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Foden mpg figures lead the field
Page 41
Page 42
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Uprated Rolls engine is a willing performer at low revs, but oh for a few more gears
THE FODEN FLEETMASTER we tested during the next run was a demonstrator from Warrington Commercial Vehicles, writes Tim Blakemore. It had started life as a 36/38-tonner with a Rolls-Royce 2651_ engine.
Uprating the Rolls engine to 290L specification is simply a matter of changing the fuel injection pump, and with that job done the sleeper-cab Fleetmaster was ready to pull 40 tonnes.
Rolls-Royce's engineers were a little concerned about this particular engine's turbocharger because its boost pressure was somewhat below par, the tractive unit having completed 41,000km (25,500 miles) in WCV's demonstration fleet before the -test started. However, there was insufficient time available to replace the turbocharger, and as it turned out the test re sults should completely dispel any fears about the engine's performance.
The Rolls-Royce-powered Foden's overall fuel consumption was by far the best of the five 40tonners. Furthermore, with only two exceptions, it consistently clocked up the best mpg figure over each of route's seven stages.
Predictably, over the A68 section the 206kW (276bhp) engine could not match the economy of the more powerful Cummins, DAF and Volvo engines, but only on one other stage was the Foden pushed into second place, and that was by the Volvo on the A74 between Gretna and Hamilton.
With a power to weight ratio of only 5.22kW/tonne (7bhp/ton) fast journey times could not t expected from the Fleetmaste and sure enough the over average speed was the slowec This difference in average spec could be a critical factor fl some operators, particular with the eight-hour driving di looming on the horizon.
On the second and third da of the test, which took just ov eight hours driving time each the faster machines, the Foch was typically about a half ho behind. On the steep hills too, course, the times were slow a; it was on these sections that few extra gear ratios would ha been welcome.
Some operators argue tV nine gears are more th; enough, and at 32 tons gross, even at 40 tonnes in flat terra that may well be true, but wh the going gets tough at t higher weight then 13 or even ratios are not too many.
While there were times on t steeper hills when the willi 290L would have pulled a hig1 gear, the next one up in the ge box was just a little too far aw even with the extra fast char allowed by the Fuller, with tonnes pulling us back.
Despite its relative lack of c suspension — Fodens use ri ber mountings at the front a coil springs with dampers at I rear — the S10 cab has be widely praised for its comfc Even with fairly light king' loads the sleeper-cab Fleetm ter has never had any unpl sant ride characteristics, creasing the kingpin load sho only improve that situation C that proved to be the case.
The Foden's front swing cle ance would not allow us couple to the deep kingpin or tion so we had to move the to its second position at 1. (3.28ft) back from the se trailer's headboard. This course decreased the king load and transferred mi weight on to the trailer bogir such an extent that the three les were over their 24-tor weight limit.
A half hour of hard work fr both the Foden and CM representatives solved the problem. We moved about three quarters pf a ton of test weights from the rear of the trailer to the front and ended up with acceptable axle loadings.
Apart from the engine this Fleetmaster's specification was very similar to the NT240powered one we recently tested at 32 tons (CM October 11) with a direct-top twin-countershaft :tiller gearbox and Rockwell 3ingle-reduction rear axle with a -atio of 3.7:1. There were some ninor differences in that the 40 onnes Fleetmaster had the atest single-piece bunk, an airissisted hydraulic clutch (in;teed of pure hydraulic) and a 3urman steering box in place of F.
I am not sure that air asistance for the clutch is really iecessary; it has a light action, flyway, and all the air asistance seemed to do on our ast vehicle was to make the ake-up more fierce and difficult • ) control.
Fodens use the same exhaust ilencer for Rolls-Royce and ummins engines and I was surrised to learn that the Rolls enme is one or two decibels noiier — surprised because no ifference in noise was noticeble from the driver's seat. But le engine does have charac
teristics noticeably different from both those of the Big Cam Cummins and the "small cam" turbo 250.
Compared to the E350 Cummins the 290L Rolls develops its maximum torque 1 0Orpm further down the rev range at 1,200rpm and its maximum power 50rpm further up the range at 1,950rpm. Both engine manufacturers recommend letting their engines "lug down", but the Rolls is a more willing performer at really low revs. In fact if you don't watch the rev counter it is easy to let the engine speed fall too low for there is no indication, no noise or vibration, to tell you that you've gone way below maximum torque speed.
On the other hand, if you don't use the tachometer with the Cummins E350 you are more likely to change down too early because the engine's exhaust note takes on a harsh edge when the speed falls to about 1,200rpm under load. It is almost as if the engine is warning you that while it is prepared to pull from lower speeds it is doing so grudgingly.
Apart from its outstandingly good fuel economy this Foden Fleetmaster distinguished itself in another way; it was the first vehicle for some time to complete the Scottish route without incident. The Ford had steeringbox problems, the earlier Fleetmaster had broken a throttle spring, the Roadtrain had to have a new rev counter transmitter, and the ERF had its clutch servo changed.
With 40 tonnes to hold back instead of 32.5 the effectiveness of the Foden's exhaust brake was noticeably reduced, but this was equally true for the other vehicles, except the Bedford which was fitted with the excellent "Jake Brake". This faster increase in speed on downhill sections was the most obvious difference between driving at 32 tons gross and 40 tonnes gross, and it meant that we used the service brakes to control speed more during these tests than we normally would. Even with three semi-trailer axles the brake frictional area per tonne was about ten per cent less with the 40-tanners than it would be at 32.5 tonnes with our tandem-axle test trailer. However, we encountered no brake fade problems with any of the vehicles, certainly not with the Fleetmaster even on the long descents into Shotley Bridge and Corbridge.
Driving the Foden for three days almost immediately after having driven the Transcontinental made it possible to easily compare and contrast the two vehicles. While the Fleetmaster's ride was good it could not match the Ford's comfort, and because it is mounted so high there is a lot more room in the Transcontinental than the S10 cab with its deep engine hump.
The Fuller gearbox installation in both tractive units gives an excellent gearchange, and really there is very little to choose between them. For my money, however, the change on the Foden is just slightly more precise. There are fewer linkages on the Foden because the selector rods do not have to cross from one side of the chassis to the other.
Fords useful, header-railmounted fresh air vents would be a welcome addition in the Foclan cab — or indeed any fresh air vents. Neither of the cabs had high interior noise levels (do any vehicles these days?) but the HSeries seemed quieter — that high mounting again, and our test vehicle was fitted with noise insulation package which is claimed to reduce interior noise by as much as 4dBA.