Author: Mike Hodges
Skimming across the top of the water on a PWC at freeway speeds is enough for most people, but some folks want to go faster. Nothing surprising there. But PWC manufacturers have agreed not to build PWCs that exceed 65 mph (with 2- to 3-mph overages allowed), so those speed-seekers are out of luck, right? Not really. While the manufacturers are sticking by the self-imposed speed limits, it is not illegal for an owner to modify a PWC — provided you don’t change the exhaust to make it exceed local noise regulations. Since modifications can affect warranty coverage, some customers prefer to wait until their warranty expires before making these types of changes.
You can modify any PWC you choose. We took a stock Sea-Doo RXT -X 260, which has a top speed of around 67 mph, and modified it with RIVA Racing’s entry-level Stage 1 Kit. You can expect to increase top speed by a little more than 5 mph with no internal engine modifications required. RIVA (rivaracing.com) offers the kit for $1,151 when all the parts are purchased together, which saves about $50. It takes about eight hours for the complete install, and anyone with average mechanical ability can do the work himself.
Before beginning any modification, you should “baseline” your PWC’s performance. Make several speed runs, record the top speed and rpm on each run and average them to arrive at your baseline. Doing so will let you know if your craft is operating properly in its stock form, so you have a valid comparison point after modifying it, to determine if the kit is working as advertised. RIVA matches compatible components into a kit to provide a combination of parts that work well together and help customers achieve their performance goals.
RIVA offers complete kits, which range from Stage 1 to Stage 4. The Stage 1 Kit includes a Power Filter cold-air intake system with a PVC thermal barrier, Catch Can/Engine Breather Upgrade Kit, Speed Control Override Module and an “R” Series pump impeller.
First, I removed the restrictive stock air-intake system, which includes everything forward, or upstream, of the supercharger. Using the template supplied in the instructions, I mounted a bracket  inside the hull just under the steering, to support the oversized K&N filter that also has a water-repellent pre-filter covering. The bracket includes a billet adapter that connects the filter to ducting that runs back to the supercharger.
Next, I installed the thermal bulkhead made of insulated PVC , which is pre-cut by RIVA to match the Sea-Doo’s interior. Doing so isolates the air intake from the heat of the engine. I fed just enough ducting through the bulkhead and installed the bulkhead in the craft between the engine and the fuel tank. Then, I installed the threaded billet adapter onto the supercharger, which enabled me to attach the tapered velocity stack to the supercharger inlet with ducting . I had a true cold-air intake system, which supplies the engine with colder, denser air, so more of it (and fuel) can enter the combustion chamber to create more power.
The stock air-intake system incorporates a return for any unused fumes or vapor from the engine breather bypass. To improve performance and reduce intercooler maintenance, I replaced the return with an included Engine Breather/Catch Can Kit. I installed a small bottle with the K&N filter on the front of the engine and ran a hose from it back to the engine breather bypass, which isolated it from the air-intake system .
Using an aftermarket kit to coax a few more mph out of your PWC is easy enough, if you follow the instructions provided and a few simple steps. The RIVA Racing Stage 1 Kit includes all the parts and templates you need, and its air intake hose diameter is noticeably larger than the standard hose .
Sea-Doo utilizes a GPS speedometer to limit the top speed of its watercraft. To get around the electronic speed governor, I installed an electronic device called a Speed Control Override Module (SCOM), which plugs directly into the craft’s diagnostic port . As soon as the PWC reaches 65 mph, the SCOM sends a false signal to the ECU, which allows it to go faster without being restricted electronically, but the SCOM creates an issue with engine speed, or rpm, that must be dealt with.
The stock pump impeller is pitched to run optimally at 7800 rpm. To go faster without hitting the engine rev limiter, I installed a special “R” Series Solas Concord Impeller , which has a steeper, or taller, pitch. Now, when the craft goes faster, the engine speed reaches 8000 rpm, just under the 8100 rpm rev limit for this Sea-Doo. The impeller is calibrated using a pitch block to ensure it is the exact pitch specification RIVA calls for and is also high-speed balanced. Standard off-the-shelf impellers don’t get this extra treatment.
The Stage 1 Kit is very easy to install and requires only standard shop tools, with the exception of a special impeller tool, which retails for $44.95. You’ll likely use it in the future, however, because once you’ve modified your PWC, you’ll probably do it again, looking for even more speed.