What grade of fuel did the engineers specify in the manual? 91 octane? Is so, USE 91. There are lots of engineering issues with design of an engine, and one of them is the intended fuel. Why second guess the designers?

I have a 2000 V70 XC Turbo. When ever possible I buy gas from stations that only sell "Top Tier" gas. This is a gas formula developed by the auto companies to help prevent engine deposits. I don't have proof but I think it helps. Not all stations sell this type of gas, including some of the big well known ones. To get more information just do an internet search on "Top Tier Gas".

All below posts are essentially correct, with KlausC the most right on. These cars definitely run at their best with minimum 91 octane. Gas mileage is also best with Premium. Depends what you want, good grammar or good taste (oops, just gave away my name). I never use less than 89 octane gas. In our XC70 with a LPT, I kind of do every third fillup with 89, two out of three with premium. The 850 R gets all Premium. Thats the lowest I'll go, unless the difference between Premium and mid-grade gets more than 10%.

Happy Volvoing.

Knock sensors will keeep you from destroying the engine with regular gasoline. You will also get poor gas mileage because the timing is retarded, along with poor performance.
We have a choice of 87, 89, 91 octane in MN. I run 89 in my cars, but I don't race them. I also try to keep the rpms between 2 and 3,000. I still get 21mpg around town and 28mpg on the highway.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

jbanks:

I've run 89 Octane in our 06 XC70 since it arrived on US soil. No knock issues, no low power issues that are noticeable unless its 95 friggin degrees out. Even then, it is just barely noticeable. After all, hot ambient temperatures are the enemy of turbocharged engines!

One of these days, I'll put the G-Tech in the car and do an 89 Octane run followed by a 93 Octane run... doubt I will find much of a performance difference!

jorrell
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92 245 250K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

I am on my second V70XC (2004), my first was a 98’. I find no real difference between 89 & 91 octane gasolines. I use 89 octane.

I always use premium. I have definately seen a drop in mileage with regular, used by accident. (I always charge my gas and write the mileage on every slip)

I do not know about newer Volvos, but I have seen a write-up on the Regina systen that said that the first thing that happens when a knock is detected is the addition of extra fuel. It mentioned that this is faster than adjusting the timing and cools the combustion chambers, stopping the knock faster.

Using regular requires that the knock suppressing system works properly all the time.

What about the knocks that happen before the system comes into play?
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 435,000 miles put on 9 bricks