.
The Engine That Powered The Sherman
Tank
The Monstrous
18 litre V8 Ford GAA: The Biggest Petrol V8 Ever Built That Powered The Sherman
Tank
Jack Knight
THE FORD GAA
We take a look at the development
history and features of an engine that powered the M4 Sherman and other
vehicles.
Starting life before World War II as
a 27-litre V12 designed for aviation purposes, the Ford GAA would eventually
becoming a world-class V8 for both military and civilian purposes.
It
was originally designed as a V12 on request from Henry Ford.
Anticipating
the start of another world war, Ford set about designing an engine better than
any competing designs.
It
was highly likely a big market for high performance lightweight engines to
power fighter aircraft would open up and Ford wanted the contract to supply
them.
He
started work on a V12 to beat Roll-Royce’s distinguished Merlin engine but with
the same 27-litre displacement.
Scroll
down for an engine start up
To win, the engine would need to be
more advanced and be more powerful than the Merlin.
After
completing his design, Ford presented to the Air Corps a 27-litre all aluminum
60-degree V12, with four cams and forty-eight valves.
The
engine had some truly modern features for the time.
Henry
Ford was so confident he would win a major contract he already had the tooling
and casting cores ordered for its manufacture.
The prototype was much more advanced
than the Merlin or the older Allison, pushing out 1800hp on its first test run.
But
to Ford’s dismay it was the Allison V12 that was preferred, due to it having
been around for a number of years previously, with many spare parts available
and the men trained on repairing and maintaining it.
These
were major considerations that would win the contract for Ford’s rival.
All was not lost, however. The Tank
Corps were in need of a V8 to power their Sherman tanks so Ford were approached
to resolve the problem of engine supply.
Ford
removed four cylinders from the unused V12 casting cores to make an 18-litre
V8.
To
speed up assembly and supply of this new engine, they simply retained the same
design from the V12, keeping the 60-degree angle and its all-aluminum construction.
The
Ford GAA, the largest petrol V8 in history, was born.
For its time the GAA was a marvel of
engineering. Due to its military role it had no belts or chains whatsoever,
everything was gear driven for durability and to reduce maintenance.
There
was a power divider to drive the cams, distributors and pumps.
A
rare sight on engines at the time, its spark plugs were located centrally in
the combustion chamber allowing for a more complete detonation of fuel.
It
was a true Double Overhead Cam engine with two exhaust valves and two inlet
valves per cylinder.
A
198lb flywheel was used to smooth out the firing order of the huge engine.
The
GAA’s capabilities were regarded as under used powering tanks, never being
properly pushed to its limits in this role.
The 18-litre V8 produced 500hp at
2600 rpm, producing a monstrous 1400nm of torque at idle. It was designed to
live at low rpms to keep sustained powerful output.
Due
to this a governor had to be installed with the limit set at 2600 rpm. Crews of
the tanks with this engine were known to remove the governor to increase rpms
and allowing more power in dangerous situations.
However without the limiter a stock
engine would rev to 3800 rpm before the valves would stop following the contour
of the camshaft lobe, and begin to float, known as valve float.
If
this happens the valves are no longer strictly controlled by the cams, and can
cause a piston and valve to collide.
An
odd feature was the two carburetors being mounted at opposite ends to each
other on the engine, making the fuel-air mixture much richer at the end
cylinders compared to the central ones, often fouling the outer spark plugs
more quickly.
The GAA V8 provided a brilliant service
on the battlefield and proved itself and soon after the war ended when the
engines began coming into civilian hands.
Because of its extreme reliability and
low sustained rpm the engine was ideal in industrial roles such as in oil
fields, trucks and boats.
After people began tinkering it was
discovered that the engine’s true potential was relatively untapped in its
standard form, having massive capabilities for increased horsepower and torque,
especially when used with a turbocharger or supercharger.
It was found that stock pistons were good up until around 1200hp
at which point the rings began to fail. The pistons themselves can crack with
moderate boost pressures.
Modifications such as replacing pistons and valve springs,
balancing moving components and adding direct injection and turbocharging, can
give a sustained reliable output of 2200hp.
Noticing this, the engine became popular on drag strips where it
performed so well it was subsequently banned from competing in the 1950s.
More recently, tractor pullers have managed up to 5000hp for
shorter durations.
The Ford GAA was rushed to service, but over its lifetime served
many different interests, proving the adaptability of the engine.
From its unequalled reliability in combat, to pushing over
double its standard horsepower with stock components it really is a testament
to Ford’s ability at constructing a solid engine.
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