Turbocharging-a future trend?
The last few days in August were quite significant in the life of the European automotive industry, though probably few people realised it. In the space of three days two new turbocharged saloons were announced, one of them, the BMW Turbo 2002 being the first European production car from a major manufacturer to be so fitted. The second, the Broadspeed Consul GT/Granada is an obvious extension of Ralph Broad's already well-known turbocharged Ford Capri 3-litre, the Broadspeed Turbo Bullit, but also significant is the almost parallel thinking revealed by Broad and the Munich engineers led by Alex von Falkenhausen.
Recently I tested the Turbo 2002 on BMW's test track near Munich and Broad's turbocharged Capri and Granadas (manual and automatic) in the Warwickshire lanes and on these separate occasions talked to Herr Helmut Bönsch, a director of BMW formerly in charge of product planning, and to Ralph Broad. What follows is a brief description and impression of the Turbo 2002, a look at the interesting turbocharger arrangement evolved by Ralph Broad around the Ford V6 and a few of the reflections on turbocharging and its possible effect on the future of the internal combustion engine from these two engineers. Hopefully Ralph Broad will be forthcoming with a Turbo Granada for full road test shortly, so descriptions and impressions of the packages containing his engines can wait. The BMW is unlikely to fall into MOTOR SPORT hands for full road test, however, for the Munich engineers have yet to overcome the problem of how to produce this particular 2002 in right-hand drive form for the British market: unfortunately their arrangement places the turbocharger exactly where the steering column should fall.
Turbocharging is nothing new in itself. Used on aircraft piston engines and Diesel engines for many years and more recently on racing cars, notably in CanAm. BMW are no strangers to it either, having won the European Touring Car Championship with a 2002 so equipped a few years ago, and it's from that racing engine that this brave venture at a mass-production turbocharged engine has been developed. Brave particularly because the main reason behind the Turbo 2002's production is to homologate it for Group 1 racing and rallying, for which 5000 separate examples must be manufactured and sold. With such a quantity at risk it's to be hoped that the standard 2002 Tii engine assembly which forms the basis of the turbocharged unit will stand up to having its power output increased from 130 b.h.p. to 170 b.h.p. The racing version in fact gave 270 b.h.p., but with considerably modified internals and Herr Bönsch told the story of how 324 b.h.p. was registered on the dynamometer one day before the cylinder head lifted, after which the engine continued to run for four minutes!
The underbonnet view of the 2002 'Turbo looks very little different to the normal Tii, for a very similar Kugelfischer mechanical injection system is used. Bosch, who were deeply involved in the development, manufacture the turbocharger through one of their subsidiary firms, KKK, not to be confused with that other organisation across the Atlantic. This 'exhaust-driven supercharger' sits deep down below the exhaust manifold on the right-hand side of the, engine, almost out of sight and the compressor part of the turbocharger is connected to the fuel injection air box by a pipe over the top of the engine. A relief valve in the air box is set to limit the charging effect to 1.5 atmospheres, though apparently this can be tampered with by knowledgeable customers to raise the blow-off point sufficient to raise the engine's output to 200 b.h.p., which should prove an instant method of legal cheating in Group 1.
So far as I understand the only modification to the standard engine unit is to lower the compression ratio to 6.9:1, a necessary safeguard to avoid detonation when blowing even at moderate pressures. Even the camshaft remains standard 2002 Tii. A larger radiator and an oil cooler are essential additions.
Maximum power is claimed to be 170 b.h.p. DIN at 5,800 r.p.m., with 177 lb ft torque at 4,000 r.p.m., sufficient to accelerate this 2,281 lb, 2002 from 0 to 60 m.p.h. in 6.8 sec. or take it all the way to a 131 m.p.h. maximum speed.
Chassis modifications are of course quite radical to enable the colossal power increase to be handled safely. The McPherson strut front suspension and inclined semi-trailing arm rear suspension remain unchanged in design, but springs and dampers arc uprated and the front anti-roll bar increased in thickness by 5 mm. Ventilated front discs are fitted of 10 in. diameter with 4-pot calipers, rear drums are increased in diameter to 9.9 in. and a pressure limiting valve included in the servo-assisted, duplex twin circuit hydraulic system. Transmission too is beefed up throughout, including the clutch, gearbox, albeit with the same wide ratios of all the BMW 2-litre cars, driveshafts and wheel-bearings. The specification even includes a limited slip differential, while the engine characteristics enable a higher final drive to be used of 3.36:1 in place of the Tii's 3.45:1.
Like the latest 3.0 CSL with its amazing collection of wings and spoilers, the 2002 Turbo is not a car for the conservative minded.Aerodynamic protrusions are again much in evidence below the front grille and on the boot-lid, while plastic wheel-arch extensions are screwed on to the shell, in order to cover the 185/70 VR 13 Michelin or Pirelli tyres on 5½J steel rims. Functional these additions may be, but they're far from beautiful, while the final touch to the 'cowboy' image is added by a mirror image 'Turbo 2002' sign on the front spoiler for the benefit of drivers in front who happen to be looking in their mirrors, which in Germany they often do.
Bucket seats with built-in adjustable headrests, small leather-rimmed wheel, 240 k.p.h. speedo, tachometer and boost pressure gauge are numbered amongst the cockpit attributes. Just as I thought that the list of alterations to the basic 2002 had come to an end, I see that the fuel tank capacity is increased to 15.4 gall., a final touch to what amounts to a complete redesign to make this machine into the perfect off-the-shelf competition car. Not a detail has been missed and the result is a car which isn't far removed from the normal idea of Group 2, yet as I've said, the intention is to homologate it for Group 1.
On the BMW test track the Turbo 2002 felt exactly as I've suggested: an homologation special with the thoroughbred characteristics of a competition car. Perhaps BMW should be praised for their bold venture into the realms of turbocharging rather than condemned for producing yet another homologations special, however, for even though they admit that the car is designed mainly with successful competition in mind, if they do produce 5,000 for Group homologation, that quantity should automatically negate the criticism. More important, this turbocharged 2-litre car could be a pointer to the future, and its service record will (or certainly should) be watched by other motor manufacturers.
One thing the Munich engineers have not managed to overcome is throttle leg, a well-known drawback with turbocharging which Ralph Broad on the other hand has endeavoured to cut down to a reasonable amount of which more later. The problem occurs when the throttle has been closed so that exhaust gases are reduced, the turbine side of the turbocharger driven by these exhaust gases is slowed down, and so, consequentially; is the compressor. When the throttle is re-applied there is a slight time lapse while the turbine regains its momentum. No doubt regular drivers of the Turbo 2002 will become accustomed to these characteristics, applying throttle early, but this could be a bad competition drawback, particularly in rallying.
In some ways the engine felt inferior to a turbocharged and carburetted 2002 I tried in England a couple of years ago. This had been modified by Bob Henderson, owner of Minow-Fish Carburetters, Lochgilphead, Argyll, and what's more it was right-hand drive. I don't think Henderson claimed such a high power output, but I do recall that there was very little throttle lag. The car was more responsive at low revs and the step as the turbocharger came in was less marked. The Turbo 2002 would potter along quite happily at low revs, true enough, yet it lacked any sort of performance until the turbocharger reached full activity beyond 4,500 r.p.m. From then on the performance was stupendous for a 2-litre saloon, spoilt only by the wide gear ratios in the 4-speed box: changing up 31 the 6,450 r.p.m. red line brought the revs down below 4,50 r.p.m again. For optimum performance the optional 5-speed gearbox would be essential.
Handling and roadholding capabilities were far beyond that of any other production 2002, the car feeling very taut, responsive and predictable, though the steering was surprisingly heavy. Several stops from an indicated 136 m.p.h. failed to make the superb brakes deteriorate, obviously an outstanding improvement over standard 202 brakes, which are very suspect under heavy abuse.
On the face of it Broad might have faced a greater problem turbochargidg a Vee configuration engine, yet the basic plumbing solution worked out very simply. In both Capri and Granada cases, Granada exhaust manifolds are used, switched from bank to bank and thus reversed so that their tail pipes face forwards. The Holset turbocharger, designed originally for Diesel engines and manufactured by Holmes-Holset of Huddersfield; is mounted centrally forwards of the engine and both manifolds are fed into it through a special twin inlet manifold.
The most interesting feature of Broad's design is his patented air pressure control valve, which is largely responsible for making the system so fool-proof and effective. It is built within and around the dashpot of a 2-in. SU carburetter, in which the damper piston and spring is retained, an ideal basis for Broad's ideas because it is made to high standards of precision. The space in the dashpot above the piston is connected to the inlet manifold by a one-way valve, so that when the throttle is closed on the overrun manifold depression lifts the piston (in this case 'valve'). The effect of this is to create zero boost, for though the turbine is still turning to some extent there is no load on it, greatly reducing throttle lag. The valve in effect opens a new pipeline between the compressor side of the turbo and the air filter through which it breathes, So that compressed air is actually recirculated. Once throttle is reapplied boost pressure shuts the one-way valve, a low pressure area is created above the piston and the valve closes allowing the turbocharger to reach its full boost of 6.5 to 7 p.s.i. When this maximum is reached at high revs the manifold pressure on the base of the piston lifts it against the calibrated spring within the SU damper arrangement. The damper also ensures that there is no flutter in the operation of the valve.
A novel and useful feature of this valve is that it has allowed Broad to build in a switch which enables the turbocharger to be 'switched off' by a key on the dashboard, ideal for when the car is left in the hands of wife, youngest son or garage mechanic: In fact the turbocharger continues to run, but when the key is switched off with the engine on the overrun a solenoid operates a stop to prevent the piston valve falling back into place, so.that the compressed air is permanently recirculated and boost is zero.
Another important feature is the complete enclosure of the standard Weber carburetter within a box, whereas most 'blow' type carburetter turbocharger systems I have seen have blown straight into a collector box mounted on the carburetter air intake, leaving the rest of the carburetter exposed. The box is partly a safety feature, for because the carburetter is under pressure, any leaks could blast out an explosive mixture. It has many other functions too, like preventing icing-up.
Fuel systems on turbocharged cars are of necessity quite complex, for fuel pressure must be regulated at high pressure. A normal carburetter needs 4 to 5 p.s.i. pressure to keep the float chamber full; the turbocharged system needs 4 to 5 p.s.i. above carburetter boost pressure. This is effected in Broad's system by inlet manifold pressure by a connection between the carburetter (below the butterfly) and a fuel regulating valve, and similarly between the one-way valve on top of the air-pressure control valve dashpot and the fuel valve. Excess fuel is recirculated back to the tank. There is of course a high-pressure fuel pump to get the liquid moving in the first place.
But Broad's system doesn't simply stop at the turbocharger arrangement: he refused to contemplate turbocharging a completely standard 3-litre Ford V6, considering that the extra loadings would blow it apart, so all his engines are blueprinted, a process which in this case demands cross-drilling the crankshaft also to overcome an inherent lubrication problem. The bowls in the piston crowns arc modified to reduce the compression ratio from 8.9:1 to 8.2:1. Even so, the blueprinting process is so effective that the Turbo Bullit/Granada engine produces 149 b.h.p. DIN at 5,300 r.p.m. with the turbocharger switched off, compared with 138 b.h.p. DIN at 5,000 r.p.m for the standard engine. Benefits with the turbocharger switched on are somewhat more remarkable, Broad claiming 218 b.h.p. DIN at 5,500 r.p.m and 273 lb ft torque at 3,500 r.p.m (compared with 175 lb ft torque at 3,300 r.p.m. with the turbo off), sufficient to give a Capri Ferrari-like performance, or make the Granada capable of disposing of BMW 3-litres with ease, but more of that in a future issue.
Broad appears to be well-advanced with turbocharger theories, but he feels that so far he and others have only scratched the surface: "I've matched the turbocharger to the engine whereas what I should be doing is designing an engine specifically for turbocharging." He steadfastly believes that turbocharging is the answer to future engine designing, not the Wankel or similar projects, and also the answer to world-wide emission problems. Turbocharging is already inherently clean on carbon monoxide and hydrocarbon emission and Broad claims that his own system will meet the 1975 European emission regulations.
With further development he is convinced that turbocharging can meet even the most stringent emission regulations the Americans can devise. He is currently working on a valve to automatically cut out recirculation at 4 p.s.i. and bring in water injection. This would enable the boost to be increased to 14 p.s.i. with gains in fuel economy and clean exhaust gas at the top end of the rev range. Water injection would enable these higher boost pressures to be reached without fear of detonation whereas to raise the boost pressure on his current engine to 10 p.s.i. would immediately cause piston detonation on full-throttle at 5,000 r.p.m. However, Broad is desperate for help from a manufacturer to help him financially prove or disprove his theories: he estimates it would cost £10,000 and three months to complete development, similar figures to the expenditure in time and money taken to develop his current Turbo engine and in either sense quite fantastically cheap by a motor manufacturer's standards.
The day is coming when the world won't be able to afford engines of high fuel consumption. Broad thinks, and he is convinced that the future will see all cars restricted to a maximum of 2-litres. But these engines will be turbocharged, of very high efficiency, low on emissions and low on fuel consumption. "All we need is a cheap, very robust engine which can be made efficient by turbocharging." Working on those lines, but using an existing engine, not one designed for turbocharging as he would like, his next project is to turbocharge a 2-litre Ford Pinto engine. Judging by his results with the 3-litre engine, the brilliant Broad could produce some startling results.
BMW have almost exactly the same thoughts about the future, according to Herr Bönsch, which is why the Turbo 2002 should be considered more as a pointer to the future than as a contemporary homologation special. Bönsch is convinced that within the next 10 to 15 years the internal combustion engine cannot be replaced for reasons of practicality by any other method: steam engines, for example, are too bulky and run at too high a temperature and pressure, other methods such as the Sterling are too costly and thirsty, while the Wankel engine . . . well, to repeat his views on that would be unfair to another German company. Instead, turbocharged internal combustion engines will gradually take over. As the situation is at the moment, manufacturers need to cut down on emissions, therefore to regain the power lost in so doing bigger engines are required, meaning greater bulk, weight and thirst, with obvious repercussions. So, like Broad he and his colleagues consider that compact turbocharged engines are the answer, of which the Turbo 2002 could be a serious forerunner. - C.R.