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Different Stages:
June 14, 2013

WMF Watercraft is at it again. Seriously, can these guys leave well enough alone? Actually, we kinda hope not, because every time this Millsboro, Delaware dealership starts digging into a client’s personal watercraft, the result is unanimously cooler than how it started. This time around, the crew at WMF got their hands on a rather stealthy-looking 2012 Yamaha FZS. Recommended by RIVA Racing in Florida, this new client wanted to make his Yamaha FZS faster.


The FZS is good… but how do we make it great? WMF Watercraft and RIVA Racing show us how.


“That’s all the direction he gave us,” recounted WMF owner Bill Forenski. “So we installed a RIVA Racing Stage 2 kit first.” Definitely faster than stock, the Super High Output 1.8L Yamaha plant was producing some much needed extra horsepower, pushing the modified runabout into the mid-70s.

“Then he came back,” Bill continued. “He wanted more so we installed RIVA’s Stage 3 kit.” Consisting of a cooling system upgrade, the 160mm wear ring, and the RIVA 160mm 20-vane pump, Skat-Trak impeller, a RIVA supercharger wheel, Athena ECU, RIVA cold air intake, RIVA rear exhaust, waterbox, RIVA Gen 3 intercooler, RIVA pump nozzle, RIVA engine breather kit, intake grate, ride plate, and boost clamp.


Key to unlocking the 1.8L Yamaha’s potential is opening up the restrictive intake manifold. From the factory, the manifold features a dense filter element which RIVA exchanges with a billet collar, allow air to freely flow.

Skip To Stage 2

Rinardo’s 2012 Yamaha FZS  build started, as stated earlier, with RIVA Racing’s Stage 2 kit. The kit effectively “unlocks” the big bore 1812cc plant, allowing it to breathe easier, respond to throttle command quicker and snort out an impressive 260 horsepower, thanks to a E1 Supercharger impeller wheel, an OEM intercooler upgrade, an intake manifold upgrade, an free-flow exhaust kit and a cold air induction kit.


Out with the old factory air intake and exhaust and
in with the new, more streamlined cold air induction
and free-flow exhaust.

Apart from pulling the factory supercharger and swapping out the impeller wheel, and removing the restrictive intake manifold filter element, rest of the Stage II kit is completely bolt-on. That the Yamaha is capable of such potency without invasive modifications or an ECU is impressive.

The cold air intake, the free-flow exhaust and intercooler kit all assist in cooling the maximum amount of inlet air, and evacuate the exhaust fumes as fast as possible without cutting up the hull.

Starting with removing all of the original air and exhaust plumbing, the crew at WMF made short work of opening up the cramped engine compartment for room to work. Next to come out was the intake manifold and the supercharger; the manifold lost its filter element and the supercharger its factory wheel. Replacing said parts were a free-flow air collar and a new E1 supercharger wheel, increasing both air flow and boost pressure.


The Stage 2 kit from RIVA Racing includes the E1 supercharger impeller, which provides more horsepower and torque throughout the entire RPM curve. Cast lightweight aluminum and CNC machined, the wheel pumps out an impressive 13psi.

 554644-507290156000634-265674745-n.jpg RIVA’s kit provided a fuel pressure regulator to set an optimal static 55psi with a rising rate (@ 1:1 ratio). The regulator mounted directly into original fuel system with OEM connectors and features a large 3/8-inch fuel return line routed through a rubber fuel tank cap. 

Cramming all that extra force-induced air down the throat of the big 1,812cc plant won’t do much good without a way to evacuate the spent gases at an equal velocity or the fuel to make that extra air do any good.

RIVA’s free flow exhaust kit replaces the restrictive sound suppression system fixed between water box and the through-hull outlet, reducing backpressure and engine temperature.

Mounting directly to the factory fuel pickup on top of the tank, RIVA’s fuel pressure regulator kit is fully adjustable and mates directly into original fuel system with OEM connectors and uses a 3/8-inch return line that routs through rubber fuel tank cap supplied with the kit.

Installation requires the removal of the stock fuel pressure regulator in fuel tank before the billet fuel pressure regulator block-off can be attached.


Final to the installation of the Stage 2 kit is the billet aluminum spacers to the factory intercooler. This increases capacity while improving water flow, making the stock intercooler dramatically more efficient.

Stepping Up To Stage 3

Sharing much with the Stage 2 kit, the Stage 3 kit takes PWC performance to the next level by maximizing pump and nozzle performance, exhaust flow, supercharger life and efficiency and engine tuning.

After all of this, you might’ve thought, “Hey, that sounds plenty fast. I bet that FZS really cooked with that kit.” The reality was yes, it sure did. But the owner wasn’t satisfied with just fast. He wanted extremely fast. So, back to work went WMF’s pro shop, replacing the Stage 2 kit with RIVA’s top-of-the-line Stage 3 performance package.

Considering that much of the Stage 3 kit is shared with the Stage 2 kit, RIVA supplied all of the remaining items to push WMF’s project Yamaha to the next level of on-water performance.

Choosing to open up the exhaust flow even more, the Stage 3 kit plumbs the spent fumes out of a new hole cut into the rear of the hull. This through-hull system is a heck of a lot noisier, but also significantly more efficient when it comes to making power and eliminating backpressure while running at high rpms.


Cutting some significant weight from the tail of the Yamaha is RIVA Racing’s through-hull free flow exhaust kit. Removing the restrictive sound suppression system, the new system blocks off the old outlet and funnels the spent fumes out of a new exit hole out of the tail.

Although the previous Stage 2 kit helped to improve the efficacy of the factory intercooler, the Stage 3 kit simply replaces the tiny cast aluminum intercooler with the very impressive Power Cooler. Dramatically more efficient than original intercooler, the Power Cooler provides 20-extra peak horsepower with exit temperatures averaging 60°F colder than the factory system.

The large, unrestricted core includes an integrated blow-off valve mount for the RIVA/HKS Blow-Off Valve, which bleeds off extra pressure when the throttle is chopped, reducing supercharger clutch wear and engine stress.


With the engine mods installed, it was time to get the tune right on the RIVA/Athena ECU. Working together with RIVA’s customer service department and tuning software, the experienced crew at WMF made quick work of getting this FZS making some serious power.

With all of this extra power coming from the engine, RIVA’s Stage 3 kit provides several components to increase the pump’s efficacy and power delivery. A new 160mm RIVA stainless steel wear ring significantly reduces cavitation while improving acceleration.

Together with the RIVA/Skat-Trak 160mm ‘R’-Series swirl impeller, the duo of parts help increase hook up, acceleration and reduces cavitation. The large, oversized blades are digitally calibrated to RIVA’s specifications and then dynamically spin-balanced at high rpm.

The final piece to the build was RIVA”s 160mm Race Pump. Although not part of the official list of Stage 3 goodies, it’s a key part to increasing acceleration and top speed while reducing that dreaded cavitation. The CAD-designed 12-vein stator is far more efficient than the factory 155mm/8-vein pump, and is made from high grade stainless steel for extra corrosion resistance.


Big power needs some place to go, and the pump is where the rubber meets the road. WMF stepped this Yamaha up with the 160mm stainless steel 12-vane stator pump, stainless wear ring and huge RIVA/Skat-Trak prop. All of which drastically increases acceleration while eliminating cavitation.

Satisfied. For Now.

The once “sporty” FZS has now become a water-boiling monster capable of 83.4mph. When asked if the client was happy with the end result, WMF Watercraft’s Bill Forenski nodded. “So far,” Bill laughed. “But it still needs some fine tuning. There’s more speed left in there.”
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