From FroggyWiki
Introduction
In the mid 1960s, Peugeot and Renault were beginning to make plans to re-enter the large, luxury car market, from which they had been absent since before World War II. However, neither marque had an engine capable of powering such a vehicle, and so they teamed up to form the 'Compagnie Française de Mécanique' in 1966 to produce a V8 engine to compete with the larger German and British manufacturers of the time.
Volvo joined the team in 1971 at which time it officially became known as the 'PRV' company. Shortly after this however, the 1973 energy crisis led to the engine being redeveloped as a V6, simply by removing two cylinders from the V8 design. And so the PRV V6 was born.
Engine Design
The PRV V6 was produced as an all-aluminium engine with cast iron wet-sleeve cylinder liners, chain-driven single overhead camshaft on each bank and a modular alloy sump that also braced the engine, the main bearing caps being bolted in place through the lower section. The two banks were angled at 90 degrees to each other, a design typically found in V8 applications, instead of the traditional 60 degree angle used for V6 engines. This created some complications in the ignition timing and crankshaft design areas that were overcome in different ways.
First Generation
The initial incarnation of the PRV V6 was a 2664cc (2.7 litre) with a three bigend journal crankshaft, with each one 120 degrees apart. The resulting firing pattern is what is known as an 'odd-fire' engine, as the pistons reach top dead centre in an alternating pattern of 90 degrees then 150 degrees apart, ie 90, 150, 90, 150, 90, 150.
The engines had 12 valves (2 per cylinder) and the distributor was driven from the back of the right hand camshaft.
The engine was available as a single carburettor (Renault 30, Volvo 26x), dual carburettor (Peugeot 604, 504) or with Bosch K-Jet fuel injection (Peugeot 604, 504, Volvo 26x, 760, 780).
The two styles of K-Jet fuel injection systems fitted to the engines were known as the 'crab' or 'octopus' manifold or the twin-plenum manifold used for areas with heavy emissions control requirements where balancing the airflow to each cylinder was essential.
The engine was bored out to 2849cc (2.8 litre) which was initially produced alongside the 2.7 litre, but eventually superceded it completely.
Second Generation
In 1984 the PRV V6 was revised to eliminate the uneven firing order of the earlier generation. Each crankpin was split into two, with a 30 degree offset between them. The big end journals were made much bigger to add strength to the otherwise weakened crankshaft. The engine now had a traditional 'even-fire' ignition pattern, each cylinder firing 120 degrees after the previous one.
Although this eliminated the characteristic rocking of the odd-fire at idle, it did induce balance issues at higher revs. On the Peugeot 505 application, balance weights were added on auxiliary shafts on the front and back of the left hand cylinder head, driven by gears from the left hand camshaft. These were not added to Volvo or Renault versions of the motor.
A 2458cc (2.5 litre) version was turbocharged for use in the Renault 25 V6. The Renault Safrane Biturbo recieved a 2963cc (3 litre) twin turbo PRV V6.
The Peugeot 605 and Citroen XM were sold with a 2975cc (3 litre) version of the engine, which was fitted with a balance shaft that ran full length of the left hand cylinder bank, above the valve gear. It had offset counterweights at each end, and was chain driven from the front of the left hand camshaft.
A 24 valve version was available for the XM and 605 as well. This had the same 2975cc bottom end, but was fitted with redesigned cylinder heads incorporating 4 valves per cylinder. It retained a single overhead camshaft arrangement, but had 9 cam lobes on each camshaft instead of 6. The two intake valves were driven from a lobe each, but the exhaust valves were both driven by one lobe in the centre. This put a great deal of stress on the exhaust cam lobes, and the valve train wore out prematurely and very few survive today. It did however produce 200hp with a catalytic converter when new.
Demise and Successors
The PRV engine ceased production in 1998, by which time production of the ES9 series of 60 degree PSA V6 engines was in full swing.
