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Ford power: Turbo H...

21th January 1977, Page 105
21th January 1977
Page 105
Page 105, 21th January 1977 — Ford power: Turbo H...
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Graham Montgomerie describes the latest changes made to Ford's Turbo 1.1 engine.

OPERATORS are divided in their views on turbocharging. Some are strongly in favour, others are just as strongly against, but in engineering terms the turbocharged engine does offer some major advantages over its naturally aspirated counterpart.

The turbocharger is a means of getting more airflow through the engine with a corresponding opportunity to increase the power output from a given size of engine; and this in turn gives better fuel economy, a higher torque rise, quieter running and lower smoke emissions at full load.

Clearly, there is a corresponding gain in power to weight ratio and last but not least the operator has a lower cost engine than a naturally aspirated engine of the same output.

But there are drawbacks to turbocharging.

The turbocharger life suffers if its lubrication is impared. Cooling is more critical as the turbocharged engine generates and dissipates more heat from the more highly loaded pistons and cylinders, The higher combustion pressures can lead to bottom end problems on big ends and main bearings and to failures of the cylinder head gasket. Turbocharging also accentuates scuff and wear problems of pistons and Pores.

Over the years since its introduction Ford has continually improved the turbo engine to the point where it is relatively trouble free. However, in the past twelve months a number of changes have been made which are now incorporated into a second generation engine called Turbo II.

Changes have been made to improve cooling and head gasket clamping. A full-flow by-pass has been introduced which ensures a strong flow of coolant around the engine under all conditions.

The two-thermostat set-up is retained but one is now set to begin to operate at 71°C releasing coolant to the radiator and closing the bypass. The second thermostat opens above 82°C and provides additional flow area. If the 71°C thermostat were to fail for any reason the 82°C thermostat will pass sufficient flow through the radiator to provide engine cooling albeit at a higher water temperature.

Also a new de-aeration pipe has been added between the high part of the thermostat housing ensuring that the thermostats are in contact with the coolant. By preventing the build-up of gas or air pockets, and allowing the pump to deliver a vigorous flow the thermostat now senses the true coolant temperature and the expansion tank pressure never rises above 6psi. The bottom radiator hose is replaced by a stiffer design and the header tank pressure cap has had its lift-off pressure increased to 7psi from 4psi.

In addition to these changes to the cooling system the head gasket clamping has been improved. This has been achieved by using a stronger bolt, torqued to a level approximately 25 per cent above the previous level.

One other change is that all the core plugs are now made from stainless steel. It has been found that very weak anti-freeze mixtures (about 5 per cent) are more corrosive than pure water. Some mild steel core plugs have been found to be very badly corroded and furthermore as a result the corrosion debris has accumulated in the radiator reducing its heat rejection capacity.

In view of this it is most important that cooling systems are kept free from debris and that anti-freeze concentrations are kept up to full strength. If there is any doubt about the condition of the cooling system Ford recommends that the system is flushed with a recommended fluid.

It is worth while stressing to drivers of turbo-engined vehicles that they need no special driving technique apart from a short idling period on initial start-up in the morning and a one-minute idle before engine shut-down. Drivers of expensive TIR trucks—which are nearly all turbocharged--accept this already.

In all turbocharged engines it is vital that the turbocharger impeller is properly lubricated and Ford recommends a "dead crank" period of 10 seconds— enough to register oil pressure at the gauge or to extinguish the low-pressure warning light—before the engine is allowed to fire. If a vehicle has stood for some days it is advisable to prime the impeller by hand and the latest Turbo II engines have a revised filter head which gives easy access for priming.

Shutting down a turbocharged engine properly is just as important as starting up. Again, to allow time for the turbocharger impeller to slow down (it can run at up to 90,000rpm) and for the impeller lubrication to stabilise, the engine should be allowed to idle for at least one minute before shutting off.

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