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by Jeff Hain

Factory Pipe 720XP with ECWI

Piezoelectric pressure sensors! Depac data acquisition recorder! Schenck eddie current dynamometer! Oscilloscope! Piezoresistive pressure sensors! DAT highspeed data recorder!  And you thought that this was going to be a test on an aftermarket watercraft exhaust system. No need to worry, because it is. When we went to Ukiah, California, in early  February to test Factory Pipe Products' XP 720  exhaust system, we too were in doubt. Were we to test a watercraft pipe or a component for the space shuttle? See, upon our arrival at the company  headquarters, owner Ross Liberty took us to a room at the very back of his building that was filled with all of the equipment we just listed. This room, which I'll refer to as Liberty's lab, is were he and his crew of technoids research and develop two stroke exhaust systems for personal watercraft.

Due to the cold and rainy weather that was present on our first day in  Ukiah, we all decided that it would be wise to stay inside and do the dyno testing portion of our test (little did we know at the time that Liberty would keep us locked in the dyno chamber until 2:30 in the morning). For this test we would use a stock 720cc Rotax engine equipped with the OE exhaust system, and then with the Factory Pipe XP 720 system. Our first dyno test would be performed with the  stock exhaust system in place. Upon our checking over the engine setup (which included checking the compression, 145 psi in the front cylinder and 148 psi in the rear; and the jetting, 67.5 low speed  jets, 137.5 main jets) with Factory Pipe technician Steve Sublet, Liberty fired the motor.

After warming the engine to operating temperature,  Liberty reluctantly turned the controls of the dyno over to PWI Associate Jeff Hain (knowing well of Hain's nickname Clamp It). Hain performed numerous runs, establishing repeatability after two or three. SeaDoo  claims the horsepower of a stock '95  model XP to be 85, and to our surprise their claim is true. Though the dyno didn't show that our motor was making 85 horsepower, it did show that it was producing 83.5. Considering the hours Liberty  and his crew have logged on the stock 720 test engine, we're pretty certain that when it was fresh, it did make every bit of 85 horsepower. In addition to its 83 plus horsepower, the stock motor  produced 68.5 ft.lbs. of torque.

With the data of the stock motor recorded, Sublet removed the stock exhaust system and replaced it with the Factory Pipe Products system. Because of the complexity of  the system,  it took every bit of an hour to install, and that was with the motor sitting out in the open on the dyno. We're told that it can take up to four hours to install in the hull if you've never done one before. With the Factory Pipe system in place, we were anxious to see what this little contraption Liberty kept talking about the Electronically Controlled Water Injection (known simply as the ECWI), does. According to Liberty, a slower sonic wave (long pipe) in the expansion chamber gives more torque at low rpm, while a faster sonic wave (short pipe) gives more torque at higher rpm. Liberty  found a way to control the speed of the sonic wave at both low and high rpm, without physically changing the lengths of the expansion chamber, giving the highest torque throughout the powerband. The ECWI injects a spray of water into the exhaust stream starting at 2500 rpm. This spray of water cools the exhaust flow at low rpm, causing the sonic wave to slow down, in turn creating more torque.  This spray of water is injected into the exhaust stream until the engine reaches 5600 rpm. From 5600 rpm up, Liberty has found that a faster sonic wave delivers the best power. To achieve this faster sonic wave, the ECWI is programmed to shut off the water injection at 5600 rpm. This drys  out the pipe, creating a hotter exhaust stream and thereby speeding up the sonic wave. Even though the ECWI  shuts off the water injection stream at 5600 rpm, the expansion chamber is still water cooled at all times by a  bypass hole in the waterjacketed head

Once the system was in place,  Sublet then richened the high speed needle on each carburetor by 1/4 of a turn. As for the low speed needles, he leaned them out to 5/8  of a turn out from their original 13/4 turns out. 

Unlike most aftermarket engine parts that usually work best in conjunction with other aftermarket modifications, Factory Pipe not only claims that their system works best on a totally stock  engine when using 92 octane pump gas, they discourage running any other modifications in conjunction with it including aftermarket flame arrestors. "Because the Rotax 720 is a  fairly high-performance engine from the factory, it is critical that the carburetors be properly tuned when running our exhaust system. We also discourage altering the stock cylinder compression or ignition  timing,"  says Liberty.

With the Factory Pipe system installed and ready to go, Liberty once again fired up the motor. This time however, Liberty would not only bring the engine up to  temperature, he would also establish the curve. Unfortunately, he didn't establish the curve he had hoped for a 100 horsepower peak. Liberty did reach a peak horsepower reading of over 98, some 15 more horsepower than the stock exhaust system produced.  And even though Liberty's goal of 100 horsepower wasn't achieved on this day, Hain was able to squeeze 99 horsepower from the mill when Liberty turned the controls over to him. In addition to the increase in horsepower,  the torque of the engine also increased from 68.5 ft.lbs. with the stock exhaust system to 80 ft.lbs. with the Factory Pipe system.

During the dyno testing, we were curious to see how the Factory Pipe system would perform without the E.C.W.I, so we disconnected it. With the ECWI disconnected, the peak horsepower  remained the same. However, the horsepower through the midrange of the powerband was lower. The torque of the engine was not only lower with the ECWI disconnected, it also peaked much later in the  powerband.

After spending more than 12 hours locked inside the dyno room OOPS, I mean Liberty's lab, on day one of our test, we were more than ready to hit the water no matter what the conditions were. So just how was the weather on day two? Let's just say that luckily for Associate Editor Hain, Slippery When Wet's Mark Phares  had supplied him with a brand new Subzero  drysuit and an Insulator jacket the day before we headed for Ukiah. For the first part of the on-water testing, which would just happen to take place at a private lake right in the middle of  California's wine country, Hain would pilot the box stock XP 720 for the acceleration and topped tests. With a slight head wind, Hain recorded numerous runs aboard the stock craft with an average top  speed of just over 52 mph. Acceleration from 0 to 20 mph took 1.69 seconds, while acceleration from 20 to 23 mph came in 1.62 seconds. From 35 mph to its top speed of 52.32 mph, the XP took 7.44 seconds, resulting in a zero to 52.32mph acceleration time of 10.75 seconds.

Once finished with the acceleration and speed testing, Hain took the stock boat through a water ski slalom course that was  set up on the lake. After numerous runs through the course, in addition to some play riding, it was time to install the Factory Pipe system. Because the Factory Pipe ECWI system uses an aftermarket rev  limiter for activation, the electrical box must be pulled out and opened for this. So he wouldn't be forced to do this work at the lake, Factory Pipe tech Steve Sublet had installed it before we hit the water. So yes, the aftermarket rev limiter, which is manufactured for Factory Pipe by Micro Touch Inc., was installed during the speed runs with the stock exhaust system. The Micro  Touch rev limiter has a fixed rev limit of 8000 rpm.

With the wind picking up and showing no sign of letting off, Hain took to the water for the acceleration and top speed testing with the Factory Pipe installed. After making numerous runs at the Stalker radar gun, we averaged the passes. Our results were as follows: The zero to 20 mph acceleration of the Factory Pipe equipped XP was 1.55  seconds, 0.14 seconds faster than that of the stock pipe. From 20 to 35 mph the Factory Pipe boat was just under a half second faster than stock, with an acceleration time of 1.15 seconds, and from 35  mph to its top speed of 56.23 mph (which is nearly 4 mph faster than the stock boat) it took 6.59 seconds.

In addition to performing radar runs on the XP with both the stock exhaust system  and the Factory Pipe system, we also took engine speed readings at wide-open throttle. With the stock exhaust system, the XP turned a maximum rpm of 6820,  while with the Factory Pipe system the mill turned 7260 rpm, for an increase in engine speed of 440 rpm.

Even though we didn't radar the Factory Pipe equipped XP with the ECWI disconnected, we did disconnect it during our riding impression. What we found is what the dyno showed. With the ECWI connected, the midrange pull of the craft was stronger, though not as noticeable as the torque curve makes it look.

Since the  wind had kicked up slightly between the stock pipe radar runs and those with the Factory Pipe (and because there was some talk on the beach as to who could make the boat go the fastest), Factory Pipe's John Richards and Hain would take to the water with the wind at their backs for some final top speed runs before they called it a day. In the end, Hain emerged victorious with a peak speed of 57.8 mph, exactly 0.5 mph faster than Richard's 57.3. For the record, let it be known that Richards was at a slight disadvantage due to his 1 inch thick U.S. Diver's wetsuit that somewhat limited his mobility. As Hain left the dock, we're pretty sure we heard him spout out something to the effect of "Long live the king."

Upon completion of the onwater testing, Hain did his best to grenade the Factory Pipe equipped SeaDoo XP. After numerous runs through the slalom course at wide-open throttle, and continuous bunny hops with the throttle pinned, the Factory Pipe XP  just would not explode as Hain desired.

Gone are the days of burned and broken exhaust couplers. With Liberty's new silicone O-ring coupling design, and his retro, hammertone bronze paint on the chamber body (reminiscent of Grandma's 1949 waffle iron), reliability and corrosion are no longer a concern. With production craft getting better and better all the time, it's no wonder Liberty has to go to these extremes when designing, developing and testing an exhaust system. This time it definitely looks as though his investment in high-tech data acquisition equipment has paid off.

At $729.95, the Factory Pipe XP 720 exhaust system isn't exactly a cheap investment either, but then, what else can you get for $729.95 that offers the performance, as well as the guarantee  of the Factory Pipe SeaDoo exhaust system? Let us know if you come up with anything.


While Personal Watercraft Illustrated believes the preceding test reliable, it is the  opinion of the reviewer only and should not be relied upon on determining the performance or safety of the vehicle. The reader should make his or her own investigation.
reprinted with permission.