V6 12 Valve rocker shaft
GTV 3.0l engine mounting
GTV6 engine mounting
156 V6 water pump impeller
GTV6 and GTV3.0l Engine ECU
The Alfa Romeo V6 Engine
The Alfa Romeo V6 is one of the classic engines of all time, it is as famous as the A series or the V12 Ferrari engines, It is and always has been revered for its creamy smooth power delivery and revvy nature. The first time we come across the engine is in the Alfa 6 where it was fed by a multitude of solex carbs however the Alfa 6 was not the best of sellers so we really did not get to “know” the engine until it appeared in the GTV6 where it sported a very early Bosch fuel injection system and it produced 155 bhp from 2.5 litres, the engine has developed from there into the 3.2l GTA engine with 250 bhp. The original V6 is a single overhead camshaft engine with a short push rod and rocker over to the exhaust valve (Pic1), the inlet valve runs directly on the cam and this allowed Alfa Romeo engineers to get a decent angle between the valves so they could get a pent roof combustion chamber. If you look in detail at the rocker onto the exhaust valve you will see the adjustment for the exhaust valve clearances and interestingly (to me anyway) if you undo the central nut on the camshaft drive pulley you can remove the camshaft to do the inlet valve clearances without taking the cam belt off, which is a nice bit of design. The engine was then enlarged to 3.0l while retaining the rocker arrangement for the valve gear and power was up to around 192 bhp in the 164 and 75 with tuned examples going up to 220 bhp. Alfa Romeo then developed the engine into a Quad camshaft design with four valves per cylinder, this instantly upped the safe rev limit by 1000 rpm, the old engines valve gear had much more inertia as it was considerably heavier and so valve bounce became a problem at higher engine speeds this was eliminated with the cams running directly above both inlet and exhaust valves. The engines development can almost bee seen in the latest 3.2 version as Alfa Romeo have “left” certain reminders in the castings of its origins, note the redundant engine mounting point on this GTV 3.0l (pic 2) compared with the mounting on the GTV6 engine!(pic 3) and on early 24 valve engines as fitted in 164’s there is the unused drive for the distributor.
The V6 has been a reliable engine with cam belt failures being comparatively rare, the earlier 12 valve engines tend to suffer with oil leaking from the hydraulic cam belt tensioner, this is usually a cheap repair to do if you already have the cam belt off, with the kit only costing around £15. Early 2.5 engines had an interesting way of sealing between the head and the block, where by the bores had a sealing ring made of aluminium that fitted over the top of them and then the water jacket was sealed by a perimeter rubber seal, this did not prove very satisfactory and was soon replaced by a more conventional gasket. Early engines also had a tendency to wear out valve guides and this was also modified during the life of the engine. By the time they developed the 24 valve engine they had eliminated most of the issues except one which was due to penny pinching on the impeller for the water pump which on some models they made of plastic which cracks from the centre outwards (pic 4) and this causes the engine to overheat at high speed, while running at normal temperatures around town, why they only did this on some models and not others is completely beyond my understanding.
The 3.2l engine also has some interesting inlet cam shafts which have a flat top to increase the time the valve is open (duration) this is one of the ways that they get that little bit more power out of the GTA engine. The later 24 valve engines also had a new oil pump which is chain driven of the front of the crankshaft and this allowed the company to finally get rid of the original distributer drive.
Some of the most interesting developments have come with the fuelling of the engine, the original Solex carb versions were not known for their economy, in fact you might have found it cheaper to just poor petrol down the inlet manifold from a large bucket. Then on the GTV6 electronic fuel injection was used, this is an analogue system which is the pre cursor to all modern fuel injection systems. If you look at the picture (pic 5) of the GTV6 ecu you will not see a micro processor anywhere whereas the GTA ecu (the small one) is a fully sealed unit and has a very large microprocessor. The early GTV6 system injects three injectors at a time while the late one fires all the injectors individually. The later system also monitors the mixture, checks for pre ignition controls the ignition advance curve as well as controlling the idle speed and many other parameters a modern engine needs to meet emission regulations. On the early system there is a separate amplifier for the ignition and the spark advance is controlled by bob weights, while the idle speed is controlled by a manually adjustable air by pass valve, how archaic is that!
Related Links: Alfa v6 Cam Belt Change | Alfa V6 Parts