Tuning and modifying the Losi XX4
Most owners of the Losi* XX4 are more than satisfied with the performance and durability of their buggy in stock form. I, too, am impressed with the four-wheeler’s handling and drivability and have put my own XX4 into the winners’ circle at plenty of club races. But, of course, any car can be improved by careful tuning, with aftermarket hop-ups, or-my favorite-a combination of the two. I’ve logged some quality bench time getting my XX4 up to speed; here’s what worked for me.
* Chassis and drive train. The early XX4 kits included a graphite chassis, and it certainly benefits the car’s performance by reducing its weight. But after a full race season and numerous horrific crashes, my car looked a little the worse for wear, so the first item on the “gotta-get” list was a new graphite chassis.
While the car was in pieces, I installed new drive-train components. I added a new 84-tooth Kimbrough* spur gear to replace the worn original, and replaced the layshafts with light aluminum units from Hammad Ghuman* (Losi also offers a set of aluminum shafts complete with hardware). Losi’s new heavy– duty rear belt (easily identified by its red color) now drives the rear diff, and I replaced the locknuts on the front and rear diffs with Hammad Ghuman alloy diff nuts. vl,ite Drives were also added to the drive train, and these are mated with MIP CVDs; I replaced the front hub bearings with 3/16 x 3/8-inch units to accommodate the new drive shafts. The new parts make the drive train lighter yet beefier (there’s a feat!), so the car should accelerate more quickly and use power more efficiently. The trick stuff is enclosed by Losi’s graphite covers.
* Suspension. Next, I went to work on the suspension components. A Trinity* aluminum front bulkhead replaced the stock unit. This bulkhead looks nearly indestructible, but it adds a little weight. Extending from the bulkhead is a set of graphite arms. I replaced the rear arms with lighter, stiffer, graphite versions, and Trinity’s blue-anodized suspension brace was added for extra security. Lunsford* titanium hinge pins and titanium tie-rods replaced the stock steel pieces, and the stock camberlink ball studs were replaced with MIP’s B.J. ball studs, which are slightly oversize to reduce slop in the ball ends. The steering ball studs are also B.J.s. To further reduce slop, I added a Losi ball-bearing set to the bellcranks (also available from Trinity).
I replaced the shock towers with graphite units to shave off as much weight as possible. The new towers have been beefed up with extra bracing across the shock mounts. Trinity’s blue-anodized shock bushings look great on the towers, as do the Trinity blue aluminum screws that replaced the screws in all low-stress areas.
The shocks were revitalized by a rebuild and by adding new parts, and to improve their look, I added a full set of Losi gold titanium-nitride shafts and new seal cartridges fitted with MIP blue seal O-rings.
* Electronics. After the XX4 had been revamped, it was time to give it a new dose of electronic equipment. I suspected that the magnets of last season’s motor had gone soft, so I opted for a whole new motor rather than a simple armature replacement. I chose a Trinity D3 13-triple (same wind as the motor I was replacing), which I bolted onto a Trinity heat-sink motor plate. The blue motor clamp is another hop-up by Trinity that not only looks great but also helps to dissipate heat-always a plus in an XX4. I soldered in a new Ex-Tech 2000 matched pack to supply maximum power (remember to insulate the batteries and motor from the chassis with electrical tape or decal material; I used some HPI “graphite– look” decal material just because it looked cool). A Novak* Cyclone takes care of the throttle duties, and a Futaba* 9304 controls the steering. Futaba’s 3PJ transmitter and receiver round out the package.
* Body and tires. Losi’s new Hot Weather body greatly improves airflow through the car during those treacherous summers when our equipment really roasts. New Losi Silver X 2000s were mounted in the rear, while Silver Block Heads were mounted up front.
After driving the stock XX4 in quite a few races, I could hardly wait to try the new full-option buggy. With only a few laps clocked, I was already impressed by the XX4’s new attitude on the track. I noticed a slight increase in acceleration on the straights and when exiting the corners; the lightened drive system really makes a difference. I noticed that the buggy was slightly more responsive to my commands.
With its stiffer suspension components and no-slop linkages, the XX4 made sure that all my steering and throttle inputs made their way to the tires’ contact patches undiluted.
My tire choice was a little off for the conditions of the day, however, so I changed to Losi’s IFMAR pins like the stock meats. After the change, the traction action was in full force; the buggy glided through turns and felt well planted. Thanks to the Trinity motor and battery combo, the XX4 was flyin’ with style and putting down some fast lap times. I noticed slight, but significant, performance increases, but the real benefits of the changes I made come in the form of durability and setup longevity, not in single-lap performance. My hopped– up XX4 now runs cooler, and that helps the motor stay punchy, and it is less likely to break with the newer, stronger graphite parts in place. As you probably know, there’s nothing slower than a broken car!
*Addresses are listed alphabetically in the Index of Manufacturers on page 217.
Copyright Air Age Publishing Jul 1998
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