Reply With QuoteThis is an article I found on the net about fuel The person that wrote it is heavely into jetboat racing.
FUEL: THE BURNING QUESTION?
Some history of fuel in America:
*** Back in the 60s the fuel was plentiful, cheap and of high quality.* But in 1972 we had the first fuel crisis which caused two things to happen to the fuel. First, the price rose from the standing price per gallon of about 30 cents a gallon, to the much higher price of 50 cents a gallon. At the same time the government was forcing the fuel manufacturers to reduce the Lead content of the fuel.
*** In 1976, the second fuel crisis struck, crippling most fuel based industries, ie. engine manufacturers, boat builders, anyone who had a high demand for fuel. This also raised the cost to the now excepted price of around a dollar per gallon. To worsen the situation, the Lead was further reduced, causing allot of engine damage, and the quest for engine development to combat the problems associated with poor burning qualities.
*** In 1990s, the Lead in all motor fuels was eliminated completely. This lead the engine manufacturers and fuel manufacturers to develop the additives we have presently, and the engines suffered a serious drop in compression in order to survive the poor fuel burning characteristics. Development of computer controls and fuel injection has partly resolved the problems in autos, but has not done much for the aging motors of yesteryear.
*** In what has been called the Muscle Era, we had motors that came from the factory with up to 12 1/4:1 compression ratios. These engines made serious power but had to have the high lead, high octane fuel to run correctly. High performance requires high quality fuel. It must contain enough Octane to eliminate detonation, the primary cause of engine damage, some lead will extend the valve life also. The introduction of hardened valve seats has helped somewhat, as well as stainless steel valves to withstand high combustion temperatures. There are some changes that can be made to the tune-up of a high compression motor to combat the problem of detonation. Retarding the timing will help to some extent, as would reducing the top RPM under load of the operating engine. But it comes back to fuel quality(Octane) to get the most out of a high compression, high performance engine.
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*** What can be done?
In a nut shell, only a few of things. These are the options available:
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1. 1. Reduce compression in the engine, and reduce overall output.
2. 2. Use extra fuel to cool the cylinder before ignition takes place.
3. 3. Use cold spark plugs to lower cylinder temperature.
4. 4. Reduce the timing of the ignition spark.
5. 5. Computerized fuel and spark management (high cost and expensive set up).
6. 6. Lastly, burn Racing fuel.
********** What fuels are available today?
*** There are the fuels that we all are familiar with at the gas station. 87, 89, 92 octane, nonleaded gas. This fuel burns acceptably in most newer cars, and causes a few problems with older cars. As far as a late 60s, early 70s big cube, high compression engines are concerned, it is a sure death if run hard on available pump gas without extensive detuning acrobatics. And the question remains, what is the purpose of having a big engine if it cant run?
*** Fuel octane is what allows engines to produce the biggest bang with the highest compression. Cut the octane and you will have a big bang as the rods smash the bearings from between the rods and crank. PREDETONATION!
Octane keeps the fuel from igniting until it is lit by the spark plug as determined by the ignition timing. High octane gas and racing gas is actually cold fuel. It must be lit with some source. On the other hand, low octane can be ignited by over compression in the cylinder, or ignited by a glowing piece of carbon on the head, valves, or piston top.
Since compression of the air/fuel mixture is what produces the power, it makes sense to go as high as possible to produce the most power.
*** The limiting factor is usually not fuel but DOLLARS!! Fuel dollars and parts dollars must be considered foremost.
*** Lets* look at Racing Gas to see the benefits. First is the octane rating. Many makers of fuel have differing octane levels of gas they produce. Each fuel has a top level of compression it can stand before going onto predetonation. The higher the octane level, the higher compression before detonation occurs. Once the compression reaches a limit that gas can not stand, alcohol must be used due to its cold combustion properties. But there is a drawback with alcohol, it takes up to 3 times the amount of alcohol* to equal what high octane gasoline delivers. Then to increase the power of alcohol, nitromethane is added to produce one of the most powerful fuels known to man. Nitromethane is 52% oxygen by content and explodes violently in the cylinder!
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*** The following statement is my opinion on manufacturers of racing gasoline!
*** I have tried most of them. Unocal 76, Sunoco/CamII, Trick, Sports are the brands I have used in the past. All will work once the tune-up is set for each.* The major difference between all the fuels mentioned is the cost per gallon.
I sell Unocal 76 Racing Gasoline for two reasons. First it is a high quality leaded gas that offers 110, 114, 118, 126 octane levels. Second and most importantly, if you use any quantity of it, is the PRICE! For the price, it is my opinion, you cant buy a better fuel than 76! And it is the CHEAPEST!!
*** Octane is reached by two factors, research octane, and mechanical octane.* The research octane is a theoretical value of compounds burning under certain conditions before predetonation occurs. Mechanical octane is the real world test that runs an engine at a specific temperature and has a variable compression cylinder that is adjusted until the compression causes the predetonation condition to occur. Take the two results from testing, add them together, and divide by 2, gives the octane rating of the fuel. R+M/2.* Each manufacturer determines the octane in the same manner. However, not all advertise the fuel the same. Some use the research number, and some use the R+M/2 number. The misleading thing about the form of advertising is that you might be convinced by the dealer that the cost is justified by the octane level of the fuel. This is not always the case. The most important value is the mechanical octane number. This is what is going to be tested inside your engine!! Always look at the R+M/2 average octane on any fuel you might be considering. It will pay off in the long run!** The use of race gas can be straight, or a mix of race gas and pump gas to get a level of octane required for your specific engine compression.
*** The following is what I recommend to my customers from real world testing on different compression engines that I have worked on over the years.* It must be noted, any engine can be run for a little while on anything, but the destruction of the engine is what is to be avoided, thats the point!!
*** The recommendations are my opinion for SAFE operation under heavy load and stress conditions:
* ? Below 9:1 compression- 92 octane pump gas. 9.5:1 can run short bursts also.
* ? 10:1 compression requires 96 light load and 98 heavy load octane. 50/50 110.
* ? 10.5:1 compression needs 89 to 100 octane 60/40 race/pump mix
* ? 11:1 compression needs 102 to 110 octane 70 to 100% race gas.
* ? 12:1 to 13.5:1 can run 110 straight with jetting adjustments to put extra fuel in the cylinder to help prevent detonation in the higher compression engines.
* ? 13:1 to 15:1 compression with Nitrous oxide injection or straight compression will require 114 octane to run safely. always look for detonation signs!!
*** These are the regular compressions that I deal with in boats, and drag car engines. Your engine may require more or less depending on how you run your engine. I have determined these SAFE formulas that have run strong, and lived long lives for my customers engines.
*** The reason for examining race gas as a fuel is the fact that, YOU CAN BUY ALOT OF RACE GAS FOR THE PRICE OF AN ENGINE REBUILD JOB!!!
*** Lastly, the fuel that pops up most frequently when determining cost* for consumption and use is 100LL aviation gas. Some people swear by the stuff, and it will work. But after contacting Unocal 76* and inquiring about AVGAS, I was sent three pages of information which changed my mind about recommending the fuel for off-road uses, boats or cars.
First it is 100 octane, which contains 2.5 grams of lead per gallon. Race gas contains 4.5 to 5.5 grams per gallon.*** Second, it has fewer hydrocarbons and must be jetted for due to the lesser amounts of hydrocarbons. (the molecules that burn in fuel).
Third, The EPA has a mandate on the books that prohibits the purchase and sale and use of AVGAS for any motor vehicle except airplanes.
Fourth, the fine is $25,000.00 for the violation of the mandate, on the purchaser and the seller, PER DAY!!
Fifth, the enforcement of the law was lax in the past, but is being looked at more and more, and is being levied increasingly.
