NEW TESTING & NEW STUFF BY GROUP K
INDEX OF SUBJECTS
3/96 Reading Radar Tests
4/96 About Resistor Plugs And Caps
4/96 Water Bypasses and Riva Pipes
5/96 Compression Readings on Rotax Rave Motors
5/96 Pro Tec Scoop grate for the 1100 Raider
5/96 Peak Water speeds - Doing the Math
6/96 R&D Flame ARRESTORS
8/96 Watercraft Connection Spark Plug Washers
11/96 Yamaha triple bore distortion
11/96 Broken Spark Plug Wires
READING RADAR TESTS - About Cold numbers-Spike numbers- Sustainable numbers- Repeatable numbers ?
Not a day goes by at Group K that some guy doesn't call us to tell us that he just radared his XYZ watercraft at 2-3 mph faster than the speeds we claim in our literature. We refer to it as a caller with "bigger numbers". While we try to appear interested, we are not. Our lack of interest is not intended to be disrespectful or disbelieving. We are disinterested because we have been lied to by our radar guns in the same way that this caller's gun is lying to him. In the past, we have never taken the time to explain to callers how their guns may be lying to them ... we still don't. However here is the written version.
WHAT ARE "REAL" RADAR SPEEDS -- "Real" numbers, as we call them, are the "repeatable" speeds measured from a machine that has been brought up to temperature by at least 5-10 minutes of full load, full rpm, operation. The following is the rundown of "other" radar speed measurements.
COLD NUMBERS -- Every PWC's will yield it's best acceleration and highest radar speeds when the engine is nearly cold. After 60 - 90 seconds of low speed warm up, most engines are safe to run at full load and full rpm. After this initial "cold pass", the boat will consistently yield slower numbers ... often allot slower. After the cold pass, the heat generated by the top end spreads quickly throughout the lower end(engine builders refer to this as the "heat sink"). Besides making the following fuel charges less dense, the added temperature also effects the ignition. Stock 701 Wave Raider ignitions, for example, will rev happily into the low 7200s during the cold pass. However after the electrics get hot, 7060-7100 is the best you can hope for. If you let the Raider sit for a few hours to get cold again, you'll get one more 7200 rpm pass out of it. Many of our callers will sit on the shoreline at their local lake waiting for the "perfect" water conditions. This is time well spent ... glass water is fundamental to getting big numbers. However they don't realize that another big chunk of their big numbers came from the engine that got cold while waiting for the glass. At Group K we can produce "big" cold numbers as easy as the next guy. However we do not print cold numbers in our literature ,or in the magazine articles we do, because they are not repeatable under average circumstances.
SPIKE NUMBERS -- By far the most popular radar guns in the business are the Stalker guns with the peak speed lock. These same guns ,with additional computer interface electrics, are the units that produce the acceleration curves you see in some magazines. We recently did a computer assisted radar test with Personal Watercraft Illustrated on our Sleeper kit equipped 1100 Yamaha. After each radar run we noticed that the peak speed was shown as 1/2 to 1 mph faster on the gun than it was on the interfaced laptop computer. This happens because the gun, by itself, cannot distinguish between a "sustained" speed and a split second "spike" speed. It normally happens, in every radar pass, that for one split second the boat is perfectly straight and level in the direction of travel. This causes a momentary speed increase that is "seen" by both the gun and the lap top. The laptop, however, is smart enough to see the split second spike for what it is... and "lobs" it off the graph. The computer will only graph the "sustainable" peak speed.
Having said all this, it's obvious that Stalker radar tests done without the laptop will regularly yield erroneously high "spike numbers". This is a point worth considering when reading various magazine test articles. In our test with PWI, they took an average of ten back to back computer interfaced acceleration passes. This test format eliminates any possibility of "unrepeatable cold numbers". While we had regularly seen spike numbers in the 66's a few days before the test, the PWI test procedure eliminated them. No cold numbers, no spike numbers. The only thing we liked about this procedure was that we knew all the other PWI tests are done the same way. They apparently know how to make their gun tell only the truth.
ABOUT RESISTOR PLUGS & CAPS --- The original intent of resistor spark plugs and spark plug caps was to reduce the amount of radio wave interference in the perimeter area around the machine. For many years we, like many engine builders, endorsed the removal of these plugs and caps in favor of non resistor types. The elimination of this extra resistance could make a visible improvement in the performance of many machines... That was then... this is now.
Many of the new PWCs are coming stock equipped with digital ignition systems. These ignitions have many good qualities, and one very bad quality. That bad quality is the great sensitivity to nearby radio wave fields. These machines come stock with resistor plugs (and sometimes caps too) In short, these resistor parts keep the plugs and caps from "talking" to the CDI box (this happens very easily). If you install non resistor plugs or caps, the enlarged radio wave field will interfere with the CDI box (usually a peak rpm) and cause the ignition to shut down. This scenario usually continues and gets worse as the machine gets hotter. Eventually, the boat won't run at peak rpm at all. Most shops will mis-diagnose this as a bad CDI box... but a new box won't fix it. Just accept the luggage that comes with the digital technology... and install the resistor plugs.
WATER BYPASSES AND RIVA PIPES ---- We recently prepared a 92 octane Hammer kit for a 701 Super Jet customer who had already purchased a Riva pipe. This pipe worked well on his limited, so we had every reason to believe it would work well on the Hammer kit (we normally use the Factory brand pipe). The boat was built and prepared as per our normal procedure. This included our cooling upgrade kit which uses a total of three water bypass outlets...no problem. But after his first outing, he commented that the boat had great mid range and top end... but real poor bottom end. After a great deal of carb tuning, the poor low end was still there. Then, in desperation, we eliminated the additional bypasses so that the plumbing was the same as his old Limited setup. Immediately, the boat had all the bottom end in the world. Install the bypasses again... no bottom end. Why ?
Evidently the Riva pipe was developed on a limited format engine. These engines are prohibited, by the IJSBA rules, from having more than one 4mm bypass outlet. That means that the rest of the water is being delivered into the pipe. Our experiences with the adjustable water input on the Factory brand pipes has taught us that if additional water is allowed in at the head pipe, it will result in better bottom end power(usually at the cost of top end power). Evidently the Riva pipes depend on this extra water into the head pipe in order to make acceptable bottom end. This does not mean that the Riva pipe a bad pipe, however it does the Riva pipe is damn sensitive to the amount of water it needs to make good bottom end.
COMPRESSION READINGS ON RAVE MOTORS --- As of this writing, we do not sell any engine kits for Sea Doo models. However this does not mean we have never developed Sea Doo engine kits. We have developed the kits for each Rotax engine, but declined to sell these kits when we experienced high "side effect" failure rates of engine components that were stock. Despite these experiences, we are prototyping a Sleeper kit for the newer 782 lay down rave motor to examine it's reliability. Without a doubt, one of the most confusing things about the available information about these engines is the measurement of indicated compression. Many shops, racers, and magazine articles seem to quote the "static compression". That is, they measure the compression with the rave valve in the down position. This yields numbers that are 20 to 30 PSI higher than the "actual" valve up numbers. Since the valve is seldom in the full down position, the valve down compression number is virtually useless. The valve down number becomes even more useless in situations where the exhaust port has been widened. For owners of Rave motors, we urge that all indicated compression numbers should be denoted in terms of "valve up" and "valve down" numbers. It is beyond us why no Sea Doo engine builders have already initiated this important procedure. This also helps to explain why rave motors have appeared to "need" unusually high compression. What they really needed was an appropriate measurement procedure.
PRO TEC SCOOP GRATE FOR 1100 RAIDER
We recently had an opportunity to test this grate on a Sleeper equipped Raider 1100. We expected the smooth water speeds to drop as a result of overstacking the front side of the pump (this has been almost standard on all previous top loader tests). It was our hope that the loss in smooth water peak speed would be small enough to offset the "significant" rough water advantage.
Much to our surprise, the smooth water speed INCREASED by 1 mph. This was an all time first for us... a top loader that "really" increased peak speed. The folks at Pro Tec deserve to sell a bunch of these grates. While we did not test the grate on a stock machine, we would expect the results to be similar. We cannot think of any 1100 that would not benefit from this grate. We are told it costs $99... it's the cheapest mph you will ever buy for the 1100.
PEAK SPEEDS - ANOTHER FACTOR IN "DOING THE MATH"
"Each boat can only go so fast at a given rpm with a given prop...there is no magic...it's just math"
At Group K we constantly receive calls from PWC's owners who make peak water speed claims that don't match the power and rpms of their engine. Joe Blow will call and tell us that his stock propped 1100 Raider (with flame arrestors and a milled head) is going 65 mph. However we know from our tests that an 1100 (bumping the limiter at 7050 rpm) will only run 62 mph with the stock prop. Of course there are always the variables of a particularly "good" hull, but no hulls are "that good". Whether Joe wants to believe us or not, we know that what he's claiming "doesn't match the math". For engine builders, it's a quick way to cut through the BS...."What prop and peak rpm are you running?"
This Pro Tec 1100 top loader grate, however, has proven to be a significant third variable. As mentioned above, the Pro Tec grate increased peak speed by 1 mph, however at the same time it pulled the motor down 80-100 rpm. We will not pretend to have any idea why this happens (perhaps some hydro dynamic engineer out there will be kind enough to submit an article to a magazine about this). For us the most important point is that the "math of speed" is so profoundly affected. This means that "doing the math" will now require knowledge of the prop, rpm, and grate. We have not experienced this with any other machine to date. It may be something exclusive to the 1100 Raiders... or exclusive to high output triples. What ever the case, it's now part of the "new math".
R&D "Power Plenum" flame arrestors
There is much marketing and "hoopla" about various flame arrestors. All the current aftermarket arrestors have their various design features... but the various PWC's engines don't know that. The only thing that really impresses us is a flame arrestor that delivers a visible "on water" increase in peak rpm along with a noticeable increase in acceleration. We consider the dyno charts and testimonials to be meaningless. In our tests on Group K modified 1100 Raiders, 1100 ZXis, Rotax Lay down Raves, and all Yamaha twin carb motors, the R&D Power Plenum flame arrestors (we think the name is too dam long) delivered better peak rpms and better overall acceleration than any other arrestors. On top of that...their less expensive. The other flame arrestor designers can say what they want... the engine has the last word.
Watercraft Connection Spark Plug Washers
This is a very innovative item that was very easy to over look. The rotational position of the spark plug may seem like an incidental detail, however it can result in a significant performance increase. The idea is to have the (properly torque'd) spark plug, end up with the overhead electrode facing the rear transfer port, and the open end of the gap facing the exhaust port. As the incoming charge loops up the back of the cylinder towards a spark plug positioned in this way, the raw fuel is deflected away so that it cannot wet the actual plug gap. This plug positioning can often "clean up" a slight rich condition, and always allows plugs to stay cleaner for longer. The real "on water" increase can be 40 - 50 rpm at peak speed. This is a detail that Group K attends to on all our in house race machinery and magazine test boats (it's fair). Unfortunately we have to accomplished this by torqueing a box full of plugs into each hole until we find the one with the perfect rotation for that particular cylinder (over torqueing to get a better rotational position can result in cracking the inner porcelain of the plug). With these washers, any plug can have the good rotational position. We think these washers are some of the least expensive horsepower and throttle response that money can buy ... get 'em.
Yamaha Triple Bore Distortion
During the 1996 season, we at Group K, have bored (and big bored) many Yamaha 1100 cylinders. Very early on, we found that many low hours cylinders seemed to be noticeably out of round...particularly the rear cylinders. After many hours of examining the situation we found one common theme...the bores were being seriously distorted (out of round) when the exhaust manifold was torqued on. We immediately assumed that either the surface on the manifold or the cylinder was not flat. Lapping both surfaces showed no "bowing" or irregularities of any kind. When the freshly lapped parts were once again torqued together, the bores were once again distorted. After repeating this process with many different cylinders and manifolds, we found another consistent theme. The two front cylinders were always distorted about .0015" out of round, and the rear cylinder was always distorted .003" - .004" out of round. We don't know why this happens, we just know that it does. It bears noting that .0015" of distortion can be eliminated during the honing process of doing a bore job... but .003" - .004" cannot.
As a result, Group K does all the boring and honing of 1100 Yamaha cylinders with an exhaust manifold torqued on. This process makes for perfectly round "installed" bores. However the bores do distort again when the manifold is removed. This causes a strange situation when we ship a bored 1100 to a customer with bore measurement equipment. We will invariably get a call back saying, "You guys bored my cylinders out of round?"....well, not exactly.
Broken Spark Plug Wires
This year, we got allot of calls from customers whose boats began to suddenly exhibit what appeared as an ignition problem. A drill of ohm meter tests, compression tests, and air leak tests confirmed that nothing was measurably wrong. One 750 Xi with this problem came to our shop for diagnosis. After checking all the normal stuff, we decided to replace the resistor plug caps. The new caps we were installing required us to cut back some of the outer insulation on the high tension leads to expose some bare wire. When we did this, the outer insulation came off with an addition few millimeters of high tension wire in it. The wires had apparently fractured, inside the insulation, about 10mm away from the spark plug cap. We cut back a little more outer insulation...and again got another length of fractured wires from further up the insulation. Eventually we cut back the insulation about 5 inches before to got to a part of the inner wire that was not internally broken. We installed the new caps, and the boat ran perfectly. We later realized that the additional resistance of all these breaks in the plug wires were causing so much additional resistance that there wasn't enough voltage left to run the engine at peak rpm.
Armed with this experience, we started checking the wires in other older boats. Not some, but most of the boats we checked had fractured wires. The most likely candidates were 650 & 701 model Yamahas (especially the red plug wired ones), and all 650 & 750 Kawasaki's. If you have never checked yours...we recommend you do so.