HPI Super Nitro RS4 RTR

Radio Control Car Action, Aug 2002 by Onorato, Paul

HPI HAS MAINTAINED A STABLE OF READY-TO-RUN KITS since offering the Nitro RS4 RTR, but the company's "super"-size cars have been strictly kits-at least, until now. In ready-to-run mode. the Super Nitro RS4's 3-belt-drive chassis arrives factory assembled with only a couple of steps required to get it rolling, and you have a choice of a Porsche 911 or a Dodge Viper GTS-R shell.

The Super RS4's larger size improves stability and gives it eye-catching good looks. It's basically a larger version of the Nitro RS4, with which it shares many of its chassis components and hop-up parts. It includes HPI's updated Nitro Star .15FE engine and the highquality. "made by Airtronics" TX-2 radio system.

KIT FEATURES

CHASSIS. The chassis plate is 2.5mm-thick, purple-anodized aluminum, and all of the screws on the underside are countersunk. Large openings in the plate reduce weight, allow debris to fall clear of the drive belts and allow access to the flywheel if a non-pull-start engine is installed. Extra engine-mounting holes make a powerplant upgrade possible.

The upper deck has a modular design and is constructed of thick plastic. A well-thought-out feature is the radio tray that accommodates the electronics; it's removable, so after-run cleaning is a cinch. In the middle of the chassis is a handy little carrying handle, and on the front is a massive, plastic bumper that helps protect the front end from the inevitable collisions.

DRIVE TRAIN. The 3-belt drive train provides full-time 4WD. I had hoped that HPI would follow the standard it set with its newly released RTR 3 and use shaft-drive instead of debris-catching belts. Who knows? Maybe a Super Nitro shaft drive is on the horizon. Adjustable belt tensioners ride on all three belts, and 22 metal-shielded ball bearings keep the rotating parts of the drive train spinning freely. A single-speed transmission with a 13-tooth clutch bell and 44-tooth spur gear sits at the heart of the drive train.

The spur gear is mounted on a layshaft with a drive belt on either side; one belt spins the rear differential, and the other leads to a second layshaft that drives the front end. A robust, plastic gear brace keeps this setup property aligned and protected. The front and rear sealed, metal, bevel-gear differentials have steel dogbones that transfer the power out to the axles, and a thick, plastic-composite disc brake with metal pads brings the RS4 RTR to a halt.

SUSPENSION AND STEERING. HPI hit the mark when it designed a sturdy, adjustable suspension system for the RS4 RTR. Sturdy lower A-arms capture the caster blocks, and adjustable upper A-arms round out the solid assembly. The front caster blocks are set with lo degrees of caster, and turnbuckles are speed for easy toe and camber adjustments. An included turnbuckle wrench makes these adjustments a breeze. The camber links and shocks can also be repositioned for further suspension tweaking. A twin-bellcrank system with a piano-wire drag link and a servo-saver on the servo instead of on a bellcrank gets the front wheels pointed in the right direction.

The factory-assembled, plastic-body, oil-filled shocks with silver-- anodized caps have dual 0-ring seals in the bottom to prevent the oil from escaping, and they absorb rough terrain very well. The shocks have been updated with a coarser thread and a cap design to help prevent cross-- threading when you reassemble them. On the outside, a stiff, black spring is speed with an assortment of preload spacers included for fine tuning.

ENGINE AND ACCESSORIES. HPI's Nitro Star 15FE has been revamped to improve its acceleration, power and durability. This pull-start powerplant no longer comes with the cast head; instead, it has a sweet-looking, purple-anodized heat-sink head for better cooling. It also features ABN construction (aluminum piston, nickel-plated brass sleeve), a rotary carburetor with a single high-end needle valve and a side exhaust.

A small, oiled-foam air filter cleans the air for the carb and stays in place without a zip-tie. Exhaust travels through a cast-aluminum canister muffler with plastic tubing that directs it out at the rear of the chassis. The 75cc fuel tank has a built-in primer.

Before I tested the Super Nitro, I replaced the stock exhaust tube with a longer one. The stock tube exits just above the rear diff and stops about an inch from the chassis; this causes the exhaust to be sprayed inside the body. I installed a 5-inch-long tube that exits behind the body.

BODY, WHEELS AND TIRES. The RTR comes with the choice of a Porsche 911 or Dodge Viper GTS-R body. The wheelbase can be extended from 280mm to 300mm simply by turning over the rear lower A-arms. This means that any of HPI's "Super-Size" bodies will fit, and so will the big bodies from Tamiya and Kyosho.

My kit arrived with the great-looking 911 body that comes with the choice of a production-style wing or race wing. Like most of HPI's bodies, it has protective overspray film, window masks, marked mounting-hole locations and a large decal sheet. The hot paint job on my 911 was laid down by Bill Zegers.