High performance Modifications for '01-'03  Kawasaki STX 1100 Di

Overview

The STX 1100 Di was introduced in 2000 as a cutting edge low emissions pwc.  Kawasaki fitted the Ficht "direct injection" system to their very reliable 1100cc three cylinder pwc engine platform, to create a model whose emissions were 70% less than carbureted models.  The computer controlled Ficht system employs timed fuel injectors, mounted on the cylinder head, that inject a predetermined amount of fuel for each engine rpm and load.  This system has several "sensors that constantly monitor air temperature, exhaust system temperature, engine rpm, throttle opening, etc.  The Ficht system has been preprogrammed to "know" exactly how much fuel to admit for every temperature/speed combination.  This set of preprogrammed fuel delivery curves are referred to as the fuel "mapping".  This mapping is what makes for the easy starting and instant throttle response that the Di models possess.

  When we modified the earlier "carbureted" versions of the Kawasaki STX, the operating rpms AND fuel demands were increased.  Meeting the increased fuel demands of those models was easily accomplished by increasing carburetor jet size and high speed screw adjustment.  Unfortunately, the Ficht system has no such adjustment.  In the automotive high performance fields, aftermarket companies often utilize aftermarket computer "chips" or ECUs (electronic control units) to alter the fuel mapping of the fuel injection systems.  The programming of the Ficht system is heavy encrypted in a way that makes these kinds of mapping modifications impractical if not impossible.

  Given this situation, we designed and developed our performance modifications for the STX 1100 Di to operate entirely within the fuel delivery capabilities of the stock mapping system.  Such modifications require a very different technical approach than what might be used on a carbureted version ... however we still obtained substantial increases.  The basic speed data is as follows (note: all speed tests done with 200 lb solo rider, 80' temp, 87 octane fuel) :

  Towing Spec Solo Spec
Stock STX 1100 Di   52-53 mph
Stage 1 Kit (87 octane safe) 54-55 mph 56-57 mph
Stage 2 Kit - (87 octane safe)  57-58 mph 60-61 mph

         About Impellers - The stock prop used in the STX Di works well for a stock machine, however there are considerable gains to be had by installing an aftermarket impeller.  For the Di we have chosen the Solas "Concord" series of impellers.  The primary feature of these props that makes them better is the combination of a more efficient hub contour and better blade design.  This design combination allows these props to process more water "per impeller revolution" than the stock prop.  The pitch numbers between the stock impeller and the Solas is completely irrelevant, because blade pitch is only a correction factor for any given hub/blade design.  Since the hub/blade design of the Solas and stock props are very different, the pitch data does not translate.

  That said, we have done considerable testing with the Solas pros to find the correct application for our kits, and the impeller choice is crucial to netting the proper target rpms and peak speeds.  It bears noting that the fuel mapping does not know impeller pitch has been changed.  It only knows how much fuel the stock prop required for a particular rpm ... and feeds that.  We consider the correct impeller pitch to be very important for each of our kit applications.  The Solas Concord pitches and applications are as follows:

  Towing Spec Solo Spec
Stock STX 1100 Di 12/18 13/19
Stage 1 Kit 12/18 13/19
Stage 2 Kit 13/19 14/20

 

 Stage 1 Kit   

Ride Plate Modification - If any one characteristic of the STX Di could be called a "problem" area, it would be the strong nose heavy attitude of the hull once up on plane.  We can only presume that Kawasaki engineers used this characteristic to reduce nose lifting when used for towing.  Whatever the case, this nose heavy planing attitude results in two problems.  First and foremost, the nose down attitude subjects the driver to a very punishing ride when the boat is being operated at high speed in rough water.  Secondly, peak speed ability is significantly reduced because of the drag from the large amount of hull surface that is making contact with the water surface (even in glass water conditions).  The most common means of dealing with this problem is to install a wedge plate between the pump and exit nozzle (thus lifting the nose), or by altering the ride plate.  Modifying the stock ride plate requires a special machining fixture to assure perfect accuracy (inaccurate machining can induce a "pull" to one side), however dollar for dollar it nets the best overall affect.

  Nozzle wedges are available for the 1100 pump, however they can sometimes affect steering control, as well as the function of the reverse feature.  For our kits, we opted to modify the stock ride plate, and found that the modified ride plate allowed for ideal nose lifting (at speed) while still offering very good steering control.  In addition, the high speed comfort for the driver is greatly increased because the elevated nose is making less contact with the oncoming rough water.  This same reduced water contact surface area, afforded by the ride plate modification, makes for a peak speed increase of about 3 mph.

Machines used routinely for towing sports do not need as much "nose lifting" as machines being used primarily for "solo" or "destination touring" type riding.  To accommodate this, we have different ride plate modification "specs" for the "towing" and "solo" machines.  When sending your ride plate for modification, please specify a "towing" or "solo" spec.

   It bears noting that some aftermarket ride plates (as well as the stock STXR ride plate) can accomplish "some" of the same characteristic we achieve with the modified stock plate.  However the down side of these other ride plates (besides the much higher price tag) is that the machine will lose the reverse. 

Exhaust Plumbing Kit  -  The stock exhaust system of the 1100 Di is termed a "wet" pipe (meaning that a small amount of water from the pipe water-jacket is injected into the interior of the exhaust pipe body).  Slightly reducing the amount of water being injected into the pipe interior can make a noticeable improvement in overall throttle response as well as a slight increase in high range power.  Our exhaust jetting kit does not make a big performance increase by itself, however in combination with the other modifications, it does offer a noticeable benefit.

 

 

Stage 2 Kit

We consider our ride plate modification to be very important from a standpoint that exceeds the aforementioned advantages.  The reduced water contact surface area resulting from this modification greatly reduces the actual "load" on the engine at all planing speeds.  Remember, the stock fuel mapping is programmed to deliver enough fuel for the heavier loads of the stock ride attitude.  With the reduced loads of the modified ride plate, there is actually a slight excess of fuel being delivered by the stock mapping.  This slight excess can then be used to accommodate some other subtle, but very beneficial engine modifications.  With all this said, it should be noted that for the stage 2 cylinder to be used, the ride plate modification must first be done.

Cylinder Modification  -  The cylinder porting layout of the 1100 Di engine is considerably milder than the porting of the earlier carbureted 1100 engines.  This milder format yields strong power at low and mid-ranges, but does not allow for large increases at high rpms.  Simply upgrading to the port timings of the earlier carbureted 1100 engines is not an option because the fuel mapping will not accommodate those higher rpm fuel demands.  For our stage 2 kits, we developed a cylinder modification that has slightly higher compression ratios, slightly increased port timings and widths, and greatly improved flow characteristics.  Since the reduced loads of the ride plate modification have made available a small amount of additional fuels, the porting and machining of the Stage 2 cylinder modification can use those fuels to yield a significant improvement in power at all rpm ranges.  Our cylinder modification does not include cylinder boring.

  This Stage 2 modified cylinder does not turn more rpms than the stock engine setup.  However, it does create a great deal more torque at all rpms that allows the machine to pull a much steeper prop.  The greater acceleration and higher speeds of the Stage 2 kit are a function of the added torque being delivered to the steeper Solas prop.  Also note that the use of the steeper Stage 2 prop will result in improved fuel range.  At full throttle, the unaltered injection system will be giving the same fuel to the 60 mph Stage 2 as it was giving the 52 mph stock boat, hence the added range.

About Cylinder head Modification -  Cylinder head milling has been a popular modification for carbureted versions of pwcs.  Since the STX1100 Di has all the Ficht injector hardware mounted in the cylinder head, we opted to leave the cylinder head completely stock, and do all the machining and compression alterations on the cylinder only.  This allows our customers to remove and set aside the cylinder head, with the injectors still intact, during the teardown process.

Cooling System -  The stock cooling system is easily adequate to deal with the temperatures of the stage 2 kit under normal usage.  However during our testing, we found that during extended full throttle runs (5 minutes and longer) the front cylinder began to run noticeably warmer than the other two.  To restore more equal operating cylinder temperatures, we fitted an additional cooling outlet to the cylinder head on the #1 cylinder.  With this optional cooling upgrade, the full throttle heating of the #1 cylinder is significantly reduced.  We would recommend this option to any customers that often run at full speed for extended periods of time.

 

About Pump Modifications -  For owners who routinely ride in rough water conditions, maintaining good pump hook up can be a particular problem.  The Solas impellers used with our kits greatly improve hook up by themselves, but there is still room for additional improvement.  For machines that are used primarily for towing sports, a "Worx" brand scoop grate can offer a quick and easy way to improve hookup.  Unfortunately, this scoop grate also reduces smooth water peak speeds by about 2 mph and slightly increases the loads on the engine.  For "towing use" machines that are primarily used at lower speeds, these are not big issues.  The same cannot be said for "solo" and destination touring machines.  For these speed and mileage conscious owners, we recommend pump blueprinting.  Our pump blueprinting removes all the interruptions and casting drafts from the pump vane body.  By doing so, the high speed rough water hook up is improved considerably without inducing additional peak speed loads or causing smooth water speed losses that come with a scoop grate.

PRICE LIST

Stage 1 Kit    

Ride Plate Modification, Exhaust Plumbing kit, Solas impeller

 

Stage 2 Kit  

Cylinder modification, Ride Plate Modification, Exhaust Plumbing kit, Solas impeller

 

Kit Price Breakdowns

Ride Plate Modification (towing)    70.00
Ride Plate Modification (Solo)    70.00
Exhaust Pipe Jetting Kit    29.00
   
Stage 2 Cylinder Modification  550.00
Optional Cooling upgrade    30.00
   
Solas Concord Impeller   (12/18, 13/19, 14/20)  265.00
   
Worx Scoop Grate (Recommended for towing only) 115.00
Pump Blueprinting 210.00
   
   
   
   

 

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/MasterCard 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.

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