This month's article continues SportQuad.com's series of articles on upgrading the performance of your typical Asian-made youth ATV. Last month we discussed how to get more air in (intake modifications), and this month SportQuad.com delves into how to get the air out, and takes a close look at three top pipes available for today's mini 50s and 90s. This stage is the most exciting since no other component added to your two-cycle engine can affect the power curve more significantly than a tuned exhaust. Fact of the matter is, the stock steel exhaust is simply not designed for performance. Good news is that many companies specializing in youth-ATV performance such as WRH Racing, Hetrick Racing, Tomco Enterprises have recognized this need and have each developed tuned pipes to fit Alphasports, Kasea, Polaris, DRR, T-rex, Dinli, Eton, etc. Some are intricate multi-segment hand-fabricated weldments, while others are die-formed pieces that look like they were production tooled.
To begin, it's probably necessary to understand a little about two-cycle exhaust pipes. Channeling the spent exhaust gases out of the cylinder is far from the only duty of the exhaust pipe. Rather, its more significant role is to assist, or scavenge, fresh fuel mixture into the cylinder as the exhaust is being drawn out. This thermodynamic mechanism is quite complex, and the physical shape of the pipe, expansion chamber, and stinger all contribute to how effective the pipe is at this task. Changing these characteristics dramatically controls how the pipe scavenges at low speed versus high speed, and therefore has quite an effect on the power curve. Since most pipes take advantage of the relationship between power and rpm, a performance pipe will generally make its peak power at a higher speed than stock. For this reason clutch adjustment/tuning is critical- you need to match the clutch to this new power peak. More on this later. For this stage of upgrade we tested three systems: Hetrick Racing's, WRH Racing's, and Tomco's EX pipe. While the first two are multi-piece hand-made TIG-welded pipes, the Tomco pipe looks like a mass-produced piece. The Hetrick pipe is available unpainted as well as chrome, but shown with Jet-Hot coating.
Right off, the weight difference between the stock and aftermarket is quite noticeable- each one about 3.5 pounds lighter (nearly 50%). The systems were installed on an AlphaSports 50 by first bolting the short header section to the cylinder and then snaking the rest of the exhaust in from the back side. The sections are held together with springs to allow for flexibility, and the rear silencer section is bolted to the frame. Note however that the Hetrick pipe will not fit an Alpha without significant modification of the battery box (as in removal). As mentioned, key to a new high-performance exhaust installation is proper adjustment of the clutch so as to optimally extract the most performance from the pipe. This can easily become the most time consuming aspect of machine modification and will be dealt with in-depth in a later installment, however most of the pipe suppliers have already done the homework for you and supply a clutch kit with their pipes. For our installation, the clutching was modified for each pipe according to each supplier's recommendations.
To add some objective results to our assessment, the Alpha was dropped on a chassis dyno and several full-throttle pulls were made (of which the average was used for comparison). As can be seen from the dyno plots, there's clearly more power from start to top-speed than stock. Both Hetrick and WRH pipes performed nearly equally, with excellent low end and a top end that pulls much past the stocker. Either of these pipes would make excellent choices for dune, trail, or MX. The Tomco EX pipe is a bird of a different color, with fairly poor low-speed power, but very impressive top end (9000rpm peak) power, easily outpowering the other two pipes at high speed. Unfortunately, the clutching modifications that were made could not pull the rpms up to the motor's hi-revving sweet spot. With optimized clutching, it's quite possible that the entire EX curve could be shifted above and beyond the others. If your rider happens to be into sand-drags or TT racing, this is probably the pipe for you. By all rights, a grown adult should not be expected to get excited by the sound of a 50cc "toy" engine, but WOW the installation of a performance pipe turned this meek mild-mannered mini into a raspy, race-ready zinger. The wide-eyed expression from our 7-year old test rider was ample confirmation that there's definitely some bite behind the raucous. Throttle response was improved, and the pull from start to top end is impressive. Horsepower per dollar, there are few deals out there with this kind of return on investment. Stay tuned for next month's issue where we'll get into the "black art" of clutch tuning. Comments or questions? -post your thoughts to the Discussion Forum
Where to get your parts- Hetrick Racing, in PA, 814-676-0477 Follow us on Twitter at www.twitter.com/OffRoadDotCom
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