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Old 04-25-2010, 04:13 PM   #1
grohl
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Default Which type of gas for small engines? (lawnmower etc)

I am borrowing my neighbors gas-powered power washer. It has a nice little 8hp Honda engine, 3000psi/3gpm. We are both "yard guys" and have a mess of small-engine equipment between us.

So, he says, "make sure you put super unleaded in that thing when you are done." He goes on to say how super unleaded is "better" for small engines, something about high compression etc etc. I vaguely remembered NOT to use super unleaded in these motors because I thought I remembered it burning hotter. Clearly I don't have a clue, is my neighbor right?
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Old 04-25-2010, 04:25 PM   #2
bigal40
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Quote:
Originally Posted by grohl View Post
I am borrowing my neighbors gas-powered power washer. It has a nice little 8hp Honda engine, 3000psi/3gpm. We are both "yard guys" and have a mess of small-engine equipment between us.

So, he says, "make sure you put super unleaded in that thing when you are done." He goes on to say how super unleaded is "better" for small engines, something about high compression etc etc. I vaguely remembered NOT to use super unleaded in these motors because I thought I remembered it burning hotter. Clearly I don't have a clue, is my neighbor right?
I run small 4 stroke engines with 87octane. Higher octane gas doesn't burn hotter, it just doesn't ignite until it reaches a higher temperature. That's why when you have an engine with really high compression you need higher octane fuel to prevent ignition in the cylinder prior to the piston reaching TDC (preignition is called pinging)
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Old 04-25-2010, 04:30 PM   #3
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Regular.
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Old 04-25-2010, 05:31 PM   #4
Kaervak
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87 octane for pretty much everything. The only exception that I've come across is our tiller, 89 octane.
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Old 04-25-2010, 05:50 PM   #5
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If you're putting anything higher than regular 87 in a lawnmower you're throwing money away. They don't have such high compression to need plus or premium.
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Old 04-25-2010, 05:52 PM   #6
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Ok, a few things.

Nearly all small engines require Regular 87 octane. There are exceptions, but most small engines don't run a compression ratio higher than 9:1. Some can be as low as 6:1. Of course, combustion chamber design plays a major role in necessary octane rating, but in general small engines are not high performance machines and do not require high octane fuel.

The higher the octane, the slower the fuel burns, and the less heat produced. Fortunate, they formulate all gasoline grades to be within 2% energy content of each other. However, this is why you aren't supposed to run premium in an engine that only requires regular. It can cause carbon buildup with an engine that only sees light duty service.

Everyone has their things. Fill it up with whatever you want, it's not like he's going to know the difference. He probably uses Marvel Mystery Oil in the crankcase also. *shrug*
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