Group K Racing Modifications for the Kawasaki SXI Pro 750

Preface -  For roughly the last five years, Kawasaki Motors has fielded a very successful watercraft racing team that operated from within Kawasaki Motor Corp.  During this time, the race team has made numerous important developments that have allowed their machines to be on the cutting edge of national competition.  Unfortunately, there was no effective connection between the KMC racing team and any aftermarket performance shop that could bring the fruits of that development to Kawasaki owners that wanted access to the latest competitive modifications.  During 2001, Kawasaki and Group K have forged such a relationship.  The KMC race team will continue to operate and race nationally as it has in the past, and Group K will be selling high performance modifications as it has in the past.  However there is now a very open exchange of information between KMC racing and Group K that exists for the purpose of creating a commercial performance source for Kawasaki watercraft enthusiasts.  In short, Group K will be the factory connected information and performance source for competitive Kawasaki watercraft equipment.

  The data in this document reflects some of the results of the information sharing between Group K and the KMC racing.  We would like to sincerely thank the Kawasaki watercraft division and the Kawasaki race team for their invaluable contributions to the information in this document.

The “Handling Issue” -  The Kawasaki 750 Stand up models have existed since 1992.  The engines of all the various versions have been very reliable, and lent themselves very well to high performance modification.  All the different Kawasaki 750 stand-up models can be a fun and maneuverable boat to ride, even when modified for higher performance recreational use.  When modified for amateur or professional level competition, the Kawasaki 750 is easily on a par with the power output of competing makes.  However when modified to this level, the significant increases in sheer speed can result in changed handling characteristics that some competition riders have struggled with.   As speeds have increased with each racing season, dealing with these handling issues has become progressively more difficult.

   Kawasaki’s race team has spent considerable time and resources to create IJSBA legal modifications to improve the closed course racing characteristics of the SXi Pro 750 at racing speeds.  The intention is for these modifications was to be  created in a way that any SXi owner could apply the modifications to their stock hull.

These handling improvements for the SXI Pro now exist.  In concert with the fiberglass fabricators of 3D-R, Kawasaki has developed an IJSBA legal, bolt on, handling modification.  This modification transforms any SXi Pro into a machine that can easily contend with racing speeds, and hold it’s own against any competition. 

   With this handling modification, the SXi Pro suddenly becomes a very serious and competitive threat in all levels of stand-up closed course racing …. That is, the Kawasaki SXi pro 750 will have an instant revival to top level racing status.  The detail information about these handling components will be discussed below.

The Kawasaki 750 Stand Up Models 1992-2002   -  The Kawasaki stand-up models exist in three different versions.  The ’92-’94 SX model was the first of the 750s, and the only version that came stock with a single carburetor.  It was fitted with 140mm pump, a diameter that would be retained by all future 750 stand up models.

   The ’95 SXi featured the new “big pin” engine format (so called because of the much larger piston pins).  These big pin engines also featured an all new cylinder port layout that employed much more radical port timings.  Instead of using the dual 40mm Kiehin carbs already in place on the ’93-’94 Xi runabout, Kawasaki engineers fitted the SXi with smaller dual 38mm carburetors, and inlet tracts that were significantly smaller than the Xi.  The smaller reed openings and inlet manifold runners, together with the slightly smaller carbs, offered a big increase in inlet tract vacuum, and thereby improved acceleration and throttle response characteristics.  The intention was to give a lift to low range power of the new cylinder design.  In addition, this intake affords better fuel range for the runabout models that used the same engine.  Despite the smaller carb size and inlet passages, these intake systems still work very well, even on modified engines.

   The ’96 SXi featured some slight changes in port timing (transfer), and a switch from the 38mm Kiehin carbs to 40mm Mikuni “I” Series carburetors.  It’s questionable whether the Mikunis are really that much better than the Kiehins, however there is clearly more tuning parts available for the Mikunis.

  The ’98-‘02 SXi Pro uses the same “big pin” motor as the ’96 SXi.  The SXI Pro also featured some subtle hull upgrades over the SXi.  However even with these hull upgrades and carburetion improvements, it was “challenging” for some  owners of race modified SXi Pros to contend with the issues of high-speed handling.

About Speeds -  Unlike the world of larger runabout PWCs, defining the straight-line speeds of high performance stand up crafts is a very subjective thing, with many variables.  Props that hook up better (and offer better lap times) will often radar slower.  The rider (and his or her weight and positioning) can make a 2-3 mph difference in the radar speeds of any given combination.  In addition, the SXi hull itself has a tendency to ride on it’s left or right hull face, but will radar considerably faster if the rider can finesse the hull momentarily on to the hull center.  Our test riders describe this as getting the boat to sit on a “row of marbles” down the center of the hull.  During these moments, tachometer numbers increase by 60-80 rpm and radar numbers jump about 2 mph.  Unfortunately, no rider can keep an SXi hull perfectly centered on that “row of marbles” for any meaningful length of time.   High performance stand up riders are far more willing to give up some peak speed ability in the interest of improved handling and control …. But how does one precisely describe the comparative values of handling qualities verses radar speeds … in truth, you can’t.

   Virtually all the handling parts described in this document reduce peak speeds by some measure … that is a given.  With the help of the KMC racing team, we have chosen those parts that offer the biggest handling dividends for the speed losses they represent.  We tend not to question the experiences of the KMC race team, and we don’t know of anyone qualified to do so.

  The only logical approach to stating speeds is to start off with a base hull setup that can operate with a wide range of engine setups.  Such a setup will not be ideal for any arrangement, but it will offer a reasonable basis for comparison.  For our tests we chose to set up our base SXi Pro hull with the 3D-R front sponsons and rear trim tabs in combination with the Worx ride plate and Worx scoop grate (160 lb rider, 50-80% fuel capacity).  Unless otherwise stated, all stated speeds will be with this setup.

The Group K Engine Kits

Stock 2002 SXi Pro 750  - 48-49 mph all stock ;  46-47 mph with spec handling package.

Sleeper Kit  -  A very reliable 92 octane combination of modifications to the stock parts that makes for a big increase in overall acceleration and peak speed.  Looks and sounds like stock … runs like a stocker on steroids.  49-50 mph

Sleeper 800 Kit -  If vicious acceleration and rock solid reliability are your goals, this 92 octane big bore Sleeper is the ticket.   This stock looking big bore delivers a brutal punch of power with every grab at the throttle.   50-51 mph

Limited 1 Kit -  An affordable combination of modifications and bolt-ons that offers the best in simplicity and reliability on 92 octane pump gas. (IJSBA Limited Class legal).  52-53 mph

Limited 2 Kit -  A reliable 100 octane package for the more serious closed course Limited Class rider.

(IJSBA Limited Class legal).  55-56 mph

Superstock 1 Kits -  An affordable 92 octane modification that gets the most bang for the buck for the occasional weekend racer.  (IJSBA SuperStock class legal).   55-56 mph

Super Stock 800cc  “Hammer” Kits -  These 100+ octane packages transform your Kawasaki watercraft into a vicious racing weapon.  The “Hammer” is a machine that intimidates the competition, and commands the respect of it’s owner.  Not for the faint of heart.  (IJSBA SuperStock class legal).  57-58 mph.

The 3D-R Handling Package

This package consists of two basic components.  The “front sponsons” are 12mm thick fiberglass panels that affix to each side of the hull, and the “end caps” that attach to the rear of the hull on either side of the pump exit.

   The rear end caps serve to keep the nose of the hull down at high speed, and thereby dramaticly reduce porpoising.  Equally important, these caps have been carefully designed to hold the nose down while the hull is at angle (while negotiating high speed turns).  Unfortunately, the end caps by themselves tend to drive the nose of the boat down very hard during high-speed straight-line operation.  Hence it is not advisable to use them alone.

  The front sponsons actually make the footprint of the forward hull a bit wider, thus offering more lift.  This added lift keeps the end cap forces from driving the nose downward during high-speed straight-line operation.  In addition, these sponsons offer better buoyancy when negotiating high-speed turns, resulting in better control.  Using the front sponsons alone is not advisable, as that could result in excessive porpoising (without the down-force offered by the end caps).

  Installing the 3D-R kit on a stock SXi will result in a speed loss of about 1 mph, but every test rider has agreed that 1mph was a tiny price to pay for the huge improvements in overall handling and control.

Exhaust Systems -   The Sleeper Kits use the complete stock exhaust system.  All the other Group K kits are intended to be run with the Factory Pipe Products “Dry Pipe”.  The term “dry” refers to the absence of any water being injected into the interior of the expansion chamber for cooling purposes (as is the case with many pwc exhausts).  The water needed to cool all the exhaust exit hoses is introduced by a fitting in the stinger tube (at the end of the expansion chamber).  The pipe body itself is cooled by a full-length water jacket.  That is, this exhaust is literally two pipes; the inner pipe, and the outer water jacket.

  The FPP Dry Pipe comes with it’s own exhaust manifold.  The port openings in this manifold are measurably bigger than the port openings in most stock cylinder castings.  IJSBA Superstock rules permit the opening of the ports in the cylinder to match the manifold, however the Limited class rules forbid this same matching.

   This exhaust system is also supplied with an electronically controlled water injection system (ECWI).  The ECWI unit injects a tiny amount of water into the interior of the head pipe only during mid range operation.  This small amount of injected water dramaticly increases the mid range acceleration.  Unfortunately, this same water can harm high rpm abilities, so the electronic sensor turns this water supply off at rpms above 6000.  Not all our kits require the use of the ECWI system, and many riders simply prefer the power delivery offered without the ECWI.  It can boil down to a preference issue.

About Muffler Systems -  The stock aluminum waterbox muffler of the SXi 750 is a very effective and functional part that is difficult to improve on.  All Limited class race machines are mandated to use this stock waterbox muffler system, however Superstock race machines are permitted to alter the muffling system so long as it complies with IJSBA sound level requirements.  Group K considers the sale and/or use of excessively loud pwc exhaust systems to be very damaging to the industry as a whole.  As of the writing of this document, we have not seen any functional aftermarket alterative to the stock waterbox that offers an “acceptable level of sound.  We intend to continue testing in this area, and will post that data as it becomes available

 

Inlet Systems

Carbs – As previously mentioned, the ’95 SXi had dual 38 Kiehins, and all subsequent 750s had the 40mm “I” body Mikunis.  In truth, these carbs are not a true 38mm or 40mm as stated.  The actual minor diameter at the venturi is about 2.5mm smaller.  For the Group K Sleeper, Limited 1, and Superstock 1 kits, Group K does a “true bore” modification to make the Kiehins a true 38mm, and the Mikunis a true 40mm.  With this mod, the carbs still offer easy starting, steady idling, and strong overall carburetion.  This affordable mod is ideal for the occasional racer and high performance recreation rider who doesn’t want to be bothered with the tuning of more temperamental larger carbs.

   The next most effective carb upgrade is the dual 42 Kiehin carb kit offered by Aqua Sports.  The best part about these carbs is that they bolt directly on to the stock ’95 manifold, and offer easy cable hook up.  We recommend the stock ’95 manifold for the 42s over most aftermarket versions because most aftermarket manifolds are made with large 46mm passage runners.  These large diameters are great for the big carbs, but they cause a loss of inlet vacuum (and thereby throttle response) when used with a 42mm carb.  The stock ’95 manifold must be opened slightly to accommodate the larger 42mm throats, but there is plenty of material for that mod.  The end result it an ideally sized manifold whose runners are only as big as they need to be.  The 42s are also a nice match for the CFM abilities of the stock reed cages and petals.

    To get performance beyond the afore mentioned carb setups, things start to get a bit more complex (and costly).  It’s understandable that the higher output and rpms of the race gas Limited and Superstock setups would require larger carbs.  However for those carbs to work to their full potential, larger reed cages are also required.  The choice of carbs and reed cages is a function of the maintenance that you are willing to live with.

   The R&D downdraft inlet manifold, with 46mm inlet runners, is the base item for all our race gas inlets.  This manifold can be used with the stock reed cages (using the R&D stuffers).  This setup can work well, but the stock reeds (though reliable) do not permit the a 46 carb to utilize it’s full potential.  For full potential, alternative “combinations” are needed.

   The primary options are choosing between the 46 or 48mm Novi carbs, as well as choosing between the R&D M-16 reed cages and the V-Force Reed cages.  The KMC team (as of this writing) uses the 48mm carbs along with the V-Force reeds.   While the V-force reeds can perform slightly better than the R&D M-16 (using the 48s), the service life of the V-Force petals is typically between 2-5 operating hours.  Since the KMC team can easily afford this interval, the V-Force gets the nod.   For optimum results with this setup, the R&D manifold requires some significant runner enlargement to accommodate both the 48mm carbs, and the V-Force cage openings.

   For those interested in a less maintenance intensive option, we recommend the 46mm Novis with the R&D M-16 reed cages.  The 46mm carbs match the existing diameters of the runners in this manifold, and the inlet opening of the manifold requires minimal grinding/matching to accommodate the M-16 reed cage.  The petal life of the M-16 reeds is roughly 3-4 times that of the V-force, and the slightly smaller 46mm carbs are a bit easier to tune.  Overall, the 46mm/M-16 setup is easier to keep in tune, and easier to maintain (reed petal wise).  The power difference between the 48/V-Force and 46/M-16 setups may be meaningful to riders operating in the very top levels of pro standup racing.  However for the bigger majority of amateur level riders, the maintenance of the 48mm/V-force combo may be hard to justify.

Reeds – Testing has shown that there is no “best” reed cage or petal for all models of engines. That is, the cage or petal that works best on one engine platform will not necessarily best for another.  As previously mentioned, the best in power (for now) is the V Force.  There is constant stream of new reed cages and reed petal parts being offered by the aftermarket.  To test every one of these products on every platform would be a years work by itself.  Especially when trying to evaluate performance increases against long-term life of the petals.  All in all, the reed makers seem stuck with one overbearing issue … the parts that last don’t offer big power increases, and the parts that offer big power increases don’t last as long.  Based on our experience, the stock reed cages petals seem to offer the best longevity.  The Carbon Tech reed petals appear to be relatively durable replacement petals for stock petals, but the power increases from them are not huge.  As new parts come forward, we will continue to seek setups that offers best power and best longevity.

Air Inlet -  The stock SXi 750 flame arrestor is a design that works surprisingly well on most recreational formats.  For all the Group K kits that utilize the standard carburetors, we recommend retaining the stock flame arrestor (with the rubber silencing nozzles removed).  The 42mm Kiehin and 46/48mm Novi carbs do require aftermarket flame arrestors.  The most free-breathing of the arrestors we have seen are the Tau Ceti and R&D arrestors.  Both work well, and are compatible with the Group K engine kits. 

  As the 750 engine becomes more heavily modified, it’s air demands increase as well.  3D-R makes a high flow hood for the 750 SXi that significantly increases air intake, and thereby overall power.  KMC team testing shows an increase of about 1.5 mph on their Superstock race boats with the use of this hood.  In addition, the carbon fiber version is 9 pounds lighter than the stock hood, and has a tighter water seal to the hull.  The 3D-R hood is available in fiberglass, or carbon fiber (neither are Limited class Legal).

  Fuel Inlet -  All the engine setups utilizing the modified stock carburetors, or 42 Kiehins, can easily retain the stock fuel plumbing and petcock arrangement.  However, the setups using 46/48 carbs cannot get sufficient fuel supply through the stock fuel line plumbing.  For these large carb setups, the stock fuel pickup/valve assembly must be replaced by a large diameter, direct feed fuel pickup.  Such a pickup is made by Cold Fusion, and used by the KMC racing team.   We strongly recommend that these fuel pickups be used on any machine with 46/48mm carburetors.

Ignition -  The stock ignition on the SXi/SXi Pro is suitable for 90% of the high performance and racing setups one might construct.  The stock rev limiter of 8000 rpm is enough over-rev for most racing platforms.  The ignition curve is also suitable for all racing platforms.  One important difference in the various 750 models is that the later SXi/SXi Pro ignitions are programmed to carry about 6 degrees more advance than the earlier SX models.  For those earlier models, the aftermarket manufactured “advance plates” that relocated the ignition trigger to offer either 3 degrees or 7degrees more advance.  Since the later SXIs carry more ignition advance already, an advance plate would only be usable (or safe)  on a 100+ octane race gas Limited 2 or Superstock 800 Hammer set up.

  The stock 750 ignition flywheel works well, but it is not a particularly lightweight part.  Reducing the weight of the flywheel rotor can noticeably improve the quickness of throttle response.  This is best done in two different ways, lightening the stock flywheel, or switching to an aluminum replacement.  The logical choice would seem to be simply switching to the lighter aluminum part, however many stand-up riders have found that an extremely light flywheel can offer response that is almost too quick for controlled recreational riding.  That is, the lighter flywheel can allow the engine to accelerate so quickly that it creates more difficult throttle control and more violent porpoising (under acceleration), making the boat more difficult to manage.  Riders call it a “light switch” feeling which refers to the “all on or all off” feeling of engine operation.  The heavier stock flywheel actually helps to dampen that light switch effect to allow for smoother throttle control.  An effective middle ground between the aluminum flywheel and the stocker is slightly lightening the stock ignition flywheel.  Group K ignition flywheel lightening only reduces the flywheel weight by about.6 pounds, however the effect is significant because that weight is taken from the outer diameter of the flywheel where it hurt the inertia the most.  More weight can be removed from the flywheel, but our testing showed that the long term life of the flywheel became questionable with excessive lightening. In addition, this mod is a bit tricky because the trigger lobe on the flywheel OD cannot be touched.  We strongly recommend the stock flywheel lightening for all recreational and Superstock kits.  Note: no flywheel modifications are permitted in IJSBA Limited Class racing.

  For those wishing to construct top level racing boats, we recommend the MSD programmable total loss ignition.  These ignitions have no charging magnets in the aluminum flywheel, making the flywheel much lighter than stock.  Since the spent voltage is not being replenished by a charging system, any voltage used is lost (hence the term total loss).  The battery can easily drive this ignition for the duration of a day’s racing …. But not much more.  The lightweight flywheel of this system offers incredibly quick throttle response, but as previously mentioned, that is only an advantage for boats set up to handle that acceleration, and riders capable of maintaining control.

   We strongly recommend that any machine using a total loss type ignition should also be equipped with a Skat Trak C-75 pump assembly (to hook up the accelerating engine), and an SE “drop nozzle” kit to help keep the nose of the boat down under acceleration.  It would be unwise to use the total loss without these mods.  For riders opting for the MSD total loss ignitions, we also recommend to use the Ultra 150 ignition coils instead of the MSD coils.  The Ultra coils have proven to be a very reliable replacement for the MSD versions (KHI part# 21121-3714).

About Displacement and Pistons -  The stock bore diameter of all 750 stand-ups is 80mm (743.5cc).  Limited Class machines are permitted to overbore to 81.0 mm (762.2cc).  Until 2002, the IJSBA restricted Superstock machines to 785cc.  For the Kawasaki 750, that allowed a bore diameter of 82.2mm (an 82.o mm piston running at max clearance).  The 2002 IJSBA rules will permit 800cc maximum displacement.  .  It bears noting that Wiseco already has available 83.0mm pistons, but they yield a final displacement of 800.3cc, and will not be permitted in IJSBA competition. This means that an 82.8 mm piston (with average clearance) would fall just below 800cc.  By spring of 2002, these 82.8mm (as well as 82.5mm) pistons will be available (from Wiseco). 

  The steel sleeve in the stock SXi cylinder is thick enough to safely accommodate pistons up to this diameter, however the overall integrity of the cylinder block is slightly weakened by the lost bore material.  Given this, the bore diameters can become affected by attached parts.  In particular, the installation of the threaded studs into the top of the cylinder block can create high spots on the bore of a stock cylinder.  As the cylinder sleeve gets bored, this effect becomes greater.  The same applies to the installation of the exhaust manifold studs and the torque forces of the installed exhaust manifold.   Since the FPP exhaust manifold is a substantial casting, torquing it on to the cylinder can slightly deflect the bore diameters.  For stock cylinders of average clearance, this is no problem.  However whenever boring a 750 cylinder (particularly to the 800cc diameters), Group K will require your exhaust manifold with fasteners and the complete top stud set, so they can be installed and torqued prior to final cylinder sizing.  This will assure a much rounder bore with no high spots.

Cylinder Porting -  The stock SXi cylinders carry port timing that is reasonably adequate for recreational applications.  However the mis-matching of the aluminum casting to the steel sleeves is significant.  All the Group K Sleeper and Superstock kits include cylinder porting and decking.  The port timings and widths are altered, and the cylinder deck high is cut to make for ideal squish clearances.  Cylinder porting has received an undeserved reputation as a modification that makes for poor low end power and or poor reliability.  In truth, professional executed cylinder porting yields improved power all through the range, and no significant increase is top end wear.  Group K cylinder porting is the result of many hours of testing, and we assure it to be second to none in terms of strong overall performance and longevity.

  All Group K ported cylinders and modified heads are prepared as a matched pairs.  This allows us to set up the correct squish clearance and compression ratio for the fuel octane that you will be using.  Without doing the head along with the cylinder, it is impossible to assure correct target performance or octane compatability.

Cylinder Heads   All the Group K 92 octane kits can operate safely and reliably with a modified stock cylinder head casting.  The stock SXi 750 head is a good quality casting, and it’s sealing properties, using the stock head gasket, are adequate for most high performance applications.

   For the more intense (and higher revving) race gas kits, there are other considerations apart from head sealing.  Most notably are the concerns of providing added support to the cylinder mount points.  When the output of the 750 engine is increased by huge margins (as is the case on the race gas kits) there is a tremendous increased load on the cylinder base mounting points.  Over time, those increased loads can cause the cylinder casting to fracture around the base bolt mounts.  In an effort to reduce these loads at the cylinder base, the KMC race team uses a “girdle” type cylinder head.  These aftermarket “girdle” heads are manufactured in a way that accommodates very long base studs.  The nuts for these studs tighten against the top surface of the head as well as the base mount points of the cylinder.  The technical intent is to hold the cylinder to the cases via “capturing” the cylinder between the head and the top crankcase.  This then reduces the loads that the cylinder mounting points are subjected to, and thereby “reduces” the likelihood of cylinder base fracturing.  It should be noted that these girdle heads are not a complete “fix” for the cylinder fracturing issue, however they do appear to be the best available solution that conforms to IJSBA competition rules.

  Many of the aftermarket “girdle” type cylinder heads are manufactured to be used with no head gasket.  These heads are machined to accept large diameter “O” rings to seal the water jackets between the cylinder and head.  This system can offer great convenience to owners who regularly remove the head for the purpose of inspection or compression changes (in the case on changeable dome heads).  The other big plus to the “O” ring setup is that it significantly reduces squish clearance without having to machine the top surface of the cylinder.  This “O” system is the stock means of head sealing on most Sea Doo and Polaris engines. 

    It should be understood that an “O” ring can easily seal water away from the cylinder bores, however no “O” ring is strong enough to seal back the pressures of compression.  “O” ring setups depend on two absolutely flat metal-to-metal mating surfaces on both the cylinder and head to seal compression.  The absolute flatness of these two surfaces is fundamental to maintaining a lasting long term seal.  Herein lies a problem with some “O” ring setups.

   As you closely inspect the flatness of a top cylinder surface of a 750, you will often find slight high spots on the top deck surface around each of the threaded stud holes.  These high spots are caused by the unthreaded shoulder of each stud pressing against the top of the threaded hole (when being installed).  On a conventional head gasket setup, the thickness of the gasket can easily accommodate this surface irregularity.   However in an “O” ring only setup, it can happen that these many high spots around the studs can make it very difficult for the head surface to fit flat and solid against the cylinder top surface.  Imperfections of this kind can swiftly lead to a compression leak.  At Group K, we lap each cylinder top surface to eliminate these existing high spots.  This lapping process does not remove material from the cylinder, but rather it just removes the “high spots”.   For “O” ring setups, we recommend lapping of the cylinder top surface after every 10-15 racing hours to assure optimum head sealing.

  Another addition concern for 750 owners using “O” ring heads is the sealing surface width.  Most heads are made to accommodate the 80mm bore of a stock motor.  However if you are preparing a 82.0mm-82.8mm top end, the sealing surface between the bore diameter and the “O” ring can become dangerously narrowed.  R&D will be making their cast girdle head kits available with larger domes and larger “O” parameter grooves to allow wider sealing surfaces on the larger bores.  Given this, we recommend only the R&D cast head with girdle kit.

Engine Lower End -  The crankshaft and crankcases of the SXi have generally proven to be very sturdy and reliable components, even in high performance applications.  For most recreational and local level racing uses, the stock crankshaft can be safely used without any special preparation.  However, for any race gas platform, we strongly recommend that the crankshaft be rebuilt, trued and welded (cranks with less than 50 hours would not require rebuilding).  It bears noting that the cranks of all SXis are manufactured with the crankpin and inner flywheels as one.  In the event of crank pin wears or becomes damaged, it is best to install a new inner flywheel manufactured to accept a separate crank pin.  After this mod, the crank will be completely rebuildable (this mod is Limited and Superstock Legal).  

    The IJSBA rules permit crankcase porting on Superstock class machines (not Limiteds).  Case porting by itself does not offer a huge increase in overall performance.  However on more heavily modified Superstock engines running larger reeds, case porting can definitely help the reeds to better meet their potential. 

  All 750s come equipped with a crankcase drain (that little black plastic knob on the exhaust).  The drain was intended as an easy way to drain the crankcases of water in the event that the engine lower end becomes flooded.  Unfortunately, the valve mechanism of the drain can cause an air leak on high performance engine packages.  We strongly recommend to remove the drain valve assembly, and cover the valve opening on the case with a special block-off manufactured by UMI.

General Assembly -  Air Leaks - Your assembled engine should be internally 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.  “Every” 750 engine being modified for higher performance should be pressure tested to assure that there are no air leaks.  Pressure testing is a standard procedure for all 750 engines assembled at Group K.

Pump & Impellers -  The stock 140mm pump is the 750 stand ups is slightly smaller than that used in the Yamahas Super Jet (144mm).  Despite this, with the right impeller, the stock pump can easily deliver the power of a modified SXi.  After much testing, we found the Skat Trak C-75 9/17 Swirl impeller to be the hands down best in speed and hook up.  This particular prop is originally made for the 75mm hub stainless steel Skat Trak pump.  Even though the hub diameter doesn’t match the hub diameter of the stock pump, it works best on all our engine setups.

For most high performance recreational applications, the stock SXi pump assembly works fine.  For owners that want to “fine-tune” the stock pump, we recommend pump blueprinting.  This pump blueprinting does not increase smooth water peak speeds, however it can make a noticeable improvement in rough water hook-up ability.

   For more serious racers, the stainless steel Skat Trak 12 vane “C-75” 140mm pump assembly is the last word in pump mods.  This pump assembly offers incredibly good rough water hook-up that cannot be matched with any other pump setup.  Since the IJSBA rules mandate that a stock pump “housing must be retained, Skat Trak installs their stainless steel insert into your pump case, hence your pump case “core” is required for this modification.

Handling Hardware -  Besides the 3D-R hull handling parts, there are other important parts worth noting.  While ride plate choice is very much a matter of rider preference, the current overall best choice appears to be the Worx ride plate.  This plate (like most of the functional SXi plates) is relatively long.  It’s other unique characteristic is it’s rearward half moon through-hole that helps to hold the rear of the hull to the water.  This plate does slightly reduce smooth water peak speeds, but the overall improvement in control and handling is well worth that loss.

  With regards to scoop grates, the two best choices are the Worx and the Skat Trak grates.  The Worx Scoop grate is a very good choice for recreational/race riders, with only a small loss in smooth water peak speed.  The Skat Trak Scoop grate is an all stainless steel part that is used on the KMC race team machines.  This grate is much more aggressive (and more expensive) than the Worx grate, and it does result in a greater smooth-water speed loss than the Worx grate.  However, we would strongly recommend the Skat Trak grate to serious Limited and Superstock competitors.

Handling Comforts -  There are several other components that can make a high performance SXi much easier to handle and manage at speed.  Starting at the controls, the UMI 4 degree handlebars have proven to be the most popular and comfortable bend.  UMI also manufactures a “turn plate” with billet handlebar clamps.  This turn plate offers quicker steering options that would be needed for closed course riding/racing.  Most riders will also opt for a billet throttle lever, but be sure the one you get will accommodate the throttle adjuster.  UMI sells an adaptor to accept the stock cable. To avoid the fatigue of excessive handlepole weight, UMI offers a handle pole spring tensioner that is very easy to install.

   While mats are generally pretty straight forward, there is an important option here.  AP Designs has designed side mats for the tray that have a 10’ long x 2” wide pad sewn into both sides close to the base mat.  These pads (called “lift pads”) allow the rider to hook either foot underneath to aid in lifting the rear of the hull over obstacles.  These are the same pads used by the KMC race team.

  As previously mentioned in the ignition section, we strongly recommend the use of an SE Racing drop nozzle for any closed course race machines, in particular those with total loss ignitions.  This system features a nozzle whose trim angle can be drawn down 10’ via a level on the left handlebar.  Pulling this lever instantly eliminates porpoising, and allows for much easier control when accelerating off of turns.  The kit consists of a complete nozzle set (exit, trim, & steering) as well as the lever, cable, and through hull tube that accommodates the cable to the nozzle.

Cooling System -  The stock SXi cooling system is fed through a series of 6mm id. brass fittings.  For the Sleeper kits, we recommend slightly increasing the size of these fittings to improve cooling capacity.  However the FPP Dry Pipe requires the input of considerably more cooling water.  The aluminum through-hull feed tube (from the pump to the engine compartment) has a 9mm id with ends swedged down to 7mm.  Rather than install a dual cooling system, Group K recommends to increase the through hull feed tube ends and pump feed fitting, to a full 9mm.  This modification better than doubles the volume potential of the stock system, and matches the feed tube diameter of the inlet fitting on the FPP Pipe.  This upgrade has the same input volume capability as two Ľ” id. feed tubes.

So You Want Exactly What MacClugage Has -  There is a perception that the engine modifications used by Chris MacClugage are some secret specs that are not spoken of so that Chris can maintain some competitive advantage … nothing could be farther from the truth.  However there are plenty of reasons why you may not want “exactly” what Chris has.  The following is a brief explanation of some of these reasons.

   Since Chris is an exceptional riding talent, he can control an SXi at speeds where others cannot.  To access those high speeds, the race team techs utilize an exhaust port whose timing is very high, and whose roof shape is very squared off (to obtain maximum exhaust port area for that height).  While this large squared off exhaust port offers exceptional high rpm power abilities, it is “very” abusive to the piston and piston rings.  In fact the abuse is so great that the effective piston and ring life is about 5 to 10% of normal.  Since this operating time is just beyond the recommended break in period for most pistons, the break in period must be done away with.  To do so, the cylinders must be set up at a clearance that would ordinarily be considered excessive.  This excessive clearance then results in slightly greater piston rocking, and thereby even more accelerated ring wear and piston skirt collapse.  This added wear reduces the “optimum performance” piston/ring service even more.  While all this equates to a very short piston/ring operating interval, it is easily long enough for Chris to complete a full day’s event.  Unfortunately after several full days of this kind of operation, the cylinder bores experience heavy wear from constantly being operated with very loose fit pistons. Since the bores are at the maximum legal bore already, there is no overboring. To maintain optimum output, the cylinder is replaced with another maximum bore ported cylinder after every third or fourth outing.

   At the same time, this same high exhaust port timing causes a loss in low-end power.   In addition there is the compression loss from running such a loose clearance pistons.  To recover that compression and low-end power, the compression ratio is increased to well over 200psi cranking pressure.  As the engine is run constantly at it’s very high peak rpm against this kind of compression, the connecting rods and bearings are subjected to extreme loads that no recreational engine would ever experience.  After a few racing hours, these extreme loads can be great enough to slightly stretch the connecting rods, and/or cause fractures of a needle-bearing cage.  Constructing heavier rods is not sensible because it would increase reciprocating and rotating weight … and the bearings are going to have to be replaced in short order anyway.   Given that any kind of crank or rod failure can damage so many other engine components, the crankshaft assemblies are frequently replaced, more out of precaution rather than failure.

   Understandably, not many racers are willing to bear the costs and considerable time to perform this kind of regular maintenance.  At the same time, most aftermarket shops (Group K included) are a bit coy about selling machinery that is so maintenance intensive.

   In truth, Chris’s SXi 750 is capable of going faster than anyone (but Chris) is capable of riding.  The other truth is that by choosing specifications that are just a tick away from the specs that Chris runs, the projected longevity of all moving parts will increase by huge margins.  The Group K 800cc Hammer kit is our interpretation of how close we can get to the output of Chris’s SXi without involving the same level of maintenance as Chris’s SXi.

 

Complete Engines – While many owners prefer to do their own mechanical work, there are plenty of folks that don’t consider engine assembly as “fun”.  For those customers, Group K can construct a complete ready to install short-block, modified to your specifications.  The 150 pound UPS weight-limit easily accommodates the SXi engine (about 115 lb) .  All short-blocks are assembled with all new gaskets and seals, and then pressure tested to assure no “rouge” air leaks.

Note that complete short-blocks carry a $35.00 fee to cover handling and container costs.

 

Complete Boats -  Group K can construct a complete turn key race boat to your specifications.  After assembly, all complete race boats are broken in and water tested to confirm tuning and performance.  Specific quotes to your specification are available for $50 billed to your Visa/MasterCard.  This quote charge is then applied to the cost of the machine upon ordering.

 

PRICES


Sleeper Engine Modification Kit (dual carb)                            639.00

(includes cylinder porting, decking and exhaust manifold matching, cylinder head modification, cooling upgrade,

 & carb “true” boring and jetting)

 

Sleeper 800cc Modification Kit (dual carb)                             1078.00

(includes cylinder big boring, porting, decking,

& exhaust manifold matching, Wiseco Pistons,

 big bore head gasket, cylinder head modification

 cooling upgrade & carb “true” boring and jetting)

 

Optional Ignition Flywheel Lightening                                          95.00

Optional UMI Crank Case Drain Block-off                                   22.00

Skat Trak C-75  9/17 Impeller                                                      298.00

Optional Pump Blue Printing                                                       210.00

Worx Ride Plate                                                                              180.00

Worx Scoop Grate                                                                          150.00

Optional 3D-R Front Sponsons                                                  225.00

Optional 3D-R Rear End Caps                                                   225.00

SE Racing Drop Nozzle Kit                                                           498.00

UMI Billet Throttle with cable adaptor                                           72.00                                                                       

UMI 4’ Handlebars                                                                           45.50

UMI Steering Plate                                                                           39.00

UMI Handlepole spring tensioner                                                 15.00

AP Designs Side Mats with Lift Pads                                         119.00

AP Designs Bottom Mat                                                                  85.00

 

Limited 1 Kit (92 octane)

Factory Pipe Products Dry Pipe with ECWI                               800.00

Carb “true boring” and jetting                                                      195.00

Cylinder head Modification (92 octane)                                       90.00

Cylinder Boring (1mm)                                                                    90.00

Wiseco 81.0mm Pistons (2)                                                        228.00

UMI Crank Case Drain Block-off                                                   22.00

Optional R&D Flame Arrestor with adaptors                            160.00

Optional Carbon Tech Reed petals                                              99.00

Optional R&D Billet Head with Girdle kit                                   278.00

3D-R Front Sponsons                                                                   225.00

3D-R Rear End Caps                                                                    225.00

Skat Trak C-75  9/17 Impeller                                                      298.00

Worx Ride Plate                                                                              180.00

Worx Scoop Grate                                                                           150.00

Optional Skat Trak Stainless Steel Scoop Grate                     199.00

UMI Billet Throttle with cable adaptor                                           72.00                                                                       

UMI 4’ Handlebars                                                                           45.50

UMI Steering Plate                                                                           39.00

UMI Handlepole spring tensioner                                                 15.00

AP Designs Side Mats with Lift Pads                                         119.00

AP Designs Bottom Mat                                                                  85.00

AP Designs Chin Pad                                                                     39.00

 

Limited 2 Kit (100+ octane)

Factory Pipe Products Dry Pipe with ECWI                               800.00                                                                       

R&D Head Girdle Head kit                                                           278.00

Cylinder Boring (1mm)                                                                    90.00

Wiseco 81.0mm Pistons (2)                                                        298.00

3 degree Ignition Advance Plate                                                    29.00

46mm Novi Carbs                                                                         877.00

R&D Inlet Down-draft Manifold & M-16 Reeds 153./419.       572.00

48mm Novi Carbs                                                                         914.00

R&D Inlet Manifold & V Force Reeds  153./516.                      669.00                                                                       

R&D Flame Arrestor Pods (for Novi 46/48s)                            100.00

UMI Crank Case Drain Block-off                                                   22.00

3D-R Front Sponsons                                                                   225.00

3D-R Rear End Caps                                                                    225.00

Skat Trak C-75  9/17 Impeller                                                      249.00

Worx Ride Plate                                                                              150.00

Skat Trak Stainless Steel Scoop Grate                                     199.00

SE Racing Drop Nozzle Kit                                                           498.00

UMI Billet Throttle with cable adaptor                                           72.00                                                                       

UMI 4’ Handlebars                                                                           45.50

UMI Steering Plate                                                                           39.00

UMI Handlepole spring tensioner                                                 15.00

AP Designs Side Mats with Lift Pads                                         119.00

AP Designs Bottom Mat                                                                  85.00

AP Designs Chin Pad                                                                     39.00

 

Superstock 1 Kit (92 octane)

Factory Pipe Products Dry Pipe with ECWI                               800.00                                                                       

Carb “true boring” and jetting                                                      239.00

Group K 92 octane porting, decking,

 and exhaust manifold matching                                                360.00

Cylinder head Modification (92 octane)                                       90.00

Cylinder Boring (+2mm-2.8mm)                                                 100.00

Wiseco 82.0-82.8mm Pistons(2)                                                228.00

Ignition Flywheel Lightening                                                           95.00

UMI Crank Case Drain Block-off                                                   22.00

Optional 42mm Kiehin Carb kit (no arrestors)                         445.00

Optional R&D Flame Arrestors with adaptors                          160.00

Optional Carbon Tech Reed petals                                              99.00

Optional R&D Girdle Head kit                                                      278.00

 

3D-R Front Sponsons                                                                   225.00

3D-R Rear End Caps                                                                    225.00

Skat Trak C-75  9/17 Impeller                                                      230.00

Optional Pump Blue Printing                                                       210.00

Worx Ride Plate                                                                              180.00

Worx Scoop Grate                                                                           150.00

Optional Skat Trak Stainless Steel Scoop Grate                     199.00

SE Racing Drop Nozzle Kit                                                           498.00

UMI Billet Throttle with cable adaptor                                           72.00                                                                       

UMI 4’ Handlebars                                                                           45.50

UMI Steering Plate                                                                           39.00

UMI Handlepole spring tensioner                                                 15.00

AP Designs Side Mats with Lift Pads                                         119.00

AP Designs Bottom Mat                                                                  85.00

AP Designs Chin Pad                                                                     39.00

 

Superstock 2 Kit (100+ octane)

Factory Pipe Products Dry Pipe with ECWI                               800.00                                                                       

Group K 100+ octane porting, decking,

 and exhaust manifold matching                                                360.00

Cylinder Boring (+2mm-2.8mm)                                                 100.00

Wiseco 82.0-82.8mm Pistons(2)                                               298.00

R&D Girdle & Head kit                                                                  278.00

UMI Crank Case Drain Block-off                                                   22.00

46mm Novi Carbs         

R&D Inlet Down-draft Manifold & M-16 Reeds 153./419.       572.00

48mm Novi Carbs                                                                     

R&D Inlet Manifold & V Force Reeds  153./516.                      669.00                                                                       

R&D Flame Arrestor Pods (for Novi 46/48s)                            100.00

3 degree Ignition Advance Plate                                                    29.00

Optional MSD Total Loss Ignition w/ Aluminum Flywheel     885.00

3D-R Carbon Fiber Hood                                                             750.00

3D-R Fiberglass Hood                                                                 410.00

 

3D-R Front Sponsons                                                                   225.00

3D-R Rear End Caps                                                                    225.00

Worx Ride Plate                                                                              180.00

Skat Trak Stainless Steel Scoop Grate                                     199.00

SE Racing Drop Nozzle Kit                                                           498.00

UMI Billet Throttle with cable adaptor                                           72.00                                                                       

UMI 4’ Handlebars                                                                           45.50

UMI Steering Plate                                                                           39.00

UMI Handlepole spring tensioner                                                 15.00

AP Designs Side Mats with Lift Pads                                         119.00

AP Designs Bottom Mat                                                                  85.00

AP Designs Chin Pad                                                                     39.00

 

Misc. Labor

Cylinder boring, sizing, & chamfer                                                90.00

Cylinder Big Boring sizing, & chamfer (2mm+)                        100.00

Crankshaft Truing and Welding                                                  180.00

Crankshaft Rebuild w/ Truing and Welding (C4 bearings)   590.00

Center Crank Flywheel Flats (2)                                                    138.00

Engine teardown and Re-assembly & Pressure Test           450.00


 

 

 

ORDER INFORMATION: SEND ALL PARTS REQUIRED FOR MODIFICATION VIA UPS TO:

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 new 150-lb. UPS weight limit makes engine shipping practical and affordable.

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 cashiers check (ups no long accepts cash for cods).   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.