Why does 89 exist?

Status
Not open for further replies.
Joined
Jul 4, 2002
Messages
1,856
Location
PA
So I heard a rumor that old regular fuels, from the leaded days, were 89 as a minimum octane. Is this why 89 is still available on the pump? I've never seen a car require 89 or better, only "premium" or "regular" ... so what's the point in offering 89? Profit?
 
The crown vic I have is said to commonly ping on 87 octane and that it usually requires 89. I don't really see the point for it either honestly.

I suppose its good if you 87 rated car starts pinging and you want to eliminate it without going all the way to premium. But you really don't save much.
 
Some folks like the extra additive content found in 89 octane gasoline. Since 89 is made out of a 50/50 mix of 87 and 93, it will have a higher level of detergent and additives than 87 octane. The slower burn of an 89 octane gas also provides a slower burn in the chamber, which can translate to a slight mpg improvement for some vehicles.
 
It's mainly for people that think a higher octane is somehow, better even though their car doesn't require it. It's popularity is helped by the fact that many stations sell it for only a couple cents more then 87 unlike 91 which sells for 20 cents more.
 
Some stations have 89 going for the same price as the 92/93 stuff. Not always, but when the prices are real high.
I'm guessing that it doesn't sell well when gas is over $3.
 
87 through 91 are relatively close in terma of how much power can be extracted from an engine. for example, if we take a typical engine, say a honda b20 and tune it for max power on 87, and 89, and 91, the 3 will have very similar power requirements, even if the 89 and 91 engines have a tough higher compression.

were talking about only a couple horsepower here folks. im sure you all know that octane rating in and of its self does not increase power. its the ability of the engine to let you modify it to higher compression ratios, change the timings, etc that increases power.

another example, my old mazda protege. it has a facytory timing of 10btdc on 87. i ran it at 14 btdc and realised a slight mpg improvment and possibly a small power gain. honestly i didnt care about power but others had dyno tested the timing change and noticed about 5hp gain. other people with this engine had tried premium and mid grade and the highest anyone was able to generally get out of it on pump gas was about 18btdc. but at that point they were actually losing power from overly advanced ignition. although it wouldnt ping on 18btdc and 91 octane, it didnt make as much power or have as good fuel economy as 14btcd, reguardless of the fuels octane rating.
 
Whether the differences between 87, 89, 91 and 94 matter depend on the specific engine you have. Generalizations are pointless and can lead to misinformed readers.

Look at your owner's manual to find minimum and optimum octane numbers for your engine. If you care about performance, buy at the optimum number. If you care about price, buy at the minimum number. If you care about efficiency, test all fuels in the range and find out where you achieve highest fuel economy. Combine that info with price to determine what costs the least per mile drive.

Performance is important to me so I buy at the optimum number (91 or 92).
 
My 06 Frontier would occasionally knock on 87 when ambient temps reached 90 degrees, but a bump up to 89 stopped it. Nissan VQs perform best with 93 but it's not required, so I bumped it up just enough to get rid of knock.
 
Well, my Sthil string trimmer says to use 89 octane so I'm sure that's why all the stations have the 89 octane gasoline.
smile.gif
 
Quote:


Some folks like the extra additive content found in 89 octane gasoline. Since 89 is made out of a 50/50 mix of 87 and 93, it will have a higher level of detergent and additives than 87 octane. The slower burn of an 89 octane gas also provides a slower burn in the chamber, which can translate to a slight mpg improvement for some vehicles.




OK, I'm not a math major... but how can a 50/50 mix of something that is 87 and something that is 93 equal 89?

Seems to me it should be 90.
 
Quote:


Quote:


Some folks like the extra additive content found in 89 octane gasoline. Since 89 is made out of a 50/50 mix of 87 and 93, it will have a higher level of detergent and additives than 87 octane. The slower burn of an 89 octane gas also provides a slower burn in the chamber, which can translate to a slight mpg improvement for some vehicles.




OK, I'm not a math major... but how can a 50/50 mix of something that is 87 and something that is 93 equal 89?

Seems to me it should be 90.


You are correct. It's 1 part 93 octane to two parts 87 octane. Ironically, 89 octane is usually priced half way between 87 & 93. That's why I never buy 89 octane. It's cheaper and only a little more trouble to fill with bot 87 & 93 in a 2:1 ratio.
 
Obtaining 89 octane is not necessarily a 50/50 mix of regular and premium. The blender can be adjusted according to the octane of the two fuels starts out with to end up with 89.

When California dropped their premium grade to 91 due to blending requirements to meet state standards, many stations had temporary signs indicating 88 1/2 octane until the blenders could be adjusted. The adjustments cannot be performed by the service station owner.
 
The initial amount of additive does more to increase the octane than subsequent amounts.
'X' amount may raise the octane 2 points, but '2X' may only raise it 3 points, and '3X' may be 3.5 points. It is non linear.
That is why adding a 50/50 mix of two different octanes will not result in simply averaging the two octane #s.
89 octane is great if you car knocks on 87, and doesn't need 91-93 to fix it.
You want as little octane as possible, and not trigger your knock sensor, or get engine knock.
I am a big fan of disconnecting your knock sensor, as they are very sensitive to ambient noise, and pull a LOT of timing. You normally get wavy power curves with them on.
If I drove in third world countries with questionable fuel, I'd reconnect mine.
 
People who buy 89 octane are usually riped-off because pricing for it - is usually right bwteen 87 and 93 octane. So really, we are cheated out of 1 octane or three cents per gallon..
 
Premium costs ~3¢ more to make than regular, but they charge 17¢ more for it; that's the rip off.
Mid grade would be in the middle somewhere; still overpriced most times. A regional chain around here often has mid-grade priced the same as regular(slow seller, me thinks).
 
Status
Not open for further replies.
Back
Top