By far the most popular Group K engine kits are those intended to run on 92 octane pump gas. In the past, our Sleeper kits could safely be run on lesser quality gasolines that were not 92 octane. However today's stock pwcs are producing alot more power, and today's gasolines are becoming alot less "high performance friendly".
Today's gasoline blends are not an answer to the needs of the latest high performance road (and water) machinery. They are, instead, an answer to the emissions mandates put forward by the EPA. The EPA has no interest in accommodating the performance or longevity needs of any fossil fuel engines ... they are only interested in reduced emissions. They believe that it is the job of creative engineers and technicians to make modern high performance engines work and live with these new lower emissions fuels.
Besides some very important maintenance issues, there seems to be "significant" variations in the quality and composition of fuels available from different distributors and different geographical areas. Creating engines and maintenance procedures to accommodate the new fuels is do-able, however accommodating the variations in fuels is more challenging. The following information will help to explain some of those variations, and how those variations may affect high output pwc engines.
THE GASOLINES -- There has been much talk about different additives used to make gasolines more emissions friendly. That is, the additives that create what has been called "oxygenated fuel". The two additives most commonly used oxygenates are alcohol and MTBE (methyl tersery butyl ether). That is, each gallon of fuel has a 10% content of one of these additives. Besides reducing emissions, the 10 % content of these chemicals has other effects on high output pwc motors.
About Alcohol -- This is a fuel that many racers have some experience with. 100 % alcohol used to be permitted in some forms of dirt track racing and is still employed by many go cart racers. It's use was abolished in many forms of racing because it's flames are virtually invisible. This very dangerous quality makes for obvious safety problems.
Inside the engine, 100% alcohol burns very clean and yields very low operating temperatures. Unfortunately it's low specific gravity means that the jetting in the carburetors had to be doubled. Jetting was very difficult because so few carbs could pass fuel at double the rate in all circuit ranges. The final death blow for alcohol use in most forms of racing was that burning twice as much fuel means that you can't cover much distance on a tank of gas. It is strictly a "short event" fuel.
To further complicate alcohol's jetting problems, the clean burning alcohol produces very little, if any, plug coloring. At Group K, we have never been big fans of fine tuning carburetion by "reading" spark plugs. The clean burning oxygenating chemicals in modern gasolines provide even less plug coloring than earlier fuels. We believe that this makes "reading plugs" even less accurate and less meaningful than it ever has been.
Variations -- In automobiles (and pwcs) a 10 % content of alcohol is definitely enough to make the carburetion noticeably leaner. Correcting for this lean condition is not difficult. However there are fuel refineries across the country that will occasionally blend in bigger percentages of the inexpensive and very plentiful alcohol. It is said that some of these blends can contain as much as 15 to 20 % alcohol. Is this legal? ... probably not. However in a world of discount gas stations located in outlying areas, a don't ask don't tell policy is in place when the price is right. If an unknowing motorist buys a load of 15% - 20% alcohol fuel, his car starts a little harder and runs a little lazier. This same load of fuel, in a high output modified pwc, can cause a lean condition with more serious results. How can you know the true content? ... you can't. This underlines the need to buy fuel for your high performance pwc at a name brand retailer, or a station that you are familiar with.
Another complication of alcohol is the high solvency. That is, it has a lesser lubricicity than the fuel it is being blended with. This higher solvency literally washes internal engine surfaces that require a presence of lubrication. In 100% alcohol race engines, this solvency is so profound that mixes between 15:1 and 20: 1 are commonly used to provide ample lubrication for high rpms (our old alcohol half milers ran on 12:1 Klotz...they loved it). Most stock oil injection systems yield a 40:1 - 50:1 equivalent mix at full throttle. For normal use in a stock boat, this is probably okay. However, at Group K, we believe that this is questionably enough oil for extended high rpm use ... particularly if 15% + blends of alcohol may be at hand. In the case of a highly tuned pwc running on oxygenated pump gas, fuel/oil mixes between 40:1 and 32:1 should be used. If your oil injection cannot deliver that, the rest should be added to the fuel.
The last significant complication with alcohol is that it attracts water. That is to say that it literally draws water out of the surrounding atmosphere into the fuel. This drawn-in water then enters the engine along with the fuel and oil. While the percentage of water content is low, it further contributes to the internal "washing" of surfaces needing lubrication. Blends that contain more alcohol can attract more water.
It is standard practice for owners of 100% alcohol race engines to purge out all the alcohol after each raceday by running it briefly on conventional premixed gasoline. Doing so assures that the alcohol will not draw a damaging water content into the carb circuits and engine internals. For those using oxygenated fuel in pwcs, this underlines the need to do proper winter storage preparation on your pwc.
In truth, the high humidity in the engine compartment of all pwc's assures that the engine will ingest some percentage of water. However the presence of water in the fuel tank and metering circuits of the carb is what can cause maintenance problems down the road.
About MTBE -- MTBE has the same basic properties and qualities as alcohol. While it has a more stable chemistry than alcohol, it still carries many of the disadvantages. It has the lower specific gravity that requires richer jetting, the high solvency, and it attracts water (although not near as much as alcohol). It is rare for refineries to blend in higher percentages of mtbe because it is not as cheap or plentiful as alcohol.
Aviation fuels -- One affordable way to get away from the problems associated with oxygenated fuels "used to be" the use of "av" gasolines. However, now all "av" gasolines are also oxygenated. Despite this, running a 50/50 mix of av gas with 92 octane pump gas is still a very effective way to raise octane and reduce operating temperatures.
"WHAT DOES ALL THIS MEAN TO ME" -- Most of today's high performance pwc owners are folks that have owned other types of high performance vehicles in the past. These owners (like us) always took for granted that any gasoline that came out of a pump would be good enough to run in any highly tuned engine. The engines that were tuned to run "on the edge" using the pump gasoline of 3 or more years ago will not necessarily have their same margin of reliability on today's pump gas. The widespread conversion to lower emissions "oxygenated" gasolines in the last couple of years has forever changed that. For stock and mildly modified machines that get moderate use, the oxygenated 92 octane pump gas is safe to use with your oil injection or a 40:1 premix. For extended high rpm use of these machines, we recommend to add a little oil to the gas (1 - 2 ounces per gallon).
The real change in attitude will begin for the high performance recreational rider. This rider usually runs the machine all (or most) of the time at full throttle, and wants to use exclusively pump gas. The two problems that this rider should be conscious of are the varying percentages of oxygenate additive and the increased solvency that comes with it.
Variable Oxygenation -- Our highest output pump gas kits are the Hammer 92 (octane) kits. It's no surprise that all our Hammer 92 customers want to get every bit of available horsepower...without having to use expensive race gas. We test at great length to find the right combination of compression, peak rpm, and carb jetting that offers consistent and reliable performance on pump gas. However, if one of these Hammer 92 customers gets a load of 20% alcohol fuel, instead of the 10% we test with, his jetting will suddenly become leaner by virtue of the fuel. For most stock (and mildly modified) machines this slight lean condition does not create a significant reliability risk. However for the high output pump gas engine, this slight lean condition can result in significant temperature related problems. If this customer has an on board digital tachometer, they will see the loss in peak rpm caused by this lean condition, and richen up the high speed screw slightly to correct the situation. Unfortunately, few customers have these tachometers, and few customers want to be constantly adjusting for different fuels. The best way to avoid all these problems is to buy your fuel from the same name brand gas station. While this is no guarantee of "zero" variations in the fuel, those variations can be expected to be slight.
Increased Solvency -- The horsepower output of Hammer 92 engines (and the higher temperatures that come with it) require an ample presence of lubrication. Here again, the occasional load of 20% alcohol fuel has an increased solvency that compromises the oil that is present. The best fix for this risk is to increase the oil supply to the engine. Premix machines should be increased to a 32:1 ratio. Machines with adjustable oil injector pumps can be adjusted for slightly more oil input. Machines with non-adjustable pumps should have 1 - 2 ounces per gallon added to the fuel. It seems silly to add oil to a machine that already has injection, however the added protection is needed for very high output pump gas motors.
OUR RESPONSE TO THE NEW FUELS -- The pump gasolines of two or three years ago allowed us to create Hammer 92 engine kits that were not much slower than the Hammer 105 race engines. That will no longer be the case with the new oxygenated fuels. Our future Hammer 92 kits will likely employ the use of slightly milder compression ratios and slightly richer premix ratios. These two changes will allow the kits to more safely accommodate the variations in oxygenates. For customers who own Hammer 92 kits that were built 2 or more years ago, reducing your compression and increasing you premix would be a good idea. Our Sleeper engine kits will still be conservative enough to run on the oxygenated fuels, so long as the customer does not attempt to increase rpm or compression beyond our specifications.
As an additional option, in 1997, Group K will be releasing a new line of "Swift" kits for most machines. These Swift kits will be an abbreviated version of our Sleeper kits that will be more forgiving to fuel quality and oxygenate percentage content. The Swift kits will require less "tinkering", less down time, and less money than the Sleeper kits. Stay tuned to our website for this info.