leaded vs unleaded fuel?

Question

If a car says that it needs 98 octane fuel in order to function I assume that means leaded fuel. Can you get unleaded fuel in the US with a similar rating that would make a car like that work?

Answer 1

Straight-run gasoline has an octane number of about 70. In other words, straight-run gasoline has the same knocking properties as a mixture of 70% isooctane and 30% heptane. Cracking, isomerization, and other processes can be used to increase the octane rating of gasoline to about 90. Anti-knock agents may be added to further increase the octane rating. Tetraethyl lead, Pb(C2H5)4, was one such agent, which was added to gas at the rate of up to 2.4 grams per gallon of gasoline. The switch to unleaded gasoline has required the addition of more expensive compounds, such as aromatics and highly branched alkanes, to maintain high octane numbers.

There are two main methods of determining octane numbers or ratings, and they produce different values. One value is the research octane number (RON), which is determined with a test engine running at a low speed of 600 rpm. The other value is the motor octane number (MON), which is determined with a test engine running at a higher speed of 900 rpm.

In the USA, Gasoline pumps typically post octane numbers as an average of the two different values. Often you will see the octane rating quoted as (R+M)/2. If, for example, a gasoline has an RON of 98 and a MON of 90, then the posted octane number would be the average of the two values or 94.

Most European vehicles will specify only the RON number, which is a higher value, and makes it appear that the vehicle needs a higher octane fuel than is available at most American gas stations. In reality, it's just the method of posting the octane value that's different, and premium grade fuel at any pump in the USA will be adequate for a European made vehicle that asks for 98 octane.

It also should be noted that High octane gasoline does not outperform regular octane gasoline in preventing engine deposits from forming, in removing them, or in cleaning the engine. Consumers should select the lowest octane grade at which the car's engine runs without knocking. Occasional light knocking or pinging won't harm the engine, and doesn't indicate a need for higher octane. On the other hand, a heavy or persistent knock may result in engine damage.

Answer 2

Octane ratings are not always related to lead content. Octane is a measure of flammability of gasoline and how it burns.

Lead was originally added to gasoline for lubrication. Once they removed lead from gas they had to start using hardened valve seats in cylinder heads to prevent excessive wear. Leaded gasoline should not be used in newer cars because it will destroy catalytic convertors and oxygen sensors.

Unleaded gasoline is available in several different octanes and blends from each manufacturer. Where I live pump gas is usually 87/89/91 for the three levels and some places sell 93 octane. The higher octanes are usually required for performance engines. I've found that larger cities often offer the higher octanes but it isn't real common. Ethanol is a alcohol/gasoline blend that has a higher octane rating but produces fewer btu's so mpg may not be as good.

When used with high performance or older cars they will always run best if you retune them to each blend of gasoline.

Answer 3

No, but you can take the heads into a good shop and they can put hardened valve seats in them so they'll be compatible with unleaded gas. We do it all the time with the old cars. Actually many of them will run pretty good on unleaded with nothing but some minor tweaking on the timing.

Answer 4

Yes. You can buy racing gas. OH!, bring PLENTY of $ with you. It's expensive.

http://www.motorsportsracingfuels.com/SunocoRaceFuel.html

Answer 5

I doubt it. Buy an octane booster.