OFNA Ultra MBX-R2

Radio Control Car Action, Jul 2001 by Vieira, Peter

The OFNA Ultra MBX-R2 is the latest addition to the Ultra series, which was last updated with the Ultra Worlds II model. The R2 is billed its a "medium-upscale" kit and combines some of OFNA's most requested features with an affordable price (for 1/8 scale) that will undoubtedly appeal to budget-minded racers-although the R2 is hardly an "entrylevel" kit in terms of its standard equipment. OFNA's David Morales summed up his goal with the R2 quite succinctly: "I did this to get peopie into eighth scale." If getting into 1/8 scale is your goal this season, the R2 deserves a look; here's how it ran for me.

DATA CENTER

VEHICLE TYPE 1/8-scale 4WD nitro buggy

BEST BUYER Experienced nitro enthusiasts, budget-minded racers

KIT RATINGS (poor, satisfactory, good, very good, excellent)

Instructions Not supplied with test car

Parts fit and finish Good

Durability Good

Overall performance Very good

SPECIFICATIONS

MANUFACTURER OFNA

MODEL Ultra MBX-R2

SCALE 1/8

STREET PRICE $259 w/o engine, radio

DIMENSIONS

Wheelbase 12.5 in. (318mm)

Width 11.8 in. (300mm)

WEIGHT

Total, as teed 124 oz. (3,515g)

CHASSIS

Type 3mm with plate upper braces

Material 6061 aluminum

DRIVE TRAIN

Type Shaft-driven 4WD

Primary Clutch bell/spur gear

Drive drafts (F/R) CVA

universal/dogbone

Differentials Bevel gear

Bearing type Rubber-sealed ball bearings

SUSPENSION

Type (F/R) Double wishbone pivot ball/H-arm pivot ball with camber link

Damping Aluminum fluid-damped shocks

WHEELS

Type OFNA lugged tread with 5-spoke

TIRES

Type OFNA lugged tread with foam insert

ENGINE AND ACCESSORIES

Engine Not included

Air filter Foam element

Fuel capacity 125cc

Manifold OFNA round port

Pipe OFNA tuned aluminum pipe

LIKES

Good-looking blue anodizing.

Precisely adjustable suspension.

Reusable nylon case.

Race-worthy performance.

DISLIKES

Rear wing broke easily.

No chassis kickup.

Accessing receiver requires tools.

Receiver pack is left exposed.

building & setup tips

OFNA plans to offer the R2 as a rolling chassis with a clear body, minus engine and radio. A nylon carrying case serves as the box and comes in handy for carrying your gear later. When you unzip the box, you'll find the R2 mostly assembled; the shocks are built and filled but must be installed. Likewise, the glued tires and rims have to be buttoned down and the wing mounted. You're looking at 10 minutes tops, plenty of time for the real work-engine and radio installation. Here are some tips to consider:

Engine installation. Make sure you install the engine mounts on the engine first; if you put them on the chassis and then try to drop the engine onto the mounts, you'll never get the mounting screws to catch the captured nuts. Once you have the engine bolted in and the gear mesh set, remove the engine-mounting bolts one at a time and apply thread-lock to each.

Radio installation. First, get the right gear. Go with an FM radio system If you can, as you'll be less likely to encounter glitching troubles. You should also install a high-torque steering servo. A "standard" servo will work well enough for you to play with the R2, but you won't have precise steering control, and you'll probably break the servo before too long. And finally, if your servos have wimpy, flexible horns, replace them with stiffer units from OFNA or GS Racing. This is especially important for the steering servo.

Thread-lock the shock nuts. If you've read even just one issue of RC Car Action, you probably know to add threadlock to all screws that thread into metal, especially the engine-mounting bolts and the various radio-tray screws. But you probably wouldn't thread-lock the shockmounting nuts (neither would I, since they almost always have nylon inserts to prevent loosening). But in the case of the MBX-R2, the nylon's grip was pretty feeble, and I headed into the pits with an unhooked shock and a missing mounting nut on a few occasions.

Swaybar setup. The Ultra MBX-R2 includes front and rear swaybars, which can be a help or a hindrance, depending on your track. Before you start messing with shock fluids, springs and preload to get the car dialed into your track, first try to disconnect one or both swaybars; if the track is very bumpy, you may not want to run swaybars at all. Swaybars help most on flat, fast, high-- traction surfaces. As always, experimentation is key.

KIT FEATURES

Chassis. The R2 is built on a 3mm, blue-anodized aluminum chassis. All the screw holes are countersunk as are the engine-mounting slots, but the engine mounts' 8mm mounting bolts still protrude from the chassis' underside. The completely flat chassis plate has no stamped-in kickup. That puts the R2 behind the curve when it comes to full-on competition buggy tech, but that won't prevent you from having a lot of fun in the dirt or making a decent showing on the track.

A plate aluminum brace stiffens the R2 by linking the front transmission, steering bellcranks and plastic center diff mount, and an additional brace joins the rear transmission to the radio tray, which is also stamped aluminum. All the alloy parts are blue-- anodized to match the main chassis.