How do today's modern engines in Volvo/Scania/Dennis buses compare in relation to their size, with the range of engines available in my driving days in the 50s and 60s, in particular Bristol AVW/BVW, Gardner 5LW/6LW,and Leyland 0600/0680. I know today's engines are more efficient and powerful, but the actual difference in size would be interesting to know. I was a driver with Bristol Omnibus Co. so as you can imagine I was very used to the above power plants, and often frustrated by the plodding progress of a 5LW Gardner, I mentioned previously an incident years ago, when I was climbing Tog Hill on the A420 early one morning,(empty), and I was passed in grand style by an AEC 8 wheeled tanker belonging to Dobsons of Carlisle, fully laden with aviation fuel bound for Lyneham Airbase. He was of course powered by something rather larger than the 5LW which I was lumbered with, large under stressed engines were not on the agenda of the Tilling Group that's for sure!
Dave Knapp
23/10/14 - 16:21
I'm not up to speed with the output and potential of modern engines but in the 1950s and 1960s almost every operator down rated their engines and also fitted governors to limit speed in the interests of economy and speed limit compliance. Stage carriage hardly required lightning acceleration or high cruising speeds. Under the 1930 Road Traffic Act all PSVs were restricted to 30mph. All goods vehicles had a 20 mph limit in built up areas until 1957 when the maximum limit for both goods vehicles and PSVs went up to 40mph. The PSV maximum limit was raised again in 1966 to 50mph, at the time BMMO had been scheduling its London to Birmingham services at 70 mph on the motorway. It is obvious from statements by drivers who got to handle vehicles with engines that were in an "as designed" state, coupled to gearboxes, chassis and bodies which gave a reasonable power output/weight ratio, that engines of the time were more than capable of sparkling performance.
Phil Blinkhorn
24/10/14 - 07:33
I am firmly in the large engine, understressed camp. AEC 691 or 760; Leyland O680 or TL11; Gardner 6LXB. For modern coaching, the popular power unit is the DAF/PACCAR MX11/MX13 (11/13 litres) - along with 11 litre Daimler Benz; Scania or Volvo units. Because of modern technology, including turbochargers and common rail, these are cleaner, more efficient and more powerful than their predecessors. If we accept the DAF engines as being a development of Leyland engines built under license, make the comparisons. Last O680 (11.1 litres) in a Leopard coach 180bhp. Last TL11 (11.1 litres) in a Tiger coach 260bhp. MX11 (11 litres) 420bhp, MX13 (13 litres) 460bhp. Conversely service buses have gone into what I call Tonka toy mode with incredibly small engines and a comparably large power output. All the latest deckers have 5 litre engines pushing out something like 220bhp. That would have been powerful for a TL11 but the AEC 760 was de-rated to 157bhp for coach applications right up to the end in 1979. Modern technology makes small engines efficient. Whether it does anything for longevity is a different matter. What they definitely are is characterless and, even they do last, people will nor want to preserve them in the way they do buses from the 40s, 50s and 60s.
David Oldfield
24/10/14 - 18:27
David, I can remember thinking that nobody would ever want to preserve a Leyland National, but now there are several in preservation, and younger (than me) enthusiasts nowadays look on Nationals as interesting heritage vehicles. Already there are at least two Dennis Darts in preservation, and last month at the Kingsbridge running day I was surprised to see several preserved minibuses! Who is to say that the modern vehicles which we find characterless will not be preserved by future generations of enthusiasts?
Another important point about modern engines is the appalling fuel consumption. My friend who runs a 1949 Bristol L5G on a weekly stage service in Wensleydale achieves 16 mpg, and I have heard of Bristol SC4LK's in the past managing over 20 mpg; modern operators can only dream of such figures.
Don McKeown
24/10/14 - 18:28
David, I have to disagree regarding preservation. Steam engine enthusiasts said no-one would want to preserve diesel and electric engines. Aircraft enthusiasts, when jets arrived, said only piston engined aircraft were worth preservation and in the 1960s, vintage and veteran car enthusiasts scoffed at the idea of preserving Cortinas, Minxes etc.. Each generation preserves its own.
Phil Blinkhorn
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