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Marcus731

13.5:1 piston with pump gas?

19 posts in this topic

I am putting a new piston in my 07 YZ450F and was thinking of using a high compression piston. I want to know if I would have any problems running 93 octane pump gas or would I need to use a higher octane fuel?

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Most people are able to use 91-93 US pump gas of a good quality with 13.5:1. But, you might run into some pinging in hot weather, or at low speeds under a load.

If so, you can use a higher octane pump gas, if you can get it, or a race fuel, or take an inexpensive route and add 10-12 ounces of toluene to each gallon of gas to bump up both the octane and the energy yield.

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Elevation is one of the biggest factors in what compression you can run on pump gas. I live at 4500 ft and run 13.5:1 on regular 85 octane gas all day long. This is on a big bore, stroked, and ported engine. Also if you run slightly on the rich side it will help to avoid detonation.

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Most people are able to use 91-93 US pump gas of a good quality with 13.5:1. But, you might run into some pinging in hot weather, or at low speeds under a load.

If so, you can use a higher octane pump gas, if you can get it, or a race fuel, or take an inexpensive route and add 10-12 ounces of toluene to each gallon of gas to bump up both the octane and the energy yield.

hi guys,

I'm installing a new 13:1 wiseco piston and i have the same problem. Here the gasoline is 95 oct max............

10-12 ounces on each gallon I calculate is almost the 12% of toluene in volume of mix....................really need so high???? :thumbsup:

Luigi...Italy...

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You will probably not need any additives to run 95 octane (RON). That's only a half point more compression than stock.

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If so, you can use a higher octane pump gas, if you can get it, or a race fuel, or take an inexpensive route and add 10-12 ounces of toluene to each gallon of gas to bump up both the octane and the energy yield.

Gray, I have this group of lunatic hot rod guys in there 60's that buy toluene from me to bump up octane in there cars. They were telling me they use a ratio of 10oz toluene and 1oz atf per gallon of gas. I have been debating on doing this myself just because the toluene would be free, but is the transmission fluid really necessary? I sometimes don't trust these guys just because they are nut jobs with a lot of money and don't care what happens to there engines.

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Toluene is a common gasoline component already, and 10oz/Gal is only 7%. I know people who use it as high as 20%. ATF won't hurt, and will add some top engine lube, but it isn't really necessary.

The crux of the question is whether you need anything at all to increase the fuel octane over what it is. If you don't have any pinging, you don't need more octane.

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Just one question..where the heck do you get 93-95 octane from? The highest I've seen in California so far is 91:excuseme:

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what the crap is this ping everyone is talking about?! ive owner like 19 dirtbikes and ive never heard the "PING" all my twostrokes sounded like they were pinging the whole damn time! what does it sound like?? what is it?!?

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we have 94 in canada
we have 94 in canada
What you have to watch for is the fact that there are three different kinds of Octane, Motor Octane, Research Octane, and the Anti-Knock Index used in the U.S. Outside the U.S., Research Octane is commonly used, mostly because the Research method gives a fuel the highest numbers and makes it look cool on paper. The Motor rating method is much more demanding and a better representation of severe use, but the same gas that has a Research Octane Number (RON) of 95 may have a Motor Octane Number (MON) as low as 85. The U.S. AKI is shown on the gas pump as an average of both methods ( (R+M)/2 ), and is thought to be a more accurate representation of the fuel's true resistance to detonation. U.S. 91 Octane is roughly the same as 95-97 RON fuel outside the country.
what the crap is this ping everyone is talking about?! ive owner like 19 dirtbikes and ive never heard the "PING" all my twostrokes sounded like they were pinging the whole damn time! what does it sound like?? what is it?!?
Pinging is the early stages of detonation. Detonation occurs during combustion when the heat and pressure get too high for the remaining unburned fuel to put up with, and the remaining fuel all simultaneously explodes in a single instant, rather than continuing to burn in a controlled, progressive wave.

Detonation is extraordinarily destructive, and must be controlled and prevented, and that is the reason for high octane fuels. In it's early stages, it has the sound of a bunch of BB's hitting the side of your engine, or bouncing around in the cylinder, but it only happens under a load. It will stop if you back of the gas.

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sounds very much like a knock. It is the pre-detonation of the air fuel mixture. I have heard it on RS250 two stroke roadracing engines and it results in damage to the piston (and head). Sounds like your piston is rattling around. It is noticeable when it happens. Older cars did it quite a bit when ignition advance was done mechanically and was out of adjustment (or not working). low octane and high compression are the 2 surest ways to cause detonation/pinging.

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ok so stuff pings when the fuel is too low octane to completely burn, then all of a sudden (after is started blowing up) the rest blows up?this causes the un-even powerwave and stresses the parts or what? crazy, ive never ran into that problem ever!

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sounds very much like a knock. It is the pre-detonation of the air fuel mixture.
There is no such thing as pre-detonation. You are confusing detonation with pre-ignition. Two different things, although either can cause the other.
ok so stuff pings when the fuel is too low octane to completely burn, then all of a sudden (after is started blowing up) the rest blows up?this causes the un-even powerwave and stresses the parts or what? crazy, ive never ran into that problem ever!
No. Normal fuel combustion starts at a single point, and burns outward from that point like a wave of flame. The unburned fuel ahead of this wave is subjected to the heat and pressure of the burning fuel behind the flame, but is supposed to wait until the flame actually touches it to ignite. Detonation takes place when the heat and pressure is too high for the fuel to resist, and all the remaining fuel detonates at once.

It's like the difference between sliding a glass dish 10 feet across a floor by pushing it quickly with a hammer and trying to move it the same distance by hitting it with the hammer.

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The crux of the question is whether you need anything at all to increase the fuel octane over what it is. If you don't have any pinging, you don't need more octane.

Well I wasn't going to put it in my bike, but my wife's car requires premium and gobbles down fuel, so I figured that I could save a few bucks a month and buy regular. I probably never will though. The car cost so damn much it don't seem worth it.

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Any car made since 1990 can probably run regular straight up without any problems. Most modern engine control systems include knock sensors that pull back the timing at the first signs of pinging (at a level you could never detect). We ran regular in the Volvo 760 Turbo we had from the day we bought it, and never had a problem. Performance may be degraded slightly if the engine has to retard the timing too much under full power, but most of the time, you wouldn't notice.

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Any car made since 1990 can probably run regular straight up without any problems. Most modern engine control systems include knock sensors that pull back the timing at the first signs of pinging (at a level you could never detect). We ran regular in the Volvo 760 Turbo we had from the day we bought it, and never had a problem. Performance may be degraded slightly if the engine has to retard the timing too much under full power, but most of the time, you wouldn't notice.

Hummmm maybe I will try regular in the Bmw then.

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