I also think that speed limiters have a big part to play.
Modern trucks are geared for 56mph, whereas older ones are geared for 60mph.
I still believe that more power gives better fuel economy though, simply because it’s easier to keep the revs in he green up hills with a bigger bhp engine.
I may be wrong, but I reckon bigger IS better with truck engines.
Denis F:
gardun:
I’m with Shrek here - at 44t a 440 is working its bollox off when a 610 would be trundling along. Or maybe not - I dunnoalthough the theory fails when you get late and thrash the 610
OK 
I’d thrash a 950 for the fastest run home (legal of course) 
gardun:
Denis F:
gardun:
I’m with Shrek here - at 44t a 440 is working its bollox off when a 610 would be trundling along. Or maybe not - I dunnoalthough the theory fails when you get late and thrash the 610
OK
Theres only one thing that makes a real difference to mpg,weight. More power means less stress on the driver and in the right hands a safer truck on the road cos you take less chances.
Although the advancement of automatic boxes and ASR etc helps. 600 plus horses against 400 can be false economy in the wrong hands. things such as tyre wear and lost traction can cost as much as the extra fuel you may use.
And where are you going to use all this extra power? You can only go as quick as the 400hp nail struggling along in front of you 
The Dutch seem to have it right with International transport and the normal fleet motor spec is 380 / 420 ps
why do Americans have V8 motors in cars big liters low RPM result low MPG relaxed driving automatic trans look what happening with trucks now
i drive a 460bhp gobstopper on a IRISH 03 plate and i can come up windy hill at 44ton still pulling nicely at 60-65mph usually drop half a split goin up on the straights its great middle lane everywere but if i was at 56 i dont think it would b so good up hills
i do agree thats the limit shud b upped to 60 tho makes life a lot easier
Scarab:
pushing out as much pollution as a sparrows backside
Excuse me while get up of the floor
had the pleasure of driving a 580 kenworth recently, nice change from my usual 430 actros, with 24 tonne on the trailer i didnt even have to drop a gear going up hills, in fact the only time i had to drop gears was to turn corners, corners now, not bends.
Limestone Cowboy:
But one day they may come into their own as may be Stan Robinson and his pals will get the go ahead to run the B doubles and be up at the 60t mark, thus requiring 610’s because the old equation stands up.
you don´t see too many 600 or so hp trucks pulling 60t combinations in scandinavia, spoke to a guy who pulls 60t with a 420 scania, he said he gets around 34-35l per 100km average
Robertthegreat:
why do Americans have V8 motors in cars big liters low RPM result low MPG relaxed driving automatic trans look what happening with trucks now
Because they can. 
With fuel prices at tuppence h’penny a gallen they can also afford to 
Robertthegreat:
why do Americans have V8 motors in cars big liters low RPM result low MPG relaxed driving automatic trans look what happening with trucks now
For the same reason they think they can build motorcycles. The roads go on forever and dont have any corners Which is just as well because a Hardly Driveable only goes in a straight line
see plenty of V8s in and around melbourne city, again as posted above, “because they can”, they tend to drive them like ■■■■■■■■■ as well
Wheelnut:
The Dutch seem to have it right with International transport and the normal fleet motor spec is 380 / 420 ps
They don’t have hills and so much stop start crap road layouts everywhere like we do here. A 380 with 44 tonnes is a bit painful. Mind you so was a 280 with 38 tonnes.
Shrek:
Limestone Cowboy:
B) the cost of fuel is going into orbit. The more oomph under the grille the more diesel is pumped through, so apart from a few ‘flash harry’s’ who buy the big 610’s etc, no one will want the added expense of owning one.…or do bigger powered motors return better mpg because they’re not having to work too hard? Do you thrash the ■■■■ off a 440 to get the performance you need or do you tickle a 600 and get better fuel economy?
I don’t know, just asking what you think. (But I’m swaying towards the bigger powered trucks to use less fuel than a smaller one).
Your swaying the right way mate.
The truck i call home at the moment started life with us as a R124 420.
We ran it for a couple of months at that before getting it remaped up to 500hp. What a difference,so much easier to drive ,changing up gear at the start of the green band instead of the top means a smoother gear change,lower revs means better fuel economy.I believe it’s probably about 1 to 1.5mpg better than what it was at 420.
Allways an interesting debate.
The reason why we aern’t all driving V8’s at 620bhp is one of pure economics.
Plus points for BIG V8’s
High BHP and Torque = less gear changing and labouring on hills and under heavy load. = £saving
Enginee and Gearbox work much less than smaller setups increasing relibility quite dramatically lowering bills. Maintenance points wider apart also
Fuel saving minimum on the flat but lower RPM’s mean a very slight fuel benefit.
Less driver Fatigue, improved gradient overtaking = Safer Driving (Scania not me)
Against
Cost the earth to buy initially, until this changes forget it for RDC’s and fleet work.
V6 engines
Basically the reverse of the above points for and against, increasing BHP though in a 6 doesn’t give a direct Torque improvement and does put additional stress on the engine. Hills are easier but lifetime of the enginee will be shortened.
O/D’s on euro work and the Irish have known the V8 benefits for years its not just a bling thing!! 
well not really!!
P.S. most large Generators i.e. ■■■■■■■ are V12 or V16 as they produce the same output as V8’sat much lower RPM’s. Lower pressures by spreading capacity over more cylinders mean that weights of engine’s are very similar
There must be a change over point where the power becomes more than what’s needed & therefor consumes fuel unecessarily.
I remember the old 60’s-70’s Austin 1300 car was more economical than the 1100 … because it didn’t need to be worked as hard to make reasonable progress.
However the P6 Rover 3500 was much thirstier than the Rover 2000… even though the 2000 did have have to be worked quite hard to maintain a spirited drive & was subsequently seen as underpowered & replaced by the 2200.
I assume this was because the 3500 was over powered.
edit: and what a gentleman’s car that 3500 was, especially the manual 3500S with PAS.
DAFMAD:
Wheelnut:
The Dutch seem to have it right with International transport and the normal fleet motor spec is 380 / 420 psThey don’t have hills and so much stop start crap road layouts everywhere like we do here. A 380 with 44 tonnes is a bit painful. Mind you so was a 280 with 38 tonnes.
The Dutch drivers I know go further than Holland and use the same hills as I do
Maybe future trucks will be hybrids and could run on alternative fuels. A small lean diesel engine mated to an electric motor which is charged on the overrun or during braking instead of energy being wasted in the retarder. The electric motor is cut in to start the vehicle or to climb hills. The maximum torque from standstill characteristic of the electric motor makes it ideal for start stop work!
There are quite a number of town buses already operating on this exact system.
Newcastle have been for some time, LIverpool getting 4 soon.
The only down side i noticed is that they tend to be noisy from the outside as the small diesel can be running at full revs even when the bus is stationary at a stop.
i think that type of bus has electric motors only and the battery is charged by a constant revving diesel engine. The engine does not directly drive the vehicle. 
