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Manual says use use 91. I've been using that for 8000kms now no issues. Today in a moment of forgetfulness I filled up a half-empty tank with 98. I used 98 in my old car. I understand this will not harm the car and just my wallet?
 

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As I understand it, putting 98 in does no harm at all. A tank of it now and then may even help in cleaning the engine. I used to do that on my previous Mazda 1.8 Astina mainly to see if it gave better mpg (Ltr/100km). Never noticed any difference.
 

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Yep putting higher octane does not harm the car. It's only the other way, if your car requires 98 and you fill it up with 91, you lose power and get engine knock.
 

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I run Shell V-Power 99 octane here in Denmark. I have the last 4 years running with V-Power in my Honda Civic with a good result, but maybe it is a big bogus ;-)
 

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I run Shell V-Power 99 octane here in Denmark. I have the last 4 years running with V-Power in my Honda Civic with a good result, but maybe it is a big bogus ;-)
I use shell v power diesel too. What I'm not sure about is what the different grades mean in Australia and the US. Are they just octane and cetane boosters or do the higher grades get all the additives for cleaning and anti-foaming that our high grade fuel gets? Anybody care to comment?
 

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I use shell v power diesel too. What I'm not sure about is what the different grades mean in Australia and the US. Are they just octane and cetane boosters or do the higher grades get all the additives for cleaning and anti-foaming that our high grade fuel gets? Anybody care to comment?
My technical knowledge on this is pretty poor! But I know we use the same RON system in Australia to calculate the octane rating as in Europe. They are advertised as containing the additives for cleaning and anti-foaming.
 

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My technical knowledge on this is pretty poor! But I know we use the same RON system in Australia to calculate the octane rating as in Europe. They are advertised as containing the additives for cleaning and anti-foaming.
Interesting. Same in the US anybody?
 

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I've always heard, from people I trust, that it cost the same to run premium as regular b/c of getting better mileage with higher octane. I think the engine can advance the timing further, sooner.
 

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Interesting. Same in the US anybody?
RON = Research Octane Number
MON = Motor Octane Number (typically 8-12 lower than RON)
AKI = Average of RON and MON.

We use AKI in the US.

https://en.wikipedia.org/wiki/Octane_rating

I've always heard, from people I trust, that it cost the same to run premium as regular b/c of getting better mileage with higher octane. I think the engine can advance the timing further, sooner.
Higher octane rating means resistance to pre-ignition (igniting before the ECU wants it to). It has no direct impact energy content, cleanliness of burn, heat of combustion, detergent package, or anything else.

If a motor is tuned to take advantage of higher octane rating, you will get better performance at mid- and high-loads. If a motor is not tuned to take advantage of it, you will see no difference.

Mazda reduced the compression ratio on the SkyActiv 2L motor in the USDM relative to the rest of the world.

Just use fuel with the octane rating recommended in the owner's manual or don't expect any improved performance using a higher rated fuel.
 

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....

Higher octane rating means resistance to pre-ignition (igniting before the ECU wants it to). It has no direct impact energy content, cleanliness of burn, heat of combustion, detergent package, or anything else.

If a motor is tuned to take advantage of higher octane rating, you will get better performance at mid- and high-loads. If a motor is not tuned to take advantage of it, you will see no difference.

Mazda reduced the compression ratio on the SkyActiv 2L motor in the USDM relative to the rest of the world.

Just use fuel with the octane rating recommended in the owner's manual or don't expect any improved performance using a higher rated fuel.
Well, that makes sense. I don't think my wife's daily commute will require any mid- or high- loads anyway.
Aussie 2.0lt engines have a 13-1 compression and 91RON is recommended. 'Guess there's no need to pay for 98. Thanks
 

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You know its interesting that higher octane fuel is less volatile than low octane. Low octane fuel basically goes “bang” and is susceptible to flash (pre-ignition) where high octane burns at a very controlled rate. That way, it is possible to produce a sustained rate of expansion to push the pistons down.

So! Tell me. Shell V Power here is loaded with all sorts of other additives here to help keep the internal parts free from gumming and carbon etc. Is the US version of any brand’s top flight fuel loaded in a similar way or is it all about this AKI index?
 

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You know its interesting that higher octane fuel is less volatile than low octane. Low octane fuel basically goes “bang” and is susceptible to flash (pre-ignition) where high octane burns at a very controlled rate. That way, it is possible to produce a sustained rate of expansion to push the pistons down.

So! Tell me. Shell V Power here is loaded with all sorts of other additives here to help keep the internal parts free from gumming and carbon etc. Is the US version of any brand’s top flight fuel loaded in a similar way or is it all about this AKI index?
I can't speak for all products from all brands in the US but, in general, the additive packages (detergents and whatnot) are the same across all of the products from a given company. Chevron advertises "Techron" in their fuel and it's in all grades. Same with BP's "Invigorate".

I checked out Shell's product marketing wank for their V-Power Nitro+ Premium and I'll be damned if I can figure out which products they sell it in. Their regular fuels are "nitrogen enriched" which was a marketing thing that started a decade or two ago when that generation of detergents came out (a bunch of fuel companies came out with nitrogen marketing crap around the same time). Basically, even their low-tier fuels have detergents in them.

Effectively, in the US, the main difference between product grades is octane modifiers and marketing garbage. I think it's telling when they obscure product information with pretty pictures and non-informative information.

Additionally, these detergent packages are mostly to help keep the intake valves clean. Normally, oil vapor, carbon and other schmoo will build up on the valves and impede airflow into the engine. This works because most engines until the last 5-10 years had fuel injected into the intake track. The detergent-laden fuel hits the valves and helps to wash the gunk off. Now most newer engine designs (and modifications of old designs) have fuel injected directly into the combustion chamber, completely bypassing the valves.

So, modern engines blunt the utility of these detergent packages anyway.

Edit: also, there's no relationship between vapor pressure (volatility) and octane rating.
 

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So! Tell me. Shell V Power here is loaded with all sorts of other additives here to help keep the internal parts free from gumming and carbon etc. Is the US version of any brand’s top flight fuel loaded in a similar way or is it all about this AKI index?
Here are a couple of videos I have found on the subject. Both are posted by "Engineering Explained" on YouTube.

The first one explains U.S. V-Power additives:

The second one tests V-Power in a performance car:

As far as I know V-power in North America is ethanol-free so the pump price should be the total cost. Most lower octane fuels contain government subsidized ethanol so the real cost to a tax paying driver is the pump price plus all subsidies. If the total subsidy is high the ethanol-free premium fuel may be cheaper to the taxpayer overall even though the pump price appears higher.
 
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