oil question

Old 04-24-04, 07:13 PM
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Question oil question

Iím kindof a performance freak and I was wondering if running synthetic oil in a lawnmower would have any effect on performance as it sometimes dose on a car or could it harm anything? I had the same question about high octane gas will it improve performance, or is it not worth it or could it some how hurt the motor?
Old 04-24-04, 07:35 PM
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High octane fuel can damage an engine unless it is made for it. Most engines are designed for 87 octane or "regular". The higher the octane, the higher the engine compression it would take to spontaniously combust and also, higher octane fuel burns slower. In other words, if an engine has a knocking sound while burning 87 octane, you would switch to 89 or 93 octane cause it is a slower burning fuel, or if a gas engine does what's called "dieseling", in other words, the engine would be running even though the ignition switch is turned off because the engine would be firing off of compression (a diesel engine fires off of compression, not park plugs, hents the term "dieseling"). To solve this preblem, you would switch to a higher octane cause a higher octane will not spontaneously combust at lower compression ratios, such as automotive engines. Racing engines have higher compression ratios, so they require higher octane levels since lower octane levels would self ignite under those higher compression ratios that racing engines develop. Some automotive engines will give better performance using 87 or 93 octane fuels, while others will run worse, and yet, some will run the same with any level of octane. Diesel fuel has a similar rating scale, except with diesel it is called cetane, not octane. Sorry for being so long winded!!!!!!

Last edited by mower17; 04-24-04 at 08:11 PM.
Old 04-24-04, 08:20 PM
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I think that there's lots of misconceptions about "high octane" gas out there. People think that they can put 110 octane gas into a regular engine and get improved performance. That's not so. Normal gasoline engines have a compression ratio of around 8.5 to 9.0 to 1. A proven method to increase HP without increasing piston size is to increase the compression ratio. High compression engines will produce more HP than a lower compression engines. The problem with a high compression engine is that the fuel tends to burn (exposively) before the spark occurs (or even after sometimes) due to the increased heat of compression. Fuels with higher octane ratings have an increased ability to resist this engine damaging tendency. If you tried to use normal 80/87 octain gas in a high compression engine it would get torn up by preignition and/or detonation. You get your performance increase not from the fuel, but from the high compression of the engine. Once you increase the compression of the engine you must then use high octane fuel to eliminate detonation and to keep from blowing holes in pistons.

Using high octane fuel inside a normal engine would not be much of an advantage. You might even have difficulty with your engine, not because the exhaust gases are hotter, but because the fuel air charge would not ignite at the optimum time.

If you are a real hard core performance freak you might try to run your engine on alcohol. If you look at the heat of combustion of that fuel you will find that it's actually LOWER than gasoline. Why then would it be to your advantage to use such a fuel? The answer, again, is compression ratio. Alcohol has a much, much higher octane rating than any gasoline. That means that you can go to the max with your increase in compression ratio without the worry of damage of your engine components due to detonation or preignition. Using alcohol means that your only limits on your compression ratio is the strength of the engine components themselves, not the disadvantages of the fuel characteristics. Why then don't the car manufacturers use alcohol in all their cars? There are two good reasons I can think of right off the top of my head. Number one, you must use a lot more alcohol per mile driven. You remember what I said about the heat of combustion? That means, per gallon, alcohol contains less energy than gasoline. Fuel tanks would have to be about 25% bigger. That's bad news for car manufacturers that are trying to get the engine components smaller so they can make passenger & cargo space bigger. The other big disadvantage to alcohol is its tendency to absorb water. Water and alcohol will completely mix and once mixed won't separate.

As far as synthetic oil goes: It's main advantage is it's improved viscosity index. It won't thin out quite as much when hot and won't thicken up quite as much when cold as a regular based oil. I use it in most of my stuff, small engines, and big. Synthetic's main disadvantage is it's increase cost.
Old 04-27-04, 08:02 PM
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The first thing you have to consider is that in my area they use the R/A 2 method which is the Research method of rating gasoline octane. In this case all engines including small engines as it states clearly in the owner and shop manuals shoud run on a min. of 90 octane gas. On an air cooled engine the high octane gas is worth it but no need to buy 110 octane racing fuel. 93 will work just fine but if you want it too run real good get 87 octane and CD-2 lead substitute or even better 93 and the substitute. Even at 9.0 to 1 compression ratio low octane is too low not to mention by running a higher octane number the engine will run cooler and this is espescially good for air cooled engines. The octane ratio of alchol is 150 and it requires carburator changes, and don't buy the high dollar racing fuel it's not worth it in less you have 10 to 1 compression. Synthetic oil can increase HP as much as 5% and its' very good lubricating properties make it worth the money to buy it!

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