. But it established that there was sufficient flexibility in USAC's rules for wings to get in through the back door.

McLaren's 1971 car, the M16, was much bolder and quickly proved itself the car to beat. With wedge body and front wings to balance a rear wing now behind the rear wheels, albeit still attached to the engine cover, it introduced F1-like aerodynamics to devastating effect. So successful was it that McLaren ran developments of it through to '76.

McLaren should have won the 1971 Indy 500, but Mark Donohue (Team Penske M16) retired from the lead with gearbox problems, and polesitter Peter Revson lost confidence in his M16's handling and finished second. In '72 Donohue won, and the M16 scored again in '74 and '76.

Sternest resistance came from Dan Gurney's All-American Racers, whose Eagles won in 1973 and '75 and should have won in '72. Here Gurney and M16 designer Gordon Coppuck discuss the M16 and AAR's response to it, which made for one of the toughest constructors' battles in Indy history.

Rivals' reaction
GC: "Wings were banned as a bolt-on piece, but in the 1970 car [the M15] we had successfully adapted the engine cover into a wing as there were no regulations specifying what the engine cover could comprise. There were complaints when we ran the larger rear wing and front wings on the M16 in 1971 but others, notably AJ Foyt, quickly copied us. As soon as the wings were put on, drivers didn't want them taken off again because they felt so much more confident and safe in the car. So it snowballed: we opened the door and everybody else rushed in. We actually helped Foyt with his early wing development because we knew once we had him on board the door wouldn't be closed again. All credit to Teddy Mayer for playing that political card. Doing the deal with Penske also meant there was another strong voice for wings."

DG "We didn't challenge the legality of the M16 because that isn't the way we did things. Our Eagle became obsolete the first time the M16 ran, but necessity is the mother of invention. Since the first Indy 500 in 1911, the increase in qualifying speed averaged maybe 1.5mph per year. All of a sudden it leapt 8.5mph in one swoop when the M16 showed up. It was a bit of a shock what happened to tradition?"

Aero development
GC: "The wedge came from the Lotus 72, which tidied up the messy airflow from a front radiator. Downforce from a wedge is quite draggy but the gain In corners more than made up for it. Once USAC accepted wings, and they were freed from the body, we reduced the wedge angle. We didn't do any wind tunnel testing before running the M16 in '71, but for '72 we used Lockheed's tunnel – no moving floor but it did run fast. We understood about centre of pressure, drag and downforce whereas others concentrated on drag. We had more drag with wings, but we knew how much we could suffer in order to generate downforce."

DG: "We had no tunnel but we had enough curiosity and fabrication capability to experiment with the '71 Eagle – we'd strap a ping-pong table to the car with an angle on it! We tried wings over the engine and behind the rear wheels, and all sorts of cooling arrangements. We couldn't conjure up a brand-new car like McLaren, but our '71 car was on the front row of every race bar one; we had seven poles and four new track records. But there was no doubt that whatever we tried and we never gave up the M16 was a superior car."

The Offenhauser engine
GC: "Although it was a 40-year-old design. the Offy largely through Herbie Porter, who'd been the first to turbocharge it for Indianapolis – produced decent horsepower and was much lighter than the Ford V8. We had our own engine shop so you couldn't say that we raced Porter engines, but Herbie was employed by Goodyear and we were a Goodyear runner, so if you blew an engine and the things were grenades you could get a replacement immediately from Herbie: a clever move on Goodyear's part because it meant that their senior teams couldn't get themselves into a situation where they were unable to participate."

DG: "We wanted to beat McLaren, not equal them, so we didn't try a slavish copy of the M16 for '72, as some others did. What we did was try to build a nice home for the Offy engine. That meant very good cooling. Also, our 1971 car had had a relatively high centre of gravity, which wasn't very smart. The realisation that we were looking at big jumps in speed took us into new territory structurally, so we had to build it more robust to maintain a degree of safety. Roman Slobodynskyj, the head of our design group, was very good at packaging a car, which in the end dictates how safe and efficient it is."

Indy disappointments
GC: "We pulled Peter Revson's car apart after the 1971 race but never discovered the problem. We were disappointed to be runner-up, especially as Mark Donohue had been leading the race before his gearbox failure. From then on we specified aircraft-quality steel for the gears, and never had a gear failure again. We used a four-speed 'box instead of the normal two-speed; there's a small power loss but it improved acceleration out of the pits and after yellow flags."

DG: "We should have won in '72 but we didn't have a test track or dynamometers to test reliability. That probably accounted for Bobby Unser's retirement. When Jerry Grant made an unexpected stop we were leading but we'd lost our radio three laps in so I had to guess why he was coming in. The only thing I could think to do was add fuel, so I waved Jerry into Bobby's slot but he needed a tyre. I tried to tell the crew not to put fuel in. but they hooked up for about 6sec. We changed the wheel, and Jerry came out and finished second, but George Bignotti had seen the fuelling from Bobby's rig, which was against the rules, and protested. They stopped our race at lap 182. so Jerry ended 12th."

Rear suspension
DG: "At Indy the handling balance of the car would alter during the race because of fuel load, tyre wear and changes in the track itself. As a driver I often found that if I could have pulled into the pits to make an anti-roll bar adjustment I'd have been able to go a whole lot quicker. With no way of doing that you just had to say, 'That's another year down the tube' – it was very frustrating. So for the '72 Eagle we conjured up a hydraulic means of shortening or extending the actuating arm of the rear anti-roll bar. You could make It shorter and stiffer, or longer and softer. It wasn't as clever as the blade system that Porsche came up with but functionally it was quite good. You could compensate as the handling of the car changed."

GC: "We used a camber compensation system in the rear suspension of the M16. Instead of the inboard pivot of the inside wheel upper link being connected to the chassis, it was connected across to the right-hand wheel. So in a corner both wheels tilted the same way to maximise cornering force. We were able to do this at Indy because all the corners there are left-handers. It was probably worth about 1.5mph over a lap, but as tyres improved in future years it became redundant and we reverted to a conventional arrangement."