New Age Boo
So how does this new Diesel produce so much power so cleanly? Well it
has a multi-valve engine, common rail high pressure Diesel injection and
all sorts of electronics; but is this really where all the power comes from?
Boost pressure is the pressure left in the inlet manifold. Without a turbo
when the inlet valve opens the engine has to suck air through all the pipes
and air-cleaner to get it. With a turbo installed the engine now has air
supplied by the turbo right to inlet valve. This means the engine now gets
plenty of air whenever it needs it. Boost pressure in the days of a SWB
Landcruiser with 2L-T engine was about 8PSI. Nowadays the boost in a
similar sized EFI controlled Common Rail Diesel can be about 18-20 PSI.
With all this air available it’s easy to put in ‘more fuel for more power’ and
burn it more efficiently. Problem is that to generate 20PSI boost pressure
you need more than magic and the trick comes from equalising backpressure on the exhaust side before the turbo.
General ‘Rule of Thumb’ for creating ‘boost pressure’: 1 PSI inlet boost
pressure needs 1-1.5 PSI exhaust gas back pressure to create it.
So you can see that the offset with having a turbo means that the engine
has to cope with a lot of exhaust gas backpressure before the turbo can
make boost for the engine. This backpressure normally is fine but it can
lead to undue strain on the engine if the turbo boost pressure in a modern
EFI Diesel is ‘wound up’ much higher.
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Offroading Online Magazine