93 Octane Not Recommended?

[KNG SNKE]

Was scanning through the owners manual and it said anything over 91 octane is not recommend. Can anyone explain why?

 

[kcobean]

I have to tell ya, I've honestly *never* noticed that. I've been putting 93 in my car since I got it, but it's been running like crap lately. Wonder if this could be the cause.

 

[dave6666]

Was scanning through the owners manual and it said anything over 91 octane is not recommend. Can anyone explain why?

They did not make 93 octane when your car was made?

Missed it at the print press?

 

[KNG SNKE]

They did not make 93 octane when your car was made?

Missed it at the print press?

my bee is a 2001. the book i looked at is for a 2002 viper. still says anything above 91 is not recommended. they had 93 octane in 2002 and 2001 for that matter. im not quite understanding.

 

[dave6666]

I have an '01. I run 93 no problems.

 

[kcobean]

I have the manual for the '01 (mine is an '01) and it says the same thing. I wasn't aware that you could have too high an Octane rating

 

[dave6666]

I have the manual for the '01 (mine is an '01) and it says the same thing. I wasn't aware that you could have too high an Octane rating

Within reason?

Are they sending a message to not run 104 with cast pistons???

 

[kcobean]

Within reason?

Are they sending a message to not run 104 with cast pistons???

Good question, but you'd think they wouldn't specifically isolate a commonly available grade of standard 'street gas' if 'within reason' is what they meant. 93 wasn't uncommon at all in '01/'02.

 

[dave6666]

Good question, but you'd think they wouldn't specifically isolate a commonly available grade of standard 'street gas' if 'within reason' is what they meant. 93 wasn't uncommon at all in '01/'02.

My point is that 93 seems to be within reason. And 104 is outside that reason. Therefore set the rule book at 91 for CYA and basic safety factor management.

 

[AviP]

Was scanning through the owners manual and it said anything over 91 octane is not recommend. Can anyone explain why?

We need Tom Fuel & Lube GoR to comment on this.

 

[BOTTLEFED]

is it a misprint?
maybe it was supposed to say "anything UNDER 91..."

 

[KNG SNKE]

its not a misprint. I just find it odd. where is the fuel experts?

 

[Tom F&L GoR]

Ford was the first to say this. The higher the octane value of gasoline, the less volatile it generally is. Lower volatility means that the rate of changing from liquid to gaseous is slower. Since an engine burns fuel vapor and not liquid, a poorly volatized fuel charge will be lean, and can make the engine hesistate or stumble. This might be a minor annoyance to the driver, but it is critically important in emissions testing. Of course, there are a huge number of other factors that also affect this; ambient temperature, coolant temperature, engine speed, load, in other words - almost everything else. The recommendation to not use higher octane is good advice, but probably actually makes a noticeable difference in very few examples. But, since there is no additional performance gain from using an octane value that is higher than needed and there is a potential performance debit from using a high octane fuel, it makes sense to only use exactly what the engine needs.

 

[dave6666]

Thanks Tom.

Seeing as my choices are 87 89 and 93, well...

 

[KNG SNKE]

so all in all, go with 91 is what your recommending? just want to clarify. ive always run 93 in my fast car, but it was turbo'd.

 

[dave6666]

so all in all, go with 91 is what your recommending? just want to clarify. ive always run 93 in my fast car, but it was turbo'd.

Based on what Tom wrote above, I interpreted the consequences of 93 versus 91 to be for the most part insignificant.

Given my personal choice of either 89 or 93, I'll go 2 over as opposed to 2 under.

Funny though, that on the gas cap door on my '01 GTS, it says "minimum 91 octane."

Not "91 octane."

Not "maximum 91 octane."

 

[KNG SNKE]

dodge is being tricky! lol

 

[PAvenomRT/10]

dave 6666,
Ever consider blending 89 and 93 to get a custom blend of 91?
PAvenon RT/10

 

[ViperTony]

Ford was the first to say this. The higher the octane value of gasoline, the less volatile it generally is. Lower volatility means that the rate of changing from liquid to gaseous is slower. Since an engine burns fuel vapor and not liquid, a poorly volatized fuel charge will be lean, and can make the engine hesistate or stumble. This might be a minor annoyance to the driver, but it is critically important in emissions testing. Of course, there are a huge number of other factors that also affect this; ambient temperature, coolant temperature, engine speed, load, in other words - almost everything else. The recommendation to not use higher octane is good advice, but probably actually makes a noticeable difference in very few examples. But, since there is no additional performance gain from using an octane value that is higher than needed and there is a potential performance debit from using a high octane fuel, it makes sense to only use exactly what the engine needs.

Tom, its interesting to see tuners advertise PCM custom programming to take advantage of 93 octane fuel. Without putting any particular vendor on the spot, is there any benefit to using 93 octane, in an NA setup, when custom PCM tuning is available? I often hear that ignition timing/spark advance could be optimized for 93 octane.

 

[DodgeViper01]

Did not even notice that in the manual and I have looked at it several times. Good point Tom.

 

[KenH]

I think it is pretty well known that higher octane gas by itself does not create power and it's higher octane rating causes it to burn in a less ideal fashion and therefore will lose a little power in an otherwise well running car. Higher octane fuel may make more power if you have knock sensors on a car and the timing is being ******** because knock is present, but this isn't an issue with Gen I/II cars.

If you are recalibrating the PCM, you can take advantage of the higher octane by advancing timing, etc. for more power. If you will be consistently running 94 octane for instance, a good tuner can tune for that fuel and optimize for power potential. Boosted and nitrous cars can take advantage of that aspect as well or by allowing more boost to be run or at least get some protection from detonation by running a higher octane. The only caution here is that if you have the car tuned for 94 and you make a trip to CA and can only get 91, you may create knock issues with your car unless you bring the octane back up with something like Torco Accelerator.

Even on a stock car, there is no significant harm or issue that will arise from running a higher octane than needed, especially if it is a minor increase like 91 to 93 and is certainly better than going down in octane. Now if you run around town in a near stock car with 104 in the tank, I would image that you are leaving some power, drivability and money on the table with no upside.

 

[Rollin4]

Thanks Tom.

Seeing as my choices are 87 89 and 93, well...

Dave, I'm with you that's the same choices I have....Next fill up. Viper has a 19 gallon tank..Let's see now 6.5 gals 87 + 6.5 gallons of 89 + 6 gallons of 93= 91. Got it!!!!

 

[dave6666]

Dave, I'm with you that's the same choices I have....Next fill up. Viper has a 19 gallon tank..Let's see now 6.5 gals 87 + 6.5 gallons of 89 + 6 gallons of 93= 91. Got it!!!!

Are the store clerks cute? Cause they'll sure be watching that act...

 

[Paul Hawker]

Agree with Tom.
At ViperDays early on many tried hi octane track fuel, and the Vipers ran much worse with it.
Unless your Viper is knocking, has been modified with higher compression etc, best to run 91 or its equalivant high altitude octane.

 

[Sandy G]

What filling stations actually sell 91? I think the old Sonoco's you could blend but now I don't see 91 octane.......so where is it?

 

[KNG SNKE]

almost all gas stations in virginia beach sell 91.

 

[agentf1]

Interesting, I will have to try a tank of 91 and see if it runs any better. I ALWAYS run 93 in all my cars. I used to run 94 when I used to be able to get it but that was pre-Viper days.

I added a gallon or two of 104 to the Z06 once and thought it ran worst.

 

[Tom F&L GoR]

The oil companies advertise their highest octane because (as of a few years ago) the increased cost per octane was about 2 cents, but the retail price increase per octane number was 5 cents. They justified it by putting 0.1 to 0.25 cents worth of extra detergent in the premium grades.

If the spark timing or compression is changed to take advantage of octane (as does a knock sensor) then sure, you'll get more power output. Otherwise, there is no advantage and possibly a small debit.

You naysayers about how little it matters - the higher octanes are less volatile, so the gasoline doesn't become vapor as quickly and is more likely to stay a liquid droplet. That means upon entering the combustion chamber and flying past the open intake valve, the droplets don't begin to swirl and tumble; they keep going and impinge on the cylinder wall. Once on the wall they stay cool and do not vaporize upon the rising piston increasing the compression pressure (generating heat.) Consequently the fuel is wiped off the wall by the rings and enters the engine oil. Gasoline likes to oxidize, so it consumes anti-oxidants, allow oil to thicken. Gasoline is thin, so the overall oil viscosity is lower. Gasoline decomposes to initiate deposits. Did you know that about 25% of the fuel additives end up in the oil for this reason - those additives are big, heavy molecules that splat on the cylinder wall? And that engines running moderately well can accumulate 2-4% gasoline because the oil never got hot enough to boil it off?

Is it a tremendous issue? Not really. I'm just letting you know because of the tendency to think that using 93 or 94 or whatever the highest available (beyond 91) is automatically good or can't hurt.

 

[kcobean]

The oil companies advertise their highest octane because (as of a few years ago) the increased cost per octane was about 2 cents, but the retail price increase per octane number was 5 cents. They justified it by putting 0.1 to 0.25 cents worth of extra detergent in the premium grades.

If the spark timing or compression is changed to take advantage of octane (as does a knock sensor) then sure, you'll get more power output. Otherwise, there is no advantage and possibly a small debit.

You naysayers about how little it matters - the higher octanes are less volatile, so the gasoline doesn't become vapor as quickly and is more likely to stay a liquid droplet. That means upon entering the combustion chamber and flying past the open intake valve, the droplets don't begin to swirl and tumble; they keep going and impinge on the cylinder wall. Once on the wall they stay cool and do not vaporize upon the rising piston increasing the compression pressure (generating heat.) Consequently the fuel is wiped off the wall by the rings and enters the engine oil. Gasoline likes to oxidize, so it consumes anti-oxidants, allow oil to thicken. Gasoline is thin, so the overall oil viscosity is lower. Gasoline decomposes to initiate deposits. Did you know that about 25% of the fuel additives end up in the oil for this reason - those additives are big, heavy molecules that splat on the cylinder wall? And that engines running moderately well can accumulate 2-4% gasoline because the oil never got hot enough to boil it off?

Is it a tremendous issue? Not really. I'm just letting you know because of the tendency to think that using 93 or 94 or whatever the highest available (beyond 91) is automatically good or can't hurt.

So Tom for people who have the 87/89/93 Octane pumps in their area, are we better off blending 89 & 93, or just going with 89 and listening for knock?

 

[viper spray]

Are you guys nuts??
Run the highest octane that your area has for sale!
It is a missprint!!