The New Generation
Ford and GM boost weight ratings for
freshly Engineered gasoline-powered
motorhome chassis


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 overloading.

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 the details.

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 @ 2,650 RPM
  • 1998 7.5-L V-8: 245 HP @ 4,000 RPM, 400 1,B-FT @ 2,200 Rpm

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 department.

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.

DESIGN IMPACT

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 required.

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


FORD V-10

New Triton 6.8L engine replaces the 7.5L V-8 in Class C chassis
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. 98fv10.jpg (11033 bytes)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 hills.
   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 operating situations.
   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.