Industry insight: Forced induction

Deep breathing

Super- or turbocharging? Or both, for ultimate pick up and top end performance? What do the forced induction engineers foresee as likely developments to defend their high performance territory?

"There are strong indications that supercharging and turbocharging have a lot of life left in them as fresh sources of extra performance from the much-abused internal combustion engine." (Motor Sport, March 1972).

For a magazine not generally given to prophecy the above passage was an unusual departure, but one which still seems to hold its value today. Although an increasing number of manufacturers have opted for the twin overhead camshaft, central spark plug, and quadruple-valve combustion chamber as their preferred route to performance in an emissions-conscious era, developments in both super and turbocharging will ensure mechanical diversity amongst performance units of the nineties.

However, such variety will only be evident outside Formula One, because of the ban on forced induction from 1988. This is relevant to the road cars we discuss here because there is a natural element of knock-on F1 glamour which has helped widespread sales acceptance of KKK, Garrett AiResearch and IHI turbochargers.

When Grands Prix are totally devoted to four-valve-per-cylinder (or many more, if Yamaha's Japanese Formula Two success proves relevant) motors of Cosworth ilk, will the turbocharger lose its TV glamour? Or will the industry simply heave a sigh of relief that no longer can Messrs Hunt and Walker describe yet another smoking hulk of former High Technology as "definitely yet another turbo failure for XYZ racing . . ."

Today's turbocharging industry is very large scale business indeed. In 1985 Garrett AiResearch alone accounted for "approximately 1.2 million turbochargers, representing more than a 50% share of worldwide production." True, a lot go onto diesel engines rather than into the high performance market, but consider the following:

"Since 1978, over 250,000 turbochargers have been supplied to Saab from Garrett Automotive Ltd, the Garrett Group's UK turbocharger manufacturing operation. In August 1986 it produced its two-millionth turbocharger, a TB-03 unit for Saab."

That British manufacturing base has been at work since 1972 in Skelmersdale, Lancashire. It employs 630 to produce 350,000 turbos annually; in 1972 the output was just 3500. Now we can see why Skelmersdale was the subject of a £10,000,000 investment scheme announced last year.

British market cars to use Garrett turbocharging go through the alphabet and price possibilities, from Austin Rover Montego and Maestro), via Bentley's enormous V8, to Volvo's surprising four-cylinder units.

Garrett defends its enormous worldwide market share through 1300 dealer outlets, all controlled by their Torrance, California, HQ. This USA base is the area from which the Formula One turbos emerge, although Group A development work is done by local centres: thus the Ford RS types, including the evolution Cosworth Sierra RS, have been assigned to Skelmersdale.

Garrett itself is just one automotive division within Allied Signal Inc, the others including brand names such as Bendix, Fram and Autolite.

Late last year Garrett vice-president Paul Craig, responsible for business development and future product planning, told me how Garrett planned to meet the challenge of the new ceramic turbocharger generation in Japan. I also asked him to comment on the stated intention of turbocharger stalwarts Renault to produce 16-valve cylinder-head designs without turbocharging. Did this not pose a long term threat to international turbocharger sales? Mr Craig smiled affably, and if he was worried about the future he certainly managed to keep that fear contained. "I'm confident about our future, we're right at the cutting edge of turbo development . I think we can not only continue to supply 50% of the world market for turbochargers, but also aim for 20% growth!"

Craig acknowledged that Nissan already sold ceramic rotor turbochargers to the public, but like many other industry observers he noted that sales were confined to the Japanese market in 1986. In broad terms he expected turbocharger development to concentrate upon ceramic rotors, "electronically controlled variable-nozzle turbine housings" and lightweight metals. Tomorrow's turbos would be smaller and feature "dramatically improved responsiveness."

The company said that such improvements "are being tested by many of Garrett's customers and may be used on production vehicles before 1990."

More specifically, Garrett's work is airned at cutting over-publicised "turbo lag". In racing this can be simply a driver's excuse, whilst on the road most sensitive drivers have little difficulty in extracting the best from current electronically-managed units. However, to meet the instant response of the 16-valve machines from Toyota, Honda, Mercedes and BMW, the turbocharger industry seems to be pinning its faith in the lighter ceramic rotor. Garrett comments that "substituting ceramics for conventional based rotors has shown improvements in vehicle acceleration of up to 20%." Garrett expects its silicon-nitride ceramic to survive happily in the 1000C/190,000rpm. environment of the turbo, Yet the primary appeal is that a lighter rotor will accelerate to boosting speeds faster than its predecessors, given that both are working on the same flow rates from the exhaust system.

The variable nozzle is one approach to the idea that the ideal turbo should adjust to the flow rate being provided from the exhaust. At low rpm a small nozzle would increase turbine inlet pressure with a corresponding bonus in gas velocity, but at higher speeds the nozzle area would be electronically increased so no restriction was imposed on exhaust flow.

I said this was one approach. The American military also funded research into varying the angle of turbine blades with the same exhaust gas speed benefits in mind. To my knowledge it showed promise on multi-litre diesel vehicles, but I have yet to see it applied to small petrol-fuelled engines.

The list of regular turbocharger users in 1987 makes an impressive contrast with 1978, the year in which Saab popularised the high performance turbo in Europe and extended turbocharging beyond its BMW and Porsche base. For nine years ago there were only eight turbo cars listed on the world market; now there are more than 100.

However, the turbocharger is not without its detractors. Oddly enough the two leading power packs in Formula One qualifying come from manufacturers who rarely offer the public turbocharging, BMW and Honda. BMW was a true European pioneer in racing the 2002 (1969) and selling the same model (1973-74) with turbocharging. Yet it confined subsequent turbocharged car sales to the previous 7-series (745i) or current turbo diesels.

Similarly, Honda offers the Japanese public turbocharging, but in Britain it stresses four-valve-per-cylinder similarities with its F1 car, omitting the turbo angle completely in its sales approach.

Honda and BMW are amongst the most respected engine manufacturers in the world, with Honda the versatile giant in comparison to Bayerische Motoren Werke. Both must believe the public is best served by the durability and economy aspects of the non-turbocharged power unit. Both have experience, wide experience, of turbocharging, yet it is not on their sales lists.

Significantly you also find Daimler-Benz outside the Turbo Club for petrol-fuelled cars, whilst manufacturers such as Toyota and Lancia have hedged their bets with superchargers as well as turbochargers.

As an alternative, superchargers are now showing signs of a production renaissance in Europe and Japan, but the numbers are still infinitesimal in Europe when compared to turbochargers. However, forced induction around a variety of engine-driven superchargers, as opposed to exhaust gas energy for the turbocharger, has improved efficiency. for Motor Sport readers will be familiar with the fact that Roots principle superchargers tend to supply excellent low to mid-range (say 1000-35000 rpm) torque and bhp figures, but their efficiency as air pressure pumps drops off as engine rpm rises.

Lancia tackled this deficiency on its 1.8-litre/450-plus bhp rallying engine by adding a KKK turbocharger to the Abarth-manufactured, rotary air displacement, Volumex supercharger system on the S4 Group B car. They got this to work with fearsome effect in World Championship rallying, and the road-going cousin (1.8 litres/250 bhp) was noisily effective too.

However, research into improving the supercharger's solo efficiency has yielded such promise that some major league operators are convinced of its future commercial merit. The Japanese multinational bank group Sumitomo (which also owns Dunlop) has signed an agreement with Clydebank based Fleming Thermodynamics Ltd, to manufacture and market its Sprintex branded unit.

Sprintex units work on the principle of twin-screw spiral compressors which revolve in precise proximity without touching. These Teflon-coated alloy-steel shafts produce claimed levels of thermodynamic and compression efficiency well beyond those of either Roots supercharging or turbocharging. The makers claim a "virtually flat" engine torque curve results, and that was my experience in a 1.9-litre Peugeot GTi. It would rev with typically "Pug" eagerness, but its forte was locomotive pulling power in fourth and fifth.

Fleming Thermodynamics is a 12-man outfit, and the precision demanded within the units limits production to a couple of examples per week. Sprintex may yet be another example of UK creativity being exported to achieve manufacturing success. However you can buy Sprintex-equipped conversions from a number of UK agents; the Peugeot I tried and liked was marketed as the Lynx by Skip Brown Cars at Taporley.

It is not a requisite of supercharger research that you be one of the many smaller scale British operations which have kept faith with such systems over the years. Within Volkswagen's enormous R&D facility at Wolfsburg, where they measure operating budgets in units of a billion Marks, a lot af attention has been paid to the G-charger.

This engine-driven supercharger has been under development since 1978 "to overcome the poor efficiency of the pre-war Roots supercharger and the noise of the vane supercharger." It works upon the principle of eccentric spirals, one within the fixed alloy casing, the other moving within to generate air pressure.

At present 40mm spirals are used, thus the G40 name for 500 supercharged Polo GTs presently trickling onto the German market. A further 500 will follow for France, but VW does not foresee extensive production for the G-charger Polo at present.

The Germans admit that the demands of developing their own electronic fuel and injection management, plus the precision engineering needed on a repeatable basis, delayed development far beyond expectation. VW has developed larger capacity G-chargers, but 60mm seems to be the practical limit, serving a 1.8 or 2-litre power unit in place of Polo's 1.3 of 115 bhp. Initial independent reports seem to back up VW's claims of extraordinary performance — over 120 mph, 0-60 mph in around 8 sec, and 29 mpg in hard use — for the Polo G40 GT.

There is much production engineering yet to be completed before we see it in a truly popular VW such as the Golf. Lancia's abandoned attempts to popularise its Volumex-branded supercharger show that the public has yet to see supercharging as a true turbo alternative. JW.