4597 Calle Del Media

Ft. Mohave, AZ 86426

+1 (928) 763-7600


Kawasaki 900-1100 – Sleeper Kits for Triples

Group K Modifications

This literature will give background information on all of our modifications for the Kawasaki 900 and 1100 three cylinder engine equipped models as well as some recommendations for the best bolt on parts. We strongly recommend that you read this entire pamphlet before deciding which modifications are right for you and the kind of riding you intend to do.

Group K will be offering only the “Sleeper” style modifications for both of the three cylinder models. These kits entail modification to existing engine parts only. The finished Sleeper equipped boats will have engine compartments that look, for the most part, cosmetically stock. The boats start and idle better than the stockers, have the sound level of a stocker, and operate reliably on 92 octane unleaded pump gas.

Our prime horsepower objective during development, was to increase acceleration as much as possible. Increasing peak speed was a welcome side effect of the work, however it was a secondary consideration. The acceleration of both these Sleeper equipped machines is instant and strong. The increase in peak water speeds are about 4-5 mph. NOTE : Broad variations in the peak speeds of stock hulls has made it difficult for us to forecast exact peak speeds for machines equipped with each kit.

NOTE: The Sleeper kit increases in acceleration and speed have a profound effect on the handling characteristics of both machines. All our test riders agreed that these machines should only be operated by riders who are experienced, physically fit, and “paying attention”. The Sleeper kit triples are machines that demand respect at all times, and should be operated only by riders capable of making consistently mature judgments.

ABOUT PEAK WATERSPEEDS – Both these machines are equipped with standard issue instruments. For owners who haven’t already figured it out … these speedos and tachometers are very “optimistic”. While the instruments often indicate speeds in the middle 60’s, that’s not reality. Stock Kaw 900s normally run in the 53 mph range, and the stock 1100s run 58s. (XP 800s run 58 on glass) In our tests with numerous Sleeper equipped test boats, the 900s run 58-59 mph, while the 1100s run 62-63 mph.

There are numerous modifications that will net slightly higher peak speeds on glass water. These include, but are not limited to, running only 2 gallons of gas (for weight reduction on the nose), removing sponsons, removing ride plates, etc. On a daily basis, we receive calls from enterprising triple owners who have radared their machines at speeds in the low to middle 60’s using mods like this. While we find these calls interesting, we don’t consider them important. It is not difficult to coax a few additional mph out of a machine if your willing to greatly compromise practicality, handling, or costs. At Group K we consider speed increases to be important only if they are a result of sheer horsepower increases available from 92 octane pump gas. We could easily gain (and advertise) the speeds of a machine with 2 gallons of fuel, no ride plate, and race gas… but that’s not the real world.

The real world is where you pull up next to a guy on an XP 800 in afternoon chop, and blow him off. In this part of the real world, there is no glass water and no radar guns. This is the world that we build our kits for.

THE GOALS OF MODIFICATION – The goals of every Group K modification is to offer the maximum possible overall power increase while making the minimum possible loss of reliability and fuel range. The primary performance problem of both three cylinder crafts was the lack of low speed acceleration. Strong low speed power is needed to permit smooth controlled turns with these large and very heavy hulls. A secondary performance interest is the peak water speed ability. Making good increases in acceleration and peak speed, without hurting reliability, is not difficult. Reliability of the three cylinder engines is seriously affected only when operating rpm’s or compression ratios are too high. All our testing with these engines has shown that reliable horsepower levels could easily be had without excessive compression, or revving the engine into the “twilight zone”. The design of our modifications insure that your engine won’t need to be “screaming” to make the bulk of it’s power.

During the development of an engine modification kit, engine builders will commonly choose a particular technical feature that the finished engine should possess. The feature that we focused on for these kits, was to meet our power output objectives while maintaining the lowest possible compression ratios. While this complicated our development work, we knew the dividends in reduced wear and reduced engine temperatures would be worth it …they are worth it. These Sleeper kits have less compression, yet more power, than any other kits we’ve built.

INDIVIDUAL MODIFICATIONS VS. A “KIT” – It would be nice if we could make one simple modification that would eliminate all the performance handicaps of these machines… unfortunately it just doesn’t work out that way. To illustrate this, the following is the general scenario of the development process we went though for these kits.

By far the biggest horsepower bottleneck on both of these triple cylinder engines is the cylinder porting. After performing comprehensive port “repair & upgrade” work to the cylinder, the compression ratio will have been reduced (as a result of increasing the exhaust port sizing). To correct for this reduction in compression ratio, the cylinder head domes are machined to a smaller volume. This modified cylinder and head combination is now able to process much more “cfm” (cubic feet per minute) of air. To accommodate this additional “cfm” need, the carburetors are bored. With the greatly increased air cfm ability of the bored carbs, the carburetor circuitry must be significantly upsized to maintain the proper fuel/air mixture. As you can see, it would be difficult to safely omit any part of the kit.

Many customers, for time or money reasons, may want to choose individual parts of these modification sets. For these customers, Group K will only offer the head modification as an individual mod. This modification, by itself, can make a noticeable improvement in overall power. However that increase is only a fraction of what the complete kit offers. The dome volume specification of this “head only” modification is the same as the “kit” specification. This means that owners who chose the head mod alone, will not need to have the head modified again if they later choose to purchase the entire Sleeper kit.

TOP END MODIFICATION – All Group K kits include cylinder porting. In the past, cylinder porting has received an undeserved reputation as a modification that causes a loss of reliability and engine life. If the porting is performed by someone with very little experience, that may be true. The porting mods used in Group K kits is the result of many months of performance and wear evaluation testing. We confidently claim that Group K cylinder porting will yield a wider power band and longer piston life than any other porting modification available anywhere.

Our cylinder porting is available in two different finish modes. Both the “Recreational” and “Competition” finish modes include all the same port timing, port shaping, and specification work. The Competition mode also includes additional exhaust port finishing and a transfer port “rough finish” that further improves fuel atomization. This additional finishing work accounts for 25% more shop time, yet contributes to only about 10% of the total performance gain (about .5 mph and a little bit of acceleration). The recreation finish is standard in the Sleeper kits, the “Competition” finish is available as an option. The cost difference…$600 vs $450. All ported cylinders are also honed.

The modified cylinders and heads are always prepared as matched pairs to assure that you have the proper squish clearance and compression ratio for the quality of gasoline that you intend to use. These cylinder and head specifications play the key role in determining the amount of overall power that the engine can make, as well as the quality of fuel that you may use. For customers who already have a milled or aftermarket head, we will need it inspect your cylinder head to confirm whether or not it is within spec range.

PISTON CLEARANCE – The original factory piston clearance setup of both machines is generally very good. Over long term use, we have found significantly more piston skirt collapsing on the Kawasaki 900 than the 1100. In either case, bore wear and piston skirt inspection should be done seasonally on triples that experience long term high rpm use. On any high output recreational packages, we recommend set-up clearances of preferably .003″ and no more than .004″. Engines intended for moderate recreational use can easily live with .004″-.005″ set-up. Piston clearance inspection is available on request, and cylinder boring (using pistons furnished by you or us) is available in oversizes of .020″and .040″. In any case, all ported cylinders are honed by Group K before return shipment.

BIG BORE CONVERSIONS – Kawasaki — As of this writing, we still consider big bore modifications to be a questionably good idea for the Kawasaki 900s. The stock sleeves in the 900 are so thin on the exhaust side of the cylinder that boring the existing sleeve is risky business. We looked into big bore sleeve kits until we learned that Kawasaki was releasing the 1100. When we learned that the 1100 had substantially longer rods (a great benefit), we figured a big bore 900 would probably have excessive piston wear problems unless the rods were lengthened. By the time you install longer rods and a sleeved/ported top end, you could afford the 1100.

AFTERMARKET CYLINDER HEADS – Most aftermarket heads are very attractive, and well made parts. However, we experienced no problems that the aftermarket heads solve. The claimed benefits of the billet heads is improved cooling and improved gasket sealing abilities. We agree that these would be very desirable qualities on a high compression engine format. However both stock engines push only 110-120 psi of compression. The Group K Sleeper kits for both machines pushes no more than 150psi. Our testing showed that higher compression ratios were not a measurable performance benefit on our kits for these triples. The many of the billet heads we have seen were machined to yield compression ratios that we found too high to be compatible with 92 octane pump gas. Our testing showed the end result of excessive compression was a huge increase in operating temperature, with an questionable increase in performance. The modified stock heads have no cooling or sealing problems that we have observed. Good cooling is a function of efficiently exchanging the heat away to the coolant, not just a function of the water jacket size. The water jacket surfaces of the stock cast heads are faceted and finished in a way that offers more than sufficient “water contact surface area” . The greater the water contact surface, the more efficiently the head exchanges the heat to the coolant. To date, we have seen no aftermarket heads that have more “total water jacket contact surface area” than the stockers.

Another claimed benefit of the aftermarket heads is a greater resistance to “warpage”. Warpage, for the most part, is more a mechanic’s “old wives tale” than a technical reality. No head, on an engine receiving a reasonable supply of coolant, can “warp”. If an engine were run at length with little or no coolant, any head will eventually sustain a distorted head gasket sealing surface. It is likely that a billet aluminum head would distort slightly less than a cast head. This is because the aluminum mass around the domes is typically so much thicker. Unfortunately this thicker mass also represents a longer heat path that reduces cooling efficiency. In situations where gasket surface distortion is an ongoing problem, the thicker mass head would be preferable. On the 150 psi Sleeper kits, this has never been a problem. We find the current billet heads to be an expensive answer to a question that no one is asking.

OIL INJECTION SYSTEMS – Both machines can be operated with the stock oil injection systems, however there are good reasons to convert over to a premix system. The injection system of the Kawasaki 900 and 1100 delivers the oil directly into the float chambers of the carbs. While this inlet point is a great design feature, this injector is not without it’s own problems. Many dealers have reported difficulties purging air bubbles out of the injector lines. Usually, a 60:1 mix along with the first tank of gas alleviates the risks that might come with his problem. However , if in doubt … convert to pre-mix.

EXHAUST SYSTEMS – As of this writing there are no aftermarket exhaust systems or exhaust system modifications that we recommend for either triple. At this time, we strongly recommend against any modifications to the stock systems other than perhaps “extrude honing” the pipe bodies.

We also recommend that a standard waterbox silencer be retained on both Sleeper kits. Contrary to belief, the stock Kawasaki and Yamaha waterbox mufflers yield excellent overall power levels in these high output applications.

INTAKE SYSTEMS – Both triple cylinder kits include carb throat boring, metering circuit upgrade, choke removal, and a primer. This conservative carb mod maximizes the “cfm” ability of the inlet systems while minimizing additional fuel consumption. Testing done with larger carbs on these kits resulted in huge increases in fuel consumption along with no significant increase in overall power. The Group K modified stock carbs offer easy starting, smooth idling, and “instant” acceleration at all engine speeds. On our 1100 kits, we also remove the “acceleration pump” that shoots a spray of raw fuel into the carbs every time the throttle is applied quickly. While this system works okay, it dramatically increases fuel consumption, not to mention that it can also cause very rich low speed operation.

Group K will offer modified cylinders and heads to customers who already have a carb kit from another aftermarket manufacturer. However this will be done with the understanding that all carb tuning and adjustment information will be the responsibility of that manufacturer .. not Group K.

FLAME ARRESTORS – The safety objective of the flame arrestors is to stop any backfire flames from reaching the atmosphere in the engine compartment. The performance objective of well designed flame arrestors is to admit the incoming air to the carb throats with the maximum possible airspeed. With respect to accomplishing both of these objectives, the stock Kawasaki 900 arrestor is the best stock design in the industry. Even the stock 1100 arrestor works well with a few simple modifications(outlined in the assembly instructions. In our testing, only the R&D arrestors performed measurably better than these stock arrangements.

REEDS – The stock reeds and cages on these machines have consistently out performed any aftermarket reeds we have tested. Some aftermarket reeds can offer better power for 20-30 operating minutes. However after that amount of time the material often “looses its memory” or begins to chip. As this happens, the performance offered by these weakened aftermarket reeds becomes worse than stock. If you do choose to purchase reed cages or petals from any aftermarket manufacturer, get an assurance that their in-house technicians will be able to help you with the carb tuning needed to get your engine running properly. These engines come stock with reed stuffers, none are needed.

ABOUT MARINA GAS – There is a great convenience to buying “on water” marina fuel for machines that consume as much gas as these boats do. The unusually high price of marina gas is not a reflection of that fuel’s high octane quality. The high price is more a reflection of the dock master’s awareness of how captive his customers are. In any case, the normally low grade of marina fuels can work fine in the low rpm, low power output motors in most boats. However, a Sleeper kit triple needs much better octane than most marinas offer. Unless you have personal knowledge of the high quality of the marina fuel at your ride spot, we strongly recommend to not use it !

IGNITION – Unlike many twin cylinder machines, the ignition system rev limiters on these triples do not impair peak water speed abilities. In past years, rev limiters were circuit items in the cdi boxes that could be easily disconnected or bypassed. The new style of limiter, employed in both triples, is a programmed micro processor. Because the programming is copyrighted, modifying the programming is illegal, as well as very difficult. This being the case, Group K will not be making any recommendation regarding rev limiter mods on these models.

The aftermarket is full of total loss ignition systems that also have no rev limiter. Because of the constant battery maintenance and the questionable reliability many of these systems has had, we do not recommend them for any recreational or amateur racing applications. Group K will not install or supply a total loss for any engine built in house.

COOLING SYSTEM – The stock cooling systems on these triples are, for the most part, sufficient for the Sleeper kits. For both machines, the entire cooling system is left pretty much stock. We do add a water bypass to additionally cool the front cylinder. Our test boats, prepared in this way, logged several hundred “full throttle” miles in endurance racing events with no temperature problems.

CASE PORTING – This is a mod that can make a noticeable improvement in overall power that comes without any loss of reliability at all. The case porting is an “all gain – no lose” modification that is usually done on cost is no object engines. (note : cylinder is required with top crankcase half to do case porting)

PUMP MODIFICATIONS – Pump blueprinting offers much better “hook up” in rough water conditions and is an important asset to machines that will be run hard in rough water conditions (as many boats are). If your machine will be operated primarily on smooth water, the blueprinting will offer little improvement for the money spent.

A variable pitch stainless impeller will be a mandatory modification for both machines. For the 900 , we recommend the 17′-22′ pitch Skat Trak “slim line” or the Solas “I” pitch prop. For the 1100, the Nu Jet is the best to date.

HANDLING – For recreational boats that will be operated primarily on smooth or slightly wind-chopped water, cutting out the center bars of the stock scoop grate will offer all the additional water access that’s needed. Aftermarket scoop grates are recommended only for machines that will be run at high speed in very rough water conditions. For riders who run their machine very aggressively in rough water conditions we recommend the “top loader type scoop grates. Be forewarned that while these top loader type scoop grates can offer better rough water “hook up”, they can also scrub off peak waterspeed (on glass water) and often cause “eye opening” deceleration when you release the throttle. Top loader grates are only recommended for closed course racing or surf riding boats.

ASSEMBLY INFORMATION – All Group K kits are accompanied by a step by step instruction pamphlet that outlines the assembly, break-in, fine tuning, and maintenance of your kit. For any further questions you may have regarding your Sleeper or Hammer kit, you’re welcome to contact us directly for assistance.

AIR LEAKS – The lower end of your engine should be totally air tight up to 8 psi. New engines pass this test with no problems. However engines with older deteriorated crank seals or brittle intake gaskets can allow outside air to leak into the lower end during operation. This “air leak” can make the fuel mixture lean enough, at high rpms, to cause a piston seizure. Air leaks, not engine modifications, are by far the number one cause of piston seizures. Group K offers a simple to use pressure test kit that allows you to test for any air leaks that your engine may have.

Sleeper Kits

Group K Price

Kawasaki 900″ SLEEPER” KIT

Includes: Recreational Finish Cylinder Porting & Decking, Head Modification, Water By-Pass, Carb Boring, Jetting and Primer Kit. (SEND Head, Cylinder, and Carb Set)


Kawasaki 1100″ SLEEPER” KIT

Includes: Recreational Finish Cylinder Porting & Decking, Head Modification, Water By-Pass, Carb Boring, Jetting and Primer Kit. (SEND Head, Cylinder, and Carb Set)


Engine Labor

Group K Price

Recreational Finish Cylinder Porting & Decking


Competition Finish Cylinder Porting & Decking


Cylinder Head Modification


Crankcase Porting & Matching


Şcarb Throat Boring & Jetting


Optional Exhaust Manifold Matching


Driveline Labor & Parts

Group K Price

Pump Blueprinting (SEND Vain Case and Impeller Housing)


SKAT TRAK Impeller 17-22 (900 Only)


SOLAS “I” Impeller (900 Only)


NU JET Impeller (KWC 5.0) (1100 Only)


Package / Upgrade / Parts

Group K Price

GROUP K Air Leak Test Kit


Cylinder Boring, Hone, and Chamfering (One Oversize)


*prices subject to change based on manufactures pricing


GROUP K • 4597 CALLE DEL MEDIA • FORT MOHAVE, AZ. 86426 • (928) 763-7600

GETTING THE WORK DONE – Most customers send GROUP K the parts needed for modification via UPS, and then do the engine assembly work themselves. We also do complete engine and pump assemblies for customers who want a finished unit ready for installation. The 150-lb. UPS weight limit makes engine shipping practical and affordable. NOTE: Group K will bill an additional $25.00 handling charge for complete engine assemblies. All orders prepaid with a cashiers check or money order will be returned freight free via ups ground service anywhere in the continental United States. All other orders will be billed to a visa/master card or sent freight collect cod cash. If you would like to pay additional for 3 day, 2 day, or 1 day return shipment, please specify your preference in a cover letter with your parts. Be sure to include your return address and day phone information in case we have any questions regarding your order. PACK YOUR PARTS CAREFULLY !!