Engine doesn't like high octane fuel?

What I have discovered: High octane and higher altitude = zero help and worse running. With my 4 cyl '86 Comanche with TBI, power changes were very noticeable, so when I went to Ouray, CO in '02 I thought I'd put a tank of premium in (I found one place with race gas before I turned onto the highway to Ouray)
   My power dropped like a rock. My "modern" engine had a knock sensor controlling timing, but the timing never advanced far enough for it to work right and it starved for power after that (before I was running 85 octane and it LOVED it. I was running a gross weight of 6,000lbs I couldn't haul up a hill after the high octane)

I run "premium" in 8:1 mills. Since the price has gone up, I have cheaped out and ran "regular" more.

I won't run plus cause there's only a regular tank and a premium tank in the ground and it mixes at the pump. So if that mixer goes bad, it does not error in your favor. You pay and extra 10 cents per gallon for regular.

Premium is not only higher octane, but has the additives in it. Running premium you don't have to use "puke-us" from Autozone or what not to keep the crud out of your system.

Plus I do run more timing and like the extra safety if I'm running it hard. Sometimes the low grade can be lower than 87 octane. It's doesn't matter what's written on the pump. The 93 I'm buying could only be 91, but it's a lot safer than 85.

That's my view on it. Spend a few cents now, or spend a bunch of dollars later.

It is not as bad as it appears at face value. We build a lot of engines and just have to pay attention to details like deck above the top fo the pistons, piston face design and metal composition, cam profile, carb size and jetting and of course the timing.  Also a well tuned engine makes a huge difference in preventing pinging.   Lots of carbon build up from old plugs, cap and wire and you are asking for trouble. Keep everything fresh and within spec and the 91 Octane is not as much of an issue.  That is one of the reasons I like electronic ignition so much.  Set it up and it stays the same basically forever.  

TEL (lead) was used as an octane booster at first. Lead was phased-out and eventually outlawed for it's toxicity and replaced with other octane improvers like MMT, toluene, and isooctane to create the original unleaded gasoline.

In 1979, some metropolitan areas were required to begin the use of oxygenated gasoline to reduce emissions. MTBE was used until 2006 and not only oxygenates the fuel, but also boosts octane, replacing the old octane boosters seen above. The majority of the country retained the original unleaded formulation above.

MTBE was outlawed in 2006 and replaced with ethanol, because ethanol directly substitutes as an oxygenate and octane booster. Metropolitan gasoline is required to have 5-10% ethanol depending on the time of year to meet the required oxygen content. Rural gasoline is not required to be oxygenated, therefore not requiring ethanol. Many state governments and businesses, however, choose to market oxygenated, and therefore ethanol, gas anyway.

In rural areas, non-oxygenated (and therefore non-ethanol) gasoline is available at some gas stations. This gas still follows the original unleaded formula that dates back to the early 1970's.
--------------------
I've personally never had problems running ethanol fuel in my old cars, and I'd think after 4 years I would have noticed something. All the gaskets, seals, diaphragms, and floats are taking it just fine, but the rubber fuel lines do soften up a bit. However, I think that is to be expected with just about any kind of volatile fuel.

The only time I've tried non-ethanol fuel was in my original post, and my engine hated it, presumably because it was Premium 91. There is a Casey's general store here in town that sells Regular 87 non-ethanol that I will have to try.

For all the Midwestern folks out there, it looks like all the Regular 87 at Casey's stores is non-ethanol.




Edited by FSJunkie - Dec/05/2013 at 4:52pm

FSJunkie wrote: TEL (lead) was used as an octane booster at first. Lead was phased-out and eventually outlawed for it's toxicity and replaced with other octane improvers like MMT, toluene, and isooctane to create the original unleaded gasoline. In 1979, some metropolitan areas were required to begin the use of oxygenated gasoline to reduce emissions. MTBE was used until 2006 and not only oxygenates the fuel, but also boosts octane, replacing the old octane boosters seen above. The majority of the country retained the original unleaded formulation above. MTBE was outlawed in 2006 and replaced with ethanol, because ethanol directly substitutes as an oxygenate and octane booster. Metropolitan gasoline is required to have 5-10% ethanol depending on the time of year to meet the required oxygen content. Rural gasoline is not required to be oxygenated, therefore not requiring ethanol. Many state governments and businesses, however, choose to market oxygenated, and therefore ethanol, gas anyway. In rural areas, non-oxygenated (and therefore non-ethanol) gasoline is available at some gas stations. This gas still follows the original unleaded formula that dates back to the early 1970's. -------------------- I've personally never had problems running ethanol fuel in my old cars, and I'd think after 4 years I would have noticed something. All the gaskets, seals, diaphragms, and floats are taking it just fine, but the rubber fuel lines do soften up a bit. However, I think that is to be expected with just about any kind of volatile fuel. The only time I've tried non-ethanol fuel was in my original post, and my engine hated it, presumably because it was Premium 91. There is a Casey's general store here in town that sells Regular 87 non-ethanol that I will have to try. For all the Midwestern folks out there, it looks like all the Regular 87 at Casey's stores is non-ethanol.

it sound like the 91 octane you got was contaminated..going from 87-91 is so minimal it couldn't be the change in octane causing the engine not to run properly. Its more likely people aren't buying 91+ octane in your area and the gas sits in the station tanks absorbing moisture.