"91 Octane, Anything higher NOT RECOMMENDED."

[GTS1997]

I just got my 2001 Owner's Manuel today. As I was reading through it I noticed on page 83 it says "Your vehicle is designed to meet all emission regulations and provide excellent fuel economy ( YEAH RIGHT ) when using high quality premium unleaded gasoline having an octane rating of 91. THE PURCHASE OF HIGHER OCTANE FUEL IS NOT RECOMMENDED."


Hmmmmm, Why not. Is 93 Octane hurting performance on my Viper?

 

[Dom426h]

http://forums.viperclub.org/grail-t...-all-gens-i-iv-designed-around-93-octane.html

 

[Tom F&L GoR]

Thanks, Dom.

 

[GTS1997]

I'm not a member yet, so I don’t have access to that post. Thanks though. Can you summarize?

 

[01sapphirebob]

93 octane will not hurt your car. I've run 93 in my '01 for 4 years now with no issues.

 

[GTS1997]

Thanks 01sapphirebob

 

[eliems]

Maybe I should save a few dollars and use 91 instead of 93?

 

[SquadX]

If it's modded and tuned then of course your tuner would advise u on what oct to run. But your relates to stock so 91 even though I ran 93 on my stock viper for two years before mods began.

To piggy back on this thread. Can u run race gas in a stock or modded car with it being tuned for race gas? Sorry about high jacking.

 

[01sapphirebob]

Everywhere I go they only carry 93 octane so I have no choice.

Maybe I should save a few dollars and use 91 instead of 93?

 

[dave6666]

Everywhere I go they only carry 93 octane so I have no choice.

Or it's the same price 91 vs. 93.

 

[Dom426h]

There is no performance benefit in running 93 in a car that was designed for 91. However there is one benefit to running a slightly higher octane than recommended. Detonation. Running too low of an octane for your motor can severely damage it. Running a slightly higher octane is extra protection that you will not have any detonation issues. Also, keep in mind that the number you see on the pump may not be exactly what you are getting. So If you run 91 and it happens to be 90 then... But i assume the engineers designed the tune with a tolerance that allows 89 or 90 to not blow up our motors.(maybe some slight detonation/pinging the most wouldn’t even notice)

On to Tunes: There IS a performance benefit to running 93 if you have your ECU optimized to run it. If your interested in this, Talk to ROE Racing, ViperSpecialty, or DCPerformance about doing a custom tune for you.
Basic options being:
1. Reprogram your stock ECU (i know DC is experienced with this)
2. Buy an SCT for about $650 that will allow you to hold multiple tunes on it so you can switch between tunes at your leisure.(89/91/93/94,ect...)

 

[Chuck 98 RT/10]

A stock Viper motor will run fine on 91 or 93. Buy the cheapest.

 

[Asp Man]

I'm not a member yet, so I don’t have access to that post. Thanks though. Can you summarize?

Sign up. Or at least PM on of the moderators to get your "owner" status.
This is exactly the kind of reason to sign up.

 

[Martin]

With the way gas is formulated today, sometimes you're actually better off from a performance perspective when you run the lowest octane that still won't cause pinging. They use ethanol as an octane booster quite often, and that has a lower BTU density than straight gasoline. The more they put in, the less actual energy you get out of a gallon of gas. That said, I tend to go with the highest octane I can get - which is an easy choice in the West since all we can get is 91. I wish we still had 92 (or 94 in my HS days).

 

[viper spray]

Run the 93 , it is better for your car than a low octane fuel mix............

 

[Tom F&L GoR]

Run the 93 , it is better for your car than a low octane fuel mix............

No, it is not. As long as the engine does not knock.

Higher octane is only that; higher octane. If the engine doesn't need higher octane, there is no benefit. You can't fill a glass more than it will hold; pouring more beer in it anyway is a waste.

There is nothing chemically better in higher octane gasoline than lower octane. Usually the components added are less good; ethanol was mentioned above and other hydrocarbon components are usually different volatility and affect starting and driveability. For instance, toluene (and the chemical family it belongs to) is high octane but low volatility and would make the engine harder to start, warm up poorly, and produce fuel dilution. Butane (also high octane) is very volatile and could cause vapor lock or simply evaporate from a vented fuel tank.

There is no relationship with engine cleanliness and octane. Cleanliness is delivered by additives, the level of which the gasoline marketer can decide independently of octane. Chevron adds lots of detergent, but to premium only. Texaco used to include lots of detergent in all three grades. Mid-level brands provide the lowest allowable level in all three grades. So paying more for premium but buying a bargain brand is actually risking forming valve deposits and fuel injector deposits.

There is no relationship between octane and any other engine criteria; life, power, smooth running, storage...

 

[slartibartfast]

Tom has it exactly right. I would add that cyclic aromatic hydrocarbons like toluene often suffer incomplete combustion due to that low volatilty and cause carbon build-up in cylinders and reduced catalytic converter life.

 

[white out]

I don't know if it is the same for Vipers, but on a turbo Subaru (WRX/STi) the ecu is constantly learning/changing its tune (within parameters). So bone stock cars are consistently faster on 93 than 91.

Can the oem Gen II+ ecu's adapt to their enviornment?

Nick

 

[slartibartfast]

You're talking fuel trim. Turbos and N/A cars are apples and oranges when discussing octane.

 

[Dom426h]

No, i think he's talking more about Ignition Timing. Newer vehicles(like the Gen4Viper) have knock sensors, and if too low of an octane is put in the vehicle it will variably change the timing to safely bun the fuel.

but yes, Turbos and N/A cars are apples and oranges with reguards to overall tuning.

so to answer WhiteOuts question: No, our ECU's are not adaptive to the octane, which is understadable considering these vipers were designed 15+yrs ago.



also to add to the disscusion, here is a similar thread posted a few years ago:
http://forums.viperclub.org/rt-10-g...nleaded-will-make-performance-difference.html
(the answer is no...)

 

[slartibartfast]

ODBI cars are not adaptive...much.. ODBII are significantly more facile.

 

[white out]

That's why I said genII plus, didn't think that the genI would have.

Thanks Dom, that is the info that I was looking for.

Nick