The Texas hill country is not all that hilly.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

When Hurricane Harvey hit the Tx. coast, 4 or more of the coastal refineries there shutdown premium grade production.

My '91 300-SELs owners manual calls for 91 octane. I have always run 93 octane premium as mid-grade in my area is 89 octane.

I had no choice but to run 87 octane and with each tank I added a bottle of STP octane booster. The car runs as good as it ever has going this route.

It's possible it would run OK with just the 87 octane gas. I have no desire to find out. As soon as the current tank is done, I'll switch back to 93 octane gas as it's once again available.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

In the 1970's I made 100 Octane Chevron Custom Supreme gas. Twelve years ago I worked on the machine at a major refinery that blended up to 17 streams of "stuff" to make gasoline from regular to 91+ octane. Regular gas gets all the dregs, anything the can get rid of gets thrown in. The 91 octane is much better components.

That can of STP octane booster won't do crap. For 18-20 gallons you need at least half a gallon or more. A quart of Methanol will help, I have even used Acetone when I had a Moris Minor pickup with a 10:1 compression 1311cc dual carb sprite engine putting out 125HP. Used to blow the doors off of hopped up VWs.

Just Google Octane boosters.

Methanol is very corrosive and acetone is a very strong organic solvent that will attack virtually all organic materials... avoid both!

If you really think you need an "octane booster" because you notice significant detonation. Add a gallon or two of toluene or xylene that you should be able to buy at hardware and home stores.

Duke

Just put the right fuel in and call it a day.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Yep - now that the Premium fuel shortage brought on by the gulf coast hurricane is past us, that's what I'm back to doing.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

The idea of false economy by switching to regular was once true, but recently the game has changed. This morning I checked with my favorite gas station (Costco) and find premium gas costs 27% more than regular. It's a ripoff. For the last year I've been filling my car with regular. My gas mileage hasn't suffered... it certainly hasn't dropped anywhere near 27%.

I also poked around the internet to find out why the price differential is so great. It's not because it costs more to refine or some other technical reason.
Turns out they charge way more for premium because they figure the average luxury car owner won't mind paying the extra cost. It's mostly the luxury cars that require premium. Screw it -- I've switched to regular.

I hope others will update their way of thinking.

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95 E320 Cabriolet, 159K

Must be a Midwest thing. 87 and 91 octane are always 20c apart here. Even at 27% difference, there is no octane booster in a bottle that is cheaper than premium.

I'm in the middle of a long trip and I tried a couple of tanks of 87 octane. Fuel economy is exactly the same but top end power is gone. It's like driving a 240 instead of a 320.

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Makes me think of how British Airways came up with Concorde pricing. They asked the business executives directly how much they thought it would cost, and seeing as their secretaries paid all their expenses, they had no idea how much it would be, so they overestimated the price big time because of the perceived status and importance of their positions

There is nothing wrong with charging what the market will bear.

If your plain house was in an area that became trendy / high end with a limited number of properties for sale, would you sell as if the neighborhood was still low end? I'd think not.

Agreed -- that's why I opt for regular.

Years back I had a 1957 Chevy. At the bottom of the distributor was an adjustment where you could choose the octane you were using. It'd be a nice feature around now.

Most here seem to know nothing about gasoline. Mid grade is simply regular mixed with 91 octane. Depending on time of the year they put in more butane for easier starting. Also they add more oxygen additive, usually methanol for lower smog production. Our fancy blending machine also calculated the Reid Vapor Pressure. It saved the refinery $200,000 a week and for a while I was the only one who could fix it.
It ran on DOS 6.22 in French, good thing I had a background in DOS.

Premium 91+ octane usually has less than 7 component streams, including higher octane gas made from n-butane and Iso-butane over a catalyst, usually hydrofloric acid. This process helped our airplanes out run the German and Jap planes.

Premium 91+ octane usually has higher amounts of cleaner additives. Older cars like my 77 450 SLC do not have anti-knock circuits so I don't use regular unless I can help it. My turbo and supercharged Mercedes cars all were able to run on regular.

Note higher altitude lowers the need for high octane. A hot engine compartment such as my 450 SLC raises the need for higher octane.

That's standard issue on every modern efi engine equipped with a knock sensor and it's done automatically. You'll only notice the difference between 87 and 91 when you step on it.

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No, the oxygenate is ETHANOL, not methanol. No manufacturer has approved methanol because it's corrosive. All California gasoline has 10 percent ethanol by volume, which is the EPA limit, and most other areas of the country have ethanol, but the amount may be less.

The advertised CR of my '88 190E 2.6 is 9.2:1 and the required fuel is "premium". That's not a very high CR, and I have been successfully using 87 PON for a decade, even after removing the R16/1 resistor to quicken up the advance curve, which yields noticeably more low end torque. With the standard US model 750 Ohm resistor, fifth was unusable below about 40-45 MPH. Now it's usable down to 30, and around town fuel economy is up to 22-24 from 18-20.

For emission testing I short the R16/1 socket and plug the vacuum advance hose, which yields the least aggressive spark advance map and lower emissions, but the engine is totally gutless below 2000. HC was always close to the limit. Now it is half and NOx is down 90 percent, so I no longer have to sweat out emission tests.

If ambient temperature is no more than about 70F and coolant temp holds at 80C it will pull from 1200 in fifth, about 30 MPH (It's a five-speed manual) with no detonation. If ambient or coolant temps are higher I simply upshift and downshift at higher revs to avoid loading up the engine below 2000 to avoid detonation. Since I only drive the 190 during winter months, detonation is rarely an issue.

It's easier with an automatic because the torque converter won't allow the engine to load up below converter stall speed, which is about 2000.

Detonation is primarily a low rev/high load issue. Modern cars can retard advance if detonation is detected. This may reduce low end torque and result in less snappy acceleration around town, but no one I have ever recommended to do this who did it noticed a difference.

Duke

I ran my m103 on 87 octane. The m112 is a completely different animal. It'll run on 87 just fine but the power loss is drastic.

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