Today we will be looking at the Cummins VT8-460 turbodiesel V8 engine that was used to power the awesome M50 and M51 Shermans, often erroneously known as “Super Shermans”. This rarely-discussed engine replaced the older Second World War-era types found in Israel’s Shermans, giving them more power and better fuel economy for a new lease of life.
The 950 cu in (15.5 litre) Cummins VT8-460 is the first incarnation of a ground-breaking design. With its development beginning in the 1950s, it is the ancestor to a lineage of engines, some of which are still used by military vehicles today.
As it is the powerplant inside their M50 Sherman, who better to share the history and design of this mighty Cummins than Frank Wood from the Eden Camp Heritage museum. Frank has already shared the history of their M50 here, and its restoration here.
Background and Development
Cummins started the design of this family of engines at Columbus Plant 1, Indiana, USA, in around 1954. Designers worked hard to perfect a replacement for the gasoline engine, with the intention of it being used in civilian haulage, specifically trucks.
The first design of its type was the V950 – “V” refers to its Vee-shape configuration, and “950” to the cubic inch (cu in) displacement of the engine (15.5 litres). The V950 is a naturally aspirated, Vee configured engine that displaces 950 cu in, or 15.5 litres. It was offered with the intake in or outboard of the Vee, and the exhaust the same.
With the V950, designers had proposed the first oversquare design Cummins had ever put on the table. After a successful design process and prototype modelling, the unit was installed in Peterbilt cab-over trucks and road tested around the United States. They were a moderate success.
They were almost the same size as a comparable gasoline engine, but had the added benefit of fuel economy. The new PT fuel system and the four valve heads ensured smooth and gutsy power delivery. The V950 led to the production of the comparatively smaller V588 and the V785, which began in early 1962. There was a large and grand press conference celebrating the achievements of the designers and celebrating the new and modern aesthetic provided by Noyes and Associates.
However, it would turn out that the V950 did not suit automotive applications – it fit nicely into some trucks, but it was not so straight forward for a vast amount of others. After further testing, it was realised that the thing was just physically too big!
It performed well in marine and industrial applications though as its massive size was less of an issue.
The result of this was that the later – and smaller – V588 and V785 engines were much more well received, becoming the go-to units for Cummins customers. This left the poor old V950 lacking and somewhat left aside.
But this certainly wasn’t the end of the V950, as it would soon find itself in the engine bays of Shermans hammering it across Israeli sands.
This is where we come to the focus of this article: the VT8-460.
Simply put, the VT8-460 is just a V950, but suped up, with some minor new parts and a turbo – it was originally rated at 430bhp (the VT8-430), but then upgraded to 460bhp for military use.
From Trucks to Tanks
In 1956, Israel agreed to buy the M50 Sherman from France. The M50 was a modified and upgraded version of the Sherman, fitted with a more powerful French 75 mm gun. They also created the M51, which had a massive 105 mm gun fitted into the Sherman. We have covered the history of this development in depth on TankHistoria here.
Eventually, Israel needed to upgrade the M50 Sherman, and this meant installing new suspension. With the installation of this suspension, extra weight was added to the tank. Therefore, the Israel Defense Force (IDF) realised it needed more power and grunt to shove the now-heavier M50 Sherman around.
Gone were the days of Continental R-975 petrol aircraft engines as were fitted to many of Israel’s Shermans – diesel was now the fuel of choice for the modern armies of the world.
Diesel provided better fuel economy, and this meant more miles from the same amount of fuel, but also it is far less volatile than its petrol counterpart, a handy feature in a tank where the logistic chain is a major concern. The other added benefit of diesel engines is inherent in how they work. They are comparatively slow turning compared to a petrol engine, and produce much of their torque lower down in the rev range.
With this slower revolution comes an added benefit: the engine has a much smaller heat signature – a handy feature for a vehicle where heat-guided arms may be used against it.
With these extra benefits in mind the IDF asked its allies for supply of the necessary equipment. The USA and Cummins accepted the bid.
The IDF order was reasonably small, perhaps some 1000 units. Cummins had the now-redundant V950 in storage facilities, and realised they could “off load” these assets to the IDF and recuperate any losses from engine, by reconfiguring the unit into VT8-430/460.
The IDF were not fools, they knew the engine was older and too big for Cummins to use in the applications it wanted, but they could use this to their advantage and certainly make good use of them. Cummins’ problem was a blessing for the IDF, as the physical size of the engine simply didn’t matter to them – it was to be installed in a tank and there was plenty of room!
The VT8-460 was tiny in comparison to the R-975 radial engine used in M4 and M4A1s, and certainly the 30-cylinder A57 Multibank which was installed in the M4A4 Sherman. It also produced more power and torque than both of those engines.
The IDF were smart in their negotiations and knocked down the price of the units from Cummins, and then tasked Cummins with making a “military” version of the VT8-430. This became the VT8-460.
The Cummins VT8-460
The VT8-460 is a V950 that has been upgraded to the VT8-430, and then upgraded again to the VT8-460. It kept the same displacement of 950 cu in (15.5 litre) as the V950, but its name no longer reflected the engine size.
Its designation works as follows:
V– Vee configuration
8 – cylinders
460 – brake horsepower output at the prop.
The VT8 is oversquare, which, as mentioned, was the first time Cummins had tried an such a design. Oversquare refers to the cylinder bore (diameter of the cylinder) being larger than the stroke (how far the piston moves up and down the cylinder).
An oversquare design gives extra room for more and larger valves to be installed in the cylinder head. It also allows for higher engine speeds, as the pistons are not moving as far or encountering as much friction. Crank stresses are reduced too, as the pistons’ peak acceleration is lower.
The VT8-460 was exclusively installed in IDF M50 and M51 Shermans.
It performed marvellously, doing exactly what it was specified for and gave great fuel economy and more power, pushing the M50 Sherman to around 30mph.
It was not all roses though as the engines did struggle with the heat, due to the exhaust’s exit location at the bottom left of the tank’s rear. This location meant a large expanse of exhaust pipe ran around the engine to the exit, carrying and trapping heat next to the block.
The IDF, true to their fashion of being remarkable engineers, simply cut a hole in the top armour deck of the tank and re-routed the exhaust straight out the top of the engine deck, giving the M50 and M51 their famous look.
We have now followed the progression of a family of engines that have been developed from the very basic design of the V950. But the story of the V950 still doesn’t end there, as the “grandchild” of the V950 is used in US Army vehicles today.
The Cummins V903
Following on from the design’s features, its failures and upgrades, the old V950 has finally culminated in an engine that the US military trusts a power unit for its fighting vehicles.
The V903 is a 903 cubic inch (14.8 litre) V8 engine that pushes out 675 bhp. In recent studies it has shown a combat readiness of over 95% – the highest of any armoured vehicle in the history of the US Army. It can be found in vehicles like the M2 Bradley, Amtracs, and even in machines such as the British AS-90 self-propelled howitzer.
Eden Camp Heritage restorations has refurbished three VT8-460 engines now, and all are available for our visitors to see at the museum – even the one in the tank!