Engine speed

UK PROFESSIONAL DRIVERS FORUMS OWNER AND FLEET OPERATORS FORUM (INTERACTIVE)
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Carryfast:

JSingh:
Thanks for the comments

It definitely does 90kmh at 950rpm. The truck has been maintained by scania for all its life so I’m guessing by some of the comments it’s probably normal for it to be sitting at 950 but is it healthy for it to keep changing down to 11th? As some of you know opticruise isn’t the sharpest of changing gears and sometimes the truck goes up an incline and realises it’s in the wrong gear and knocks it down to 11th 1/4 way up the incline and then obviously you lose the momentum!!

Is the only option to change the diff? What would you guys suggest doing? Btw it’s a 520 so perhaps it’s designed to get best fuel economy but I’m averaging 7.5/8mpg. I’ve got other trucks giving me minimum 9/9.5mpg for the same work

Has it got a manual option.If so leave it in manual and experiment with downshift and upshift points.Bearing in mind that,according to it’s graphs,it will put out around 380 - 500 hp under full load between around 1,000 rpm - 1,300 rpm.While anything much over 1,400 rpm is realistically just burning money bearing in mind that it’s only putting out less than an extra 20 hp at 1,900 rpm than at 1,400 even under full load.On that note who needs revs or a ‘run’ at the hills although 950 rpm at anything other than very light engine load could possibly be costing fuel rather than saving it.While it’s my bet that any of the big power Scanias would do better on fuel with an 18 speed Fuller,to allow the driver to optimise engine speeds under all types of engine load conditions,than a 12 speed auto. :bulb:

I used to drive an R730 and it sat at 58mph and that did 8mpg so i would say your R520 needs looked.I would say it should sit between 1200-1300 rpm any truck i’ve driven has sat about there.

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I have a PDF from Scania but cant attach it here, this is copied from it

Consideration must be taken to variation in vehicle cruising speed when aiming for engine cruising speed below ~1100 rpm. A lowered vehicle cruising speed then might cause a downshift, giving more operational time on a lower gear, consequently with higher cruising revs than intended.
If economy gearing is reached on direct gear Scania Opticruise also support the GRSO905/R and GRSO925/R gearboxes for Low-rev cruising. This gives best possible fuel economy. Special consideration must be taken to take-off ability when Low-rev cruising is chosen.
Low-rev cruising
Low-rev cruising intends to reach economy cruising speed on direct gear and to use an overdrive gear beyond this. Low-rev cruising is recommended only with Opticruise and GRSO905/R or GRSO925/R gearboxes. The purpose with Low-rev cruising is to run at direct gear, with economic engine speed and low energy losses in gearbox, when most of the fuel is consumed. The overdrive is engaged when coasting downhill or when cruising speed is maintained with low engine output. Fuel consumption is gained in low power operational points and/or by storing free kinetic energy when coasting downhill at low engine speed, consequently with low engine friction losses.