U.S. octane requirement question

Post by **CIK7** » 08 Mar 2026, 19:35

Outside the US, a different octane rating is used. For my post I'm using the US numbers.

In the manual (pic below), it shows the NA is higher compression (10.5:1) and turbo is lower compression (8.5-9.0:1). I already knew that. My understanding is that a lower compression engine can use regular 87. The higher needs 91. But either Volvo wants us to use 91 or someone has trained us to think we need to use 91 on the lower compression engines. What is it that I am missing?

Post by **abscate** » 09 Mar 2026, 03:37

Compression ratio is the static ratio of chamber with piston down and piston up. When a turbo boosts, it pushes extra air into the cylinder and the effective pressure in the cylinder is higher? How much? I’m not sure.

I run either 91 or 94 in my turbo cars and 91 in my NA cars

Post by **volvolugnut** » 09 Mar 2026, 08:24

When my preferred local station stopped having premium, no ethanol fuel a couple years ago, I started using the low octane fuel. No noticeable problems.
I believe the ignition controls will adjust if knock occurs with low octane fuel.
This is on 2001 V70 T5. Also 2001 Mercedes E320.
volvolugnut

Post by **MoVolvos** » 09 Mar 2026, 09:53

.
Have been using Premium ever since it came out. Still remember using Leaded fuel especially in V8’s without CAT. The smell of muscle car exhaust

.

Wife noticed when I tried to save money by trying 87 and she doesn’t know anything about cars. Never had a CAT, fuel, ignition or code from potential fuel related issues.

Have 100K on a set of Iridium on the 03 Odyssey at 259K and still running smooth.

.

Post by **scot850** » 09 Mar 2026, 12:10

Has anyone checked their gas mileage when running regular gas? I tried it with a couple of cars that were advised to used premium gas by manufacturer's. In both cases the mileage reduced to the point where the saving made it pointless.

Neil.

Post by **CIK7** » 09 Mar 2026, 12:15

scot850 wrote: 09 Mar 2026, 12:10 Has anyone checked their gas mileage when running regular gas? I tried it with a couple of cars that were advised to used premium gas by manufacturer's. In both cases the mileage reduced to the point where the saving made it pointless.

Neil.

Maybe I'll try on the gray 850 if I get the white 850 as planned.

454cid · Post by **454cid** » 09 Mar 2026, 12:53

MoVolvos wrote: 09 Mar 2026, 09:53 .
Have been using Premium ever since it came out. Still remember using Leaded fuel especially in V8’s without CAT. The smell of muscle car exhaust .

I had to re-read that, as at first, I interpreted CAT as Caterpillar.

.

Post by **matthew1** » 09 Mar 2026, 15:09

Remember premium differs by US state. Here in Colorado it’s 91 octane. In lower elevations it’s 93 octane. So, another variable.

Post by **scot850** » 09 Mar 2026, 17:20

Here Premium is 91 which is at similar elevations to Denver. We also have 93 and 94 options, but they are not called premium,

Neil.

Post by **matthew1** » 09 Mar 2026, 17:43

Interesting. I think there are some between 91 and 100, but they're very uncommon. There are one or two places in the metro area that have 100 octane "race gas" and it's pretty darn expensive.

Here's more octane talk: https://www.matthewsvolvosite.com/volvo ... iscussion/