When your engine is designed for premium gas and tuned by Polestar, it is not operating optimally on regular gas. Higher octane gas is harder to ignite, so enables the turbocharged engine to run at higher compression ratio before detonation. The turbocharger uses higher compression ratios to boost the amount of gas in the cylinder resulting in a more efficient engine. For the long term, using regular gas is not good.

Older cars that were not designed and tuned for high octane gas did not benefit from premium gas. But when a manufacturer tells you the engine specifically requires premium gas, you need to use premium gas.

 

I see post like this all the time and you'll get both sides that tell you premium only and others that say the engine can handle regular. My question is why buy a performance model if you are just going to go against what the engineers who developed the engine and the tuning reccommend and put crap fuel in it? I have a standard T6 and only run premium fuel or ethanol free when the price is down. I have run regular and I'll admit that I didn't notice a significant reduction in power, but it did idle like ****, and if the idle is **** with no load on it I could only imagine what it was doing when i was pushing it down the interstate. Also as you pointed out for a difference of a few hundred a year why risk a $6k motor?

 

I see post like this all the time and you'll get both sides that tell you premium only and others that say the engine can handle regular. My question is why buy a performance model if you are just going to go against what the engineers who developed the engine and the tuning reccommend and put crap fuel in it? I have a standard T6 and only run premium fuel or ethanol free when the price is down. I have run regular and I'll admit that I didn't notice a significant reduction in power, but it did idle like *, and if the idle is * with no load on it I could only imagine what it was doing when i was pushing it down the interstate. Also as you pointed out for a difference of a few hundred a year why risk a $6k motor?

"My question is why buy a performance model if you are just going to go against what the engineers who developed the engine and the tuning reccommend and put crap fuel in it?"
What if I want a hardtop convertible and don't care about slightly reduced performance? As best I can tell Volvo c70 is the only option that that the car company says it won't hurt the engine.

 

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I can't remember the last time I ran anything other than Premium in any of the cars. Never encountered a CAT, spark plug fouling or rough running issue. Had experimented with Reg and can feel the difference in every car besides lower mileage. Depending on the brand and octane rating there will be a reduction in mileage and performance including smoothness of the engine.

As to your question, there are no sensors which causes the computer to change engine management from that of a Polestar to Non Polestar settings. To fully answer both your questions however.

1) If you car calls for Premium and you use Reg the performance will diminish greatly. Due to Pre-ignition / knock / pinging the computer will dial back timing to keep the engine from damage. Performance is down and you will give the car more fuel to keep up with the performance you are use to. It is already requiring premium so using regular perhaps may feel like you are driving a Non Polestar but it's not because the computer has a Polestar or Non Polestar program to choose from.

2) Problematic and potentially damaging because the car is already programmed for Premium.


Excerpt From: Engineering Explained: High vs Low Octane Petrol

Engineering Explained: High vs Low Octane Petrol

With fuel prices staying fairly low recently, is it worth it to shell out extra cash for some premium petrol? And what do those numbers mean anyway?

www.carthrottle.com

"The octane rating of a fuel is a measurement used to indicate its resistance to engine knock. A fuel with a higher octane rating will have more resistance to knock. Another way of thinking about this is how much compression that fuel can handle. A higher octane fuel can be compressed (along with air) more without detonating as a result of the heat from compression."

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In the segment below from the link and then the video following there seems to be a contradiction if the Premium fuel is better. I can tell you from experimenting since the late 70's with Leaded to Unleaded and Lower to Higher Octane fuels there is a difference as indicated in the video. Performance, mileage and engine smoothness even differs between Chevron vs Costco. Chevron remains number 1 and Costco 2nd on my choice of fuels. As mentioned also the cars run smoother and cleaner as I've never had rough running issues.

3. Will road cars perform better with high octane fuel?
.

 

Use premium fuel.

 

2015.5 XC60 R Design 3.0.

I know it calls for premium gas. I usually average it out just over 91 and have no problems. All is fine.

But I have read that both Ford and Mazda have turbo charged engines that reduce horsepower by about 30 through use of regular gas.

I am familiar with how Mazda notes the reduced horsepower - I used to have a CX-9.

Volvo doesn't do that, pretty sure it just indicates on the fuel door for optimized cars that you need Premium.

 

whatever the manual says....

 

Would be fascinating to do a real world long term test on this subject (NOT engines on a test bench in a lab). I would love to see 2 identical cars, bought brand new, driven similarly, one on regular only, the other on premium only, get them to 100K, then pull the heads for an examination. Something tells me the valves would look much better on the one that's been on premium only.
When you run low octane on a high compression motor, doesn't the computer retard the timing to prevent knock? So people say "Meh, my car runs just fine on regular," which it CAN, sure, for a while. But I believe that causes issues in the long term.

I only gamble running regular when it's a rental. Pro tip: Don't buy used rentals.

 

Would be fascinating to do a real world long term test on this subject

I would love to see that, too! What actually happens when you run a modern engine on a lower-than-specified octane gas?

No guessing, opinionating, or prognosticating. In God we trust. All others; bring data (or photos).

 

I would suspect you would have burnt valves, use 91+ octane follow your owners manual.

 

Got evidence? Or are you guessing?

 

I can partially answer my own question. I ran a GTI on track days and was able to log a bit of engine data. I ran 93 octane but saw that two or three degrees of timing would get pulled from a couple of cylinders at the end of the straights. I did not feel it and it did not cause any mechanical problems.

 

So your knock sensor was working correctly

 

Key word in my sentence is suspect, it's a guess, are these engines GDI?

 

Recent Volvos are GDI, as was my GTI.

It's pretty easy to see that lower octane will cause ignition timing to be retarded somewhat, and that peak power would come down a little, but what would be the effect on long-term durability? I've never seen anything that addresses that question.

 

I mean personally with seeing cars being serviced at 40,000 miles and sometimes earlier for top end cleaning (walnut blasting) on GDI engines calling for lower octane ratings, I would stick with premium; that's just my opinion.

I've never seen any side by side results, would love to but I don't think the R&D guys at Volvo will show those results, they will just report what they find works best for the engine, hence why it's recommended.

 

2015.5 XC60 R Design 3.0.

I know it calls for premium gas. I usually average it out just over 91 and have no problems. All is fine.

But I have read that both Ford and Mazda have turbo charged engines that reduce horsepower by about 30 through use of regular gas.

My 2010 XC60 3.0 T6-I used regular and it was just fine but it was not Polestar.

I do understand cost savings are perhaps a few hundred dollars a year difference but

Question is regular gas in my 3.0 Polestar will the car reduce performance to non polestar levels or will it be problematic?

I always use Top Tier and Premium fuel in my S60. Even though it could us regular. I noticed a performance difference the few times I tried in the beginning. I'm not sure if the 15.5 XC60 permitted the use of regular, but it certainly shouldn't be your go to. These engines are meant for premium fuel.

 

Here is some nightmare fuel...

These things can happen when you experience severe knock for a long time, but that is not what happens in our modern knock-controlled engines.