In recent years, manufacturers have been
wise to limit themselves to diesel chassis for motorhome models of 35 feet and longer in
order to provide at least some payload capacity Weight-carrying limitations have forced
builders to limit lengths and features in order to minimize the possibility of
Both Ford and GM have introduced new, heavier chassis, and the buying
public undoubtedly will see gas-powered "biggies." The Ford F53 Super Duty
F-Series and the Chevrolet P12 chassis introduced during the Louisville trade show in
December are capable of significantly increasing the size and weight potential for
gasoline powered motorhomes.
Both chassis are configured very similarly, using front engines,
leaf-spring suspensions and solid axles front and rear, as well as four-wheel power disc
brakes. Straight frame rails and other elements that ease the coach builder's body-design
task have been implemented in each chassis. Beyond those attributes, the difference is in
A major boost in gross vehicle weight ratings (gvwr) and gross
combination weight ratings (gcwr) has given the F53 a sizable increase in payload
potential. The new chassis is available in 18,000-pound gvwr and 20,500pound gvwr
versions, along with a smaller 15,500-pound-gvwr model. The gcwr for all models is 26,000
Pounds. Wheel bases range from 178 to 228 inches.
Front-axle capacity has been bumped from 6,000 to 7,000 pounds for the
two heavier chassis, and a new rear axle, capable of handling up to 13,500 pounds, has
been engineered for use in the 20,500-pound chassis. The front-tread width has been
widened from 71.7 to 80.9 inches for extra stability. Wider, lower-profile tires
(245/'7ORl9.5) have been added on the redesigned chassis. Power disc brakes are used all
around, and four wheel three-channel anti-lock brakes (ABS) are standard.
The Triton 6.8-liter V-10 is the standard engine for the F53 chassis,
replacing the venerable 7.5-liter (460-cid) V-8. The V-10 bests the old engine by 30 hp
and 10 lb. ft of torque. Here's how the old and new engines stack up:
- 1999 6.8-L V- 10: 275 HP @ 4,250 RPM, 410 LB-FT
- 1998 7.5-L V-8: 245 HP @ 4,000 RPM, 400 1,B-FT
The V-10's power comes in a bit earlier and peaks at somewhat higher rpm-a broader
power band that makes for a more drivable versatile engine under heavy-load conditions.
Ford's old standard E40D four-speed automatic transmission has been replaced with the new
4RlOO four-speed automatic with overdrive. Essentially an E40D shell with modified
innards, the 4RlOO includes enhanced electronic controls for improved shift performance,
improved lubrication and other details.
We had an opportunity to testdrive prototype coaches built on the new Ford F53 chassis
models. Both the 18,000- and 20,500-pound-gvwr chassis garnered high marks from the
drivers for ride and noise level, but the heavier chassis got the nod in the handling
On freeways, two-lane backroads and hilly terrain, the V-10 powered the motorhomes with
the same vigor as its elder brother, the 7.5 V-8, with a noticeable improvement in
throttle response. Its exhaust noise is different, as befits an engine with an extra pair
of cylinders, and the air induction sound is quieter than that of the 7.5 engine.
The new 4RlOO transmission shifted smoothly, and although Ford took some of the
firmness out of the shift patterns, performance was still satisfying for the driver. Less
pedal effort was needed for solid and controlled stops. All told, the new Ford F53 ably
demonstrates the results of myriad improvements.
The net result of these new chassis' availability is that motorhome manufacturers will
be able to build larger gasoline-powered coaches while reducing the possibility of vehicle
overloading. For example, a 34-foot basement-model Class A that has a marginal payload
capacity when built on a 17,000-pound-gvwr chassis will have better capability on the
18,000pound chassis and certainly will be well-positioned on the 20,500-pound version. In
most situations, the use of rear tag axles as gvwr-boosting aids should no longer be
Now that these new heavy chassis are about to hit the road, manufacturers are gearing
up to introduce a number of luxurious 35- to 40-foot coaches designed to rival diesel
pushers in livability, but with more affordable price tags. by Jeff Johnson
Ford versus Chevrolet Chassis Comparison
New Triton 6.8L engine replaces the 7.5L V-8 in Class C
by JEFF JOHNSTON
Ford has introduced its new Triton V-10 gasoline-powered engine, the
first 10-cylinder power plant available in a Class C cutaway motorhome chassis. The
manufacturer claims the new engine will give motorhome owners upgraded performance in the
form of increased fuel economy and improved acceleration, hill-climbing and towing
ability. As a direct replacement engine for the venerable
7.5-liter (460-cid) V-8, the 6.8-liter Triton V-10 is part of Ford's new modular family of
light-truck and automobile power plants. The V-10 is first available in E-Super Duty
motorhome chassis and Econoline vans; we expect it will be available in Class A chassis
soon. The engine is rated to produce 265 hp at 4,250 rpm and 405 lb-ft of torque at 2,750
rpm, as compared to 245 hp and 400 lb-ft at 2,200 rpm for the 7.5-liter V-8 in RV chassis
applications. Multi-point fuel injection regulated by Ford's fifth-generation Electronic
Engine Control (EEC-V) system provides efficient, clean-burning use of the fuel.
Although it displaces 6.8 liters, somewhat smaller than the old 7.5-liter V-8, an
efficient new design that includes overhead cams, a serpentine accessory drive belt and
other state-of-the-art features give the engine the guts to do the job. Ford developed a
V-10 instead of a new, larger V-8 because it allowed the company to make use of many
existing Triton V-8 components, thus, the "modular" engine concept. The V-10
shares 58 percent of its parts with the V-8 engines in the Triton family.
A fail-safe cooling system is part of each Triton V-10.
In the event of a cooling-system failure, the engine runs on alternating sets of cylinders
to allow one set to cool off before switching back to it. If the temperature reaches a
critical level, the engine shuts down to prevent costly damage.
A new instrument panel with redesigned controls, a new bumper and grille, a
new engine cover and stronger floor assembly are among the other changes made to the
E-Super Duty chassis for '97.
During a recent Ford media event to introduce the V-10, we had an opportunity
to take a 270-mile test drive through the country around Nashville, Tennessee, behind the
wheel of a Fleetwood Tioga Class C powered by the V-10 engine and fitted with a 4.63:1
axle ratio. The motorhome weighed 12,470 pounds with full fuel, but no water or propane
aboard, and the chassis was rated 14,050 pounds gross vehicle weight rating (gvwr). One
feature of the V-10 that stands out is its quiet, smooth-running performance. The engine
vibration and noise transmitted to the driver's area are minimal, coming through as no
more than a low murmur. Kicked in the pants with the pedal to the floor, the Triton V-10
simply purrs a bit louder than normal. A Ford engineering spokesman explained that the
V-10 has sequential cylinder ignition, a feature that helps smooth its operation. A
balance shaft in the left cylinder head likewise aids in damping vibrations. The chassis'
sound-deadening insulation package has been improved to further quiet the passenger
compartment. Although quieter than its 7.5-liter predecessor, the V-10 still rumbles
enough to let the driver know a powerful engine is at work.
Like the other Triton engines, the V-10 is a
high-revving son of a gun. It incorporates a fuel-cutoff device that engages at 5,150 rpm
in first or second gear, and 4,800 rpm in third or overdrive gear. This device slowly
reduces the fuel to the engine, which in effect prevents the operator from over-revving it
during hard acceleration or hill climbs.
We topped a 5 percent grade at 53 mph in third gear,
with some throttle to spare, and a 6 percent hill slowed us to 48 mph in second gear, once
again with some extra gas-pedal travel left over. In both examples, the road was too curvy
and the traffic was too busy to drive any faster with safety. Due to the nature of the
roads, we didn't start up these hills at 55 mph or better highway speeds. Each was
approached at about 45 mph, and our top speeds were recorded after accelerating up the
Throughout the drive, the engine felt as though it was
easily, if not effortlessly, packing the coach down the road. Some motorhome engines
always appear to be working hard to maintain headway, but the V-10 made short work of the
task and seemed to be loafing along with the sizable Class C load. The engine and coach
were well-matched for power and weight.
Our overall fuel economy came in at 8.1 mpg, somewhat
better than the average we've seen from the old 7.5-liter V-8, over the 270-mile route
that included hills, some freeway and a batch of stop-start driving. Ford claims the V-10
can deliver from 13 to 25 percent improved fuel economy, as compared to the 7.5 in similar
We were impressed with the new V-10's performance. It
toted the load with ease and has the potential for improved fuel-economy figures, which,
while moderate at best, can add up in the long run.
We topped a 5 percent grade at 53 mph in third gear,
with some throttle to spare.