Allison V-1710 Engine

Key Specifications (Prior to racing modifications)

Note: Many Unlimited Hydroplane Allison's originated from a batch of 750 V-1710 G6L/R engines intended for the North American P-82E/F. These engines were surplused in the 1950's by the Air Force. These engines differed from other Allisons primarily in the areas of lower compression ratio, an auxiliary supercharger and speed/density fuel injection. The boat racers routinely increased the compression, and discarded the auxiliary supercharger and injection system in favor of the more available Bendix-Stromberg Injection carburetors.

Introduction

The Allison V-1710 was one of the most important large U.S. aero engines, with over 70,000 engines produced from the time of the first in 1931 to the last in 1948. The engine was produced in large quantities in the early1940's for several important fighters of WWII including the P-38, P-39, P-40, P-51A, P-63, and P-82. While the debate over the merit of air-cooled -vs- liquid cooled engines had raged in the 1920's, each was recognized to have certain advantages. As the only liquid cooled U.S. designed engine of the second-world war (the Rolls-Royce licensed Merlin being the other significant liquid cool manufactured by Packard as the V-1650), the V-1710 exhibited the advantages inherent with liquid cooled engines. These advantages include low frontal area and high short-term peak power output thanks to the coolant heat-sink, higher power because of the greater heat rejection capability of liquid coolant, and packaging flexibility. The air-cooled engines advantages are primarily the weight savings and reliability inherent in eliminating the liquid cooling system.

Allison, which became a part of general motors in 1929, invested private funds in the development of a liquid-cooled V12 engine at the urging of Allison General manager Norm Gilman. While the U.S. Army Air Corp (U.S.A.A.C.) showed no interest, the Navy supported development of an experimental engine to test the basic design as a precursor to a reversible airship engine. The successful V-1710-A was test run in 1931 and delivered 650 hp at 2,400 RPM on 80-octane fuel. It featured the same 5.5" bore and 6.0" stroke as all succeeding V-1710's, weighed 1,010 lbs, had a 8.25" supercharger turning 7.3 times faster than the crankshaft, and had a compression ratio of 5.8:1. The engine featured a distinctive internal-spur gear propeller reduction drive (initial ratio was 0.66) which in late series models was replaced with more conventional external spur gearing. Modification were required half-way through the first 50 hr test run, and Allison took this opportunity to increase performance by increasing the supercharger gear ratio to 8.0:1. This engine completed its 50 hour test run in 1932 at a rating of 750 hp at 2,400 rpm.

Both the Navy and U.S.A.A.C. were now interested in the V-1710, the Navy placing the anticipated order for reversible airship engines designated V-1710-B and the U.S.A.A.C. designated V-1710-C. The Navy engine eliminated the supercharger (rotary induction blower) in favor of two carburetors placed in the Vee of the engine. The engine was designed to reverse from full power one direction to full power the opposite direction in less than 8 seconds, while driving a remote mounted propellers mounted on outriggers equipped with swiveling heads which allowed thrust to be directed vertically or horizontally. The engine power would be transmitted by 16' driveshafts to the remote transmission and gear arrangements in the swiveling heads. Allison had already designed such drive systems and transmissions for use in the Navy Airships USS Akron and USS Macon. The U.S.A.A.C. version was designated V-1710-C and featured a supercharger impeller enlarged to 9.5", a 2:1 propeller reduction drive in a longer nose casing, and a stiffened crankcase. Additional changes were required to overcome severe harmonic vibration problems caused by the long nose and change in reduction gearing which caused damage to crankshafts, reduction gears and cylinder blocks.

A significant redesign was undertaken by R.M. Hazen in 1936 which lead to an increased compression ratio of 6.0:1, improved combustion chambers which reduced the length of flame channel, improved piston and rings, and changed manifolds for better air-fuel distribution. This "C"-model passed its 150 hour type acceptance test in 1937, establishing a rating of 1,000 hp at 2,600 rpm at sea level. The definitive Allision which was the foundation for all future engines was now established -- penthouse-type combustion chambers with four valve per cylinder, overhead camshafts in each cylinder block with forked roller cam followers actuating pairs of valves in each cylinder, blade-and-fork connecting rods. Subsequent engines differing primarily in induction system and reduction gearing. A number of incremental improvements were made during the life of the "C"-model including increase in compression ratio to 6.65:1, eventually leading to "C"-models with takeoff ratings of 1,150 hp at 2,950 rpm and supporting 3,500 rpm for overspeed during dives.

The "D"-model featured a remote reduction gearbox in a pusher configuration for powering the Bell Aircraft XFM-1 Airacuda twin-engine fighter.

The power unit on the "E" and "F" engines were identical, with crankshafts, connecting rods, pistons, cylinder blocks, valve gear, and intake manifolds among other components completely interchangeable. The "E" featured a remote propeller reduction gearbox for the Bell P-39 Airacobra (and P-63 Kingcobra) driven with a 10 ft extension shaft turning at crankshaft speed between the engine and reduction gear. The "F" had a conventional integral tractor propeller reduction gear Lockheed P-38 Lightning and Curtiss P-40 Tomahawk. A turbocharged V-1710-F17L/-F17R engine equipped with ADI produced a WER of 2,300 bhp at 3,000 rpm with 90 in hg,, developing a BMEP of 355 psi. The "E" and "F" engines were the bread&butter Allisons, with these engines used in large volume on several major fighter programs of WWII. A total of 66,658 "E" and "F" types were built -- 18,998 "E"-type extension shaft engines were shipped, mainly for P-39 and P-63 aircraft, and 47,660 "F" models were shipped, mainly for P-38 and P-40 airplanes.

The ultimate V-1710 was the "G" series which brought together all of Allisons design and manufacturing experience to produce an outstanding engine in almost all respects from earlier engines. The V-1710-G was incorporated a number of desired improvements identified in 1943 by Wright Field (U.S.A.A.F. engineering/procurement organization) and improve performance to 1,725 bhp at 3,400 rpm. To improve performance, the 12-counterweight crankshaft developed in late 1942 was used to increase the maximum rpm to 3,400, the induction path was improved to increase flow, and improvement were also made to the supercharger, cylinder heads, and accessories section. One interesting characteristic of the "G"-series was the large proliferation of features and configurations -- short-nose integral reduction gears or extension shafts, with and without auxiliary superchargers, both 9.5" and 10.25" engine supercharger impellers, one or two-speed supercharger drives, a range of supercharger drive ratio's, three compression ratio's, pressure (injection) carburetor, speed density injection, or port fuel injection, and both left and right hand rotation. These engines became the most desirable to racers because of the high-revving crankshafts and improved detail design. A total of 763 were produced -- a batch of 750 V-1710-G6R/-G6L consisted of virtually all the "G" series production. When this batch of engines were declared surplus in the 1950's, they were said to to have been the engines which powered Unlimited Hydroplanes into the 1990's (Daniel D. Whitney, "Vee for Victory", pg 278). This same source describes how the Unlimited Racers traded performance for engine life, modifying engines to deliver as much as 4,000 hp.

The most remarkable engine was probably the V-1710-E27 experimental turbo-compound engine. This unique engine was the first turbo-compound or "power-feedback" engine and was way ahead of its time. Based on an E-22 power section with auxiliary stage supercharger, it used a General Electric CT-1 power turbine which was adapted from the exhaust turbine of a CH-5 turbosupercharger. The turbine drove the crankshaft through a 5.953 reduction gear. The engine compression was reduced to 6.0:1 to facilitate high supercharger boost pressure of 100 in hg (35 psig). Using 115/145 PN fuel with ADI injection, this engine was able to develop 2,980 hp at 3,200 rpm and 100 in hg boost from sea level to 11,000 feet. In addition to the remarkable power output, the engine demonstrated a 19% improvement in specific fuel consumption during cruise. Had the inlet exhaust temperature not been limited to 1750° F, it is certain even more power could have been developed. The temperature proved to be easily exceeded during full-power operation, so the engine was never placed into service with the P-63 as intended.

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".