4597 Calle Del Media

Ft. Mohave, AZ 86426

+1 (928) 763-7600


Polaris 1050 Engine

Group K Modifications

This document will outline the Group K modifications available for the ’96 – ’99 2 and 3 seat Polaris 1050cc models. Group K offers three different levels of modification for the 1050’s. They are as follows:

Limited Kit – This affordable modification is ideal for the recreational owner who wants a noticeable increase in overall performance without major teardown work. The Limited Kit offers easy starting, strong acceleration and a noticeable increase in peak speed.

Sleeper Kit – This kit is intended to yield the maximum performance increase, while maintaining good reliability and fuel range. This kit offers very significant increases in overall acceleration and peak water speed while still retaining the stock exhaust system and ignition.

Hammer Kit – This kit, which utilizes the Factory Pipe Products “triple pipe” exhaust system, is an all out competition/grudge racing engine mod. The 2 seater Hammer kit is the quickest and fastest pump gas machine we have constructed to date. The Hammer modifications are intended to work in concert with these pipes to make for the biggest performance increases, for the money spent. These kits will be available for the ’98 and later two seaters as well as the three seaters (at such time when FPP releases that system for the SLTX’s). The performance stats of these kits are as follows:





97/99 SLTX

54/55 mph

56/57 mph

60/61 mph

64/65 mph

98/99 SLHX/SLX

61/62 mph

63/64 mph

66/67 mph

70/71 mph

About The Stock Machines – The domestic built 1050cc Polaris engine has a good reputation for delivering overall power along with good reliability. The 3 seater SLTX has excellent handling and hook-up abilities that make it well suited to handle increased horsepower levels. Like many 3 seaters, the SLTX has “acceptable” high speed turning characteristics. The added power of the Group K kits can also help the rider to better “steer” the boat using thrust. Just the same, the SLTX is a hull that has limited turning abilities (from a competition perspective).

The 2 seater SLXH/SLX models, while built as high performance sport boats, require significant considerations with respect to high speed handling. The 2 seater 1050 turns very aggressively, and is an outstanding straight-line “grudge racer” where water conditions are very smooth. However as water conditions become rougher, the short 2 seater hull can become somewhat difficult to control. Increasing the horsepower of the 2 seater hulls can compound this high speed rough-water handling problem. We outline several modifications that can noticeably improve this handling. However even with these improvements, the 2 seater will never be a good rough-water machine.

CYLINDER HEAD MODIFICATION – All of our kits include cylinder head dome modification, however the dome volume and shape specifications are different for all thee kits. While each “head” is actually two separate parts (dome and water jacket shell), we only need the domes for our modification work. This head modification has a two fold purpose. First, to accurately set the compression ratio/head volume. The second is to set the correct squish angles and clearances, which helps reduce detonation.

It bears noting that, during our testing, we found that the 1050 engines do not respond well to big increases in compression ratio (as some other pwc’s do). During our testing, we found that running excessive compression resulted in large increases in operating temperature, and very minor increases in performance. This is particularly true for the triple-pipe Hammer setups. While our head mods do net various compression increases, those increases are not huge. Along with this, the operating temperature of all thee cylinders is not identical. To help correct this, the compression ratios of the 3 domes are staggered (slightly different) to help equalize the combustion chamber temperatures.

CYLINDER PORTING – The Sleeper and Hammer kits both 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 these kits are 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. All Group K modified cylinders and heads are prepared as matched pairs to assure that you have the proper squish clearance and compression ratio. These specifications play the key role indicating the amount of overall power that the engine can make, as well as the quality of fuel that you may use. If you have aftermarket domes that you want to use, we must inspect them to assure that they are within the spec range for our top end set (we will not prepare any “1 piece” heads for use with our kits).

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.


Limited and Sleeper Kits – The stock 1050 carbs are denoted as 38mm, however they actually run about 35 mm at the smallest part of the venturi. For our Limited and Sleeper kit, we have chosen to bore the stock carbs to a true 38mm, and refine the jetting calibration for that throat diameter. This arrangement allows for instant starting, steady idling, and strong acceleration under all conditions. As part of this carb modification, we remove the choke butterflies. Since the 1050 carbs have accelerator pumps (that spray raw fuel down the carb throats), we use 7 – 8 pumps at the throttle lever to “prime” the carbs for cold starts. Once the engine is warm, starting is instant without any priming at all. Together with the high pitch impeller, these modified carbs allow the Sleeper modified boat to offer better fuel consumption, at cruising speeds, than the stock SLTX. The installation of larger carburetors has always been considered a popular bolt on modification. However installing these (often very expensive) carbs, on a recreational machine like the 1050 Sleeper, results in very questionable increases in performance and significant increases in fuel consumption.

Hammer Kits – The triple pipes of the Hammer kit do require an increase in carb throat size to deliver the full potential of power. For our Hammer kits, we chose to use the 42mm Keihin High performance carbs. These tapered throat carbs bolt directly onto the stock inlet manifold and match up perfectly to the stock flame arrestor and throttle cable. The only modification required to accommodate them is the opening of the passages in the inlet manifold, and the installation of a 3rd pulse line for the center carburetor. This 42mm carb kit (including linkage , gaskets, and pre-jetting for your 1050 kit) is the least expensive and most effective carb upgrade we have seen for the 1050 engines. These carbs allow for smooth idling as well as “violent” acceleration from all speeds. To be sure there are many “larger” throat carb kits available for this engine. Our testing indicated that these “other” larger throat carbs consumed a lot more fuel than our 42’s, but produced no more power. For added ease of installation and synchronization, Group K can attach the “rack bars” from your stock Keihin carbs on to your new 42’s. For this modification, simply send the carb bars along with you other parts for modification.

All of our 1050 kits utilize the stock reed cages and petals. There are many aftermarket replacement reeds that can offer improved performance…for a few operating hours. However after that, the material of these other petals can begin to “lose it’s memory” or begin to fracture. As this happens, the performance gradually becomes “less than the stock part”. No aftermarket replacements (to date) have offered the combination of longevity and performance that the stock parts offer.

Along that same tack, the stock 1050 flame arrestor is a well designed part that met all the mechanical needs of our kits. It offers a good combination of air inlet and water spray protection. Installing an aftermarket replacement will have a negligible effect on performance.

EXHAUST SYSTEMS – The stock 1050 exhaust system is capable of delivering very good overall performance for recreational applications. We do not consider the stock pipe or waterbox to be a handicap of any kind on our Limited and Sleeper Kits. There are a number of aftermarket waterbox mufflers available for the 1050’s. While these waterboxes can offer a noticeable improvement in overall performance, they also yield a very significant increase in exhaust sound level. Given the general publics sensitivity to the pwc sound level issue, we choose not to include these waterboxes as part of our kits. Quite frankly, we find that there are plenty of other ways to yield ideal power levels without resorting to louder exhaust components.

THE FPP TRIPLE PIPE SYSTEM & THE HAMMER KIT – In fall of 1998, Factory Pipe Products, of Ukia California, released their aluminum triple pipes for the 1998 SLXH 1050 (this version of the pipes will not fit the ’97 SL1050 nor the 3 seaters). These pipes are constructed as “completely water jacketed pipes”. That means there are actually 6 complete pipe bodies…the 3 interior expansion chambers, and the 3 exterior water-jacket chambers. This complex construction is one of the reasons for the “attention getting” $2500 retail price tag.

Understandably, the FPP pipes were originally designed and intended for use on heavily modified IJSBA tour race machines. Given this, all the original testing and development was conducted only on such racing engines. When FPP decided to sell the triple pipes as part of their normal product line, their first order of business was to confirm the performance ability of the pipes on a completely stock machine (which is the standard goal for all their products). While the triple pipes certainly offered a noticeable performance gain on a stock machine, the increase was not on the order of what most customers would be expecting for a $2500 price tag.

It was at this time that FPP contacted Group K to help with the development of a “minimum modification” package that would allow the triple pipes to deliver a much bigger chunk of the potential power they had to offer. Since we already had considerable experience with the 1050 engines, we already had a pretty good idea of which modifications an FPP equipped 1050 might best respond to. Our Hammer Kit is the end result of that testing. At this writing, we have completed the development of the ’98 SLXH Hammer kit using “production” triple pipes from FPP. All our SLTX triple pipe tests were conducted with a set of “pre-production” pipes. Given this, we expect to revisit the 3 seater tests when true “production” pipes are available.

IGNITION – The stock ignition on the 1050 motors has a rev limiter that engages between 6700 – 6750 rpm. The Limited and Sleeper Kits are both intended to be used with the stock ignition and limiter (the Sleeper gains added speeds by pulling a steeper impeller). We found no benefit by using a “higher rpm limit” cdi box on these two kits.

The Hammer Kit mandates the use of a Hot Seat cdi box , which eliminates the rev limiter. The Hot Seat boxes can be set up with different ignition timing values. All our Hammer kits use the most retarded setting of 23 degrees. Running more ignition advance with our kit results in higher operating temperatures, but not high power output.

COOLING SYSTEM – For owners who have not already done so, the 1050 cooling can be much improved by removing the plunger and spring that are mounted in the cooling bar (next to the thermostat). The standard cooling system (with thermostat ) works fine for the Limited and Sleeper kits. We would recommend that the thermostats be replaced each season. The Hammer kit uses no thermostat, and requires modification of the cooling bar (send the cooling bar with your top end parts).

ABOUT FUEL OCTANES – All of our 1050 kits are intended to run on 92 octane unleaded pump gas under normal use. The Hammer 2 seater is a machine capable of 70 mph on pump gas, however running at full speed for 5 miles non-stop is not “normal use” for anyone. The collective heat from extended full rpm operation simply generates more heat than any 92 octane fuel can support. For Sleeper and Hammer kit owners who intend to use their machines under extreme or competition use, we recommend a 50/50 mix of avgas (race gas) with the 92 octane. This octane enhancement offers a big safety buffer against detonation, and the piston damage that detonation can potentially cause.

LOWER END PREPARATION – For the recreational power output of the Limited and Sleeper kits, the stock lower end of the engine needs no special preparation. We would qualify that by saying that any 1050, with over 100 hours on it, should be a candidate for a lower end rebuild. The crank seals in the 1050 Polaris engines are not “last forever” type parts. For customers planning to build a Hammer Kited machine, we strongly recommend a crankshaft rebuild on any crank with over 60 hours on it. The high output and rpms of the Hammer kit can deal a death blow to an already weakened crank bearing. For all owners building a Hammer kit, crankshaft truing and welding is considered mandatory to avoid crank journal twisting between cylinders.

Perhaps the most important preparation we could recommend for ALL 1050 owners would be to pressure check their engines. This should not be confused with “compression testing” (which is altogether different). Pressure testing involves pressurizing the lower end of the engine to 8 – 10 psi (with the inlet and exhaust manifold ports blocked off air tight). If there is an air leak of any kind, your in-line gauge will show the pressure drop. If you have air leaking out, that means there is raw air leaking “in” during operation. This “air leak” will induce intermittent lean conditions that can result in piston scoring. We have seen such an uncommonly high occurrence of air leaks on 1050 engines (particularly at the ignition housing/crankcase joint), that we consider this to be a mandatory inspection. Air leak test kits for your 1050 are available from Watercraft Connection (503) 232-2026.

IMPELLERS AND PUMPS – The 1050’s come stock with a “swirl type impeller. These impellers offer great hook up in rough water because of the great amount of impeller-blade/water-contact surface area. Unfortunately this blade design generates a lot less peak water speed than more conventional design props. The Limited kits can work fine with the stock impeller, however we recommend Solas impellers for the Sleeper and Hammer Kits. The two primary pitches used are the “Xo” pitch, and the steeper “X1” pitch. The Xo prop is used on the 3 seater Limited and Hammer formats, while the X1 is used on all the rest. While these props can work fine “out of the box”, we have seen some significant production pitch variations. The pitching of the impeller for the Hammer kits must be more accurate than what we have seen “out of the box”. Furthermore, the Hammers require slightly steeper pitches than the Xo and X1 carry. We can custom pitch these impellers for the Hammer kit customers. This re-pitching is absolutely mandatory for Hammer kit machines to net the best peak water speeds.

The 1050’s come standard with an aluminum cast vane body (behind the impeller). While this vane body performs well, the relatively thin aluminum vanes tend to be easily damaged by debris passing though the pump (rocks in particular). This damage is not crucial on a recreational machine, however it can be very crucial to the peak performance of the high output Hammer Kit. For Hammer kit owners that experience this pump damage, we recommend the all stainless steel “D-75” vane body made by Skat Trak. The Skat Trak stainless steel vanes are both thinner and stronger than the original aluminum Polaris part. The $695 price tag is a little hefty, but this will be the last (and best performing) vane body you will ever buy.

DRIVELINE – All 1050’s have a rubber cushion drive coupler mounted to the back of the engine. On older 1050’s, this cushion is notorious for disintegrating, causing a very bad vibration. If you are planning to modify an older 1050, we strongly recommend to replace this cushion.

Directly behind the driveline cushion is seal carrier, which holds the seals that keep the water from coming into the engine compartment (Polaris calls this a bearing carrier, however it holds seals…no bearings). The seals in this carrier become easily worn, and should be replaced seasonally on recreational machines, a bi-annually on Hammer kits.

HANDLING – The hulls of the 2 seater and 3 seater are completely different, hence the modifications needed for improved handling are also completely different.

2 SEATER HANDLING – There are no modifications that can make the 2 seater Polaris a good rough water machine. However it is possible to improve it’s ability to “deal” with rougher water conditions. Perhaps the biggest problem of the 2 seater is the porpoising. Based on out testing, the majority of this porpoising is caused by the nozzle wedge (between the exit nozzle and the vane case) that aims the water thrust slightly upward. Polaris installed this wedge to help lift the front of the hull away from the water (resulting in slightly higher speeds on smooth water). Unfortunately this same thrust angle serves to compound the porpoising problem. Some owners have reversed this wedge to improve rough water handling and reduce porpoising. The porpoising is certainly reduced, as is the smooth water peak speed (by 3 – 5 mph). Our approach to the problem is different. We remove the nozzle wedge altogether. This still makes for a “slightly” nose heavy ride that offers good control in semi-rough water. We then machine the ride plate in a way that lifts the nose of the hull slightly away from the water surface (on smooth water). The net result of this combination is reduced porpoising and improved acceleration, with no loss of smooth-water peak-speed ability. The angle and face of our ride plate modification requires considerable accuracy, hence the cost. Too little cut causes a noticeable loss of speed, while too much cut causes viscous porpoising at all speeds.

During all our 2 seater tests we used the stock scoop grate and sponsons. To date, we have not found aftermarket replacements that offer a significant handling improvement and still maintain the good peak water speeds of the stock parts.

3 SEATER HANDLING – The 3 seater has a whole different problem. The SLTX hull has an somewhat nose heavy attitude in the water. This nose heaviness makes a very questionable contribution to steering ability, and an unquestionable loss of peak water speed. Furthermore, this nose heavy ride causes the rider to take excessive punishment (through the handlebars) in rough water conditions. The single easiest fix for this is the installation of the Ocean Pro ride plate. The negative angle on the bottom of the O/P plate helps to lift a good portion of the front of the hull off of the water, resulting in noticeably better speeds and rpms. Despite the reduced water contact area, the 3 seater 1050 still turns very well at speed. For high speed rough water applications, we recommend to remove the stock 4-degree nozzle wedge with a 2-degree wedge. For owners who do more smooth water riding, the 4-degree nozzle wedge can offer a little extra nose lift, and thereby ride comfort. This 4-degree wedge is not advisable for high speed rough water riding, as it can yield excessive nose ride height.

HULL FINISHING – When you take delivery of any new 1050, the bottom surface of the hull is very smooth and shiny. While this finish looks real nice, it is totally non-functional. The ideal bottom surface finish is a non-shine finish created by numerous full-length front to rear “scratches”. The best way to accomplish this finish is with a piece of very coarse emery (40 – 60 grit is best). All the sanding strokes should be front to back (continuous) for the full length of the hull. The deep, full length, scratches should eventually eliminate any part of shiny surface. While this preparation may not look attractive, these scratches will act as thousands of small rudders that will make the hull track “a lot” straighter in all water conditions. These scratches will also allow for much better surface holding in high-speed turns.

We consider this preparation to be mandatory for our 2 seater 1050’s. The added nose lift, offered by our ride plate modification on the two seater, means that there is slightly less “steering” hull contacting the water surface. A shiny hull, at this attitude, can tend to “seek” at high speeds. This sanding preparation allows the same 2 seater hull to run arrow straight at peak speed, along with much more responsive steering control.

ABOUT INCREASED RPM’s – For all the Limited and Sleeper kits that use the stock rev limiter, the stock oem driveline arrangement works very well. Like most other Polaris models, the 1050’s employ a large diameter spacer to set the pump case and impeller several inches further back on the hull. This “rear-set” position of the pump improves hook-up and peak water speed. However this pump assembly also uses a relatively long drive shaft (considering that this shaft is not rigidly supported anywhere along it’s length). This additional length is not a real problem for the 2 seater machines, regardless of operating rpm. However the 3 seaters are another story. High performance 3 seaters are often run at high speeds in very rough water. This operation allows for the engine to make thousands of “un-loaded free revs” followed by sudden hook-up loads. This constant loading and unloading (under full throttle) can take a premature toll on driveline bearings. If the rev limiter is eliminated, this same scenario takes place within a higher rpm range. These increased rpms, along with intermittent pump loading, can cause the stock drive shaft to bow at it’s center, and begin to rotationally “whip”. This “whipping” will usually take place as the 3 seater 1050 engine is sustained over 7000 rpm in rough water conditions.

During our tests, we attempted to resolve this problem by installing a 4″ shorter drive shaft (used in another model), and then moving the spacer that “rear-sets” the pump to the back of the vain body. Note that when this spacer is moved, the pump losses some of it’s excellent hook-up ability. Unfortunately, the boat becomes slightly slower and “less agile” without the rear-set pump exit. In the end, the best solution was to use the Hot Seat heat-treated drive shaft (long version), with the stock rear set pump arrangement. Please note that this drive shaft/pump issue is only a concern on 3 seaters being revved over 7000 rpm. The high rpm 2 seaters become impossible to ride at the high speeds (in the rough water) that might cause these load problems.

Limited Kit

Group K Price

Limited Cylinder head modification


Carburetor Boring and Re-jetting


Ride Plate Modification (2 seater only)


Ocean Pro Ride Plate (3 seater only)


Solas X1 impeller (2 seater)


Solas Xo impeller (3 seater)


Includes Recreational finish cylinder porting, head dome modification, carb boring, and jetting. (SEND head domes, cylinder, & carb set)


Optional Competition Finish (for cylinder porting)


Ride Plate Modification (2 seater only)


Ocean Pro Ride Plate (3 seater only)


Solas X1 impeller (2 and 3 seater)


Includes Recreational finish cylinder porting, head dome modification, carb boring, and jetting. (SEND head domes, cylinder, & carb set)


Hammer Engine Labor & Parts

Group K Price

FPP Triple Pipe Exhaust System


Optional Competition Finish (for cylinder porting)


42 Keihin Carb Kit
Includes pre-jetted carbs and linkage


Inlet Manifold Modification
to accommodate 42mm carbs


Primer Kit


Hot Seat “high rev” CDI Box


Crank shaft Truing and Welding


Engine Teardown and Reassembly (with pressure test)
**NOTE: Group K will bill an additional $35.00 handling charge for engine assemblies via UPS


Hammer Driveline Labor & Parts

Group K Price

Ride Plate Modification (2 seater only)


Ocean Pro Ride Plate (3 seater only)


Solas X1 impeller (2 seater)


Solas Xo impeller (3 seater)


Pitch adjustment For Solas Impellers


Heat Treated “long” Driveshaft


Skat Trak “D-75” Stainless Steel Pump Vane Case



Group K Price

Cylinder boring, hone, & chamfering (one oversize)


*prices subject to change based on manufacturer’s current 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 !!