Sold on 89 Octane

[alphawolff]

Curious as to the data that brought you to this conclusion - the people who designed the engine disagree.



I, and many others, have seen zero power difference running 87 octane. We have also seen zero gain in fuel efficiency. Note that the factory HP and torque ratings were established on its recommended fuel grade (87). So essentially you are claiming that you see higher than rated HP on higher octane fuel...which is not somethin that's been found to be typical.

Don't assume that your experience is the same as others, nor that your experience is the most common.

I have owned and driven multiple PUG 3.6L engines. The 89 makes a massive difference in the summer. You can *physically* feel the engine retarding timing. I really can't put it into words any other way, but I promise you it is a big difference. If you're not aware of what engine timing variation feels like then you probably wouldn't notice. We're talking maybe a 10-20 HP difference or something during an event like this, so I suspect you're right and that most people just won't notice it. They're Jeeps not racecars. It doesn't add power, it just prevents it from losing power during certain situations such as high ambient temperatures and high load.

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[TheRaven]

I have owned and driven multiple PUG 3.6L engines. The 89 makes a massive difference in the summer. You can *physically* feel the engine retarding timing. I really can't put it into words any other way, but I promise you it is a big difference. If you're not aware of what engine timing variation feels like then you probably wouldn't notice. We're talking maybe a 10-20 HP difference or something during an event like this, so I suspect you're right and that most people just won't notice it. They're Jeeps not racecars. It doesn't add power, it just prevents it from losing power during certain situations such as high ambient temperatures and high load.

I also have driven multiple PUG 3.6's. I've used both 87 and 93 extensively and even done instrumented testing. In the vehicles I drove there was no measurable power difference felt or indicated.

You may be seeing power loss due to environmental variables and mistakenly accrediting that to the fuel...but 2 points in octane is NOT going to make a 10hp difference in ANY situation.

 

[alphawolff]

I also have driven multiple PUG 3.6's. I've used both 87 and 93 extensively and even done instrumented testing. In the vehicles I drove there was no measurable power difference felt or indicated.

You may be seeing power loss due to environmental variables and mistakenly accrediting that to the fuel...but 2 points in octane is NOT going to make a 10hp difference in ANY situation.

1. 100 degrees outside
2. Heat soak the engine
3. Floor it up a hill in 3rd gear

 

[TheRaven]

1. 100 degrees outside
2. Heat soak the engine
3. Floor it up a hill in 3rd gear

Why would you do that?

The contest here isn't to create a theoretical situation that would be extremely hard on the motor...in fact we should all be doing our best to take care of our engines and not abuse them purposefully. Premium fuel isn't going to save you from the damage you cause with abuse.

 

[alphawolff]

Why would you do that?

The contest here isn't to create a theoretical situation that would be extremely hard on the motor...in fact we should all be doing our best to take care of our engines and not abuse them purposefully. Premium fuel isn't going to save you from the damage you cause with abuse.

I just gave you an example where 87 octane will retard timing to prevent knock, where 89 octane would not retard timing. I'm not saying to go beat on your engine. If you're just babying your jeep around all day then it literally does not matter.

It's only in high load high RPM situations that knock will occur, which 89 helps prevent

 

[TheRaven]

I just gave you an example where 87 octane will retard timing to prevent knock, where 89 octane would not retard timing.

No you didn't. In the situation you mentioned, even 93 wouldn't stop timing from being pulled. It would be slightly less, but it wouldn't be nearly enough of a difference to make a measurable difference in power.

 

[Windshieldfarmer]

Granted 20% is high, but it’s more like 15%. I agree it’s still on the high side. As for elevation Denver is around 5000 feet, and the western part of Kansas is about 3000 ft. Environmental conditions will also play part. On this day the difference in weather between Denver and Kansas was negligible. However, my hands on experience from my gear head days (30 years ago) tells me that timing has a huge effect on engine performance. I also expect that the octane is not the only factor giving the better performance. But I don’t know enough about the refining process to speculate. It’s my understanding that there are different grades of gas, even within the same octane rating. Like I said this is anecdotal. As such it should not be taken as evidence proving the theory.

Average speed could also come into play…there is a lot of construction between Ingalls and Dodge City for instance with a 50 mph limit. I drive out there a lot.”

 

[Windshieldfarmer]

Ethanol will eventually ruin any engine. (IMHO). I agree on 89 octane and even better if you can buy non-ethanol corn gas! I get between 1-2 more mpg when I use non-corn gas.

I think non ethanol gas is probably better than 10% ethanol and it’s likely your fuel mileage is a little bit better since ethanol has less energy than gasoline. That said a 10% ethanol blend does not ruin automobile engines…that’s simply untrue. If it did, manufacturers would not warranty long engine life while allowing ethanol usage….like Hyundai does to 100,000 miles.

Anecdotally, my farming family in South Dakota routinely runs pickup trucks using ethanol to 150,000 miles without engine failures…over many years. Personally I’ve used ethanol for 25+ years and never had a “ruined” engine of any type. Furthermore, non ethanol gasoline is expensive where I live, about 70 cents per gallon more (if I recall correctly). Given that I would spent an extra $4,500 on gasoline over the course of 100,000 miles…I personally don’t see the value…

 

[NWJeepr]

Ethanol will eventually ruin any engine. (IMHO). I agree on 89 octane and even better if you can buy non-ethanol corn gas! I get between 1-2 more mpg when I use non-corn gas.

Are you able to provide any proof that modern engines (and fuel systems) are harmed by regularly using ethanol-blended gas? Or is this mostly anecdotal, an old wives tale?

 

[roaniecowpony]

No, I wouldn't know any difference. I do know I haven't had any issues. I did have the intake off for the oil cooler and the top side of the valves looked brand new. I will say I got some 93 no ethanol in Nebraska when I was driving to California. That was my best tank of fuel. 16.3 mpg vs and average of 15 with all the other tanks.

Ethanol will clean up the backside of valves pretty good.

 

[roaniecowpony]

Ethanol will eventually ruin any engine. (IMHO). I agree on 89 octane and even better if you can buy non-ethanol corn gas! I get between 1-2 more mpg when I use non-corn gas.

We aren't running a 100% ethanol. The modern engines which are ethanol compatible, have stainless steel rings and corrosion resistant coatings on pistons, valves and other parts. It's not perfect, but it's better than running ethanol in old 70s engines.

 

[Trails]

Are you able to provide any proof that modern engines (and fuel systems) are harmed by regularly using ethanol-blended gas? Or is this mostly anecdotal, an old wives tale?

Ethanol can become a problem when fuel "sits" for a while in a vehicle that is not used regularly. That is why marine gas at marinas is ethanol free. Boats often sit un-used for long periods of time between uses. It does not necessarily "ruin" an engine, but can cause some 4-figure $ expensive repairs, as I found out the hard way on a boat of mine.
If it the Jeep is used regularly, so the fuel is regularly turned over, then ethanol is not likely to cause issues.

 

[roaniecowpony]

When I was a young kid just out of high school, I went to work for a man that was well respected in racing circles for his engine knowledge and accomplishments. He had worked at Ford, Chrysler, White Diesel, did the design work on the Donovan 417 block, created new head/port castings for Bignotti-Offenhauser Indy engines, and many more things I can't recall or never knew. He had a Masters in mechanical engineering and his career path was engines. His shop had the contract with Chrysler Direct Connection for porting the cylinder heads on 340 wedge, and 426 Hemi heads. We also installed huge valves in the 426, which I hand made myself, by the hundreds.

During my stay with Bob Mullen, he taught me that "swirl" and "squish" area in a combustion chamber will lower the octane requirement. I'm sure there's more to it, but those two characteristics are still utilized today to accomplish running higher compression with lower octane.

Bob Mullen went on to work for Garrett Airesearch to head the design team dedicated to turbo development exclusively for the Renault F-1 team when they were dominating the class.

 

[azjl#3]

Surprising, the knock sensors don’t adjust the timing ? Old muscle car guy who twisted distributors doesn’t get why not to use the longer burn of higher octane for increased power/efficiency. Even early computers like my 95 V10 PU, it went from ~12 mpg down to ~8 mpg with the new reformulated “clean” gas. A good $5K (90’s $) of performance upgrades including a tune with more advance and back to ~11/12 mpg with a good power gain. Premium required but for a good mpg gain with a good power gain due to being more efficient is well worth the extra cost of premium.

funny you mention v10 triton. My class c has it in the e450 frame. Always 8.5mpg at 87, doing all this trial and error, i loaded up with 91, no small feet at 50 gallons. No mpg gain noted yet, but seems more power during long steady climbs.

 

[alphawolff]

Are you able to provide any proof that modern engines (and fuel systems) are harmed by regularly using ethanol-blended gas? Or is this mostly anecdotal, an old wives tale?

Our manual specifically states to not use ethanol above 10% iirc. Without a flex fuel sensor the PCM is just guessing and can only manage about 10% without causing issues. In an ideal situation you'd have 0%, but that really isn't available in a lot of places. I doubt you'd see any difference in power output going from 10% to 0% without an engine tune accounting for the difference.

E85 is actually a massive power booster when your engine is tuned for it. The more ethanol the more fuel you need to inject, but it helps cool the cylinders compared to regular old gas. This allows for even more advanced timing since the risk of pre-detonation is lowered.

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