Googling ‘regular vs premium’ returns an astronomical number of contradicting threads and test results on the use of different kids of fuel in different engines. I always believed that one should simply follow the manufacture recommendations for the car you drive… I recently purchased a 2017 VW GTI fully expecting to have to pay for the premium fuel; all engine specs on the VW website are specified for the premium fuel. My expectations were also reinforced by the dealer where I was told that using low octane (regular) fuel may lead to ‘carbon buildup’, which would be expensive to clean. To my surprise, when I open the gas tank door I saw that the minimum octane number is 87… After looking through the discussions on various VW forums, I found that most GTI drivers use premium fuel. But the reasoning, in most cases, does not go beyond “If you can’t afford the $3 per fillup difference with getting premium you shouldn’t have bought the gti”, which does not satisfy my scientific curiosity. I would greatly appreciate a more educated opinion on whether it is worth or even recommended for my car to use the premium. Thanks!!
Some where in your manual it will have the fuel requirements. The people who wrote it know best. If it says premium fuel required end of discussion. If it says premium recommended then 87 octane is fine.
You could just use premium until the factory warranty is expired.
Note that if it says premium recommended, it most likely means that the car will lower the engine’s output in order to avoid damage, so while you will not hurt the car, you will hurt its performance as long as regular gas is in the tank. And if you went to all the expense of buying a GTI, I imagine you’d not be overly interested in lowering its performance.
Thank you for your recommendations guys. I am OK with going with the manufacture recommendations. But as I have said it tells that the minimum octane rating is 87 AKI. I am trying to understand the reasons why the popular lore, including the dealer, recommends the premium?
It is simple, premium fuel is what the horsepower ratings , 0 to 60 and other published statistics were made with. In everyday driving I doubt if you could tell the difference.
The dealer is going to say premium because if they say regular unleaded they leave their selves open for customer complaints.
First off, let me say, “Nice Car!”
I have not seen or ridden in a GTI newer than the mid-eighties one I had for a company car, but I’d be willing to bet the newer ones are as fun to drive, if not more so.
This is a performance car. If you want performance, use premium. If you’re just going to dawdle around, use regular 87.
The premium/regular debate aside, I would be sure to use “Top Tier” gasoline brands in this car. Volkswagen ordinarily recommends this, according to the vehicle’s Owner’s Manual. You very likely already use Top Tier fuel.
Enjoy the ride! I’m a little green with envy. 
CSA :
If you want the full explanation, the higher the octane rating of gasoline, the more it resists burning. So 87 burns more readily than 91. At high compression ratios, using gas with too low an octane rating can cause it to burn faster than it should so that the energy gets output while the piston is still on its way up the cylinder. Now you have an explosion pushing down on a piston which is being forced upward by the connecting rod. Keep doing that, and things get damaged.
So cars have a device called a knock sensor - it detects when this is happening and adjusts the timing of the spark so that the fuel will burn later. But that reduces performance. So you use higher octane gas so that you can keep your high-performance engine settings without worrying about those premature explosions that break things.
Thank you very much for the answer and kind wishes!
What, exactly, does your owners manual say?
The minimum octane rating 87 AKI.
I have 2006 Pathfinder, that thing tells 87 minimum, Premium recommended “for the best performance”
I’ve also followed numerous discussions on forums to get my engineer’s curiosity satisfied about “why would I use one or another?”
here are some specks of experimental data
PERFORMANCE: engine is definitely smoother, quieter when on on Premium, acceleration is a little bit more energetic on Premium
MPG: multiple people report 3-5% MPG improvement when on Premium, I confirm this result, essentially “a little bit better”
based on $/benefit, I’ve settled to Regular, as performance difference is negligible
the only reason to use Premium for me is in winter-time: some guy on Pathfinder forum was making the argument that winter mix is using more oxygenates, which this particular engine does not like, it SEEMED to me that engine really performs better on summer-mix-Regular to compare to winter-mix, so I follow his recommendation to use Premium in winter months… although it might be a superstition… no hard data to back it up
Thank you Andriy.
It says more than that, doesn’t it?
Not really…
“Never use fuel with an octane rating lower than 87 AKI/91 RON. Using lower octane fuel may cause expensive engine repair.”
And that “The recommended gasoline octane rating for your engine is listed on a label inside of the fuel filler flap”, which says 87 AKI.
Wow, I expected more. I’d use premium Top Tier gas, to address both the turbocharging and the need to keep the direct injection system as clean as possible.
if it is direct injection, I would imagine it is less sensitive to detonation as it is “almost diesel” 
CSA
My 2016 Mustang GT is one of those cars that recommends premium, but only requires regular. Last summer, when I went to the outer banks I filled up with 93 octane before I left, on the trip down I got 26.3 MPG, 95% of the trip was highway with the cruise control set at 75 MPH with the A/C on. On the trip back I filled up with 87 octane, took the same route, even stopped at the same place for lunch that I stopped at on the way down, same cruise control, same A/C, and same temperature (give or take 2 degrees), traffic was virtually the same each way. On the return trip I got 25.1 MPG. Which is about a 5.5% difference. Speaking from a strictly fiscal standpoint. I’d be money ahead to use regular bur I use premium, as that’s what’s recommended and it’s engine has 11:1 compression without the benefit direct injection.
Assuming this data is empirical from your experience in the car in question, I’d consider it definitive. Smoother idle, quieter operation, and better acceleration on premium would suggest that the ECU is making compromises in valve timing, ignition timing, and/or fuel metering when using regular that are causing combustion imbalances in order to prevent preignition from regular octane.
I’d use premium.
If the data is from research only, you might try a half-dozen tankfuls of both (enough to ensure that unintentional blending isn’t affecting the data) and see what your results are.
I’ve ran it through 2-3 tankfulls, guy on Pathfinder forum has long comute, he reported something like 10 full tanks for each experiment, so his result is better statistics-wise, but mine did not really deviate from his.
Manufacturer recommends Regular, but suggests Premium for “improved performance”.
The performance difference is subtle/negligible other than smoother ride.
Fuel economy on Premium does not offset MPG increase on Premium, when converted to dollars.
People in Pathfinder forums break spears long time what to use, but nobody reported bad impact from running it on either over long mileages… no wonder since manufacturer specifically tells Regular is the one recommended.
I second @common_sense_answer suggestion to use TopTier gas, whatever grade is suitable, as it really helps keeping fuel system clean in long run.