Driving a turbo-diesel

[candapack]

Came across an old review of my van - 2007 coachbuilt on a Boxer with a 2.8 HDi engine.

It mentioned the "high revving" 2.8 engine (standard was the 2.2) provided opportunities for better fuel economy if it was

"driven at engine speeds that ensured the turbocharger was working efficiently"

 

Can someone explain that please? Should I rev high going through the gears from stationary, but cruise at, e.g., 60 - 65 (about 2500rpm) which is generally what I do, or is fuel economy improved at higher cruising revs (and thus higher speeds).

It doesn't seem right driving faster, getting their quicker, AND saving fuel. :-D

[colin]

you should drive at a speed that suits the turbo, ie. don't let it labour at to low a revs, not having driven a 2.8 i can't tell you what revs that might be.

p.s. i would guess that 2500rpm is fine.

[Rayjsj]

candapack - 2014-02-09 9:18 PM

 

Came across an old review of my van - 2007 coachbuilt on a Boxer with a 2.8 HDi engine.

It mentioned the "high revving" 2.8 engine (standard was the 2.2) provided opportunities for better fuel economy if it was

"driven at engine speeds that ensured the turbocharger was working efficiently"

 

Can someone explain that please? Should I rev high going through the gears from stationary, but cruise at, e.g., 60 - 65 (about 2500rpm) which is generally what I do, or is fuel economy improved at higher cruising revs (and thus higher speeds).

It doesn't seem right driving faster, getting their quicker, AND saving fuel. :-D

 

I think they are talking about 'Turbo Boost', the 'kick in the pants' that you get get when the Turbo 'cuts in'

below a certain rev range the turbo 'drops out' it should be quite apparent if you listen for it.

The idea is to keep the Turbo boosting, without letting it drop off boost. (is that English ??) by letting the revs drop too low in 5th or 6th gear, = Engine working efficiently.

As said before, 2500 rpm, should be enough to keep the Turbo working.

(any Experts want to elaborate on that ?) Ray

[candapack]

Thanks both.

[George Collings]

There are some reviewers who although higly experienced in driving know little about what goes on under the bonnet. The worst talk rubbish.

 

All other things being equal the smaller an engine the higher it will rev. The bigger the piston the higher the destructive forces involved in stopping and starting it at the top and bottom of every stroke.

 

By 2007 Fiat knew a fair bit about turbocharging commercial diesels. Typically the turbo is working effectivly from about 1200 rpm upwards. below 1000 the turbo is providing little extra air and you are effectively driving an old fashioned naturally aspirated diesel. It feels flat and its doing the engine no good due to the long gap between power strokes. As the revs rise the flywheel smoothes out the lumps and the engine runs smoother and smoother untilit gets up to its governed maximum speed.

 

Most commercial engins are designed for optimum fuel efficiency at 70 mph but by then a fair bit of fuel is burned overcoming wind resistance, slow down and fuel consumption improves. Slow down too much and you loose the gains the turbo obtains by extracting waste energy from the exhaust gasses.

 

My experience is that best economy is found in the 45-55 mph range.

[bolero boy]

colin - 2014-02-09 9:23 PM

 

you should drive at a speed that suits the turbo, ie. don't let it labour at to low a revs, not having driven a 2.8 i can't tell you what revs that might be.

p.s. i would guess that 2500rpm is fine.

Agree with colin, here. Our van seems to sail up most inclines in top as long as it has 2500 rpm on the rev counter. At, say 2000, the van will gradually slow, requiring a change down.

[lennyhb]

With the newer 2.3 the only problem I have had is when negotiating steep hills (1 in 6 or steeper) with hairpin bends, don't change down soon enough and the revs drop below about 1500 turbo goes off boost and engine literally dies & need frantic gear swapping & pumping with right foot.