What octane for stock motor?

[Mopar Boy]

What octane do you guys with stock motors run? 93? 94?

At VOI I was told by one of the motor driveline specialists 93 is more recomended than 94. Even says so in my owners manual. Over the last few weeks it has got me thinking. Would 94 hurt? Is it just plain not needed? Is it a cleaner fuel?

In everyone high performance vehicle myself, or dad has owned, new or old, we have always run 94. Now I do not know!

Anyone have any thoughts?? How about some tech on why one is better than the other too!

Thanks!

Robert

 

[dave6666]

Where do you get 94? I use 93 from Exxon in my '01.

Tom........................

Hi Tom.

 

[Mopar Boy]

Where do you get 94? I use 93 from Exxon in my '01.

Tom........................

Hi Tom.

As for 94, Sunoco. They are right around the corner from me and they sell 94.

As for Tom, please forgive my ignorance, but, who is Tom???

Robert

 

[dave6666]

As for Tom, please forgive my ignorance, but, who is Tom?

OMG Freakin God!!!

He's the fluid mix expert.

Ex oil blend mix dude or something. I'm chemical engineering, maintenance and construction, Tom's the "blend" guy for hydrocarbon and other automotive fluids.

Tom is great.

 

[dave6666]

Here's some good stuff by Tom...

http://forums.viperclub.org/2554295-post11.html

 

[Mopar Boy]

OMG Freakin God!!!

He's the fluid mix expert.

Ex oil blend mix dude or something. I'm chemical engineering, maintenance and construction, Tom's the "blend" guy for hydrocarbon and other automotive fluids.

Tom is great.

Oooohhh! THAT Tom!

He he. Sorry. My bad. Gonna shut up now and let the post continue. Don't mind me....

Robert
(Obviously still a green thumb.....)

 

[Tom F&L GoR]

Hi Dave. Heard you called.

What octane do you guys with stock motors run? 93? 94?

At VOI I was told by one of the motor driveline specialists 93 is more recomended than 94. Even says so in my owners manual. Over the last few weeks it has got me thinking. Would 94 hurt? Is it just plain not needed? Is it a cleaner fuel?

In everyone high performance vehicle myself, or dad has owned, new or old, we have always run 94. Now I do not know!

Anyone have any thoughts?? How about some tech on why one is better than the other too!

Thanks!

Robert

Any higher octane than needed won't help at all, will cost more, and sometimes will hurt performance. The higher octane fuels are typically less volatile and when the fuel is less likely to evaporate, it enters the combustion chamber as (very) small droplets instead. This leads to stumble or hesitation, harder starting, and the fuel drops hit the cylinder wall and end up in the oil. Ford has gone so far as to not recommend premium fuel.

There is no reason higher octane should be cleaner; cleanliness is a function of additives.

Lastly, it costs about 2 cents per octane number above 87 to produce. 94 octane therefore costs 14 cents more and you are paying how much?

Thanks for endorsements, Dave.

 

[plumcrazy]

tom, but isnt it hard to ALWAYS hear detonation ? im guessing DLM had a good reason for all his knock sensors and test equipment when he was tuning on the street. i remember him telling me you cant ALWAYS hear it and thats why he does what he does...

and i know you only need what octane your car requires and any extra is a waste but NOT bad.

 

[Tom F&L GoR]

tom, but isnt it hard to ALWAYS hear detonation ? im guessing DLM had a good reason for all his knock sensors and test equipment when he was tuning on the street. i remember him telling me you cant ALWAYS hear it and thats why he does what he does...

and i know you only need what octane your car requires and any extra is a waste but NOT bad.

Yes, it can be hard to hear. It's a problem because some knock causes heat, which promotes more knock, and more...

But the question was about stock engines. I'm sure DLM is doing something because it's not stock and he's outside the OEM "performance envelope."

I'll argue a little about "bad" high octane fuel. I was at a time trial day in Connecticut and a fellow Viper owner was there with his prepared car. He hadn't run it in a month or so he said, and since it was mostly a track car, used only "race gas." It was cool and he couldn't get it started. When it did catch, there was a plume of smoke and it stalled right away. He was in a panic because he never had problems before. I told him to keep it at a high idle for a few minutes and it would then be fine. As it turned out, his race gas was very low volatility (further a problem in cooler weather) and not enough was turning into a vapor. Engines don't run on liquids, only vapors. When it warmed up a little it was fine.

This doesn't mean you have to warm it up and everything's HD (***** dory.) The raw fuel washes oil off the cylinder wall. The raw fuel dilutes the oil. The excess fuel causes combustion chamber deposits. The fuel in the oil accelerates oil decomposition. Higher aromatic levels in the fuel may decompose elastomers and seals.

Lots of BM (Boogie Men) but it's only to illustrate that you don't get a benefit if you only do one thing (higher octane), and that it's an entire package (like DLM) to achieve the benefit.

 

[viperpalmer]

When would you recommend higher octane fuels? And if higher octane fuels can cause so much negative factors what do you recommend for my family cars that are recommend high octane fuels. Why do so many foreign manufacturers recommend high octanes? I mean if a 450-510Hp Viper engine cant combust it fully why do the 250-300 Hp foreign counterparts?

 

[Tom F&L GoR]

Let's differentiate between high octane at the pump and high octane race gas. Race gas will certainly have a few debits to give you the very high octane benefits. Pump gas is going to be mostly indistinguishable from regular in a car designed to use high octane pump gas, like your Viper, Lexus, etc.

Higher octanes are used for high cylinder temperatures caused by high combustion pressures and high compression ratios. A 2.0L 250HP engine has higher temps than an 8.0L 450HP engine. A turbo 3.0L will also. It's not engine size, but horsepower per cubic inch. Some OEMs will wring more power out of a smaller engine (and therefore suggest premium) because small engines provide better fuel economy.

That said, even Ford published a tech service bulletin to advise owners not to use premium due to the emissions increases caused when non-premium use engines used premium anyway and had hesitation problems.

Lastly, let's realize we are out on the fringe here and many of these examples may not show up. I'm just pointing out what may happen since otherwise you may think you've spent more money for a better fuel, and then have a problem that you can't figure out (and dismiss the idea it might be the fuel.)

 

[mike007]

I can only get 91 octane , is that ok, or should I add booster?

 

[Mopar Boy]

Thanks for the in deapth explenation. That makes sense.

In also going with what Mike is saying, all said and done then, what should be considered "correct octane" for a Viper?

Robert

 

[plumcrazy]

booster doesnt work. and 91 is fine if you're basically stock.

tom, you agree ?

 

[plumcrazy]

id say the correct octane is different for every viper. whatever octane doesnt knock (detonate) is the right one.

extreme heat or cold will change that though i bet.

 

[Tom F&L GoR]

Plum's got it right. Octane booster is misleading because they talk in "points" which are really tenths of an octane, not whole octane numbers. When Dodge recommended 91 for the Viper, you bet they ran it in the heat and cold, etc, etc, so 91 should be fine for 99.999999% of the stock engines out there.

 

[SoCal Rebell]

booster doesnt work. and 91 is fine if you're basically stock.

tom, you agree ?

91 is fine, I ran the crap outta mt 2000 stock motor on the track with no problems

Tom, do you agaree

 

[Viblur]

Tom - thank you for taking the time on all of your posts. They always provide the detail required to answer the q, and then some. The info you provide has saved me some dough for sure.

 

[Mopar Boy]

Thanks Tom! That answers my question AND explains why. Thanks!

Robert

 

[Vipuronr]

Just noticed this post, interesting question.

I have a Sunoco station right around the corner and he said that they no longer offer 94 octane fuel. So, I have to stick with Mobil 93, as I don't see anything better.

Thoughts?

Peter

 

[bluequadcab]

Ok, you guys have me confused. And now I just came back in from checking my Viper. My 1994 RT10 says Premuim Unleaded Fuel Only, on both the gas gauge and the fuel filler door. So are you telling me later models don't need premuim? I've tried other grades of gas and the Viper doesn't run as well and gets worse gas mileage. That being said, I went 340 miles on the fall foliage cruise with premuim gas and still have an eigth of a tank left. Another question, does a gen 1 have a low fuel light?

 

[96GTS]

From what I've heard, if you don't have a computer that has been reflashed to take advantage of the higher octane fuel than you are simply wasting your money. If you have seen posts about how someone got 500hp on 91 octane and 575 on race fuel, than they have probably spent a lot of time on a dyno getting their car dialed in and might have a switch to tell the computer which setting to use (one for the street and another for the track).

When in doubt...follow the owners manual.

 

[Tom F&L GoR]

Just noticed this post, interesting question.

I have a Sunoco station right around the corner and he said that they no longer offer 94 octane fuel. So, I have to stick with Mobil 93, as I don't see anything better.

Thoughts?

Peter

94 is not "better" if the engine only needs 91. 93 is still more than enough. The only effect of higher octane is on your wallet.

 

[Tom F&L GoR]

Ok, you guys have me confused. And now I just came back in from checking my Viper. My 1994 RT10 says Premuim Unleaded Fuel Only, on both the gas gauge and the fuel filler door. So are you telling me later models don't need premuim? I've tried other grades of gas and the Viper doesn't run as well and gets worse gas mileage. That being said, I went 340 miles on the fall foliage cruise with premuim gas and still have an eigth of a tank left. Another question, does a gen 1 have a low fuel light?

Premium is a marketing label. In different states or countries, Premium can be anything from 90 octane to 96 octane. The owners manual I believe should specify 91.

Octane (assuming you aren't massively knocking and pinging) has no effect on fuel economy. Even the use of alcohol (like 10% ethanol) only accounts for a 3% decrease from 100% gasoline. But I don't think you can find 100% gasoline anymore, so I don't know what you are comparing to.

Getting around 20MPG is not too uncommon for Vipers in normal consumer driving. No fuel light in a Gen 1.

 

[Tom F&L GoR]

I'll try a dumb analogy here.

Octane is like a tough-skinned balloon. You have to really squeeze hard to pop a 91 octane balloon and even harder with a 94 octane balloon. You want more than a 91 octane balloon because the piston in the engine will squeeze and pop an 89 octane balloon and cause knocking. But any balloon will pop with a pin-***** - the spark plug firing. When the pin pops the balloon, it doesn't matter if you had a 91 or 101 octane balloon.

That make sense?

 

[Tom F&L GoR]

OK, I see that my choice of verb for poking a balloon with a pin is a word banned by the mods.

Any balloon will pop when "stabbed with a pin."

 

[bluequadcab]

Premium is a marketing label. In different states or countries, Premium can be anything from 90 octane to 96 octane. The owners manual I believe should specify 91.

Octane (assuming you aren't massively knocking and pinging) has no effect on fuel economy. Even the use of alcohol (like 10% ethanol) only accounts for a 3% decrease from 100% gasoline. But I don't think you can find 100% gasoline anymore, so I don't know what you are comparing to.

Getting around 20MPG is not too uncommon for Vipers in normal consumer driving. No fuel light in a Gen 1.

Thanks for the answer on the fuel light and all your great info. I'm the third owner of my Viper and there was no owners manual or instructions of any kind. I've been learning as I go but have learned so much in the past year having joined the VCA and meeting Chuck Tator and his right hand man at Tators Dodge. Where I live we have 10% Ethanol, it used to be MTBE before that started showing up in the water supplies. Most gas stations here have a choice in octane of 87 or 89, 91, and 93 or 94, some have as low as 86 octane.

 

[bluequadcab]

I'll try a dumb analogy here.

Octane is like a tough-skinned balloon. You have to really squeeze hard to pop a 91 octane balloon and even harder with a 94 octane balloon. You want more than a 91 octane balloon because the piston in the engine will squeeze and pop an 89 octane balloon and cause knocking. But any balloon will pop with a pin-***** - the spark plug firing. When the pin pops the balloon, it doesn't matter if you had a 91 or 101 octane balloon.

That make sense?

I understand the analogy and that octane is just to keep the gas from exploding/burning before you want to. Eventually we want that to happen, but we want it to happen at a specific time. Not having any information before this thread, other than what my gas gauge and fuel door say, I understood premium to mean that if I didn't put the highest octane the gas station had, bad things might happen to my engine. Putting in the highest octane gas may have been a waste of money, but cheaper than buying another engine. In my test with low and midgrade, just to see how my car would react, my gas mileage went down and the car didn't appear to idle and run as well. Every tank I figure out the gas mileage, so that part I can verify, but I don't have a VEC or something to verify that the car isn't performing as well. Do I need to flash my computer or something as others have mentioned? I thought OBD 1 cars were limited in what can be done with their computers. The discussion of what our Vipers are supposed to take octane wise if not modified is what was confusing to me, there didn't appear to be a straight answer.

 

[mdurbahn]

How does altitude effect this? I drive from 6000' to 10000' feet, does that mean lower octane gas is ok to use?

 

[ViperTony]

Thanks for the answer on the fuel light and all your great info. I'm the third owner of my Viper and there was no owners manual or instructions of any kind. I've been learning as I go but have learned so much in the past year having joined the VCA and meeting Chuck Tator and his right hand man at Tators Dodge. Where I live we have 10% Ethanol, it used to be MTBE before that started showing up in the water supplies. Most gas stations here have a choice in octane of 87 or 89, 91, and 93 or 94, some have as low as 86 octane.

Jimmy, is that all you're using? I thought you had a secret ingredient?