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Gas Quality


Terminator20's Avatar
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06-07-04, 05:13 PM   #1  
Gas Quality

Because of the fact that gas quality is not what it used too be, is it not true that we should be running Premium or plus in our small engines? I have actually noticed a difference using plus in my Murray rider. It does not make tiny puffs out of the muffler anymore. This was allways doing this when I was running it with regular. I was actually told by a Stihl service dealer that I should run premium on my trimmer. When asked why, he said that it will misfire sometimes, and especially at high idle. Well, I have been using premium in my trimmer and it has been running perfect. I bet you if I used regular, it would not be. What do you guys think about this?

 
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jughead's Avatar
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06-07-04, 05:45 PM   #2  
To my knowledge there is only a couple of octane points between regular gas and premium. The main reason for premium is to obtain a little better knock supression when using a higher compression engine. The idea that premium fuel is in some way "hotter" is, I believe, false. I'm sure that B&S, and Tecumseh design their engines for the average burn characteristics of regular fuel.

My guess is that if you get fresh regular or fresh premium and actually make some measurements of HP, and temperatures you would be hard pressed to tell the difference between the engine performance of the two different gasolines.

I've yet to see a reliable source state that premium fuel has any advantages other than knock supression in a higher compression engine. Single cylinder engines in regular use on lawn & garden equipment don't fall in that category.


Last edited by jughead; 06-08-04 at 05:38 AM.
 
Terminator20's Avatar
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06-07-04, 06:02 PM   #3  
I have another question. I have seen that commercial walk behind mowers can be bought with a 2cycle engine or 4cycle engine on them. Why would you want a 2cycle engine on a mower? What are the advatiges? To my knowledge on 2cycle engines, there are none. They are louder, put off more emmisions, and don't have the power of a 4cycle. I have been trying to understand this for 2 years now.

 
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06-07-04, 08:26 PM   #4  
2 cycle engines put out more power for their displacement. This allows for a smaller and lighter motor to be used. 2 cycle motors also put out more lowend torque then a 4 cycle motor.

 
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06-07-04, 11:31 PM   #5  
Correct...2 cycles have lots more power than 4 cycles per cubic inch, not less. And they are lighter. They aren't necessarily any noisier (depends on the muffler). They do pollute more though.

As far as the gas goes, Jughead is right. Premium gas burns SLOWER than regular gas, and in fact gives a slight DECREASE in power from your engine. It is designed to burn slower (that's what the octane does). This is to eliminate spark-knock (pinging) caused by fast detonation and higher compression.


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06-08-04, 05:55 AM   #6  
The main advantage of a two cycle engine is it's ability to be used at many different angles. It's also lighter per horsepower than a four cycle engine. If you think about it, a two cycle engine gets it's lubrication from the fuel and that fuel it typically drawn into the crankcase by suction. The oil/gas vapor thereby lubricates the rotating crankshaft and the moving piston. There is no oil bath on the bottom of the crankcase like there is on a four cycle engine. Think what would happen to the oil bath if you used a four cycle engine on your chain saw. I know I just did some cutting with mine and I operated the engine at some wierd angles, even upside down while cutting off some branches on a tree in my yard. If you compare the horsepower to weigh ratios of engines the winner would be the turbine engine, followed by the two cycle engine. On a theoretical basis the two cycle engine ought to have twice the horspower of the same sized four cycle but it just doesn't because it can't do a very efficient scavenage of the cylinder gases in the real world operation.

The bottom line: if you want an engine that can operate at just about any angle that is as small & light as possible, pick on a two cycle engine. That's why you see them on weed wackers and chain saws. That equipment must be light and operate at wierd angles. You see two cycle engines on small & light motor cycles because of the power to weight ratio. These motor cycles may also be operated at different angles if they are rough terrain or hill climbing bikes.

 
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06-08-04, 08:42 AM   #7  
Ah, I see now. I understand the difference now. Thankyou guys for the information. I allways wondered about that.

 
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