Carbs. and Blended Gasoline

Is it true that carburated engines do not suffer the same mpg loss that fuel injected engines do when using the standard 10% ethanol blended gasoline. Some recent postings on this forum make this claim.

There is less energy available in ethanol than there is in gasoline. Put ethanol in your fuel tank and you have less energy than you would have if you put gasoline in the tank. Less available energy dictates less mpg, regardless of form of delivery.

So the claims of different effects on carbs vrs fuel injection are bunk?The postings are still in the “recent” line-up,just no one cares to dispute.It was something like 02 sensors have trouble with ethanol.Iam open to listening.

In carbs, the fuel is metered by calibrated little orifices called jets. Ethanol is stoichiometric at a richer fuel/air ratio than gasoline. That means that if you put 10% ethanol in a carb that is jetted perfectly for gasoline, your mixture will be too lean and your power and mileage will suffer. If your mixture is too rich in the first place, then the 10% ethanol will correct the mixture resulting in more power as well as better economy.

Electronic fuel injection reads the oxygen sensors in the exhaust and corrects the mixture automatically compensating for ethanol as well as high altitude etc. Both altitude and ethanol changes the fuel/air ratio in carbs and the mileage loss of the lower energy is compounded by a wrong fuel/air mix.

Look, it’s really simple. A gallon of ethanol won’t move a car as far as a gallon of gasoline. Period. Put either fuel into an engine any way you like. Use injectors. Use a carburetor. Use an eyedropper. Use a firehose if you like. It doesn’t alter the basic fact that there simply isn’t as much energy in the ethanol.

The poster in the thread claims that the F.I. systems suffer the effects of the blended fuel more than the feel as you seem to that the F.I. systems should be able to adjust to the blended fuel.He claims that blended fuels were introduced at the time of carbs.Read “Brand name vrs Generic”

I believe BLE is correct. You need to read his message carefully. If I understand BLE correctly, he is stating that both FI and carb will make some adjustment with blended fuel, but those adjustments will not be the same and the effect will be different.

However one thing remains blended fuel has less potential energy and can not produce the same mileage assuming the same engine efficiency. I believe that the results of BLE’s comments is that the carb MAY (or may not) accidentally result in improved efficiency. If the carb is running a little leaner, it may improve the mileage enough to counter the reduced energy, but at the expense of derivability or other issues.

Here’s what I was trying to say.

A carb makes no adustments for ethanol. Ethanol not only has less energy, but it also takes more of it to use up the oxygen in the air, so, a carb that is adjusted to be stoiciometric, that is just enough fuel to consume all of the oxygen and no more, will not be stoiciometric with an ethanol blend.

Closed loop fuel injection adjusts the fuel flow automatically to keep the mixture stiociometric or nearly so when ethanol is in the gas. It only loses mpg because of the lower energy content of ethanol.

With carbs, not only is there less energy content, but the performance of the engine is impacted by a mixture change as well which can compound the problem. In some cases, a carb may be adjusted too rich for gasoline and an ethanol blend, by correcting the fuel air mix, may actually give better gas mileage. However, this carb would get better gas mileage still by being readjusted to be correct with gasoline and using gasoline. There are a lot of shade tree hot rodders out there who think that drilling out the main jet is a quick and easy way to more performance and a lot of them end up with plug fouling engines that run like crap and spew out black smoke. These people would probably need E-85 for their cars to run right or maybe even methanol.

There is also a possibility that a carb can use ethanol blend to compensate for the mixture change that results when you visit the high altitudes of Colorado or New Mexico.

I wouldn’t worry too much about the effects of engine performance when E10 is used in a carburated engine. Instead, I would point my concern on what the 10% ethanol does to the internal elastimers of a carburator. When carburators were designed, there was no thought put into the design for ethanol blended gasolines. So just a 10% concentration of ethanol in the gas can destroy internal carburator components. When ethanol blended gasoline was mandated as a main motor fuel in Minnesota in 1997, there were some vehicles with fuel injection where the ethanol damaged the fuel injectors.

So my suggestion? If you have anything with a carburator, don’t run any concentration of ethanol gasoline thru it.


I agree with all that B.L.E. says. I just want to add that traditional carbs before the era of catalytic converters, from the '70s and earlier, almost always were set up slightly rich to ensure good drivability. So these older vehicles could see an increased MPG under the right conditions with E10 fuel. One of the original arguments for oxygenated fuel was to reduce emissions in older, rich running vehicles.

Also, for awhile there were closed-loop carbureted cars, like some 86-89 Accords. They will react the same way as fuel injected engines to E10, with a reduction of MPG.