HPI Nitro RS4 3 type SS

THE ALL-NEW, SHAFT-DRIVEN NITRO RS4 3 DEBUTED AS AN RTR (see the June 2002 issue of RC Car Action for the review), but HPI hasn't forgotten us do-it-yourself types. Whether you like to build your own so you know the job was done right, or you plan to make some mods along the way, or you just like to build, you'll be glad to know that you can now assemble a Nitro 3 from the ground up. You'll also be glad to know that the kit car isn't "just" a Nitro RS4 3; it's a "Type SS," which means you get the new Nitro Star 12R SS engine (good for more than lhp, says HPI), a smooth-flowing, round-port manifold, 2-speed transmission and steel turnbuckles-a combination that adds up to more tunability, more power and more speed. Exactly how much more? Well, that's why we test carsCHASSIS. HPI has been building its nitro cars on 2.5mm purple-anodized chassis for a while now, and the SS is the latest. The chassis sides are radiused for extra strength, and the underside is fully countersunk, as expected. An elaborate molded enclosure for the receiver battery with a separate cover for the receiver itself fills the left side of the chassis, and it's also home to the externally mounted steering and throttle servos. The receiver cover is screwed down, but battery access is gained by removing a single body clip. Two more body clips secure the entire radio-tray assembly, and this makes it easy to remove all the electronics without reaching for a single tool.

DRIVE TRAIN. The Type SS shares its essential shaft-drive parts with the RS4 MT and Super Nitro Rally, so you know they're tough. The front and rear gear diffs each house two spider gears, and their cast metal ring gears are spun by chunky bevel pinions with deeply meshing teeth. The front diff has the additional feature of a stiff spring between the spider gears. The spring forces the gears against the outsides of the diff case, which adds resistance to the diffs action and reduces its tendency to "unload" when a wheel breaks traction. Plastic gearboxes surround the diff and pinion gears to prevent any nasty parking-lot stuff from reaching the parts, and steel dogbones join the diffs to the 2-speed transmission in the chassis' center. Steel 'bones are also used to link the stub axles to the drive train, and all of the parts spin on a combination of rubber-seated and metal-shielded ball bearings.

The Type SS's 2-speed transmission shifts centrifugally via a spring-loaded steel drive dog that engages a hardened drive pin. Two drive-dog springs are included to match the transmission's shift-rpm range to the type of engine being used; since the Type SS includes a high-output race engine, the stiffer of the two springs is used. To further tune the transmission's shift point, spring preload is externally adjustable via a setscrew.

Unpadded steel caliper plates squeeze a single plastic brake disc to slow the Type SS. A fiber disc is available as an option, but HPI makes the most of the stock disc by giving it a thick, 4mm cross-section and molding it of very hard plastic.

SUSPENSION/STEERING. The Nitro RS4 3 borrows its suspension parts from the well-proven RS4 2, which means you get a lower H-arm/upper camber link setup. But instead of using non-adjustable plastic camber links (such as those on the RS4 3 RTR), the Type SS includes steel turnbuckle linkages for fast camber adjustments without disassembly. The steering tie rods are also turnbuckles, so toe-in is just as easy to adjust. In addition to changing camber-link length, there are two inboard and two outboard camber-link positions to choose from for the front end, and two inboard and four outboard locations in the rear. Other suspension geometry changes can be made by swapping included parts; the stock steering hub carriers provide io degrees of caster but can be replaced with 8-- degree parts, and the kit's standard rear uprights, which deliver 2 degrees of rear toe, can be swapped for 1-degree versions.

Plastic-body shocks suspend the car and are filled with "no. 300" shock oil, which is equivalent to 30WT silicone fluid. Only one set of shock pistons is provided, but it's doubtful the Type SS's target buyers will miss the tuning option of extra pistons; I didn't. Purple-anodized collars and plastic eyelets cap the bodies, which do not use internal bladders, and progressive-rate springs do the actual shock-absorbing; clip-on spacers are used to set ride height.

ENGINE AND ACCESSORIES. The Type SS gets its name from its engine-the new Nitro Star 12R SS. Thanks to its blacked-out case and purple-anodized heat-sink head with natural-aluminum accents, the engine is a looker, but it's what's inside that counts. Thanks to porting described as "aggressive," HPI claims the 12R SS unloads more than 1hp when its 2-needle, rotary carburetor is opened. The sleeve is special, too; it's coated with nickel-silicon carbide, an extra-hard material that shouldn't be confused with plain nickel. This new coating is harder than chrome, less hazardous to the environment to produce, and very slippery. It's already popular in full-scale racing applications; you can find nickel-silicon-carbide coatings on the pistons of super cars and racing motorcycles. It's serious stuff. The exhaust system is also a critical part of the power package. The Type SS includes the same composite-plastic, dual-chamber tuned pipe as the RTR Nitro 3, but a free-flowing tubular exhaust manifold replaces the RTR's square-cornered, cast header