Octane question

Mr. Detail · Post by **Mr. Detail** » 28 Jul 2018, 10:47

Just going thru the owner's manual while waiting in the car and I noticed concerning gasoline octane they recommend 91 octane for all Volvo engines. Now over the year's, including my old '98 S70, I always filled up with 87 octane because I am cheap.
What I wonder is do you guys all fill-up with a specific recommended octane or perhaps add an additive to boost the 87 Octane?
My present vehicle is a "non-turbo" but it sounds like they still recommend 91. Where I live, 91 octane is 40 cents more per gallon than the regular.

loveMy850 · Post by **loveMy850** » 28 Jul 2018, 13:24

I always use mid grade 91 I one time messed up and accidentally picked up the wrong nozzle. My volvo did not like it at all!! I'd recommend 91, its bad enough we get poor gas as it is, so protect your self and your volvo the best you can. 20 cents goes along way. I'm having problems and I went to a cheap gas station. Still used. 91 but I'm wondering....

loveMy850 · Post by **loveMy850** » 28 Jul 2018, 13:26

Sorry my bad, but 40 cents goes along way..

Post by **oragex** » 28 Jul 2018, 14:07

I'd say it comes to how good your engine condition is... in theory at least the non turbo should run the 89 without pinging (detonation) even in hot days when accelerating from a lower speed while climbing on a steep road.

These engines have more than one potential problem that can cause engine ping (the air intake thermostat is just one of them). I've also recently suspected a faulty or stuck exhaust cam hub to mess with the ignition timing and cause pinging as well (still investigating on this one).

Post by **June** » 28 Jul 2018, 16:17

I believe the NA engines have a high compression number which means premium fuel would be beneficial. I tried over the years with various Volvos all got better mileage with premium and felt more powerful.

Gasoline, oil,brand of parts, etc are all preference to the buyer. If you deviate from what the manufacturer recommends ie put 87 octane fuel in a car where 91 is recommended be aware it may shorten the service life of the engine. June

Post by **ljsommar** » 28 Jul 2018, 20:47

Nothing to contribute with anything knowledge based to back it up, but my 2002 V70 2.4T continues to run great. I purchased with 78K miles in 2011, it now has 210k. Previous owner and I rarely put in anything but 87 octane. It gets 27 MPG locally (suburban driving) and 34+ on long trips. I do drive sedately and never noticed any increase in mileage with hi-test the few times I tested it on highway trips. The only thing I noticed was it costs a lot more.

Post by **abscate** » 28 Jul 2018, 21:30

You have to be careful comparing octane number six as I believe the manual discusses a Research octane and you’re pump I see labeled with an average octane number of RoN+ROz

When we spar with an EU me,bet of what octane they use, their 97 octane is the same as our 93

That cheap 87 we use is the same as the EU 91.

I’m using whatever fuel June uses so that we 1-2 BmDubs R again.

Post by **June** » 28 Jul 2018, 22:48

abscate wrote: ↑28 Jul 2018, 21:30 You have to be careful comparing octane number six as I believe the manual discusses a Research octane and you’re pump I see labeled with an average octane number of RoN+ROz

When we spar with an EU me,bet of what octane they use, their 97 octane is the same as our 93

That cheap 87 we use is the same as the EU 91.

I’m using whatever fuel June uses so that we 1-2 BmDubs R again.

June

Post by **Rattnalle** » 29 Jul 2018, 00:31

abscate wrote: ↑28 Jul 2018, 21:30 You have to be careful comparing octane number six as I believe the manual discusses a Research octane and you’re pump I see labeled with an average octane number of RoN+ROz

When we spar with an EU me,bet of what octane they use, their 97 octane is the same as our 93

That cheap 87 we use is the same as the EU 91.

I’m using whatever fuel June uses so that we 1-2 BmDubs R again.

IIRC the Swedish instructions say min RON91 recommended, min RON87 usable but with lower performance. Its impossible to find lower than RON95 in most of Europe so for us it isn't an issue.

Turbos have much higher actual compression but can also lower it by lowering boost thus compensating for poor fuel while a N/A engine is stuck with what's it's got, more or less. When it does hit the limit it'll be more noticeable. The turbo will just lose power.

Post by **abscate** » 29 Jul 2018, 05:29

Turbos have much higher actual compression but can also lower it by lowering boost thus compensating for poor fuel while a N/A engine is stuck with what's it's got, more or less. When it does hit the limit it'll be more noticeable. The turbo will just lose power.

The compression ratio (squeezed volume to full volume ) on a turbo engine is lower than an NA, but as Rat points out, the turbo can boost to much higher. The ECU essentially adjusts the compression ratio by controlling boost and also mitigate system timing to control knock. Maybe it does both?

I’m pretty sure timing is closed loop with the knock sensors, I don’t know about boost. The critical nature of the wastegate rod adjustment implies it might be open loop on boost