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sunrunner

What Octane do you use?

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MrSteele
An old farmer, many years ago, told us to always use "ethylene" gas in his tractors. He used the highest test octane in all his equipment from lawnmowers to combines. We rarely worked on his engines for tune-up problems. I run 92-93 octane in all my small engines, 2 or 4 cycle, and have literally burned the electrodes out in the plugs. The engines will run with weaker ignition, less compression, and run well. One Briggs I finally quit using when I had a replacement rebuilt would not run on regular gas, but ran decent on high test. It simply did not have enough compression to run on lower test gas!

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jdm
I read on one of the tractor sites that using the higher octane gas was a waste of money as lawnmower engines did'nt have the compression to take advantage of it. I had always used the higher octane until then. I stopped the practice and noticed no difference. Now I wonder. Does anyone know for sure?

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TimJr
You have the science behind octane completely backwards. By definition of sorts, the octane rating is a number given to fuel to rate its ability to resist detonation (spark knock) or self ignition. That is why racing engines use 110 plus octane - they have high compression, lots if spark advance, and high heat. A low compression engine requires less octane, unless it has a very poor head design,or a few other factors such as incorrect tuning or other problems. Racing, or high test gas will not "run hotter", and it doesn't "burn cooler" either. All myths - check out any fuel company's web site. You are wasting money by running premium fuel in a small engine, except for some 2 cycles which are high compression and need it. An older Briggs can run on 77 octace. Not sure about a modern OHV one, but 87 is definitely OK. If you have literally burned up a spark plug, you have other problems that need to be fixed - possibly clogged cooling fins causing extremely high internal temps, or blocked airflow to the engine in general. Premium fuel isn't always cleaner either - all gas must meet certain standards, but some companies will add more additives to the premium fuel though. The most important thing we can do is to not let the fuel get too old - generally 30 days or so, and keep the can and fuel tank clean of debris - proper fuel cap, clean the fill area before opening the cap etc.. Partially my opinion, experience, and education on fuel and engines - I encourage everyone to check their engine manuals and surf the web for more info on engines and fuel ratings - there is a lot to it. Tim

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russ02
Tim is right. The only possible gain, and it's only a possiblity, are the added detergents not in the 87 fuel. Since many of us run pre-'76 engines that were meant to run on leaded gas... Does anyone know how Briggs dealt with the removal of the lead from the fuel? How about those who now have to run with ethanol blends? I've lost 3-4 mpg in my car on the alcohol mix.

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TimJr
As for the alcohol - it has a pretty high octane rating, so that is okay. But, it's BTU's are different than gas. The big thing is the carb fuel mixture. Gas burns ideally at around 13 to 1 air to fuel. Alcohol burns at 6 to 1 air to fuel, therefore requiring twice the fuel to be delivered to a given engine. Nitromethane burns at about 2 to 1 - next time you see a top fuel dragster, check out the raw fuel being spit out while they are idling, because they have to pump such a ridiculous amount of fuel into those engines. Tim

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BLT
Briggs has somewhat endorsed no lead fuel for older engine as the are no longer large deposits on exhaust valve. At the time they also said that they experieced no difference in performance that anyone would notice. It's been thirty years being on no lead and leaded gas is hard to find. Also for the most part, all engines built today are designed to run on 87 octane gasoline.

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ridgerunner
I just put in what I have around. I've ran from one extreme to the other in the Big-Ten. From realy old 87 octane to running 114 leaded octane (useing up left over fuel from my tubbed F-100) And the stock original 1965 Briggs didn't care one way or the other what it was burning. The only difference is that the 114 smells alot better when burned:D. -Paul

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MrSteele
The burning up I refer to is the electrode burned completely away, as in the case of running LPG in an engine. The electrode will burn well into the plug before any problems such as misfire occur running on LP. Those plugs may have been in the engine for several years and kept on running. Mine are the same way. I only replace a plug if the insulation is cracked, extremely rarely for any other reason. I'll keep the higher test in the tanks.

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HubbardRA
Octane requirements are almost directly related to compression ration. Lower octane fuels actually have a faster burn rate, while higher octane fuels burn slower, but contain somewhat more energy. As the fuel is compressed to higher pressures, the burn rate increases. If the burning speed gets too fast it will cause pinging, or audible detanation. This is when the burn rate gets so fast that it is trying to explode rather than burn. Not good. Most garden tractor engines run compression rations between 6:1 and 8:1 which works quite well with 87 octane. When the compression ratios run between 8.5:1 and 9.5:1, then 89 octane may be required, depending on ignition timing. Above 9.5:1 compression will usually require 93 octane. If a high octane fuel (such as 93 octane) is used in a low compression engine (such as an older flathead garden tractor engine) the air/fuel mixture will not burn fast enough. This will mean unburned fuel will be thrown out the exhaust, and the full energy of the fuel cannot be used. In the lower compression engines, the lower octane fuels will actually produce more usable power. When I was tractor pulling I tried various octanes fro 87 up thru the Cam II fuels. For the engine I was running at the time I ended up using 89 octane. Why? Suzuki motorcycle engine with 9.25:1 compression. It made the most power and had the best throttle response on 89 octane. I do have one friend who uses Cam II or 110 octane aviation fuel in his tractor. Why? His engine has been modified and runs a 13.5:1 compression ratio.

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maxtorman1234
I run 87 in everything, Briggs and Kohler engines, all except for my K341 with the 0.050" removed from the head, I have to run 93 in it because it has a higher compression ratio.

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MikeES
I tried little Turbo Blue (I believe 105+ octane) in our pulling tractors and lost significant performance. I try to get 89 non ethanol gas but hard to find. I end up with BP 90 octane without ethanol is the only thing I can find without ethanol. I have noticed a slight performance decrease with ethanol fuels.

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reynoldson
Right now I'm building a kohler k301 "stock" engine for a puller. I've read a couple of articles that state "about 10% to 13% more power can be produced with E-85 or methanol fuels." Does anyone agree with this statement or is it false? I'm undecited as of yet.

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HubbardRA
The additional power that can be realized with alcohol comes from the fact that there is excess oxygen in the fuel itself. Engines are limited in how much air they will pump into the cylinder. We can jet the carbs to put the correct amount of fuel with that air. The power of an engine is dependent on the amount of air/fuel mixture that is being compressed in the cylinder on each piston stroke. Having the excess oxygen in the alcohol is like injecting more air into the cylinder, so it does produce more power than gasoline if set up correctly. I would also say that the 10% to 13% power increase is probably stretching it some for E85. Pure methanol usually will not give much more than that. For years I pulled against guys who were running methanol. I used gasoline, because I could not see that the small power increase was worth the hassles associated with running pure alcohol. Remember that alcohol reacts with the aluminum in carburators and causes a white powdered corrosion. It will plug up the jets, and will completely ruin a carb if left in it. Most guys who used it would clean the carbs nearly every pull. One guy I knew would shut off the fuel and run the engine till it burned all the fuel in the carb, then fill the carb with gasoline to flush any remaining alcohol.

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MikeES
The go-cart racers have a portable tank and run the engine with some gasoline. If not their engines are seized up by next weekend. Most cart engines are bored very tight with soft rings and with the tight tolerance + alcohol + aluminum = stuck engine. With pulling tractors the alcohol burners usually run snowmobile type carbs. (Mikuni) vs. the Kohler or Walboro carb. To burn E85 (see if your pulling club allows it, in my area they do not) will require as Rod stated major rejetting including boring out the jets in your carb. See Brian's pulling tips http://members.aol.com/pullingtractor/flywheel.htm

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