A 1925 supercharged 2-litre V12 GP Delage engine
The first word on this topic is: DIFFICULT
To begin with, the engine installation does not allow adequate space for the exhaust manifolding and from here on it doesn’t get any better!
The standard Fulvia manifold is a poor thing indeed. Its internal diameter at 32mm is too small; it has “blended” junctions which are not good, and it has very unequal length primaries. Matters are worse on the 1600 since the only difference is the fact that 1600 manifolds are made of stainless steel, presumably to cope with all the heat; I have seen them red hot. Incidentally, some of the replacement exhaust systems are even worse. At least the originals had proper bends. I have seen some systems where there is considerable necking at the curves; such systems are rubbish and should not be used - let alone sold; the original is already too restrictive.
Certain suppliers do offer special manifolds but I have never seen one I liked, all being more or less copies of the works ones that I have seen, which did not impress me either. Of course all offer a good improvement on the inadequate original, but they could be so much better! Whilst I was manager at Evolution Engineering in London, I organised the development of an improved manifold. At the time we had a customer who was fed up with the after market “Group IV” manifold fitted (!) to his car. It didn’t fit! I told him we could do a bit better, so we borrowed his manifold to get a basic idea of the layout and set out to produce a better one, in stainless steel. A considerable time was spent making a pattern which was then passed to a specialist company to manufacture. The enormous trouble I had with this is quite another story…
A stage in making the pattern, using a mocked-up engine and gearbox as a jig
In the end, the manifold was a success. As may be seen from the pictures, instead of blended junctions as used by the works, we incorporated collectors. It was fascinating to fit the first one to our customer’s car. The first thing we noticed was that the exhaust was quieter; I put this down to controlled expansion at the collectors. However, what gave the greatest pleasure was hearing the customer tell me about the substantial improvement in torque that the system provided, especially since this is precisely what I had forecast.
The Evolution Engineering Fulvia manifold (before the fabricators corrected the errors)
As an historical aside, some of you may remember the story of the (eventually) very successful Vanwall grand prix cars in the 1950s. They used an exhaust manifold that was pretty advanced for the time and observers remarked how quiet the cars were. The irascible Vanwall boss Tony Vandervell, loved to tease the Ferrari team with their Lancia-derived V8s, by 1957 a bit outdated. He pointed at the Ferrari exhaust pipes from which a colossal noise was emitted and joked, “That’s where your power’s going”!
When producing parts for after-market sales, one must consider the installation of the parts and so the Evolution Engineering manifold was designed to be a straightforward fit and to mate with the standard exhaust system. The enthusiast who is able to accept something more challenging in this regard has more freedom in choice of design. The picture below shows a home-made manifold that I know worked very well indeed. To fit it though, the head must be removed and the engine tilted slightly. It runs over rather than under, the left-hand driveshaft. The manifold was made by welding together numerous bends cut from spare or second-hand exhaust systems. The collectors were simple fabrications in sheet steel, whilst the flange was an original from a scrap manifold machined to accept larger primaries (35mm bore).A very effective home-made 4/2/1 exhaust manifold featuring long primaries
Finally in this section, a few observations about manifolds. If you decide to make or perhaps specify your own, remember that the aim is to have all the primaries, i.e. the pipes that lead from the ports, equal length – with respect to the exhaust valve, so the Fulvia’s unequal length ports must be allowed for in the design. Whilst I have a four-into-one manifold on my car, a 4-2-1 is really better (with primaries 1 & 4 and 2 & 3 being coupled together of course), both for tractability and for ease of fitting. Curves should be smooth and all bends must be mandrel bends with no “necking” so often seen on poor-quality replacement systems as I remarked above. The 2-into-1 section should be of such a length so that when added to the primary length, the total is the tuned length that is to be employed. For most Fulvias I suggest something between 28 and 36 inches (71 – 91 cm). A good compromise is to make the primaries about 16”(41cm) from the exhaust valve so that the second (2-into-1 section) should be between 12 and 20 inches (30 to 50 cm.) long excluding the length of the collectors. Collectors should be constructed with their sides at an included angle of around 14 degrees and it is essential that the pipes are cut off cleanly where they enter the collector – it is even better to have a tapering “tongue” that enters the collector but this is tricky to make). Internal diameter of the primaries should be 1 3/8” (35mm) and of the secondaries 1 1/2” (38mm). In a perfect world, the length of the single pipe which follows the 2-into-1 collector, should be the tuned length when it meets the silencer. This is usually impossible on a Fulvia for clearance reasons. Perfectionists could employ a small expansion chamber here… The internal diameter of the single pipe should be 2” (51mm) or perhaps a little more.
I make no excuse for writing at length on this subject, which really deserves at least another 1000 words! I believe the exhaust to be critical in getting the best from an engine and given the inadequacy of the standard arrangement on the Fulvia, something that should be dealt with as a priority even if it is difficult and expensive.
Next time, I take a look at the fuel system