Driving technique: Does it really impact fuel usage?

[800301]

Thanks. That makes sense. The shorter (i.e. more) block sections though will need extra funding on top of basic renewals costs. Current DfT parsimony suggests that could be a tough sell.

If we were to actually upgrade a mainline to ETCS without it being an overlay system I’m pretty sure the benefits would outweigh the cost but the way it’s looking at the moment where no one likes paying for anything, I doubt I’ll ever get to experience it

 

[ac6000cw]

I think it was Salford City Transport back in the 50’s decided to order their buses with the larger 9.6 litre engine over the smaller 7.4 litre unit.

Their thoughts were (I assume based on proven running with both), was that a larger engine being used lightly (not laboured), uses less fuel than a smaller engine working harder. It seemed to be the case too.

In general IC engines are at their most fuel-efficient in the middle RPM range, but there's all sorts of other variables in play (like how well matched the engine and transmission characteristics are, and usage cycles in a particular application). But I'm not surprised that the 25% larger engine was overall more economical.

Many decades ago when I used to read car magazines regularly (before I was old enough to drive one!), some car models were available with a wide range of engine options e.g. the Ford Capri had options from 1.3L 4 cyl to a 3L V6, reviews often commented that a particular engine size was the 'sweet spot' of drivability versus fuel economy - the small engines had to be driven hard just to get around at a reasonable speed, whereas the big engines probably spent a lot of their time in less-efficient RPM ranges (and were heavier/had higher frictional losses/used more fuel when idling etc.).

However, in the case of a class 66 for example, it’s not quite as cut and dry. Notch 8 produces around 3000hp at the rail I think it is, where 7 produces 2300. But N8 uses 25% more fuel as the supercharger and turbo are both in.

Small point - turbocharged EMD 2-stroke diesel engines use a single, special, turbocharger that is mechanically driven in lower RPM/lower exhaust gas flow situations, with the mechanical drive automatically disconnecting (via an overrun clutch mechanism) when the exhaust gas flow is sufficient to drive the compressor from the exhaust turbine alone - from what I've read, that happens around notch 5 or 6. There is not a separate supercharger (blower). Non-turbocharged EMD 2-stroke engines use a mechanically driven Roots-type blower instead.

AFAIK, max hp at rail for a class 66 is around 2600-2700hp and 2300-2400hp in notch 7. According to this post - https://www.railforums.co.uk/threads/class-93-tri-mode-loco.210779/post-7142500 - a 66 is most fuel-efficient in notch 6, a bit worse in notch 7 and much worse in notch 8.

 

[voyagerdude220]

I was told years ago that the pedal in my car that uses the most fuel is the brake. Logically, this is true, but planning ahead is required.

I strongly agree. It drives (excuse the pun) me mad when say I'm on a dual carriageway driving gently at a constant 25-30 mph towards a red light in the distance or just letting my car idle, whilst many overtake me, only for me to end up undertaking them at the traffic lights.

Or similarly I'll slow down a bit when approaching busy junctions/traffic lights and try to maintain a steady speed whilst judging how fast traffic ahead of me appears to be moving.

 

[Unobrow]

Charles Baroth , Salford City Transport, a visionary ahead of the game. Transformed the reliability & availability of vehicles in the fleet.

He certainly was. Bought quality products, looked after them with preventative maintenance and as is generally accepted, had the smartest fleet in the country for a good 15 years. Fleet managers of all modes of transport could still learn a lot from him.

== Doublepost prevention - post automatically merged: 5 Jul 2026 ==

I was told years ago that the pedal in my car that uses the most fuel is the brake. Logically, this is true, but planning ahead is required.

If you use the brake more, then you have put excess energy into the system. Coasting is better where possible, provided that the required timings can be achieved.

The conditions on the railway are less variable than on the road, so it should be easier to achieve a consistent and efficient power and coast strategy.


Where regenerative braking with electric traction is available, then the situation may be different.

Absolutely correct. Momentum is your friend in fuel efficiency and time. I tend to lose speed earlier and coast at a low speed towards a red. If it steps up, the brakes are off and I’m not using as much fuel starting from rest. Of course if I have to stop, I’m already at a low speed so no sphincter twitching moments as it were. Whilst it’s not quite as easy to apply that technique on today’s busy roads, forward planning can still make a huge difference to fuel economy, with usually virtually no or an insignificant loss of time.

Small point - turbocharged EMD 2-stroke diesel engines use a single, special, turbocharger that is mechanically driven in lower RPM/lower exhaust gas flow situations, with the mechanical drive automatically disconnecting (via an overrun clutch mechanism) when the exhaust gas flow is sufficient to drive the compressor from the exhaust turbine alone - from what I've read, that happens around notch 5 or 6. There is not a separate supercharger (blower). Non-turbocharged EMD 2-stroke engines use a mechanically driven Roots-type blower instead.

AFAIK, max hp at rail for a class 66 is around 2600-2700hp and 2300-2400hp in notch 7. According to this post - https://www.railforums.co.uk/threads/class-93-tri-mode-loco.210779/post-7142500 - a 66 is most fuel-efficient in notch 6, a bit worse in notch 7 and much worse in notch 8.

Thanks for that interesting insight. I was always told they had both, and have wondered a few times where the supercharger was hidden lol. I was going off the in cab EMD2000 system for the hp figures, which agree with our notch 7 figures, but show more for notch 8 than you suggest? It was an assumption on my part that these are at the rail figures.

 

[hwl]

I was going off the in cab EMD2000 system for the hp figures, which agree with our notch 7 figures, but show more for notch 8 than you suggest? It was an assumption on my part that these are at the rail figures.

EMD 2000 shows electrical power at the alternator terminals.

At low speeds (up to ~15mph) Notch 8 supplies too much power to the traction motors (more than normal adhesions levels for those traction motors can cope with) which is another big reason not to use Notch 8.

 

[172007]

In general IC engines are at their most fuel-efficient in the middle RPM range, but there's all sorts of other variables in play (like how well matched the engine and transmission characteristics are, and usage cycles in a particular application). But I'm not surprised that the 25% larger engine was overall more economical.

Many decades ago when I used to read car magazines regularly (before I was old enough to drive one!), some car models were available with a wide range of engine options e.g. the Ford Capri had options from 1.3L 4 cyl to a 3L V6, reviews often commented that a particular engine size was the 'sweet spot' of drivability versus fuel economy - the small engines had to be driven hard just to get around at a reasonable speed, whereas the big engines probably spent a lot of their time in less-efficient RPM ranges (and were heavier/had higher frictional losses/used more fuel when idling etc.).



Small point - turbocharged EMD 2-stroke diesel engines use a single, special, turbocharger that is mechanically driven in lower RPM/lower exhaust gas flow situations, with the mechanical drive automatically disconnecting (via an overrun clutch mechanism) when the exhaust gas flow is sufficient to drive the compressor from the exhaust turbine alone - from what I've read, that happens around notch 5 or 6. There is not a separate supercharger (blower). Non-turbocharged EMD 2-stroke engines use a mechanically driven Roots-type blower instead.

AFAIK, max hp at rail for a class 66 is around 2600-2700hp and 2300-2400hp in notch 7. According to this post - https://www.railforums.co.uk/threads/class-93-tri-mode-loco.210779/post-7142500 - a 66 is most fuel-efficient in notch 6, a bit worse in notch 7 and much worse in notch 8.

Wonder why its confusingly called a turbocharged engine when its a twincharger?

 

[WestAnglian]

I travelled on a GWR full-load test run of the fast-charge class 230. We were told that the most significant factor affecting battery range was driving technique. That surprised me, and I think it surprised GWR a little.

 

[ac6000cw]

Wonder why its confusingly called a turbocharged engine when its a twincharger?

It only has a single 'charger' (compressor), which is driven by both an exhaust gas turbine and a mechanical drive. It can't just be a turbine-driven compressor as 2-stroke diesels always have to be 'pressure charged' as the fresh intake air is also used to push out (scavenge) the remaining exhaust gases (during the lower part of the piston travel). At low RPM there isn't enough energy in the exhaust gas flow to drive the compressor (from the turbine) sufficiently to create the necessary intake air flow, so you need the mechanical drive.

4-stroke engines have separate exhaust and intake strokes so can work 'normally aspirated', using only ambient air pressure to push fresh air into the cylinder.