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What are MTBE's negative effects? MTBE may corrode fuel injectors and aluminum passages and hardens some plastic and rubber components in fuel systems, but the gas also usually has some additives to prevent this. More of a concern for owners of 2-stroke engines may be that it could dilute petroleum-based oils and influence engine lubrication.
The good news is that the new synthetic oils are not affected, so if you haven't switched to synthetic oil, now would be a good time to do so. Synthetic oil mixes also reduce the corrosive tendencies of the alcohol content, so it pays off with extra protection for bearings, aluminum parts, and injection equipment.
The racing gas game is now in a state of confusion, and a real problem for racing organizations attempting to police rules to make the game fair. With the addition of MBTE to pump gas, pump gas now often does not pass the di-electric test, because it has a 2.7% higher oxygen content than "old" gas.
Some race gas manufacturers still use lead as an additive to get their high-octane ratios (110-118), and these gases may pass the meter. Other race gas makers have taken advantage of the alcohol additive situation and produce some 100-octane "pump gas" with up to 22% alcohol, which gets you close to 4% oxygen enrichment. We tried some of this stuff from our local drag strip, and it pegged the meter at the grass drags. When we bought some Amoco Ultimate 92 off the local gas station, it also registered high.
Race organizations are now in a quandary, but some have moved the limit and use the new formulated 15% MBTE gas as a baseline, while others supply gas at the track to make sure everyone's on a level field.
Racing gas is continuously getting more expensive, but those who run modified engines with higher compressions requiring more than 92 octane are left with some alternatives to cutting costs. Adding an octane booster can raise the level five to eight points, and today's boosters also contain anticorrosive additives that benefit the MBTE formulated gasolines.
Another alternative is to buy leaded racing gas and mix it with some 92 pump gas to reach your desired level. Klotz supplied us with the accompanying chart (p. 66), which shows you what combinations of 92-octane pump gas, and their 113-octane race gas produces your desired octane ratio.
We usually mix 50% when we test new products just to have a safety margin until the jetting is right. This gives us an octane of 102.5, but mixing one gallon of race fuel to four gallons of pump gas still gives 96.2 octane, which gives plenty of protection and good performance.
Through the steady advance of technology, manufacturers are now increasing their use of knock sensors to protect against engine damage. On Yamaha's carbureted machines the ignition will retard when the sensor discovers engine knock, and according to Yamaha this has cut warranty burn downs by 90%. So Yamaha owners, make sure the sensor is connected.
New fuel injection systems also can richen the mixture when knocking is discovered, and this is even more efficient because it quickly cools down the piston and combustion chamber.
The new injection system on the Polaris Fusion starts with advanced ignition, and as soon as knock is detected it both retards ignition and richens the mixture until the engine runs normal. This is an ongoing process and continually adjusts the engine to different conditions, and may even adjust to the wonders of Mother Nature like the fine powder snow we love to play in.
This new technology will ensure that future snowmobiles will adjust themselves, but in the meantime, if you have a recent carbureted machine it would be good to do some research at your dealer to see if there are new jetting procedures available for today's reformulated gas.