A turbo-charging breakthrough
Just over a year has gone by since Ferrari first showed the 126 CK to the Press at a gathering in Italy, and that was less than a year from the time that murmurings began to come from Maranello that Ferrari was abandoning the 3-litre unsupercharged engine for Formula One in favour of a 1 1/2-litre forced-induction engine, and that by way of exhaust-driven turbo-charging. The turbo-charged Ferrari won its first race, in Monaco, last May and by any engineering standards that is a remarkable achievement for an engine of totally new conception for the designers. When Keith Duckworth’s DFV Cosworth V8 won the first time out, that was an engineering landmark, though it must be admitted that much of the knowledge for the design of the DFV was gleaned from the previous 4-cylinder F2 engine.
The initial surprise with the Ferrari was that it was a V6-cylinder, for before its appearance I recall speculating on its cylinder layout and discarded 4 cylinders as not enough and the V6 layout as having been tried by Renault and not found to be a roaring success. A V8 or V12 was a possibility, though Ferrari’s history of racing V8 engines has not been very good, and while Maranello have nothing to learn about the V12 engine, such a layout seemed a bit complicated and bulky for a 1 1/2-litre engine. When the 126 CK appeared as a wide-angle V6 I realised that it was inevitable, recalling the 1 1/2-litre V6 engines of 1961-1965. The next surprise was to find that Ferrari engineers had mounted twin KKK turbo-charger units on top of the engine, close up to the rear bulkhead of the fuel tank, seemingly creating an enorinous concentration of heat in a shielded area. The plumbing and pipe-work looked a nightmare when the second prototype appeared for practice at Imola last September, but nonetheless it made a good impression, being faster than the old T5 flat -12. It sounded like the Renault-turbo, rather dull, very flat, and popped and spluttered on acceleration until the exhaust gases got the turbines whizzing round at peak revs. which in turn spun the compressors to push air into the inlet tracts at the desired pressure (anything from 20-35 p.s.i.). One reader who was at Imola complained bitterly about the sound of the new Ferrari. He had lived for years on the glorious sound of a 12-cylinder engine from Maranello, and said “It just ain’t right. The thing sounds like a knackered Formula Ford.” It was a good description.
At that debut of the turbo-charged Ferrari the Scuderia made it quite clear that it was not ready to race and there was no intention of taking it to North America. “It will be ready for the 1981 season” they said. During the winter months information kept filtering back from Italy that the Ferrari-turbo was going very quickly and that “throttle-lag”, the dreaded disease of the turbo-unit slowing down on the over-run, when the exhaust gas pressure reduces, was being eliminated. One of the reasons given was that Ferrari had abandoned the exhaust-driven turbo-charger in favour of the positively-driven Comprex Pressure-wave Supercharger, made by Brown Boveri in Switzerland. As the Comprex unit is driven by a toothed belt direct from the engine it does not slow up when the throttle is closed, any more than the engine itself slows up. When the team arrived at Long Beach for the first Grand Prix of the FIA World Championship it looked as though the Comprex Pressure-wave Supercharger was the way they were going, though they did have the KKK turbo-charging system with them.
As things turned out the Comprex system gave a lot of trouble and was abandoned before the end of practice, in favour of the exhaust-driven turbo-compressor units made by Kuhnle, Kausch & Kopf (KKK). It had been almost exactly six months since I had first heard the turbo-Ferrari and I could not help thinking that it didn’t sound like a knackered Formula Ford at Long Beach, but I dismissed the thought as there wasn’t a flat-12 Ferrari engine to compare it with. The Comprex system made a really exciting new sound, so when the team abandoned it I suppose I switched off my attention. Another noticeable thing was that the Ferrari-turbo car got off the mark much more swiftly and cleanly that the Renault-turbo, which was still popping and spluttering at low r.p.m. When Villeneuve actually led into the first hairpin at Long Beach the feeling was that it was all down to him, in spite of the turbo-charged engine and “throttle-lag”.
When next I heard the 126CK engine, at the San Marino Grand Prix at Imola, in May of this year, it sounded remarkably “sharp” and out of slow corners it was as quick as any Cosworth V8, if not quicker. During practice it was possible to watch from behind the car as it went into sharp corners and the first thing you noticed were the two bright orange lights that came on when the driver lifted his foot. These orange lights were fires burning in the exhaust pipes, not at the ends but deep down actually in the turbines themselves, and the moment the driver opened the throttles the fires went out. The way the two Ferraris got off the starting grid it was clear that “throttle-lag” was non-existent. At Zolder it was more apparent that the Ferrari turbo-charged engine “picked-up” like a DFV or a Matra, while poor old Renault were still spluttering and banging. At Monaco a chance remark by Keith Duckworth set me thinking and poking about on the Ferrari engine to see what went where, and what did what. In Spain some further close scrutiny and lots of discussion with Brian Hart revealed the “secret” of the non-existence of “throttle-lag” on the Ferrari 126CK. It is not a new idea, having already been used in America in the industrial and commerical world, but it is new for a highly-stressed racing engine and the fact that Ferrari have got it all working in such a short space of time more than justifies the admiration given to Mauro Forghieri and his engineers, by other engineers in the Formula One world.
Basically the problem with exhaust-driven turbo-chargers is simply that when you shut the throttles and the power is off, the drop in exhaust gas pressure allows the turbine to slow down, and thus the air compressor on the same shaft, also slows down and inlet manifold pressure drops off. Not until the exhaust gases can spin the turbine back up to its working speed can the air compressor deliver the required p.s.i. into the inlet manifold. What is needed is some method of keeping the turbine running at maximum, or near maximum speed. Of course, a positive drive to the turbine would solve the problem, but such a drive would absorb power and defeat the object of turbo-charging. The principle that Ferrari uses is to make the turbine work as a power-turbine when the exhaust gas pressure is low and this is done by making it into a gas-turbine when the throttle is closed. When the throttle is shut you still have compressed air in the inlet manifolding, though it is dropping in pressure rapidly as the compressor slows down. The residual air pressure is fed through a valve into the turbine entry and on to the turbine blades that are very hot. Coming through the exhaust system is unburnt gas from the cylinders containing fuel because the petrol-injection system is continuous, so if you get your mixture strength right and the temperature inside the turbine right you will get combustion inside the turbine. The gases then expand and their only way out is to spin the turbine and escape through the exhaust pipe. So, just as the turbine is about to slow down, due to the exhaust gas pressure from the engine dropping, combustion takes place, the unit becomes a gas-turbine and the air-compressor is whizzed back up to its working speed and your inlet manifold is charged with high-pressure air, all ready for when the engine needs it, which is when the driver opens the throttle.
This sounds pretty simple, but needless to say it is not, and the Marelli electronic device that meters the fuel to the injection unit has got to be pretty clever. As can be imagined, if the mixture in the turbine is not right either nothing will happen, or too much will happen at the wrong moment. Also the mixture has to be right in the cylinders for when the engine is asked to start work again. The linkages between the driver’s throttle pedal, the change-over valve in the inlet manifold, the butterfly valves to the air compressors, the throttle-slides to each bank of cylinders and the control of the metering unit are complex in the extreme. The two turbo units sit on top of the engine, close together, mounted on a heat shield between the turbines and the compressors. For the sake of compactness the three exhaust pipes from the right-hand bank of cylinders feed the left-hand turbine, and the three from the left-hand bank feed the right-hand turbine. Each compressor feeds air into its own inter-cooler, mounted in each side-pod, just ahead of the engine, and from each intercooler a large tapered inlet manifold runs rearwards to feed the three cylinders, on its own side. Close to the outlets of the air-compressors a balance-pipe runs across the engine, under the two units and in the middle of this is the all-important valve which releases air into the exhaust svstem by way of a bifurcated pipe let into the turbine manifolding. With the inlet manifold made of aluminium and the exhaust piping made of Inconel heat-resistant steel, the joining of these two together would cause a headache for some designers! Air going into the compressors passes down from the top of the bodywork into an L-shaped pipe for each unit, and in the entry of each L-shaped inlet pipe is a conventional butterfly throttle valve. These are on a common spindle operated from a link-system from the cable running forwards to the pedal in the cockpit. This cable operates a cross-shaft in front of the engine from which throttle slides, moving fore-and-aft, operate in the inlet manifold on each bank of cylinders, close up to the cylinder head. The left-hand slide also operates the linkage to the fuel metering unit which is mounted behind the engine. From the cross-shaft linking the two butterfly valves on the compressor entries a rod runs down to the valve in the balance pipe, which opens as the others close. What is not known is the open-to-shut relationship between the butterfly valves, the release valve, the throttle slides and the metering unit.
That the system works is evident from the way the Ferrari 126CK gets up and goes out of slow corners. That win at Monaco now begins to make sense. You could be forgiven for wondering why Renault have not used the same system, but a brief study of the layout on their V6 shows that mechanically it could not be done. They have separated their two turbo units completely, one to each side of the engine, each with its own pressure-release-valve (waste-gate), so that they work independently from each other, apart from the butterfly valves into the compressors being linked together. On the Ferrari the exhaust pressure release (waste-gate) is a single unit in the middle fed by both turbines, with a single adjusting screw. Renault could utilise the system for each layout, but it would be very fraught for you might get 30 p.s.i. on one bank of cylinders and only 28 p.s.i. on the other, depending on how your gas-turbines “lit-up” and that would make for a very rough power plant! Also, Renault do not use slide-throttles close to the cylinder heads, and this may be a vital part in the Ferrari system.
The chance remark by Keith Duckworth was “I’ve seen what Ferrari have done to overcome throttle-lag and I’m going home to try it on our Indianapolis DFX, not that we really need it for USAC type of racing”. That remark roused my curiosity. In Dijon Mauro Forghieri confirmed that what Brian Hart and I had sleuthed-out was correct. You’ve got to admit that the Scuderia Ferrari do know about engines, and Enzo Ferrari has always maintained that the heart of a racing car is its engine. – D.S.J.
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