Indianapolis: The Offenhauser Story - The Power AND The Glory
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Drake Engineering - Offy Racing Engines

Offenhauser Racing Engines

 1935 - 1978
Harry Miller
Apart from a spell of about four years, the Offy engine, as it was called, dominated American oval-track racing for decades. Not that development stood still; in the thirty years that it dominated, the engine changed in many ways, and, thanks to the use of turbo charging, the power output increased from about 300 to around 800 bhp. Even more amazing is the fact that the engine was originally designed in the mid 1920s, and was first used in track racing in 1930.

Harry Miller (1875 - 1943)

It was designed by Harry Miller, one of the most outstanding of American automotive engineers and, although it powered some track cars in the 1930s, it only came into its own after World War 11. By 1960, the Offy engine was looking decidedly long in the tooth, and some competitors started looking for a more modern engine. Then Ford decided to get deeply involved in Indianapolis racing, and in 1963 showed that a special version of their pushrod engine could compete with the Offy.

By the end of 1964, the Ford engine, now boasting twin overhead camshafts per bank of cylinders, had made the Offy obsolete - so much so that the company that made the Offy engines took to building the Ford engmes. However, in 1965, the regulations governing USAC racing were altered so that supercharged engines became favored again. So, in 1966, a smaller version of the Offenhauser engine appeared with a turbocharger.

By 1968, this engine was on top again and, despite some more changes to the regulations, there seemed to be no reason why the Offy would not continue winning for years to come. In unravelling the rather complex background to the Offenhauser engine, it is necessary to go back to the 1920s, when Harry Miller's cars and engines dominated American track racing. Although Miller tends to be remembered for some of his less practical designs that he evolved in his later years, he produced some superb engines in the 1920s.

Leo Goossen and Fred Offenhauser

Miller had always been a man of tremendous imagination, but, in these early days, he was aided by two men who were able to keep that imagination within practical limits. The two men were Leo Goossen, a young draghtsman who had previously worked at Buick, and Fred Offenhauser, his shopforeman. Goossen was able to turn Miller's ideas into sound designs, while Offenhauser made sure that all the bits and pieces could be made - and that they were made properly. Miller's first important design was a 183 cu in (3-liter) straight-eight with four valves per cylinder. Significant features were the separate barrel crankcase, and the use of a combined cylinder block and head.

This engine won at Indianapolis the first time it appeared there. When the regulations were changed in 1923, to limit engine size to 122 cu in (2 liters), Miller came up with a new straight-eight, but this ad two valves per cylinder in a hemispherical combustion chamber, this being one of the first racing engines to appear anywhere with this layout. However, Miller's real run of success was from 1926 to 1929 when his straight-eight 91 cu in (1.5-Iitre) supercharged engines ruled supreme over the US racing scene. This engine had a bore and stroke of 2.19 x 3 in, and developed about 250 bhp at 8000 rpm. It had five main bearings, but retained the basic layout of the earlier Miller engines.

The Post Depression Indy Austerity Formula

It was in this highly successful period that Miller designed the engine that was to become the Offenhauser. It was a 151 cu in (2.5-liter) four-cylinder engine with two valves per cylinder, designed as a marine racing engine for Dick Loynes, one of the boat-racing champions of the times. Because it was intended for marine use, it was much more robust than the others racing engines but, again, it retained the basic Miller layout. Following the depression of 1929, what might be called an austerity formula was introduced at Indianapolis, superchargers being banned. Miller straight-eights continued to be the most popular engines for Indianapolis, but Bill White, one of the leading figures in track racing at that time, thought that a 'big-four' might give better torque than the eights, especially since it could be half a liter bigger.

At that time, Miller was in the east, well away from the factory in the Los Angeles area, so White asked Goossen and Offenhauser to modify one of these marine engines for track racing, which entailed increasing the displacement to 183 cu in (3 liters). To the amazement of the diehards, this engine proved competitive against the straight-eights. Miller went bankrupt in 1933 and, two years later, Offenhauser started to build the 'big-four' engines for track racing, with Goossen acting as consultant, and this is why the engine was called an Offenhauser and not a Miller. Ironically, although Miller had been scathing in his references to what Goossen and Offenhauser had done to his design, he bought two engines from them for his Indy cars in 1937, both of 255 cu in (4.16 liters).

Meyer and Drake

Soon afterwards, Offenhauser was asked to build a supercharged 183 cu in engine for the Novi car, and this was designed by Goossen. From then on, this engine took up most of the time of the two men and so, after the war, the Offy engine became available for someone to build again. This time it was Louis Meyer and Dale Drake who joined forces to build 275 cu in (4.5-liter) 'big-fours'. Although 183 cu in supercharged engines were still permitted at Indy, the fact that they had to stop for fuel, and were generally unreliable, made them unpopular, and until 1962 the normally aspirated Offy engines built by Meyer and Drake held an undisputed grip over oval racing.

1955 version of the Offy engine, as used in a Midget car
1955 version of the Offy engine, as used in a Midget car.

1965 supercharged Offy , which developed 525 bhp
Although Offenhausers were most powerful in turbo-charged form, they were also build in normally aspirated and mechanically supercharged form. Pictured above is a 1965 supercharged Offy , which developed 525 bhp.

By the early 1970s the Ford V8 with quad camshafts was almost as competitive as the Offy. Pictured above is the Sunoco McLaren with which Mark Donohue won the Indy in 1972.

Offenhauser 159cu in fitted with a Roots type blower
Above is an Offenhauser 159cu in fitted with a Roots type blower. This image clearly shows the internal splines to take the special multi-plate racing clutch, with timing marks around the whole circumference.
In its basic layout, the engine resembled Miller's early designs very closely., There was a separate aluminum-barrel crankcase, with side windows covered by cast plates. The cylinder block and head' were built as a large and fairly complex alumium casting, and there were four valves per cylinder. The five- main-bearing crankshaft was machined from a solid billet, and the connecting rods were unusual in that they were of tubular construction instead of the con- ventional I-section. A train of gears at the front of the engine drove the camshafts and the auxiliaries, including the oil pumps for the dry-sump lubrication system.

Hilborn-Travers Fuel-Injection

These engines were equipped with the Hilborn-Travers fuel-injection system, a very crude design, which proved adequate for the limited speed range required at Indianapolis. Fuel was injected continuously into the inlet manifold, and the metering was controlled entirely by the position of the throttle, no account being taken of speed or load. Although the layout of the OfIY engine seemed pretty archaic, it was this which gave it its long life. The use of a separate crankcase made it much easier for changes in the bore and stroke to be made, while the use of an integral cylinder block/head unit eliminated one of the bugbears of high-performance engines, gasket failures, and this was to become very important later on.

The tubular rods were far from ideal when it came to resisting the loads they carried, but they could be made easily on a limited production basis. The shank of the rod could be turned on a lathe and then drilled, which was a much simpler way of doing things than milling away the normal I-section shank. In that early post-war period, the Offys were producing about 300 bhp which was much less than the supercharged Novi 183 cu in (j-liter) engine was producing. However, since the Novis were hopelessly unreliable, this did not worry Meyer and Drake unduly.

Nevertheless, in 1952, Meyer and Drake decided that they should be ready for the Novi if it was successful, so they built a supercharged engine. To obtain the necessary 183 cu in (3-Iitre) capacity, the stroke of the standard engine was reduced, and this involved the use of a special crankshaft, connecting rods and pistons. With a Roots-type blower, the engine developed 500 bhp at 6500 rpm by 1954, but the ultra-conservative racers decided to stick with their unsupercharged engines. The Offy engine remained in control, and this situation continued even after the regulations were changed in 1957. This time, only a small change was made, the capacities of unsupercharged engines being reduced to 256 cu in (4.2 liters), and supercharged engines being limited to 171 cuin (2.8 liters).

By this time, the Offy engine was so much a standard part of Indy cars that different owners specified different ways in which the new capacity was obtained. So the bores and strokes were either 4.15 x 4.63 in, 4.22 x 4.5 in, or 4.38 x 4.25 in. Of these, the 4.22 x 4.5 in dimensions were most popular, and the engines developed about 325 bhp at 5500 rpm. The fact that these different sizes could be produced was an indication of the versatility of the design of the engine. Although the organisers had not had the sense to alter the relationship of the supercharged capacity to that of un supercharged engines, the Offy continued to hold sway, and the power was gradually increased until it was developing 407 bhp at 6000 rpm, with a maximum torque of 380 lb ft at 4800 rpm in 1962.

These figures were obtained by Ford when they tested one of the engines to see what they were up against. The power-output figures were obtained on methanol, the fuel that was used at Indy for many years. Ford were able to match this output on methanol - which gave about 13 per cent more power than petrol - with an aluminum version of their 256 cu in engine. Later, Ford developed a version of the engine with twin overhead camshafts per bank of cylinders and, by 1964, these engines were developing 475 bhp. In comparison, the Offy engines were only able to turn out 440 bhp by sacrificing reliability, and it seemed that the era of the old 'big banger' was over.

Meyer and Drake evidently thought so, because they approached Ford with a view to building the V8 engine for them. Since Ford were having some difficulty in controlling costs, they readily agreed. For 1965, Meyer and Drake were able to extract 500 bhp from the Ford engine, so as far as the Offy engine was concerned, that seemed to be that. Just then, though, the organisers decided they wanted to reduce the amount of fuel carried by the cars to lessen the fire hazard, and they decided that the solution was to make every car stop twice in the race to refuel. As so often happens when rules are meddled with, the result was quite different from that intended. Now that two pit stops had to be made, fuel consumption was no longer any problem, so the answer seemed to be to bring back the supercharged engine.

Fitting the Garrett AiResearch Blower

Meyer and Drake built an engine with a 4.12 in bore and 3.12 in stroke and fitted the old Roots blower. The engine gave 530 bhp, which was enough to make them think the project might be worth proceeding with; then the possibility of using a turbocharger was suggested by Garrett AiResearch, one of the turbo-charger manufacturers. Although the turbocharger performed the same function as a supercharger, it incorporated a turbine which was driven by the exhaust gases, so it was driven by waste energy, whereas the supercharger absorbed power as it was driven. With very little development, Meyer and Drake were able to get 625 bhp at 8500 rpm, and so if some sort of reliability could be achieved; the Offy could be back on the winning trail.

The engines were first used in 1966, and they were all unreliable, one finishing eighth. Meyer and Drake set about sorting out the bugs. First, they went to an iron block to try to increase the strength of the engine, and then they started looking into the cooling problem. In the 1967 race, seven turbocharged Offys raced, but still most of them suffered from overheating. For 1965, the cooling system was redesigned. This work paid off when the turbocharged Offy won at Indy in 1965. Because the cars with turbocharged engines were so fast, it was decided to reduce the engine size to 160 cu in (2.65 liters), but this change in the regulations hardly affected the Offy engines, whose bores were reduced to 4.03 in. By this time, though, Meyer and Drake had learned enough about the turbocharged units to be able to revert to an aluminum cylinder block, though different from the early design.

The Cosworth-DFX

After 1973, USAC rules evolved to limit fuel consumption and turbocharger boost levels and more competition for the Offy began to appear. Still, Offy-engined cars dominated the USAC trail in 1974. In 1975, although an Offy won at Indy, the title went to A. J. Foyt, using his own development of the Ford V8. The year also saw the arrival of the Cosworth-DFX -a turbocharged version of the DFV Formula One engine - which became the latest in the long line of threats to Offy supremacy. A DGS-Offy won the championship in 1976 but five of the thirteen races went to Cosworth and Foyt-Ford power. Far from letting the Offy fade out and die, Drake Engineering and many of its customers rose to the challenge.

While Drake's new designer, Hans Hermann, planned a new 90° V8 with integral block and heads, the Romlin-Lightning team designed a new car around a 'lay-down' version of the engine and this car was tested towards the end of 1977, but despite promising results the Offy's last victory came at Trenton in 1978, in the hands of Gordon Johncock's Wildcat. The last time an Offy-powered car raced was at Pocono in 1982 for the Domino's Pizza Pocono 500, in an Eagle chassis driven by Jim McElreath, although two Vollstedt chassis with Offenhauser engines failed to qualify for the 1983 Indianapolis 500.
Dale Drake next to an Offy powered Indy Car
Dale Drake, who set up his own tuning form to prepare Offenhauser engines in Santa Ana, California, stands by a supercharged Offy engine Indy car.
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