Kawasaki SXR 800 – High Performance Mods

Carbs – The SXR comes stock with 40mm Mikuni “I” body carburetors. . In truth, these carbs are not a true 40mm as stated. The actual minor diameter at the venturi is about 2.5mm smaller. For all our pump gas kits, we do a “true bore” modification to make the carbs 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 the high price or temperamental tuning that comes with many larger carbs.

Inlet Manifold – The stock SXR inlet manifold has well designed passages that make it an excellent part for higher performance applications. It’s only drawback is the cast in crossover passage that exists between the two inlet runners. This passage is originally intended to offer smoother low speed response for the stock, lower rpm, configuration. Unfortunately, significant changes in port timing (as in our kits) have a big impact on inlet “signal”. The end result is that this crossover passage contaminates the clarity of inlet signal at high rpms. This contamination causes inlet signal to progressively weaken during a long full throttle run. This progressively weakening signal results in a progressive leaning out that can result in detonation damage to a piston. With the Sleeper and Hammer Kits, we block this passage with a high-grade epoxy, and then install the correct carb jetting for the true bored carbs and the blocked inlet manifold.

Reeds – All our Pump gas kits utilize the stock reed cages and petals. There are many aftermarket reed petals available for the stock cages, however we have consistently seen the best long-term performance and wear using the stock OEM reed petals. The larger reed cages (R&D M16 & V-Force) can have merits on setups that use 46mm or larger carbs, but they offer limited increases when used with the 40mm true bore carbs of our pump gas kits.

Air Inlet – The stock SXR flame arrestor is a design that offers excellent protection from water in the engine compartment, and can offer very adequate air inlet access. For all our pump gas kits, the stock flame arrestor can be used (with the rubber silencing nozzles removed). For owner who is not concerned with excessive water exposure in the engine compartment, there is a small advantage from installing individual “pod” type flame arrestors. We prefer the R&D or Tau Ceti arrestor kits.

About Fuel Consumption – For many riders, fuel range is a big consideration. Our kits that retain the stock exhaust system will offer range very close to that of a stock machine. The installation of the Factory Dry Pipe certainly makes for a huge increase in power, however it also nets a big increase in fuel consumption. One of our tests includes a 24-mile partial throttle cruise on smooth water (actually our break-in run). The Hammer 91 kit consumed every bit of the 5-gallon fuel load to complete this ride, while the Sleeper still had a third of a tank left after the same ride at the same speeds. We would presume that running the Hammer Kit at higher speeds (or using larger carbs) would considerably increase this rate of consumption. To be sure, The FPP pipe equipped Hammer is “a lot” faster than the stock pipe Sleeper. However for riders that don’t intend to spend much time over 52 mph, the added range of the Sleeper could be an important quality.

Fuel Inlet – All our pump gas engine setups utilizing the modified stock carburetors can easily retain the stock fuel plumbing and petcock arrangement. However 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.

Cylinder Porting – One of the big design changes between the SXR and the previous Sxi750 motors is the cylinder port timing. The SXR has considerably milder port timings than previous 750 motors for two reasons. First, the milder timings allow for lower emissions to help make “50 state” marketing easier, and second, allowing for improved low range acceleration characteristics.

In the past, cylinder porting has received a bad reputation for making machines unreliable or “high rpm” biased … and that may be the case for poorly executing porting. The porting modification we do for our Sleeper and Hammer kits is intended to increase power right from the very bottom of the rpm range to the top. We spent many weeks testing to find the combination that works best for our SXR kits. The end result is porting that offers great overall power as well as exceptional long-term piston and ring life. Please note that we typically prepare ported cylinders and modified heads as matched pairs so that we can assure the correct squish clearances and compression ratios for the fuel octane you will be using.

About Displacement and Pistons – The stock bore diameter of the SXR is 82mm (781.2cc). Limited Class and Super Stock machines are permitted to overbore to 82.9 mm (798.4cc). Before 2002, the IJSBA restricted Superstock machines to 785cc. For the old Kawasaki 750, that allowed a bore diameter of 82.2mm (an 82.0 mm piston running at max clearance). In 2002, the IJSBA rules permit 800cc maximum displacement. . It bears noting that Wiseco already had available 83mm pistons, but they yield a final displacement of 800.3cc, and are not be permitted in IJSBA competition. This means that an 82.9 mm piston (with average clearance) would fall just below 800cc. These 82.9mm (as well as 82.5mm) pistons are available from Wiseco in a “racing” version. These racing pistons feature a cutaway skirt, boost port feed hole, and thinner rings. We have had excellent results with these pistons, and strongly recommend them.

The steel sleeve in the stock SXR 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 also slightly deflect the bore diameters. For stock cylinders of average clearance, this is no problem. However whenever boring a cylinder (particularly to the 798cc 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.

Cooling System – Generating more power means generating more engine heat. To contend with this heat, our Sleeper and Hammer kits include a cooling upgrade that significantly reduces top end engine temperatures. An additional water outlet fitting is provided with our kits to work with this upgrade.

Exhaust / Ignition System – The changed cylinder porting layout offers a considerable challenge for those tuning the SXR for IJSBA Limited class competition …. And those making tuning parts for that application. In particular this was a significant challenge for the development team at Factory Pipe Products. They were faced with the job of making a good high rpm pipe for a cylinder whose port timings were not “co-operating” well. In order to make a pipe that delivered good overall power on a completely stock machine, the technicians at Factory Pipe included the use of a 7-degree ignition advancer plate (supplied with each FPP SXR pipe). The additional ignition advance of this part makes for big increases in overall power, without having to increase compression at all. The FPP pipe, with the 7’-advancer is a 91-octane safe setup, so long as there are no other modifications to the machine. When we developed our 91-octane Hammer kit, we opted to not use the advancer, and get our bottom end power gains with cylinder porting and compression. With stock ignition timing, we could increase the compression by a big margin, and still remain 91-octane safe. Since the OEM ignition has its limiter at 8000 rpm, a limiter mod is not required.

For our Hammer 2 Kit, we merely install the 7’-advancer plate that comes with the FPP pipe. This combination makes a lot more overall power … and heat. The detonation risk of this setup is much too high for 91-octane, and so 105+ octane is required to control combustion temperatures and avoid detonation.

The stock SXR 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 Sleeper and Hammer kits. Note: no flywheel modifications are permitted in IJSBA Limited Class racing.

About Oil & Fuel – Kawasaki recommends a premix of 60:1 (10.5oz/5gall) for the stock 6500rpm SXR. For our slightly higher revving Sleeper kit, we recommend 40:1 (16oz/5gall). For our much higher rpm setups that use the Factory Pipe, we recommend a 28:1 premix (23oz/5gall). The exceptionally high rpms of the Hammer setups require the added lubrication to protect against the extra heat, and the higher surface speeds of all the moving engine parts. Contrary to belief, the added oil in these higher revving setups does not significantly increase smoking or plug fouling … and it is the best “reliability” insurance you can buy.

We are constantly approached by owners who are trying to craft a way that can allow them to get race gas horsepower, without having to run expensive race fuel. Sadly, it just can’t be done.

Normal “octane boosters” are capable of making really poor gas into decent gas, but they cannot make good gas into race gas. That is, normal boosters can make 86 octane to 89. However the same booster can only make 91 into 91.5 or 92. We discourage the use of octane booster except in emergencies.

One alternative used by many is to run aviation fuel (aka “av gas). Av gas is usually around 100 octane, but av gas has other properties that are important. One of the main qualities that makes av gas desirable for aircraft use is that it is actually lighter (per gallon) than conventional gasolines. This reduced weight is important for small underpowered planes that need to be as light as possible to take off.

Normal gasoline molecules have two “ends”. The “light” end of the molecule ignites easily, and burns with a quick low temperature flame (as a piece of newspaper would burn). The “heavy” end of the molecule is harder to ignite, but burns with a much hotter flame (as a log would burn). To make av gas lighter, the heavy end of the molecule is omitted to reduce the weight of each gallon. Since most aviation engines are low rpm motors, they experience little power loss. However if 100% av gas is used in a high output pwc engine made for race gas, there is a visible loss of power because the “heavy” ends are not there to contribute to the making of power. All that said, we consider it a great idea to mix 50/50 av/91oct fuel for “Hammer 1” kit owners who want a little extra temperature protection during exceptionally hard operation. A 50/50 mix still contains enough “heavy” ends” to allow for good overall power and has a much-improved octane over straight 91-octane.

Engine Lower End – The crankshaft and crankcases of the SXR 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 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.