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#1

Anyone else find it frustrating when an articles headline is not fulfilled by the text of the article?
Today’s article about octane. Could be summed up as “if your car requires high octane gas-use it”. The rest was just filler.
two questions I have:
If your 87 octane vehicle with knock sensor get more power with higher octane? Since the knock sensor alters timing and perhaps fuel mixture in order to prevent pre-ignition.
Does higher octane contribute to a cleaner (fewer deposits) engine, or increase deposits in an 87 octane vehicle?


#2
  1. Using a higher octane fuel than the manufacturer recommends gains you nothing except loss of money.

  2. Using a lower octane fuel than the manufacturer recommends can lose you power and MPG

  3. Using a lower octane fuel than the manufacturer specifies can cause engine damage.

edit: the exception to No. 1 is if your engine is old and has heavy carbon deposits, you may benefit with a higher octane.


#3

I like people that come to the point and spit it out. Bill should have written the article and it would have been a lot shorter.


#4

I read the article and did not find it to be “filler”


#5

“If your 87 octane vehicle with knock sensor get more power with higher octane? Since the knock sensor alters timing and perhaps fuel mixture in order to prevent pre-ignition.”

You might get slightly more power for the 1% of the time the knock sensor is in action, but I bet you wouldn’t notice it.

"Does higher octane contribute to a cleaner (fewer deposits) engine, or increase deposits in an 87 octane vehicle? "

Neither, just in terms of octane. But some premium gas has a higher amount of added detergent than the same brand’s regular. But I just use “Top Tier” regular, with its higher than minimum required level of detergents.


#6

@BillRussell and @texases make some very sound points, good stuff there.

20-30+ years ago premium gas had a higher octane rating with the addition of more octane and other heavier hydrocarbons. These were a little harder to burn and also provided more energy when it did burn. Since they were harder to burn they were less likely to pre ignite and cause knocking. Years ago the refiners also used the regular gas storage tanks as a dumping ground. If they had a 1/2 million gallons of regular and needed to purge a line of a few thousand gallons of jet fuel/diesel/premium etc, it would get dumped into the regular tank. It would get lost in the dilution and would increase the octane rating of the regular a bit. No harm, no foul. They could not do this with the other fuels as they had tighter specs and in the case of jet fuel much more critical operation ranges. These days they no longer waste the diesel / jet fuel by dumping it, the manufacturing process is much tighter and better controlled so very little is wasted and needs to be purged out.

Also today octane is raised by putting additives in the gas. Ethanol, MTBE (no longer used) and other stuff is added to retard the pre ignition. No where near as much octane and other heavier hydrocarbons are needed to get the octane number raised.

Some interesting discussions can be found on Google, the link below has some good info, some a bit of a stretch too


#7

@Steve, I quit reading the link when I read that the 55 gallon barrel of Xylene cost $500 and the author deduced that it cost him 50c/gallon. And I feel certain that Xylene will damage plastic and rubber components in the fuel system eventually, if not sooner.

And it is likely illegal for the public to have barrels of xylene at their home.


#8

Not worth the trouble. 99.99% of all cars that require premium are fine with pump premium, if not more.


#9

There was a puzzler in the last week or two about 110 octane gasoline, apparently used by race car enthusiasts. Just wonder what is it about race cars where 110 octane provides some benefit, but not so much for ordinary cars? It seems like there’d have to be significant benefit for the race cars b/c 110 octane presumably costs quite a bit more than 91.


#10

George, perhaps the engines are designed with a much higher compression ratio?


#11

My memory is very, very hazy on this but I seem to remember someone running some kind of automotive product scam a dozen years ago.
It seems to that it involved some outfit in San Diego with a small warehouse full of drums of Xylene.

They were breaking it down into 10 or 12 ounce bottles or whatever and charging 40 or so bucks for their miracle product.


#12

In the late 60s 100 octane premium was common and quite a few brands had 105 octane and 110 was available from one oil company. The 10.5+ compression ratios of performance cars required it. Ford’s 1963 pace car 390 sounded like a can full of washers was being shaken when accelerating from a stop unless filled with 100 octane of certain brands. I seem to recall that Sinclair was dependable while Lion was hit and miss at best. Of course Amoco 100 octane of that time was ‘white’ which Cadillac and Harley recommended but a lot of people didn’t trust it. It wouldn’t chalk the tailpipe which was a status symbol for gear heads.


#13

I don’t think that xylene is illegal to have, but it is highly flammable. I wouldn’t want a lot of it around. It is also toxic. If had had control of barrels of it, I would store it in a ventilated, temperature controlled steel shed to reduce the hazards of being near it when required.

Xylene is already present in gasoline, but I think increasing the amount is asking for trouble. One of its major uses is as a rubber solvent. Before adding it to gasoline, I’d run a test to see what effect it has on the same type of rubber in the fuel system. Put a piece of rubber in the gas/xylene mixture I want to use, remove it after a week, and weigh it to see if it gets heavier due to swelling. If so, don’t use the xylene. Swelling is the first part of disintegration. Of course, it will be in contact with the fuel system for a lot longer than a week and the test should be repeated for months until satisfied that there is not swelling or disintegration. It seems easier to just by the correct grade at the pump.


#14

RE: xylene Just for kicks we would put test tube stoppers in a small beaker of xylene, the stoppers would double in size in a week. Don’t think I would trust the stuff anywhere near a car.


#15

I guess I wasn’t clear on my original post. The question on my mind about deposits was related to whether or not higher octane gas had better detergents to prevent or clean deposits.
Some of my question related to experiences with pre computer, pre fuel injection engines.
Things such as ‘run on’ aka dieseling from carbon buildup. Knock usually also caused by carbon build up. As to power, on old cars you could eek out a little more power by advancing the timing a few more degrees that factory specs.


#16

If you get a top tier gas, the amount of detergents in your gasoline will be fine, not matter what grade you buy. She’ll is top tier and is among the lowest prices for gas around me.


#17

Or you could get gas at Costco . . . I believe they’re top-tier now, as well

The price is certainly competitive with all the filling stations, if not lower


#18

The higher the compression ratio, the higher the power but also the higher the octane number required.


#19

I guess I wasn’t clear on my original post. The question on my mind about deposits was related to whether or not higher octane gas had better detergents to prevent or clean deposits.

Depends. It may. Shell’s V-Power has more of their proprietary detergents and additives than their regular unleaded. 7 times more detergents than the federally required standards.

I only use name-brand oil company gasoline, and whatever octane rating the car calls for.


#20

Ah, so the purpose of 110 octane for racing engines isn’t so much that 110 octane is more powerful, but that for the engines to be more powerful, they must use higher compression ratios, and that requires the use of 110 octane; otherwise they’d ping like crazy and damage the engine during the race. Thanks for the explanation, that makes sense.