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Re: Is 91 octane a must for my car? [Re: Kestas] #5026245 02/28/19 07:08 AM
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I think you also have to think about the type of driving you're doing. Most of my driving these days is spent crawling in rush hour traffic. Very few places, if any, where I can truly gun it.

So even though my car recommends premium, I fill up with regular. Doing so saves me about $800 every year, which isn't chump change. Maybe for some people that's nothing, but it [censored] me off knowing I'm paying up to 25% extra for gas and getting nothing out of it. Now if I could really unleash my engine all the time, I'd be putting in 94 octane if I could, which would justify the extra money being spent.

Re: Is 91 octane a must for my car? [Re: Kestas] #5026576 02/28/19 02:08 PM
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ndfergy Offline
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The attached video should clear up a lot of these myths.

The ~14 minute mark emissions test is very intriguing: there was more unburnt fuel while running the higher octane fuel. Upon reflection that makes sense given that higher octane requires a higher temperature to ignite. So, if the consumer still feels more comfortable using a higher octane fuel when not required, go ahead it's your money. However, bear in mind it might be a detriment (fuel dilution) in colder climates.



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Re: Is 91 octane a must for my car? [Re: ndfergy] #5026598 02/28/19 02:26 PM
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That's interesting higher octane fuel requires a higher temperature to ignite. I didn't think that was the case, I thought it was more resistant to detonation.


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Re: Is 91 octane a must for my car? [Re: kschachn] #5026692 02/28/19 04:00 PM
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ndfergy Offline
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Originally Posted by kschachn
That's interesting higher octane fuel requires a higher temperature to ignite. I didn't think that was the case, I thought it was more resistant to detonation.


Seemed logical in my thought process when thinking temperature, however, that same thought process excluded volatility. My bad.

Could it be more to do with the computer management not being able to fully realize an optimal advanced timing? Or, or both, does the slower burn time of premium fuel, if that’s correct, also factor?


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Re: Is 91 octane a must for my car? [Re: ndfergy] #5026713 02/28/19 04:20 PM
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I'm not sure, I always have to think about that. Generally detonation is the propagation of a reaction by a shock wave and usually those substances that truly detonate have the oxygen and the carbon and/or hydrogen on the same molecule (like TNT). When the gasoline mixture in a combustion chamber ignites via compression and heat it generates a shock wave (knocks) but I don't know if further combustion is propagated by the wave itself or not.

I also don't see how the octane rating directly affects the burn rate, but of course there are ways to increase the apparent octane rating other than by varying how highly branched the hydrocarbon molecules are. Octane rating is resistance to compression ignition and I think burn rate is more directly related to the average chain length of the gasoline mixture. But someone might correct me on that.

This discusses burn rate:

http://www.whitfieldoil.com/171.284/vp-racing-fuel-
https://www.sunocoracefuels.com/tech-article/beyond-octane


1994 BMW 530i, 246K
1996 Honda Accord, 280K
1999 Toyota Sienna, 420K
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Re: Is 91 octane a must for my car? [Re: PeterPolyol] #5026722 02/28/19 04:25 PM
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Originally Posted by PeterPolyol
Nissan et al: "How can we legitimately advertise the absolute theoretical best peak HP and fuel economy values in our literature and sales material?"
Marketing team: "I know! How about we suggest premium fuel in the manual so customers can't have a legitimate output or MPG claim when they inevitably fill up with regular."
Nissan et al: "That's perfect! Just transfer the onus to the consumer, brilliant. Regular drivers will think they have access to the advertised horsepower at all times and the only people at risk to ever find out the octane-dependent truth on a dyno are likely to run premium anyway. THAT'S how you sell a 263bhp car as a 307bhp car. 90% of buyers don't even understand how HP is derived this is great! Good job team, now you're all laid off!"



The efficiency hit is less than 5% not nearly 20% as you stated it's a non factor.


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Re: Is 91 octane a must for my car? [Re: bbhero] #5026726 02/28/19 04:30 PM
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Originally Posted by bbhero
First off Kestas ... don't take anything I put in there personal. I certainly don't mean for it to be that way.

Now, it is also quite possible and I do believe there are cases where are vehicle recommending 91-93 that can and do run very well on 87. I don't think that's outside the realm of possibility. In fact I believe it does happen for a number of different applications.

Do I like "getting my money's worth or value"?? Of course. But it depends upon circumstance. Some areas it really matters about getting maximum value and in others it really is not a big deal. Me buying a nasty tasting Smithfield spiral ham that I smoked on the grill for 3 hrs and that cost $30-40... I'm am seeing red. Me buying a spiral ham for $18 from Harris Teeter that is really tasty after being smoked for 3 hrs and I'm happy as all get out. In this instance... that kind of value matters. A LOT.

Do I think that Shell 93 or Valero gives me my money's worth?? Ahh yeah. Do I have a team of researchers, computer models, lab tests to prove that?? Ahh, no. I'm not worth millions and millions of dollars to be able to afford that. But hey, it's not a big deal to me. Never has been. I used to run Amoco ultimate 93 in all my cars for years. Why?? Well, my step father worked at the local Yorktown refinery where it was made. Support the home team so to speak. Did my hooptyfied Dodge Omni need it?? Negative ghostrider. Did my Mercury Tracer need it?? No way. Did my Ford Probe need it?? No there as well. But, did I care?? No. These 3 cars were the ones I had while in high school. I PAID for my own gas. I had a job. I understand the value of a dollar hard earned and worked hard for. I worked in a grocery store stocking shelves and taking customer's groceries out to their cars. What little extra the Amoco ultimate cost me was not a big deal. It was 20 cent more per gallon than 87. Gas was $1.30-$1.50 per gallon then for 93. That extra bit of money I paid was not worth straining over. If it wasn't a big deal then... it sure isn't one now either.

I still think about my brother in law who runs 87 in his cars that should get 93. Mind you him and my sister make very, very good money. House paid now for a couple of years in a very nice neighborhood, paid CASH for my niece to go to Va Tech all 4 yrs equals 80k dollars, bought her a quality Honda for $12,000 with CASH, paid CASH for my nephew to go to a private school 30k.. which he failed at. So, we are talking about someone who is doing quite well at the end of the day.. and he is too cheap to put 93 in his car. Crazy in my mind. Like $10 per filling up is going to be that big of a deal to him?? Ha!! It's just odd to me about his thinking on that. I'm not knocking him on it. It just is a head scratcher to me given his circumstances. But hey, se la vie.

At the end of it all Kestas value can depend upon one's value placed upon the situation. Yeah I know someone can crunch statistical numbers all over here there and everywhere. And... that's wonderful. I don't knock anyone who thinks about it that way. Hey, if it makes you happier then go for it. In some cases I do that myself. As mentioned with my spiral ham reference a bit ago. Smithfield ham= terrible value and taste. Harris Teeter ham= great value and great taste. Win-win there. When it comes to food I do take value into strong consideration. USDA grade A Top Choice beef steaks on sale like ribeyes for $7.99 a pound is a great deal. Do you really NEED Prime graded ($24 a pound by the way) steaks to have a great steak?? No. I have cooked many USDA grade A top choice steaks that were just as well marbled and tasted as good as a Prime graded steak. In this... value matters to me. In your situation Kestas your value matters in terms of cost per filling up with gas. Nothing wrong with that at all. I hope that it works out good for you in that. I apologize if I seemed to be writing down to you in my previous post. It wasn't my intent. But, it may well have seemed that way. I am sorry if what I typed came across as such. Heck, if we were hanging out and talking about this it would've been much easier to see what was really going on. Sure hard to type stuff and it be taken in the right fashion. But, I just need to do a better job about that huh smile




This entire post only states you like to spend more money on premium fuel. Just spending money.


make the inside of your engine oil cap white.
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Re: Is 91 octane a must for my car? [Re: Kestas] #5026743 02/28/19 04:47 PM
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speaking specifically to the OP's platform the VQ engine is completely protected against low octane damage. It simply won't happen. I would also think there would be a noticeable drop in throttle response, perhaps a bit of a surge as you load it up and the computer retards the timing. Fuel mileage is unlikely to change a lot., just a little.


On our RAM, recommended for 89 minimum, using 87 is virtually unnoticeable. No hit on mileage either, and performance easily exceeds our needs.


On our 6.0 Chevy Express, recommended for 87, there is a distinct improvement in shift quality and "feel" with an increase to only 88 octane E15. So some vehicles can and do show a perceptible change with octane.


But anything newer is going to simply adjust.


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Re: Is 91 octane a must for my car? [Re: kschachn] #5026744 02/28/19 04:47 PM
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ndfergy Offline
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Interesting reads, thank you.

So the conclusion is slower burn times with premium is not an absolute but formula dependant. With that ,I would imagine the variance from premium to regular in this regard is small to account for the variety of engines out there.

Regardless, the takeaway is using premium when not required is a waste of money.


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Re: Is 91 octane a must for my car? [Re: Kestas] #5127863 06/07/19 12:47 PM
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My last vehicle that specifically said "91+" was my '04 Lincoln LS.


Yes, it could and did run without more than the occasional knock with 87, but I didn't make a habit of running it other than about a month when I tested it extensively. I saw a 1-2mpg hit(averaged over 1 month of running) vs. what I was use to with 92/93. The cost difference(even with a 20-25¢ markup for premium, which is what it typically was back around '08-09 when I was testing) was not enough on its own to justify buying premium. The overall operation of the car-from idling to just all around driving was quite different, though-on 87 it was a lot like driving the Town Car that my mom had at the time(which had the 4.6L 16V modular hauling IIRC a tick over 5000lbs, vs. the 3.9L DOHC 32V AJ-V8 hauling ~3500lbs as in the LS) and not the sports sedan the car was supposed to be. Within a few miles of filling the tank up with 93 after running 87 for a month, it felt like I'd done an engine swap in the car.

Two years ago, I bumped the compression in my MG to 9.5:1. I know this is not high by modern standards(or really even pre-emissions standards) but it makes a non-computerized engine somewhat more knock sensitive than the 8.8:1 the car shipped with. I can get it to run without more than an occasional knock(accelerating up a steep hill), but I have to pull the timing a lot that both performance and gas mileage suffer by a whole lot-to the point where off the line burying my foot gives almost no response until the engine winds up to ~2500 rpms, and I get hit for 5mpg or better. On 92/93, I run it at 34º maximum advance(vac disconnected), which translates to about 20º BTDC at idle. On 87, I end up pulling the advance back to about 28º max, which turns into 14º at idle. There again, with a mechanical distributor, you can't readily the characteristic of the advance curve-you can just shift the range over which it's happening-and the distributor responds according to rotational speed and vacuum. I COULD probably run it on mid-grade and turn the max advance back to 32º, but I like how it behaves with that much spark advance.


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Re: Is 91 octane a must for my car? [Re: dave1251] #5139807 06/21/19 03:15 AM
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No...

I do because ultimately....
My car will run better on it... That's where I place my value on. Not on "saving" money on that... And in my owner's manual... 93 is recommended. Yeah I know the stupid word gamesmanship... Not required... However... That simply means... Your car will not run well and it will be a dog. Nope. Don't want to do that...


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Re: Is 91 octane a must for my car? [Re: bbhero] #5139812 06/21/19 03:50 AM
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Well, five vehicles on regular gas here … but you are not standing next to that Nissan wondering if the gas pump will ever click like our Tahoe … or why did it already click like our Fusion Hybrid … so it’s not unreasonable to feed a peppy 3.5L car the good stuff …
However, I’m ready for a single grade 91 and diesel only in the US … let the cards fall where they may.

Re: Is 91 octane a must for my car? [Re: Kestas] #5192415 08/20/19 08:17 PM
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It is not a must to use 91 octane, but I would recommend using 91 octane in your car since the cap recommends it.

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