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By Jeff Hain

When it comes to Yamaha performance, Riva Yamaha is one of the watercraft industry's key players. Riva has been involved in racing for well over a decade and has won numerous World and National Titles. Riva is also currently working on setting the speed record for a personal watercraft with a GP1200R that has reportedly peaked at a top speed of 87 mph. So, when Riva owner Dave Bamdas rang to see if I would be interested in testing a couple of his company's newest modified craft - Big-Bore GP1200Rs - I jumped on the opportunity. Bamdas had two Big-Bore Yamaha WaveRunner GP1200Rs - one equipped with Riva's Stinger3 exhaust pipe, the other with Factory Pipe's triple pipe exhaust system. However, to find the differences between the exhaust systems of each of these craft really wasn't why I wanted to test the boats. The claims he made about the two craft's top speeds are what made me want to test them. He claimed the single-pipe boat would do 70-plus miles-per-hour and that the triple-pipe-equipped boat would do 80-plus miles-per-hour - both on pump gas. Considering the GP1200R does about 63 mph out of the crate, a claim of 70 mph on pump gas didn't seem that unbelievable, but 80 mph on pump gas... well, that I had to see, and ride, for myself. So I immediately made airline reservations - destination: Florida. Once in Florida, my plan was to meet Bamdas, Riva tuner Tim Judge and marketing man Mike Hodges at Riva's private test lake in Pompano Beach to test both the Big-Bore craft.

In an effort to get optimum radar-run conditions, we met at Riva's lake at eight o'clock in the morning the day after I arrived in South Florida and began the testing with acceleration and top-speed runs. After all, the top-speed claims that Bamdas had made were the most important part of this test. Wouldn't you agree? For the radar runs, Judge (who weighs 190-pounds) rode the two boats while I ran the radar gun and laptop. The conditions for testing were near perfect at Riva's test lake - there was only a slight wind ripple on the water. Just so you know, the Riva test lake is fresh water and it is at sea level. Judge first rode the single-pipe-equipped GPR, and low and behold, the boat did just what Bamdas claimed it would do - an average peak speed over multiple runs of 71.13 mph. But, while the single-pipe-equipped, Big-Bore GP1200R did over 70 mph, out of the hole, it was slow. Out of the hole, the craft would just spin its impeller - big time! The Big-Bore GPR came off the line like a Top Fueler coming out of the burnout box at the strip. From an idle, the boat took over three seconds to get to 20 mph, but from 20 mph and up, the boat accelerated decently. The craft accelerated from 20 mph to its 71-mph top speed in 13.94 seconds. Not blistering fast, but remember, the boat was running on pump gas. At speed, the single-pipe, Big-Bore engine turned 7060 rpm. Once we had solid numbers with the single-pipe Big-Bore, Judge hopped on the triple-pipe-equipped Big-Bore GP1200R. Just like its single-pipe-equipped counterpart, the triple-pipe beast also burned its impeller off the line. The zero-to-20-mph time of the triple-pipe boat was nearly identical to that of the single-pipe craft at 3.27 seconds. From 20 mph to 35 mph, the triple-pipe craft wasn't much quicker than the single-pipe-equipped boat either, with a time of 0.89 seconds to the single-pipe craft's time of 0.92 seconds. But, from 35 mph to its peak speed, the triple-pipe-equipped GP1200R pulled away from the single-pipe craft. The triple-piped Big-Bore went from 35 mph to its average peak speed of 79.87 mph in 9.25 seconds - 3.77 seconds quicker than the single-pipe Big-Bore went from 35 mph to its nearly 10 mph slower top speed. While Judge didn't get Bamdas' claimed top speed out of the boat on our multiple-pass average, he did get a one-time peak speed of 80.28 mph from the triple-piped Big-Bore. The peak engine speed of the craft was 7780 rpm. For your information, both craft were filled with five gallons of fuel at the beginning of the radar runs. While the triple-pipe-equipped Big-Bore didn't do Bamdas' claimed 80-plus mph on every run, the boat's speedometer did consistently show top speeds of 91 to 92 mph, which would excite most weekend warriors.

Once through with the speed testing, I put on my wetsuit and life vest and jumped on the single-pipe Big-Bore. From witnessing the boat during the radar runs, I knew I wasn't going to be impressed with the craft's out-of-the-hole performance, and sure enough, I wasn't. The last time that I rode a boat that spun the impeller this bad was when I sucked a bunch of rocks through the pump of one of our long-term test boats. But hey, this boat was about top speed, not acceleration. According to Judge, he could easily fix the out-of-the-hole impeller spin, but not without taking away from the craft's top speed. But again, according to Bamdas, top speed is what the Big-Bore Kit is all about.

At speed, the single-pipe Big-Bore handles much like a stock GP1200R does: When the water gets choppy, the boat has a tendency to porpoise. Cornering was also like that of a stock boat, and I found that a neutral trim setting work well all around. The boat carbureted well throughout its entire powerband, whether riding in a straight line or carving through a slalom course. Like the triple-pipe Big-Bore, the speedo on the single-pipe Big-Bore also read a little high - about 10 mph - at speed.

 After riding the single-pipe Big-Bore, I jumped on the triple-pipe version, and out of the hole it felt as though I hadn't changed boats at all. But once the impeller stopped spinning and the boat came on plane, the difference in the two craft was very apparent. I immediately knew which setup was for me. At around 35 to 40 mph, I could feel the triple-pipe Big-Bore engine's power valves open as the boat accelerated to speed. Even with its increased mid range and top speed, the handling of the triple-pipe Big-Bore was also very similar to that of a stock GPR. Although the triple-pipe boat was nearly 10 mph faster on the big end, the two Riva boats corned almost identically and, like the single-pipe Big-Bore, the triple-pipe craft had a tendency to porpoise when the water got a little rough, though it was a little more pronounced at speed. On one occasion, the impeller on the triple-pipe Big-Bore did break loose on me in a turn, causing the boat to feel as though I was coming off-line. But hey, again, the boat was set up for top speed. Overall, both of the Riva Big-Bore GPRs tracked unbelievably well, especially when you consider their top speeds.

So, now that you know exactly how each of the two Riva Big-Bore GP1200Rs ran, and what I think of their on-water performance, let me fill you in on what the modifications to each craft consist of.

As you now know, Riva offers two versions of its Big-Bore GP1200R Kits - one with its single-pipe Stinger3 exhaust system, the other with Factory Pipe's triple-pipe system. And for the most part, that is the biggest difference between the two boats. The engine modifications to both craft started out with truing and welding the OE crankshaft. Next, Riva modified the crankcases to accept the larger, 86mm pistons. This modification consisted of grinding off the lip at each cylinder opening in the cases. Once finished with the cases, Riva bored out each of the engine's three cylinders (which are Nikasil-coated) to accept the cast-iron, Big-Bore cylinder sleeves. After the sleeves were dropped into the cylinders, they were bored to accept Riva-modified, 86mm pistons and decked for a true cylinder-head surface. The port openings in the sleeves were then matched to the cylinder ports, which included a slight raising of the exhaust port. Included with the Big-Bore sleeves are Riva's exhaust valves, which are matched to the cylinder's exhaust port and feature captured pins. The Riva Big-Bore piston kit includes Riva-modified pistons, piston rings, top-end bearings and circlips.

Once the cylinder work was complete, the engines were ready to be assembled. Included with the Big-Bore cylinder kit are new base-gaskets that have a larger bore and are 0.060 of an inch thick. The stock base-gasket is 0.018 of an inch thick. The thicker gaskets are required because of the different height of the Big-Bore pistons. Due to the fact that the piston diameter of the Big-Bore Kit's pistons is 6mm larger than the stock pistons, larger-diameter combustion-chamber domes were required, so Riva used its three-piece, girdle-type cylinder heads with 48cc domes. With the 48cc domes and the flat-top 86mm pistons, the 1359cc mill (which Riva likes to reference as a rounded-up 1400cc) had a cranking compression of 145 psi with the exhaust valves closed and 135 psi with the valves open - and it is pump-gas safe (super unleaded), according to Riva, when used with Riva's Pro Series Digital Ignition and the properly selected timing curve. The Riva GP1200R ignition has four preset timing curves, one of which is designed for Riva's Stinger3 exhaust pipe, and another for triple pipes without porting. In addition to its different timing curves, the ignition also has an adjustable rev limiter, which is also a must with the Big-Bore Kits. Judge had the rev limit set at 9000 rpm on both the single-pipe and triple-pipe Big-Bores. Other features of the Riva Pro Series Digital Ignition includes four different exhaust-valve maps and an instrumentation warning override system, which eliminates the buzzer and warning light that automatically come on when the GP1200R's OE catalytic converter is removed and replaced with an aftermarket exhaust. Judge had both Big-Bores' exhaust valves set to open at 5800 rpm, and both craft were equipped with longer-reach, NGK BR9ES spark plugs.

On the intake side of the engine, modifications to both Big-Bores included the addition of Riva's reed stuffers to the OE reed-valve assemblies, rejetting of the stock carburetors, and the addition of Riva's E/Z Tune Kit, which includes replacement adjustment screws for the carburetors that feature a T-handle design, for ease of adjusting the carbs. Believe it or not, the stock choke system remained intact on each engine, as did the OE intake manifold and reed-valve plate. In an effort to control fuel pressure within the carbs, Judge added a restrictor jet to the carburetor return line on each boat. The stock air box was also replaced on both the single-pipe and triple-pipe engines with Riva's flame-arrestor kit, which includes three individual, non-absorbent flame arrestors; three billet-aluminum flame arrestor adapters; and three water-repellent prefilter covers.

On the exhaust side is where the two Big-Bore mills differed. On the single-pipe Big-Bore, the OE exhaust system was retained from the cylinders up to the point where the system's catalytic converter starts. This is where Riva's all-new Stinger3 exhaust pipe replaced the GP1200R's catalytic converter. In addition to adding power, the Stinger3 also drastically reduces the weight of the engine's exhaust system, in turn reducing the overall weight of the craft. On the Big-Bore, Riva equipped the Stinger3 with a Jet Works In-Line Adjustable Water Restrictor, which allows for fine-tuning of the exhaust. On the triple-pipe Big-Bore, a Factory Pipe exhaust system - which includes three manifolds, head pipes and expansion chambers - replaced the complete stock exhaust system. In addition to exhaust-pipe modifications, Riva's Free Flow Exhaust Kit, which replaces the boat's restrictive sound-suppression system, was also used on each boat. Both boats retained their stock waterboxes.

One modification that Riva made to the Factory Pipe exhaust system is that they remove the debris screen and the water jets from the system's water-log manifold and installed a Riva inline water filter/restrictor (into which they installed the jets from the Factory Pipe water log manifold) in each of the three head pipe's water lines. This allows a slightly higher volume of cooling water to the engine. According to Judge, the single-pipe Big-Bore produces about 190 horsepower, and the triple-pipe version produces in the neighborhood of 220.

In an effort to turn the increased power of both Big-Bores into speed, the OE impellers in both of the Big-Bore craft were swapped for Solas' 14/20 Concord impellers. The OE impeller washer, which is 2mm thick, was left off the impeller shaft in an effort to set the impeller back in the stock pump housing. For durability, a Riva billet-aluminum impeller cone replaced the rubber nose cone on each craft's impeller. Other modifications to each boat's pump setup included the replacement of the stock pump cone with a Riva GPR Performance Pump Cone, which has the same contour as the OE reduction nozzle and actually tightens up the nozzle's volume; and the addition of Riva's Pro Pump-Seal Kit, which stuffs the voids around the OE pump shoe in an effort to reduce cavitation.

Water is fed to the impeller on each craft through a Riva GPR top-loader intake grate. While Riva offers three different intake-grate setups for the GPR, Judge has found that the company's single-scoop, one-bar/two-bar grate works the best for top speed. And again, that's what these two craft are all about.

In an effort to keep the craft's handling intact, Judge also replaced both the GPR's OE ride plates and trim tabs with Riva's GPR Performance Ride Plate and GPR Trim Tabs. Riva claims that its ride plate alone is worth a couple of miles-per-hour over the OE ride plate on the GP1200R. Unfortunately, I wasn't able to test just the ride plate at the time. The increased length of the ride plate and trim tabs helps reduce the craft's tendency to porpoise. The final modification to both Big-Bores in the handling department was the addition of Riva's GPR Pro Series Sponsons, which replaced the OE sponsons on each craft. The sponsons, which are bolt-on, feature three-position adjustability and are designed to improve both straight-line tracking and cornering.

Other modifications to the craft include the addition of a fuel line on the triple-pipe boat from a modified fuel tank pick-up (the screen was cut out of the fuel tank pick-up and a piece of fuel line was added to it to increase its length) to the main carburetor fuel-feed line, and dual cooling lines from the pump to the engine/exhaust on both boats. The dual cooling was achieved by installing Riva's High-Flow Pump Strainer to the OE pump.

So, the only real difference between the single-pipe-equipped GPR and the triple-pipe-equipped GPR is just that - the exhaust systems. Okay, so the single-pipe boat that we tested did still have its oil-injection system, whereas the triple-pipe-fitted boat was set up for premix. Judge opts for Klotz R-50 oil at a premix ratio of 32:1.

Generally, Riva recommends running premix; however, the single-pipe boat will run fine using the oil-injection system if desired. According to Judge, however, with the increased rpm that the triple-pipe engine turns, premix is a must.

Now, the question is: Are the Riva Big-Bore Kits worth the money? Well, if you own a GP1200R and you have the need for speed, then the answer is certainly yes. So, the next question is: Which of the two Big-Bores is for you? The triple-pipe version is definitely the one for me; however, I would give up some top speed for less cavitation out of the hole - but that's just me. The difference in the price of the two kits is about $2500, and while all of the parts in both kits are available separately, Riva does offer a discount if you buy either of the complete Big-Bore Kits.

So, if you own a GP1200R and speed is your thing, then one of the Riva Big-Bore Kits is probably just what you need.



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