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Discussion Starter · #1 ·
Just wondering who here runs with lower than 93 octane on their S40 T5s. I use 93 octane but the cost difference is pretty steep right now (50 to 60 cents/gallon). I know that we can run on 87 but I have found I get better gas mileage when running with 93...but that improvement doesn't make up for the cost difference right now.
 

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Personally, I wouldn't run anything less than 91 octane and I always seek out Shell 93. My thinking: the cost difference gets me better mpg, performance and less worry about fuel-related issues down the road (gunked up from poorer gas).

However, I'm sure 89 would be fine, too. It all comes down to personal preference and budget!
 

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It all depends. I think you can safely run regular. I did for a while and it wasnt a big deal... i got the tune for 91 so thats all i use now. 91 is the best we can get at elevation. and i also use only fuel with additives , like (top tier) fuels or shells' v-power, but dont go to shell much. 91 top tier is good enough for me.
But the car will run on 89 and probably wont knock.. but in order to do that the ECM wont advance timing and efficiency may go down slightly, and i was told it will pull timing to reduce pre-ignition. Wont be dangerous but i think performance will be reduced slightly.
I say do what you've gotta do, i dont think it'll hurt. I did it at least a year. and i doubt my previous owner did ever haha.
 

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If your gonna do that pay attention to your MPG, you may end up paying more if you have to fill up more after from poor MPG.


"Embody god... Then go crazy"
 

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Like Brown said, the best we can get in Colorado is 91. I've never run regular, but I'll use midgrade (87) on occasion. Aside from a KN drop-in, my car is stock and I haven't noticed an appreciable difference between the octanes (in terms of MPG and performance).
 

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I'll flip flop from 91 to 93. You can use either grade without any repercussions. Haven't noticed any mpg gain using 93 over 91. I get between 25-28 mpg per fill up.
 

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It depends on your logic.. If 93 is making your engine run more efficiently, then it's running more efficiently. Do you want your engine to run as efficient as possible? I guess that's the real question.
 

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It depends on your logic.. If 93 is making your engine run more efficiently, then it's running more efficiently. Do you want your engine to run as efficient as possible? I guess that's the real question.
Then you would tune to run like 109 or something not 93 lol.
 

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I'm taking about what the engine is currently designed for. If the MPG exponentially increased by going to 109 it might be worth it though lol
 

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Most efficient how, horsepower, mpg, afr? To be most "efficient" you need to get dynoed and have it tuned.
 

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I think you're missing the point. 93 is making the car more efficiently, than 87. So if you had to pick between the two... I would pick the one that makes it run the most efficient.
 

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It should but not always the case.
 

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Wow. I only run 87 (regular) in ths car. I have no issues, other than squeaks, creaks, rattles, and the crap ride from these elevate springs. If premium can fix those issues, I'm in.
 

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If you get better MPG, it's probably not that big of a price difference. But you can run 87. It's a personal preference. The manual states it has to be 87+, but recommends premium.
 

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I've never run regular, but I'll use midgrade (87) on occasion.
Wait, your mid grade is 87? What the heck is regular? Regular around here is 87, mid grade is 89...
 

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pretty steep right now (50 to 60 cents/gallon)
Even at the $ .60 that's STILL $1.00 LESS than is was just a little over a year ago. What did you use then? Look as dollars per mile, not MPG and we're all WAY ahead right now vs 1-2 yrs ago. Will you stop driving when it hits $3.00 -$3.50.. $10.00!!! for reg?
 

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Just wondering who here runs with lower than 93 octane on their S40 T5s. I use 93 octane but the cost difference is pretty steep right now (50 to 60 cents/gallon). I know that we can run on 87 but I have found I get better gas mileage when running with 93...but that improvement doesn't make up for the cost difference right now.
Your analysis is spot on if you want the cheapest cost per mile. Just make sure you use a Top Tier fuel & can live with the reduced performance.
50-60 cents just floors me. Here it's a 10 cent jump to each grade. 87 base. 89 10 cents more, 91 20 cents more. You must have some refinery issues near by.

MurrrC01 You should definitely try a couple tanks of premium. Performance will increase & the mpg increase (if you keep your foot out of your new found power) should more than make up for the increased pump cost. Your actual fuel bill should go down.
 

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Discussion Starter · #20 · (Edited)
Even at the $ .60 that's STILL $1.00 LESS than is was just a little over a year ago. What did you use then? Look as dollars per mile, not MPG and we're all WAY ahead right now vs 1-2 yrs ago. Will you stop driving when it hits $3.00 -$3.50.. $10.00!!! for reg?
You analysis is spot on if you want the cheapest cost per mile. Just make sure you use a Top Tier fuel & can live with the reduced performance.
50-60 cents just floors me. Here it's a 10 cent jump to each grade. 87 base. 89 10 cents more, 91 20 cents more. You must have some refinery issues near by.
When the gas prices were closer to $4.00/gallon the cost differential between 87 and 93 was around 40 cents...10% bump in price is worth paying to put the preferred fuel in. With the price at $2.20/gallon for 87, the bump up to premium is closer to 25%. Is it cheaper than it has been in the past? Sure...just seems to be a lot more than what I could be paying.

I'm not sure why the price is so different between grades. I'm in Mass. but I see similar differences across the border in NH.
 
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