4597 Calle Del Media

Ft. Mohave, AZ 86426

+1 (928) 763-7600


Kawasaki JS 440- High Performance Mods

Specs for '81 - '92 Models

This literature will give background information on all of our modifications as well as some recommendations for the best aftermarket 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 with your 440. The format of our 440 engine modification kits are as follows : STOCK KAWASAKI JS 440 Peak waterspeed – (sea level, flat water) 29.5 mph

SLEEPER – Intended for the average recreational rider, this engine kit consists of modification to existing pieces only. The engine compartment of your finished Sleeper will look 100% cosmetically stock. The Sleeper will start and idle like a stocker, have the sound level of a stocker, and run on 92 octane pump gas.

Peak waterspeed – (sea level, flat water) 40.1 mph

HAMMER 92 (octane) – Intended for the serious recreational rider, this 440 kit shares many of the Sleeper kit mods along with a cost conscious selection of aftermarket bolt on parts. The completed Hammer 92 is as easy starting and reliable as any stock machine This is the fastest 92 octane pump gas compatible 440 kit available anywhere.

Peak speed – (sea level, flat water) 44.5 mph

HAMMER 105 (octane) – Intended for the serious super stock class racer, this kit offers national class competitive power output along with the best in race level reliability. This Hammer kit requires 105+ octane fuel at all times. Peak waterspeed – (sea level, flat water) 46.2 mph

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 power band range. The biggest performance problem the JS 440 has is the lack of low speed acceleration. Strong low speed power is needed to permit smooth controlled turns, as well as getting heavier riders up on plane. The next biggest performance problem is the lack of peak water speed ability compared to all other crafts. Making good increases in the acceleration and peak speed of a 440, without hurting reliability, is not difficult. Reliability of the 440 engine is seriously affected only when the engine is allowed (or forced) to turn excessive rpm’s during a big percentage of total operating time. All of our testing with 440 engines has shown that competitive and reliable horsepower levels can be had without spinning the engine into the “twilight zone” rpm range.

There are many aftermarket companies that build very high rpm 440 race boats for their sponsored team riders. When recreational riders purchase the same parts and modifications used by racers, they ultimately end up with the same unreliable “no bottom end-all top end” engine that the racer has. This is not what any recreational rider wants. In fact even among racers, 440 super stocks with lots of bottom end power, along with a wide tractable power band, are always more desirable. The high rpm engines used by the top pro riders will typically get a new crankshaft every 25-30 operating hours. Few recreational riders can afford that.

DESIGN WEAKNESSES – The 440 engine has only two significant design weaknesses. The first is the long term strength of the crankshaft, and the second is a tenancy to develop air leaks.

CRANKSHAFT – The stock 440 crankshaft is actually a very well built unit. Unfortunately, many 440’s will still have the original crankshaft in the engine. For a later model ’90 or newer machine that’s not a problem, however there are many 440’s with five or more seasons on the stock crank. Under the loads of stock power output, that five year old crank might last another five years. However the added rpms and power loads of even a mild modification can easily be the death blow to a well worn five season crankshaft. If your considering modifications, and you doubt the integrity of the crankshaft … replace it. Truing and welding the 440 crankshaft would only be necessary if you intend to use the machine for racing or very hard recreational riding.

AIR LEAKS – The lower end of your 440 should be totally air tight up to 8 psi. Newer engines pass this test with no problems. However engines with 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 are by far the number one cause of watercraft piston seizures. GROUP K offers a simple to use pressure test kit that allows you to quickly test for, and locate, any air leaks that your engine may have.

TOP END MODIFICATION – All GROUP K 440 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 440 experience, that may be true. The porting mods used in all our 440 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.

Contrary to rumor, the earlier style aluminum 440 cylinder has no significant mechanical or cooling advantages over the later style iron cylinder. Other engine builders who chose unusually radical port formats that yield poor low speed power often mandate the use of the aluminum cylinder. Our tests showed identical performance from both cylinders modified to Hammer 105 specs. Cast iron cylinders modified to Hammer 105 specifications will be prepared to be run with a .020″ copper head gasket. All other kits will be prepared to use a std. thickness .040″ head gasket.

All GROUP K porting includes cylinder decking and matching of both manifolds. Cylinders and heads are typically prepared as matched pairs only 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 must use. The Hammer 105 can not and should not operated at high rpm’s on pump gasolines. In like, the 92 octane kits should never be run on 87 or 89 octane regulars.

PISTON CLEARANCE – It’s common for new 440 cylinders to have as much as .005″ of piston to cylinder wall clearance. (set-up clearance is .003″ ; wear limit is .007″) On any racing or high output recreational packages we recommend set-up clearances of no more than .004″. Engines intended for moderate recreational use can easily live with .005″-.006″ set-up. Piston clearance inspection is available on request, and cylinder boring (using pistons furnished by you or us) is available to oversizes of .060″. In any case, all ported cylinders are honed before shipment.

EXHAUST SYSTEMS – While the Sleeper kit utilizes the complete stock exhaust system with slight modifications, the 440 Hammer kits are intended to be used with aftermarket exhaust components. Both Hammer kits yielded the best overall power using the Coffman “Classic” pipe (with the Westcoast “Works” pipe at a close 2nd). Using an aftermarket exhaust manifold is a mandatory item on the Hammer 105 and a strongly recommended option on the Hammer 92. We recommend to use the same brand pipe and manifold where ever possible.

Because of the piercing sound that a high output 440 can make, we recommend that a stock waterbox silencer be used on the Sleeper and Hammer 92. Contrary to rumor, the stock waterbox yields very good overall power levels in all pump gas applications. The Hammer 105 should be fitted with a rear exit exhaust used together with the Jetcraft Eng. dual resonator mufflers. These mufflers permit the engine to pull easily into the higher rpm ranges while maintaining tolerable increases in sound level. The resonator mufflers, used with a side exhaust exit will not pass the IJSBA or U.S. Coast Guard sound level limits. The Jetcraft Eng. muffler rear exit tube gave our 440 test boats the best overall performance and best sound levels when resonator mufflers where used in the nose of the boat. With many rear exit systems we experienced terrific “deep water re-start” problems due to the amount of water that backed up in the exit tube. The Jetcraft rear exit offered the best deep water starts of any system we tested.

INTAKE SYSTEMS – The standard 38 Mikuni carb is an excellent carburetion choice for all modification levels of the 440. Internal circuit upgrades are mandatory for all the 440 kits. Since the choke plate screws so commonly loosen and fall down into the engine, replacing the choke mechanism with a primer system is recommended for all 440’s. Carb throat boring, which improves high rpm output, is an option recommended only for the Hammer 105 kit.

For the Sleeper, we provide a double mesh stainless steel screen to replace the pumice stone element in the stock flame arrestor case. In our tests, the popular K & N replacements performed well as long as they were perfectly dry. However when they became even a little wet, they offered very restricted air intake ability until they were removed and allowed to dry out. For our Hammer kits we recommend only the Westcoast velocity stack flame arrestor replacement. The intake mesh of this element is so high in the engine compartment that it is exposed to very little water spray. Whatever spray it may be exposed to will not clog the all screen element in any way. Boring the Westcoast stack to perfectly match the mouth of the 38 carb is available as an option.

IGNITION – The stock 440 ignition has no built in rev limiter, however it does have an unusually heavy flywheel that slows throttle response and acceleration. Our ignition flywheel lightening option offers a very noticeable improvement in throttle response on all three 440 kits with no loss of reliability whatsoever. The much lighter aftermarket aluminum charging replacement flywheels offer an incredible increase in throttle response along with an equally incredible price tag. The price of these aluminum “charging” flywheels would easily be worth the performance for a racer with a Hammer 105. However for the recreational rider, we recommend the lightening option. The reliability of the total loss ignitions we’ve tested has been so poor that we do not recommend them.

COOLING SYSTEM – All of these 440 kits can operate reliably with the single input cooling system and our cooling system upgrade. For customers who prefer to prepare their machines with a dual or oversized input systems, we can also prepare the special exit plumbing needed to make those systems work.

DRIVELINE – The force of impeller thrust, with the 440 style pump, is delivered to the driveline bearing holder mounted on the back wall of the engine compartment. The constant load of this thrust can break the fiberglass wall on heavily modified high output boats. To abate this problem, we recommend the use of a Westcoast bulkhead bearing support on both 440 Hammer kits.

The use of a lightweight driveshaft can noticeably improve acceleration ability on racing 440’s, however it’s often a relatively small performance increase that comes for a very high price. If value for the money spent is a high priority for you, a light driveshaft should be among your last modifications.

PUMP & IMPELLER – Early style 440 pump cases were manufactured with no stainless steel impeller housing sleeve. These early pumps were adequate for stock machines, but fall short badly for high output use. If you have an early style pump, it should be replaced with a new version that has a stainless sleeve. A 16′ Skat Trak impeller and nozzle boring are mandatory modifications for all Group K 440 kits. Riders under 120 lb. may experience better results with a 16.5′ pitch on the Hammer 105 only. Aftermarket scoop grates are recommended for all kits, however brand make is not crucial.

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 (as race boats are). If your machine will be operated on only smooth water, the blueprinting will offer little improvement for the money spent.

HANDLING – For all 440 models, a slightly longer aftermarket ride plate is a big handling asset. The longer plate reduces “porpoising” (the nose of the jetski bouncing uncontrollably) and improves high speed stability. An aftermarket scoop grate will help to maintain a better supply of water at the front side of the pump. For riders who run their 440 very aggressively in rough water conditions (as a racer might do) the “top loader type scoop grate

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, your are welcome to contact us directly for assistance.


Group K Price

Includes: cylinder porting, decking, and manifold matching, cylinder head modification, cooling system upgrade, carb circuit upgrade, flame arrestor mod, exhaust body modification, exhaust resonator modification, pump nozzle boring. (SEND head, cylinder, manifolds – intake and exhaust, carb, arrestor, and pump exit nozzle)


Sleeper Kit Individual Labor Prices

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Engine Labor

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Engine Parts

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Driveline Labor

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Driveline PArts

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Additional Options

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*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 !!