We continue the second part of our two part series on the history of the Allison engine.

At one time in the sport of Unlimited hydroplane racing, piston power was the only way to go. All teams used Rolls Royce Merlin and Griffon engines, as well as the turbo and supercharged Allison V-12s. As a new owner in the sport in 1986, Ed Cooper was determined to keep the "Thunder" alive in the sport. While many teams were slowly switching to the turbine power in the late 1980s, Ed and his team kept on using and then perfecting the Allison V-12 engine.

The result---many piston powered speed records, race wins and the coveted Gold Cup.  Cooper and driver Jimmy King will keep the "Thunder" alive in the Big Red Turbinator for many race fans heading into the 2010 race season.

Allison-powered Hydroplanes

The Allison V-1710 was an important hydroplane powerplant from the dawn of the modern piston era after WWII until the turbine engine retired these engineering marvels. Thanks to the availability of high-powered airplane engines from WWII, the Gold Cup class metamorphosed into the Unlimited Class, a true national circuit which remains active to this day. In 1946 the Miss Golden Gate III became the first hydroplane to be powered by an Allison V-1710 -- she was designed and driven by Dan Arena. She was a three-point tail-dragger (tips of the two sponsons and the tail of the hydroplane). While she set a competition lap record of 77.9 mph during the1946 Gold Cup in Detroit, the Allison over-powered the 26-1/2 ft hull making her very difficult to control. The next year the Dossin Brothers of Detroit introduced their Allison powered Miss Peps V which was driven by Danny Foster. This boat earned both major Unlimited Hydroplane titles for 1947 -- the Gold Cup and the National High Points Championship.

In 1950 another significant milestone was established by an Allison powered hydroplane -- the Slo-mo-shun IV, owned and driven by Stan Sayres set a new mile straightaway record of 160.322 mph, topping the previous record set by Sir Malcom Campbell's Bluebird II by almost 20 mph. Two years later the Slo-mo-shun IV raised the mark to 178.497, with a one-way run of 185.627 on Seattle's Lake Washington. This boat was the first successful "prop-rider", with the rear of the boat riding on a half-submerged propeller instead of the tail of the boat as with the previous "tail-draggers". For the next 20 years boats used a Slo-mo type design or they were not competitive. The Slo-mo-shun boats brought the Gold Cup to the West for the first time, and would keep the Cup in Seattle for 5 years, with Allison powered Slo-mo's retaining the Cup from 1950-1953, and a Rolls-Royce Merlin powered Slo-mo successfully defending in 1954. This era marked the dawn of the enduring Seattle-Detroit hydroplane rivalry.

Some of the more interesting Allison boats include the 1950's G-22/U-70 Such Crust III, a huge 10,000 lbs hydroplane using two Allison V-1710's in tandem and another giant 10,000 lbs boat, the twin-tandem Allison powered Gale VI. Both of these big boats were designed to handle the rough East-coast river courses. Another significant Allison-powered boat was the Miss Madison of 1971, which overcame long odds to win the Gold Cup in her home town to the delirious delight of the home-town fans.

Another significant Allison milestone was the 1962 mile straightaway record set by the Allison-powered Miss U.S. I of 200.419 mph set at Gunthersville, Al, driven by Roy Duby. This was the first boat to break the 200 mph barrier, and this record stands to this day for piston powered boats. In 2000, a second tier turbine team eclipsed the 38 year old record for propeller driven boats by establishing a 202 mph mark. It is expected that the top turbine teams will attempt to establish a meaningful propeller-based record at the end of the 2000 season now that the revered 38 year old standard has been broken.

The last significant Allison-powered boat was 10th hull to be campaigned under the Miss U.S. banner. She began competition in 1974 and finished in 1976, when she became the first and only turbocharged Allison to win a gold-cup, the last Allison-powered boat to ever win a Gold Cup, and the last Detroit-based boat (at least up to the present) to win the coveted Gold Cup. This is the boat now owned by Unlimited Excitement and featured elsewhere at this site.

However, the history of Allison boats is not closed. Throughout the turbine era which began in 1985 with the National High Points Championship by the Miller American equipped with a Lycoming T-55 turboshaft engine, Allison-powered hydroplanes continue to challenge the supremacy of turbine boats. There is still one Allison-powered boat competing in the 2000 season. While the odds are long, many fans are pulling for the boat filling the air with the great roar from the past -- the warbling growl of an Allison-powered boat with its prop loading and unloading as it bounces across the water. The whoosh of a turbine will never fill the air like the growl from an Allison!

Allison V-1710 Description

The V-1710 is a conventional overhead cam liquid cooled Vee-type engine with 4-valve pentagon roof combustion chambers using two 6-cylinder monoblocks bolted to a split crankcase. The engine has a propeller reduction gear or extension drive on the "grunt" of the engine as defined by Allison and an auxiliary case on the rear. Cylinders were numbered from the rear, with the bank to the left when viewed from the rear (auxiliary section) called the left bank and the other bank the right. Unlike automotive engines, the cylinders were numbered 1L to 6L on the left and 1R to 6R on the right, 1L being the the cylinder next to the auxiliary drive on the side of the coolant pump, the 1R cylinder being located next to the auxiliary section above the oil pump.

Type: 12 cylinder 60° Vee liquid cooled

Cylinders: Bore 5.5 in (139.7 mm), Stroke 6 in (152.4 mm), Displacement 1,710 cubic inches (28 liters). Compression ratio 6.0:1 (other versions typically use 6.65:1). Two cylinder blocks of six cylinders each comprising a cast aluminum-alloy cylinder head, six hardened steel cylinder barrels and a cast aluminum-alloy cooling jacket. Barrels held in head by a shrink-fit and are enclosed by coolant jacket. Jacket secured to head by studs and to cylinder by nut threaded over each barrel (and torqued to 2,200 ft-lbs!). Each cylinder-block secured to upper half of crankcase by 14 studs extending through the head. Combustion chamber has two intake and two exhaust valves and two diametrically opposed park plugs. Steel intake valve inserts, forged steel stellite-faced exhaust valve inserts.

Pistons: Machined from aluminum-alloy forgings. Three compression rings above piston pin -- one keystone ring in the top groove and two conventional rings, and two oil-control rings in a single groove below. Floating piston pin retained by snap-rings at each end.

Connecting Rods: Fork and blade type made from steel forgings machined and shot-peened. Connecting rod bearings consist of two flanged steel thin shells lined with nickel-silver-tin, and clamped in the forked end by two bearing caps. Center portion of the outside diameter of the bearing is covered with an overlay of nickel-silver-tin which acts as journal for the blade rod. Blade rod fits around the overlay and is held in place by a single steel cap. Bronze bearing pressed into the small end for the piston pin. Big-end bearings lubricated under pressure from crankshaft, small-end bearing lubricated by splash.

Crankshaft: Counter-balanced six-throw seven-bearing type. Each end of the shaft has a bolt flange which provide mountings at the front for a flexible splined coupling for driving the reduction gear pinion and at the rear for a dynamic torsional vibration balancer. Splined to the hub of the dynamic balancer is the outer member of a hydraulic damper. An inner member is connected to the outer rigid member by a flexible quill shaft and reacts against the outer member through a hydraulic fluid to minimize single-node low frequency torsional vibration. This damper provides the driving connection between the accessories housing and the crankshaft.

Crankcase: Two aluminum castings split on horizontal centerline. Large studs on the face of the upper half pass through main bearing webs on lower-half to clamp the two halves over the bearing shells. All main bearings are steel flanged shells lined with nickel-silver-tin. Center main bearing provided with faced flanges which bear upon the center crank cheeks to provide axial location (and absorb thrust loads) for the crankshaft. Cast magnesium-alloy oil pan bolts to the bottom of the crankcase lower half. Oil is scavenged from front and rear or the oil pan.

Valve Gear: Two intake and two exhaust valves per cylinder. Stellite-faced sodium-cooled nichrome-alloy valves. The stems of the exhaust valves are parallel to each other and angled 22.5° with respect the the cylinder axis. The intake valves are also parallel to one another and angled 22.5°, the resulting angle between intake and exhaust valves being 45°. The exhaust valve seat was cut at a 45° angle to the valve stem, while the intake was cut at a 30° angle. Single camshaft operates six rocker arm assemblies top of each cylinder bank -- each rocker arm assembly consists of a two forked rocker arms pivoting on a plain bearing (one for the exhaust valves and the other for the intake valves), each with a single rolling cam follower which forks to actuate both intake or exhaust valves by means of articulated lash adjusting screws. Each camshaft is driven by bevel gears through separate inclined shafts from the accessory housing. Pressure lubrication to cam bearings supplied through hollow camshaft.

Accessory Housing: Accessory housing mounted directly to the rear of the crankcase and is driven from crankshaft through harmonic balancer/hydraulic vibration damper. Contains supercharger and auxiliary gearing, with drives for the engine supercharger impeller, auxiliary stage supercharger, camshafts, magneto, starter, oil pump, water pump, tachometer, fuel pump, generator and vacuum pumps. The housing also contains the supercharger and provides mounting provisions for the carburetor and those accessories listed above which are not contained within the engine.

Induction: Bendix Stromberg SD400B3 speed/density injection system consisting of a injection pump which meters fuel based on engine speed and fuel-air density (charge pressure and temperature) and a throttle contained in a throttle body located between the auxiliary stage and engine stage superchargers. The throttle is normally open with speed being regulated by varying the speed of the auxiliary stage supercharger as described below. All metering is accomplished within the engine-driven injection pump. Fuel injected into the engine stage supercharger impeller (as was ADI when activated). ADI derichment by means of ADI pressure sensing in the injection pump. The engine supercharger feeds the intake ports by means of a induction pipe which feeds rams-horn type intake manifolds at the center of the engine, the induction pipe is located in the "Vee" of the engine below the intake manifolds.

Supercharger: The engine supercharger (second stage supercharger) is contained in the accessory housing and is driven from the flexible inner member of the hydraulic vibration damper. The impeller is 10.25" diameter with 15 vanes and includes a separate rotating reverse-curved inducer guide vane inlet guide, the relationship with the impeller being maintained by the common splined shaft. The diffuser is cast integrally with the supercharger cover, which also contains the inlet to which the injector throttle body mounts. The impeller is overhung, with the shaft supported by two floating lead-bronze steel backed bearings placed on both sides of the supercharger drive gear. The bearing are pressure lubricated with engine oil.

The auxiliary stage is contained in a separate assembly coupled to the engine accessory section. It is intended to provide a critical altitude of 25,000 ft by delivering air to the engine supercharger at pressures close to sea-level when at critical altitude. This requires large volume of low density air to be handled by the auxiliary supercharger -- because of the density of the air at 25,000 ft the supercharger must move 2.23 times more air volume than the engine supercharger, and compress the air to about 2.7 times to deliver sea-level conditions. The auxiliary stage drive was obtained by a power-takeoff from the starter gear which connects to a driveshaft incorporating a universal joint, the driveshaft being contained in a tube coupling the engine accessory section with the remote auxiliary stage. The driveshaft hydraulic torque converter connected to the step-up gears contained in the auxiliary supercharger housing. The torque-converter provides variable speed for the supercharger by varying the amount of oil and therefore the coupling of the torque converter. The speed controlled by a boost-regulating system, permitting infinitely variable control of the speed of the auxiliary stage which was used to control manifold pressure so that power could is controlled while the throttle remains wide-open. The auxiliary supercharger consumes 490 hp from the crankshaft at the 2250 hp WER rating.

Ignition: Ignition is a Bendix-Scintilla DLFN-6 magneto unit which combines two magnetos into one unit driven by a single drive shaft. The 4-pole magneto mounts to the top of the accessory section, with the driveshaft passing through the supercharger induction outlet pipe. The magneto is driven at 1.5x engine speed to obtain 6 sparks per engine revolution, and the exhaust magneto timing leads the intake timing by 6° (points open/coil fires at 34° BTDC for exhaust and 28° BTDC for intake), and is composed of two independent high-tension magneto coils excited by the engine driven magneto shaft's 4-pole rotating magnet. Each coil is connected to a set of points is actuated by a 4-lobe breaker cam on the magneto shaft. The points are connected to a condenser inside the magneto and to the coil and "P-lead" which connects the magneto to the cockpit magneto switches.

Separate high-tension (HT) leads from each magneto connect to distributors located on the accessory end of each head and driven by the camshaft. The intake distributor (which distributes the HT voltage to the intake spark plugs which are located in the "Vee" or inboard spark plug location) is located on the left bank and the exhaust distributor is on the right bank.

Each distributor rotor has two independent terminals -- the "M" terminal which connects the the magneto HT lead by a center spring terminal, and a "B" or booster sliding ring connection. The "B" distributor finger leads the "M" by 30° and is used only on the intake distributor side. During starting, a battery powered booster coil is energized by the starting switch to facilitates starting by retarding the ignition timing 30° during cranking (which reduces the torque produced by the engine due to the fixed ignition advance) and provides a hotter spark than the magneto can produce at low cranking speed.

Lubrication: Dry-sump pressure system. Circulation maintained by a single pressure pump and two scavenge pumps, all of the gear-pump type. Pressure is regulated by a pressure-sensitive balanced relief valve. Spring-loaded check valve prevents oil entering system when engine is stopped. Large tube in upper half of crankcase distributes oil to main bearings, through which it enters hollow portions of the crankshaft. This tube also carries oil to reduction gears, reduction gear pinion bearings, and propeller governor pad. Oil for accessory drives and valve gear is carried by tubes and drilled passages in accessory the housing. Oil from valve gear drains to crankcase through passages at both ends of the cylinder-block. Oil for the hydraulic vibration damper operation is also supplied from the engine pressure system.

Coolant: The coolant employed is a mixture of 70% water and 30% ethylene glycol. The coolant in the closed loop pressurized system is circulated by a centrifugal-type pump to the cylinder blocks and from the cylinder blocks to a small-capacity header tank and from the header tank via a radiator to the coolant-pump inlet. The flow of coolant air through the radiator is controlled, whether manually or automatically, through a temperature-sensitive device which controls radiator shutters. The header tank, which incorporates features to ensure the efficient separation of steam and coolant, is provided with a loaded relief valve which seals the whole coolant system up to a predetermined pressure. This pressurizing of the system raises the boiling point of the coolant and permits the use of smaller radiators. The header tank relief valve maintains the pressure in the system and also incorporates a suction-operated valve which admits air, if for any reason the pressure falls below atmospheric.

Starting: Direct cranking electric starter motor composed of 28V series would electric motor with integral 3-stage planetary reduction gear (approximately 100:1 reduction gearing) engaging a dog geared (1:1) to the crankshaft. Booster coil employed to retard and increase ignition during low-speed cranking. Primer system consisting of one injector nozzle in each of the four legs of the rams-horn intake manifold, fuel being controlled by solenoid valve from the pressure fuel supply.

Auxiliaries: Mounted to and driven by takeoffs on the accessory section. Include starter, tachometer generator, fuel pump, generator and vacuum pumps.

Propeller Drive: External spur-type reduction gear supported at front by ball thrust bearing and at the rear by a large roller-bearing. The pinion gear is mounted between two plain bearings and is splined to and driven by the crankshaft by a flexible coupling. The front scavenge oil pump is located in the reduction gear housing and the propeller governor is mounted on the rear of the housing in the Vee of the cylinder-blocks. The housing is provided with oil passages to supply both the governor and engine oil pressure for the hydraulic propeller blade pitch actuators. Reduction gear teeth are lubricated by an oil nozzle supplying three jets of oil directly on the teeth.

Engine Models and Applications: For a complete listing of the V-1710 models and derivatives, readers are suggested to see Daniel Whitney's "Vee for Victory!" or Graham White's "Allied Aircraft Piston Engines of World War II".

Reprinted from the Hydroplane and Raceboat Museum website and Unlimited Excitement.com