Asp rc engine

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CHANGE YOUR VEHICLE'S GEARING. Nitro enthusiasts rarely consider simple gear swaps to alter performance. It's easy to get caught up in a discussion of tuning issues and parts for nitro engines, but altering gearing is by far the cheapest bolt-on mod. Nitro engines have pronounced power bands, and mating your vehicle's gearing with your engine's power band can produce surprising results. For high-revving engines, you can drop a tooth or two on the clutch bell or go up a few teeth on the spur gear to bring the "meaty" part of your engine's power band into the equation. Do the opposite for engines with lots of low-end grunt; go up a tooth or two on the clutch bell, or drop down on the spur gear to get plenty of acceleration and still attain high top speeds.

It's equally important to consider what you plan to do with your vehicle when you alter its gearing. If you're not worried about low-end punch but are looking to drag race with a friend across a large parking lot, you'll get the most bang for your buck by going up several teeth on the clutch bell or going down a few teeth on the spur gear; you'll see a marked increase in top speed if you don't mind sacrificing some off-theline acceleration. Undergeared engines reach maximum rpm quickly; just keep in mind that you might break a connecting rod or a crankshaft when an undergeared engine is spun at maximum rpm for an extended time. Altering your gearing can solve those problems.

Similarly, if you want to race on a short track with tight curves and do not need excessive top speed, you can drop down a tooth or two on the clutch bell for more low-end punch. To check out how various gear combinations affect vour vehicle's drive-train ratio. check out our online gearing calculator at radiocontrolzone .com/cars/ calculator/asp.

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INSTALL A TUNED PIPE, AND TUNE THE HEADER. Yet another affordable, highly effective bolt-on modification is a tuned pipe. Ready-to-run vehicles and most box-stock nitro vehicles include either a cast expansion muffler or a very basic exhaust pipe. Though these exhaust systems do reduce engine noise by stifling the production of exhaust gases, they rarely do anything to increase an engine power. Tuned pipes are engineered to work in concert with a 2-stroke engine's power band and to allow the engine to make power more efficiently. Tuned pipes are available for nearly every RC model; check your vehicle's option parts list, or check out aftermarket tuned-pipe manufacturers such as Trinity, Novarossi, O.S. Engines and MIP for models to fit your particular vehicle and engine combination.

Altering the length of your engine's exhaust header/manifold can also increase performance. Alter the distance between the header and pipe by pushing them closer together inside the coupler. Longer headers make good bottom-end power, while shorter headers produce better top-end power. If the header and pipe touch when you shorten the distance between them, cut 1/8 inch off the header using a rotary tool. Time your vehicle's performance with a stopwatch over a measured distance, and run the vehicle between each cut. Stop cutting the manifold when the engine performance has stopped improving or when you're happy with its performance.

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INSTALL AN ADJUSTABLE PERFORMANCE CLUTCH.

Racers in every racing class agree that your vehicle's clutch drastically affects overall vehicle performance. Clutches harness the engine's power and transfer it to the drive train, so no matter how powerful your engine is, it will still feel soft without a performance clutch. Bolting on an aftermarket clutch is simple, and tuning it for maximum performance is equally easy.

Tenth-scale nitro touring cars and stadium trucks typically come packaged with a durable but conservative clutch system. MIP's circular "4-in-l" clutch and OFNA's 3-shoe clutch are both offered for most 1/10 vehicles, and both types may be tuned for maximum performance with a few simple steps. Eighth-scale buggies and trucks are also supported with aftermarket performance clutches; Fioroni's sliding clutch system, MIPs circular performance clutch and Trinity's K-Factory performance clutch all increase overall buggy performance.

Tuning a new clutch is as important as buying one in the first place. With the new clutch installed, mark a distance of approximately 50 to 75 feet, and test your acceleration there. From a standing start, nail the gas. For rapid off-the-line acceleration, tune the clutch shoes for a slightly higher rpm stall. Tuning the clutch shoes is as simple as cutting 1/8 inch of shoe material off the trailing edge of each one. Run the car after each clutch "tune," and continue to cut 1/8 inch off the shoes until acceleration has stopped improving. Removing too much material can cause the shoes to wear prematurely, however, so stop cutting as soon as you're happy with the acceleration.

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BOLT ON A LARGER COOLING HEAD. High operating temperatures drain horsepower, and to a certain extent, the cooler you can get your engine to run, the more power you can make. Several aftermarket manufacturers offer larger, more efficient cooling heads than the stock ones included with your engine. Dynamite, O'Donnell/DuraTrax and MS) all offer excellent bolt-on cooling heads that can significantly reduce your engine's running temperatures.

As long as the cooling head is designed property and has the correct headbutton clearance for your engine, an aftermarket head can allow you to tun, your engine slightly leaner to extract more power at lower temperatures. Installing a larger cooling head does not allow you to run the engine at exc sively lean needle settings, however. The largest cooling head on the planet won't protect your 2-stroke if you tune it to run excessively lean and excessively hot, but it will allow it to run more efficiently and with slightly more power.

When installing an aftermarket cooling head (if it's a 2-piece head), pay close attention to the head button or the button area. Thin brass shims are placed around the button to insulate the head from the combustion chamber, and they must be installed on your new head to retain the proper head clearance. Without these shims, the engine will overheat and run poorly and might be damaged if the piston hits the head button. Tune an engine with an aftermarket cooling head in the same way as you tune an engine with a stock head: tune the engine for best performance, and check its head temperature. Chances are that with a slightly leaner needle setting, your engine will run slightly stronger at the same or lower operating temperature than it did before the cooling-head swap.

TECH Q & A

I keep having trouble with my T-Maxx; it has a stock TRX .15 with a pull-starter. Every time I try to start it, the one-way bearing slips. I have replaced the bearing several times, and it works well for a while. But if I take the pull-starter and one-way bearing off, clean them and reinstall them. the engine starts easily until it runs out of gas. After I've refilled the tank, I have a hard time starting It. I have been told by my hobby shop that if I drill a small hole in the back of the pull-starter case, that will solve the problem. What do you think?

Willie Selman [email]

Willie, when the bearing is worn and covered with moisture, fuel residue, or castor oil from the exhaust, it will slip. I spoke with the people at Traxxas about this, and to fix it, they recommend that you replace both the one-way bearing and the starter shaft. As you've discovered, replacing only the oneway bearing will not solve the problem because the starter shaft wears as the bearing wears. The starter shaft spins with the crankshaft at the actual engine rpm, so in effect, any contamination inside the starter housing will "polish" the shaft until it's out of round. Your TRX .15's one-way starter bearing will have a long life if you replace the starter shaft when you replace the bearing.