FACTORY PIPE BOLTS OLD PIPE ON NEW BOAT, GETS SERIOUS SPEED
 By Glenn Hansen

This really is recycling at it's best. Kawasaki recycled a popular standup watercraft, turning the 750SX into the 750SXi for the 1995 season. Then Factory Pipe, of Ukiah, California, recycled their 750SX Limited Pipe, and turned the SXi into a serious speedster.

Kawasaki's 750SX standup watercraft has served many  enthusiasts well from its introduction in 1992 to its final production year of 1995. And we know there are thousands still on the water. When the manufacturer introduced the new (read: recycled) 750SXi standup for the 1995 season, we all knew the faithful and true SX's days were numbered.

Resourceful aftermarket parts manufacturers such as Ross Liberty at Factory Pipe, quickly went into their  recycling bins to see what they could reengineer to get more horsepower out of old parts and into a new boat.

The Factory Pipe 750SX/SXi Limited pipe is one of the best examples of recycling to hit  the water.

EVERYTHING IS USEFUL
The best thing about recycling is it assumes that everything has value, from old 750SX exhaust pipes to rainy and cold days in Northern California.

I visited  Factory Pipe last spring to be the first to test the Electronically Controlled Water Injection ((ECWI®) exhaust system the company created for the 720cc Rotax engine in a SeaDoo HX. We tested that boat on a Friday, it performed admirably (see Watercraft World, August 1995), so I had an extra day in wine country.

We opted to evaluate my second choice, Factory Pipe's recycling ability with the 750SX  Limited pipe in a 1995 Kawasaki 750SXi.

THE STOCK CRAFT
The 1995 750SXi developed 75hp, 13 horsepower over the 750SX thanks mainly to twin Keihin 40mm carburetors, compared to the single carb in the 750SX.

No standup before it had produced as much power as the 750SXi. But as powerful as the twin carbureted engine is, the stock exhaust system is designed more to be quiet than it is to draw  every last bit of power from the engine. And for a stock watercraft, noise reduction is of great importance, especially when the boat already runs with 75 horses plenty for many riders on the 329 pound boat. (Kawasaki engineers should be commended for the work they've done to lower exhaust noise emitted from their new watercraft. Noise quelling water jackets around the exhaust pipes, and rubber covered exhaust outlets are just two of the techniques that the manufacturer has used to near perfection to help keep our fun quiet.)

But for those enthusiastic 750SXi owners and productive aftermarket performance shops, Kawasaki did leave a lot of room for horsepower gains in the SXi's engine.

FACTORY PIPE AS RECYCLER
Factory Pipe built the 750SX exhaust system in 1994, and the pipe was quickly recognized as a  must have for 750 owners. The stock 750SX developed 63 horsepower (59 HP tested by Factory Pipe in the company's dyno lab). With the 750SX limited pipe, the engine produced  78 horsepower, as measured in the lab again.

On the water, which is what we riders really care about, the slightly modified 750SX gained substantial top end and midrange power.

Like the stock 750SXi, the stock 750SX was equipped with an exhaust system designed more for a quiet ride than a high-powered ride. Again we commend Kawasaki, and other manufacturers for designing quiet exhaust  systems, and leaving the extra power for the aftermarket manufacturers.

But before you think that the pipes created by Liberty and Factory Pipe are real screamers, understand that they are engineered to keep your watercraft within the rules written for racing events sanctioned the the International Jet Sports Association, which limits the noise level emitted from a watercraft to 86db (measured from 50 feet away). Most states have similar regulations regarding the noise level of a watercraft. The legal limit for noise is 82dB in Minnesota, California, and most other states. Check your state's boating laws to know for sure.

To keep the sound down further, and to best take advantage of exhaust performance theory, the Factory Pipe 750SX/SXi Limited pipe uses a "center bleed" design. The exhaust gas exits the pipe in the center of the expansion chamber, not at the end. "With this pipe, the sound wave is not as strong in the middle of the pipe as at the end," says  Liberty. This centerbleed design lets the sound wave build the best performance while keeping the noise to a minimum.

The 750SX was a popular watercraft for enthusiasts as well as aftermarket parts builders. Nearly every company in the pipe business had an exhaust system for this craft. Though it would be nearly impossible to determine which pipe worked best for the 750SX from 1992  to 1995,  we do know that the Factory Pipe 750SX Limited system was a popular choice for racers and was named Aftermarket Product of The Year for 1994 by another magazine. Ross Liberty claims that the 750SX Limited  pipe is "one the best performing pipes we've ever made."

Pipe builders at Factory Pipe created some 300 test pipes before they reached a consensus on the final design for this system.  Because Factory Pipe fabricates exhaust systems by hand, rather than pouring them into a foundry mold, the company can make design changes quickly during the research and development of an exhaust pipe.

What Factory Pipe builders came up with from all that effort is a pipe for the 750SX standup that produced significant gains for the craft. In tests performed separately form the builder's own tests, the 750SX Limited pipe added 700 rpm to the engine,  and pushed it five to six mph faster than the stock craft.

REUSE, RETEST, REAP REWARDS
Kawasaki introduced the 750SXi for the 1995 season, and parts makers everywhere wished their 750SX parts would work. "We  had hopes that the 750SXi would work well with our 750SX Limited pipe," says Ross Liberty, "but we had no expectations."

Sure, the 750SX and SXi watercraft use the same 743cc Kawasaki engine. But that base engine is also in several models, including the STS, the 750ZXi, and the SS model runabouts. These engines are the same, but different.

To get more horsepower, the SXi uses twin 40mm carbs, connected to a revised intake manifold that uses a balance tube to equalize the carbs' efforts for more low end response. For better top speed, the cylinder porting has been changed, without raising the compression. And to handle all this new power, most engine parts were beefed up for  durability.

To make this recycled pipe fit the 750SXi, Factory Pipe merely revised the cylinder mounting bracket to hold the choke and throttle cable, redesigned the stinger for more motor mount clearance, and updated the new pipe's tuning specs.

Yes, The SXi pipe is also tunable like the 750SX pipe before it and that is perhaps the part's greatest feature. To tune this pipe,  the user  injects water into different sections of the pipe to change the exhaust gas temperature, and as such the performance.

Your craft's exhaust system does much more than simply dispel burned gas from the  engine.  It also controls the engines power.

Sound waves move back and forth through the exhaust system. When the cylinders' exhaust ports open, a sound wave carries burned gas from the engine. This not only moves out burned gas, but helps create the correct pressure inside the cylinder to allow the fresh gas/air mix in. Just before the exhaust ports close, a sound wave comes back from the tail cone of the pipe, helping the fresh gas mix stay in the cylinder. A problem arises because when the rpm changes, the port timing changes. But at a constant temperature inside the pipe, the speed the  sound waves travel does not change; the waves and The exhaust ports are no longer working together.

Some pipe manufacturers will have you correct this problem by changing the length of the pipe to  set the exact exhaust timing you desire for a certain rpm. You change the length by cutting the pipe at either the head or the tail cone, as advised by the pipe builder.

With Factory Pipe's tunable  system, you change the temperature inside the pipe by injecting water at different intervals.  By changing the temperature of the exhaust gas inside the pipe, you change the speed at which the sound waves travel, effectively changing the length of the pipe. However, you can tune a Factory Pipe system as often as you like with just the turn of a screw, no pipe cutting required. Water is injected  through small holes that are controlled by small hex head (Allen) screws. With this system, you can change the performance of your pipe for cold water or warm water riding. Or you can get low end  power one day, then top speed power the next day or even the same day.

TEST RESULTS
We ran our 1995 750SXi in Lake Mendocino in Northern California.  The day started out rainy and cold perfect weather for testing wine making techniques in the Russian River Valley of this grape region. Then it turned just rainy. But we skipped the wine tasting and chose to simply test the pipe.

Now that we  have touched on the history of the pipe, and tunable pipe theory, there is little left but the results. And they are good.

We tested the stock boat, using a Stalker Acceleration Testing System and  radar gun on an undisturbed section of the lake. Taking the average of four top speed runs and four acceleration runs, we recorded an average speed of 49.85 mph. From the acceleration runs, we recorded a 0 to 40mph  time of 3.84 seconds.

For a stock craft, the acceleration runs were acceptable, but left room for improvement. The top speed of near 50 is impressive. Many riders are happy with less, and  may not even be able to handle 50. But we wanted more.

The installation of the new pipe is simple, especially on an otherwise stock craft. Factory Pipe recommends the use of K&N flame arrestors  and different carburetor jets with this exhaust setup. (We know owners who have used Ocean Pro Vortex filters with equally good results.)

We ran the 750SXi with Factory Pipe installed in equally calm  water. Our top speed runs were thrilling, with an average speed of 55.2 mph recorded. On a 329 pound hull that is just 28 inches wide, this feels very fast. And you get there fast, too. We clocked four  acceleration runs 0 to 40 mph for an average time of 3.13 seconds.

For most standups (and though only two new models are available, there are still many models on the water) getting to 50 mph is a dream. This lightly modified 750SXi gets there in just six seconds.

Since we always try to perform these tests in near perfect conditions, your results may vary. But we're certain that no matter where you ride, the improved power offered by the 750SX/SXi Limited pipe will give your craft much stronger pull out of corners, as well as the thrilling top speeds we reached on the water.

reprinted with permission