Stupid Lean Out Question

[tdsongster]

Ok, so don't flame me for asking this. As you lean out an engine it makes A LOT more power. It also makes A LOT more heat.

I know that with more heat comes the problem of pre-detonation. However, can that be offset by running a higher octane fuel?

We still have the problem with heat, especially in an air cooled engine like a 400 EX. Is the higher heat just to hard on the metals that make up the motor, or is it a lubrication issue where the oil begins to cook?

Thanks


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[2004exrider]

running a little lean will give you a lttle more power but its going to run a lot hotter. If its lean enough you will get pre det issues like you said, but can also wear out the engine faster. You can burn up valves and even burn a whole in your piston. I wouldnt suggest doing it, just run the right fuel air mixture and it will run strong enough for ya.

Jimmy

[F-16Guy]

Higher octane won't cure the heating problem associated with a lean condition. The incoming fuel charge is the primary coolant for the top of the piston, so if there's a lack of coolant (atomized fuel), then you'll have overheating.

[F-16Guy]

The effects of severe overheating could be damage to the metal, but that is usually a secondary effect as a result of the breakdown of oil. Ideally, the crucial metal parts of an engine will never touch each other because they're seperated by a pressurized buffer of oil. If the oil breaks down and allows the soft metal bushings to contact the harder metal parts, things will come apart pretty quickly. That's why jetting and oil cooling are so important to a built 400ex.

[bwamos]

Originally posted by tdsongster
Ok, so don't flame me for asking this. As you lean out an engine it makes A LOT more power. It also makes A LOT more heat.

I know that with more heat comes the problem of pre-detonation. However, can that be offset by running a higher octane fuel?

We still have the problem with heat, especially in an air cooled engine like a 400 EX. Is the higher heat just to hard on the metals that make up the motor, or is it a lubrication issue where the oil begins to cook?

Thanks

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Here's basically what's happening...

You gain power the closer you come to a perfect burn. This is generaly at 14.7:1 air/fuel ratio with gasoline. Anything beyond that is considered lean. You can-not gain power beyond that point, since there's no fuel left to burn.

In a lean condition, greater than 14.7:1 air/fuel ratio, there's more oxygen than the fuel will consume. The ignition/burning of the fuel is an oxdiation process, yes, the same thing as rusting steel. Once that fuel is all burned up, you are leftover with superheated oxygen. That oxygen is very hungry. So it doesn't care what it burns/oxidizes. Therefore, since there is no fuel, the next closest thing that is the easiest to oxidize is the aluminum piston, aluminum head, and your bare steel rings. Basically, the superheated oxygen will eat you're engine. That's why your plug turns white. It's white rust.

Race fuel will only hinder pre-detonation. It won't protect against the eating of your engine. It's not there anymore. ;)

Generally in endurance type race (XC, MX, TT, etc.) they generally run 13:1 - 13.5:1 keeps the engine cooler, better throttle response because you dont get the temporary lean condition when accelerating, and is still a very efficent burn.

Drag racers tend to go with a 13:1 ratio on the bottom and closer to a 14.5:1 on top. But, they only sustain that for a few seconds at a time.