PERSONAL WATERCRAFT PERFORMANCE MODIFICATION

This literature has been prepared by GROUP K specifically for the purpose of helping customers to make more educated buying choices. It is our hope that the information in this pamphlet helps them to build a machine that appropriately suits their riding skills as well as their budgets.

There is much excitement over the new generation of high output 1995 three cylinder machines. These machines are sure to be at the center of high performance interest ... for a short while anyway. Later parts of this pamphlet will speak to the matters of the triples. However most of this pamphlet will focus on the more popular 2 cylinder boats.

AN OVERVIEW - In the past, the high performance parts and modifications used by most recreational riders have been very similar to the parts and modifications used by most of the competitors in the IJSBA (International Jet Sports Boat Association) National Tour. In past years, the aftermarket high performance shops used their sponsored racers specifically to promote the effectiveness of their modifications for a particular model of watercraft.

Personal watercraft racing was intended to be a fun amateur sport utilizing machines that were easy to afford and easy to maintain. Personal watercraft racing was not intended to be a "professionals only" sport that mandated the construction of very specialized and very expensive non- production machines ... not until 1993.

THE MECHANICAL AND FINANCIAL REALITIES OF RACING - After 1993, the IJSBA competition rules set an across the board engine displacement limit of 785cc for all two cylinder modified classes of racing. The 785cc limit is based on the displacement of a Kawasaki 750 engine that is bored 2.0mm oversize. The result of this rule has been the creation of several very expensive "special purpose" modified class racing engine formats.

While at first this sounds very exciting, the reality is that these machines are questionably safe for anyone but professional racers to operate, and unquestionably too expensive for recreational riders to maintain.

This has caused a very difficult situation for many aftermarket race shops engaged in the business of selling engines to customers for pro level competition. These shops have invested tremendous amounts of time and effort into the development of very high output 785cc twin cylinder engines. In most cases, the shop's original goal is to sell identical versions of these engines to the racing and high performance recreational public.

However after completing the development of these "no holds barred" engines, they realize the questionable wisdom of selling what they have created. The specialty components, modifications, and attention to detail in these engines, assures that the cost of constructing one will be very high. Despite the quality of the workmanship and the very high cost, these engines are virtually intended for self destruction. The intense loads of high output and high rpm will wear out most of the internal moving parts in a few hundred operating minutes ... not a few hundred operating hours. There is no way around this mechanical reality.

Therefore the shop is faced with one of a few choices. A) Sell a very expensive and very powerful engine that wears out expensive moving parts in very short amounts of operating time. B) Sell a slightly "watered down" version of the pure race engine that has a reliability factor that most customers can live with. Unfortunately, these engines still have the same price tag as the original with much less power. C) Tell prospective customers flat out that they can only buy slower versions of the top race engine. The race team engines are not for sale.

Very few shops make choice "A" . Selling expensive engines that fail frequently is just plain bad business. It virtually assures that no customer will be completely happy. It is a product that is destined to result in ill will and a bad reputation. Many shops make choice B. Unfortunately, these customers become angry anyway when they realize that their engine has the "replica" price tag without the "replica" horsepower. Several shops make choice C, however it assures that you will enrage the customer even before he spends any money ... more bad business.

The watercraft manufactures involved in IJSBA competition are all interested in their machines winning a national championship. However most are not interested in having expensive and troublesome, "in-house factory race teams". They prefer to pay an existing race shop, like those mentioned above, to operate and manage the race efforts on their behalf. These manufacturers also understand the a fore mentioned business dilemma of developing expensive and unreliable engines that can't be sold to the public. These manufacturers acknowledge that they will need to pay the race shop the price to develop and maintain such engines. For the manufacturers this is a sweet deal. They, as a boat manufacturer, don't want to be accused of racing with special engines that can't be bought ... they won't. Furthermore they realize what bad business it would be for their selected race shop to sell the fast, unreliable engines to regular customers. The "unavailability" of these unreliable purebred race engines assures that the selected team riders will have to deal with a minimum number of competitive privateer riders on the national tour. This scenario also explains why so many large race shops are fielding top national pro racers ... yet never run ads promoting the sale of identical engines with identical performance numbers.

All this said, it's apparent that most professional class personal watercraft racing equipment is as relevant to the recreational rider as NASCAR equipment is to the average motorist. While information about the construction and components of 60+ mph modified race machines may be amusing for some recreational riders, that information will have little or no relevance to the equipment that most recreational riders use on their own machines.

MODIFIED WATERCRAFT FOR THE COMPETITIVE RECREATIONAL RIDER - There are many racers who want to do occasional recreational riding, and recreational riders who want to occasionally race in a sanctioned (or sometimes unsanctioned) race events. These riders are interested in a reasonably priced machine that is fast enough to beat all their buddies, yet controllable and reliable enough to still be used as a "toy". It has been our experience that 48-51 mph stand ups and 55-59 mph sit-downs fill this bill.

When stepping back from the peak speed and power requirements of a national racing, the construction costs of a competitive machine drop dramatically. Because of the slightly lower power output expectations (compared to the pro mod racer), machines in this category can easily utilize single (or stock dual) carburetors, the stock charging ignition systems, and often the pleasantly quiet stock water box mufflers.

The following is a listing of some reliable and affordable high output engine packages produced by GROUP K, shown with the respective peak speeds, fuel quality, and approximate retail cost of modification (assuming that the engine starts in stock form) :

JS 550 '91-'93 Sleeper 92 unleaded premium 45.8 mph 505.00

JS 550 91-'93 Hammer 92 92 unleaded premium 47.4 mph 1085.00

JS 650 SX Sleeper 92 unleaded premium 45.9 mph 540.00

JS 650 SX Hammer 92 92 unleaded premium 49.6 mph 1185.00

JS 750 SX Sleeper 92 unleaded premium 50.1 mph 499.00

JS 750 SX Hammer 92 92 unleaded premium 52.3mph 1147.00

JS 750 SX Hammer 105 105 leaded or unleaded 54.3 mph 2096.00

JS 750 Xi Sleeper 92 unleaded premium 53.1 mph 580.00

JS 750 Xi Hammer 92 92 unleaded premium 54.8 mph 1640.00

JS 750 Xi Hammer 105 105 leaded or unleaded 56.3 mph 2267.00

JS 750 ZXi Sleeper 92 unleaded premium 56.2 mph 580.00

JS 900 ZXi Sleeper 92 unleaded premium 58.5 mph 1050.00

Yam 633 SJ Sleeper 92 unleaded premium 45.1 mph 499.00

Yam 633 SJ Hammer 92 92 unleaded premium 48.2 mph 1156.00

Yam 685 SJ Hammer 92 92 unleaded premium 51.8 mph 1456.00

Yam701  SJ Sleeper 92 unleaded premium 49.6 mph 499.00

Yam 701 SJ Hammer 92 92 unleaded premium 51.2 mph 1365.00

Yam 701 SJ Hammer 105 105 leaded or unleaded 54.7 mph 1972.00

Yam 701 Wave Raider Sleeper 92 unleaded premium 57.2 mph 680.00

Yam 701 Wave Raider Hammer 92 92 unleaded premium 59.6 mph 1765.00

Yam 1100 Wave Raider Sleeper 92 unleaded premium 63.2 mph 1150.00

The "mph per dollar" numbers speak for themselves. What the numbers don't say is that a JS 550 is the perfect power to weight balance for wave jumping, the 650 Yamaha is the ultimate in reliability, and the 750 Kawasaki's and 701 Wave Raiders (while very fast) are a bit "skittish" at very high speeds.

For any local level modified racer in the novice, expert, or veteran classes ... the above engine kits will be all the speed and power that'll be needed to beat everyone in your class. For nationally competitive expert and local pro racers, a 52-55 mph boat will do the job. The accent should be on building a machine that is what you need ... not a replica of what some top pro racer is supposedly using.

ABOUT THE NEW 3 CYLINDER MACHINES - At Group K, we foresee tremendous popularity (for the meantime) of these machines. Unfortunately we also foresee more expensive engine maintenance for owners of these models (not to mention "attention getting" fuel consumption rates). So much so, that for many recreational owners, the triples might be questionably practical or desirable. The boat manufacturers understand that there will always be a small group of customers for whom "bigger" will always mean "better". The relatively small production runs of these high output flagships is intended to serve the needs of these customers.

For each vehicle design, there eventually comes a point where bigger is no longer better. Examples of this are, American muscle cars of the late '60's, 1200cc cafe style street bikes, and 500cc motocross motorcycles. All these machines have a certain amount of ownership appeal. However, actually owning and operating them on a regular basis becomes questionably fun, and unquestionably expensive. Slightly down sized versions of all these machines have become the accepted "ideal balance" of size, performance, and practicality. We foresee a similar scenario for the new, large displacement triples. In time ... twins will be quicker, better handling, and more financially practical.

Despite all this, there will still be many triple owners who will be seeking additional performance. At Group K, we have developed "SLEEPER" modification kits for these three cylinder machines. However, the primary focus of these kits is to improve acceleration ability, smoothness of power delivery, and fuel mileage... as well as speed.

THE LIMITS OF SAFE RIDING SPEEDS - Since personal watercraft are relatively short marine vehicles their maneuverability and stability can be seriously affected by huge increases in peak water speed. While few current two cylinder personal watercraft are capable of exceeding 48 "actual" mph, nearly all the 650cc and larger vehicles available today are relatively stable at speeds up to 47-48 mph. Recreational riders that have fallen off at 48+ mph know that this is about as much speed as they need for general recreational riding.

At speeds in excess of 48 mph, virtually every watercraft hull, to date, will begin "seeking" and/or "coming around". "Seeking" is the point at which the handlebars no longer solely control the direction of the boat. At the threshold of seeking, the rider can still control the movements of the boat, however this control is maintained with a combination of weight transfer and body English. Every different hull design has it's own threshold of seeking. Because of manufacturing tolerances, any one particular boat can have a slightly higher threshold than the rest of it's production line brothers, but this is uncommon. If more speed is applied to a hull that is already seeking, the hull will start "coming around".

"Coming around" or "swapping ends" are terms used to describe the handling characteristics of a very short boat being propelled from the rear by a very powerful drive force. At very high water speeds, it's crucial for the nose of the boat to be centered directly in front of the thrust exit of the pump. If the nose makes water contact just slightly off to one side of that centerline, the force coming from the pump can instantly push the back of the boat around to one side. The resulting momentum can cause a boat to instantly turn itself sideways while at peak speed. The swift stop associated with swapping ends at 50+ mph seldom causes any damage to the machine, however it's always a very "physically memorable" experience for the rider.

Aftermarket scoop grates and extended ride plates can slightly raise the threshold of seeking, however beyond 50 mph, they have little if any effect. At GROUP K, we have conducted a great deal of peak water speed testing with most of the popular personal watercraft hulls. The following is a list of the various hulls and their respective thresholds of seeking, as we have experienced them. Chronic "coming around" exists about 3-4 mph beyond the seeking threshold. It's our recommendation that exceeding these "seeking" thresholds should only be attempted by very experienced and physically fit riders.

JS 300/440/550 44 MPH JS 750 SX 47 MPH JS 650 X2 47 MPH

JS 650 SX 45 MPH JS 750 Xi 49 MPH JS 900 ZXi 57 MPH

SUPER JET 45 MPH WAVE RUNNER VXR 46 MPH WAVE RUNNER 3 47 MPH

WAVE BLASTER 46 MPH WAVE RAIDER 50 MPH WAVE RAIDER 1100 60 MPH

As you can see, virtually any Kawasaki or Yamaha personal watercraft will experience chronic "coming around" at speeds in excess of 50 mph and questionable control of any kind above 55 mph. It bears noting that "coming around" is a phenomenon experienced by virtually all high speed racing vehicles on water and ground. Perhaps the most extreme versions of this are the relatively short 200+mph Indy type racing cars. Steering these vehicles in a straight line is full time work since, at speed, the only thing they want to do is come around. This is why race drivers of all vehicles, PWCs included, need to possess exceptional concentration, strength, and reaction skills.

The only effective way to significantly reduce "coming around" is by extending the vehicle's total length . That's why fuel dragsters are built to be so many times longer than they are wide. Many of the new generation of high performance runabouts also have longer hulls for this reason. Unfortunately, IJSBA racing rules prohibit the extension of existing hulls, which means that few performance shops will ever consider doing it.

SEEKING GOOD DOLLAR VALUE - With the increasing engine displacements of personal watercraft, and the availability of many worthwhile high technology performance parts, building a watercraft that meets all your performance needs (as well as your budget) is not difficult. What can be difficult, is wading through the myriads of advertisement claims and questionably believable magazine articles to determine the best way to spent your money. At Group K we do not distribute or promote any lines of performance products. We do, however, recommend aftermarket parts and modifications that net the biggest power gains when used in conjunction with our kit modifications. In an effort to get the most power from our kits, we test nearly every aftermarket part that's available. If a part or modification proves to be reliable and also nets a sizable power advantage over all others, we strongly endorse it's use to all our customers.

STRAIGHT TALK ABOUT POPULAR BOLT ON PARTS - In the course of developing our Hammer kits, we had opportunity to test many aftermarket bolt on parts. To be considered as an eligible "Hammer" component, parts had to measure up well in performance vs. price as well as long term reliability. In some instances, the performance results of our tests were nowhere near the manufacturer's claims. The following is some background on some of those tests, along with our impressions of why our results did or did not coincide with those performance claims.

MULTIPLE CARBS - On machines that come equipped with dual or triple carbs, Group K modifies and upgrades those existing carbs. Modifying the existing carbs has consistently resulted in a better performing and less expensive alternative to buying an entirely new multiple carb kit.

All GROUP K engine kits for single carb equipped machines (except the SledgeHammer racing engines) retain a single carburetor intake system for several very good reasons. From the testing we've conducted, it seemed that most of the "bolt on" dual carb kits on the market exist as a result of customer requests, not as a result of genuine performance increases seen in prototype testing. While some of the dual carb kits we tested (on the popular 650cc+engines) did offer slightly improved mid-range, none of them yielded better peak water speeds along with better throttle control. Most of them yielded less reliable starting and on going tuning difficulties. We also tested a few dual carb kits (from many so called "reputable" aftermarket companies) that performed worse in every way when compared directly to a good single carb. No one was more surprised than us. The few dual carb kits that do offer slightly improved acceleration, do so at an additional retail cost of $400.-$600. This price, along with greatly increased fuel consumption, makes them a very poor performance value on anything other than a pro racing engine.

FUEL INJECTION - In the later 1990's many new watercraft engines may be built with fuel injection systems in an effort to comply with forthcoming EPA standards that will be mandated for all recreational watercraft. The high performance aftermarket injection systems available today fall into two categories, electronic and mechanical. The electronic systems we have seen, besides being terribly expensive, lack so many fundamental safety features, we consider them to be unsafe for any application. Of the safer mechanical type, the best developed system is probably the one offered by MRD. This MRD system, though very expensive, (about $1100.) can be a worthwhile value to the "unlimited budget" professional racer. However, it's questionable whether the long term durability and the difficulty of tuning is suitable for even professional racing applications. Many pro racers have recently abandoned fuel injection.

REED PETALS - Many after market manufacturers make large power increase claims related to the reed petals or reed cages they sell. In our testing on all Kawasaki and Yamaha watercraft engines, we have never one time seen a lasting power increase from the installation of any of the "so called" high performance reeds. We have found some that provided an increase over stock for 20-30 operating minutes. However after that amount of time, the material either chips or begins to lose it's "memory" (it's ability to seal flat and firm against the cage) Since our test results have never matched the manufacturers performance claims, GROUP K recommends only stock reed petals for all it's engine kits.

TOTAL LOSS IGNITIONS - These ignitions originally became popular on 440cc and 474cc race engines in the early 1980's. These older engines had a very heavy stock ignition flywheel that seriously slowed acceleration. The poor low rpm power of the radically ported older race engines made low speed acceleration matters all the worse. The total loss flywheel, which weighs a fraction of what the stocker weighs, helped solve both of these problems at once. Unfortunately, these ignitions also developed a reputation for killing batteries and failing suddenly for no apparent reason. The on going failures associated with these ignitions are still so common that we do not recommend them for any recreational application. Today's current 650cc-750cc engines generate so much low rpm power and acceleration that an ultra light flywheel appears to be the answer to a question that few people are asking (anymore). We instead endorse the lightening of the stock ignition flywheels, and brain box circuit modifications that disable the rev limiter. These modifications offer excellent reliability and good performance increases.

CHANGEABLE DOME CYLINDER HEADS - These heads are ideal for customers who intend to prepare an engine that will sometimes be run in a broad range of altitudes (3000+ ft. variations) The interchangeable domes can be a quick and effective way to change compression ratios. However our testing showed no significant improvements in engine cooling. GROUP K does, however, recommend these heads on all race gas Yamaha engines. The additional bulk of these aftermarket head castings offers more reliable long term head gasket seals.

LARGE REED CRANKCASES and BIG BORES - Even the IJSBA has recognized that most racing engines can easily generate "scary" peak speeds without having to resort to these very expensive larger reed crankcases. More recently it has become very fashionable to convert 701 cased Yamaha engines to the new Wave Raider cases. Most people who have made this conversion have been disappointed to learn the power increase was negligible. New cases with "different" or "larger reeds" are not always a guaranteed passport to more power.

"Big boring" is an easy way to increase displacement, however it is not always problem free. On most personal watercraft engines, sealing the head gasket of a big bored cylinder becomes a very difficult job. If your buying a big bore, ask the technician about special head gaskets or sealers that you may need for a lasting gasket seal. Be aware that virtually all of the current "stock bore" high output engines already have head gasket sealing difficulties.