98 Octane vs. 95 octane?

[2nd Hand Yank]

I topped up a tank that probably had 5 Litres of 95 left in it with 10 Litres of 98 octane, since that's all one service station had.

I don't know if I was imagining things, but wow!
My motor sings a lot better, a lot smoother and seems to rev more easily.
I drove the rest of the way home a bit throttle-happy.

I have no idea why my old L Series is liking the higher octane fuel since it wasn't designed for it...

[steptoe]

try tramping on the acc pedal a bit more at lower revs my Brumby responded well at lower revs with 98

[mud_king91]

98 i shigher octane= better explosion or bigger bang... treat your engine like a male the bigger the bang the happier it is

[discopotato03]

Octane is ONLY an advantage if an engine is detonating - it does nothing else .

The reason high octane fuel works in some circumstances is its harder to ignite which makes it less likely to "auto" ignite in the chambers .

Unknown fact that lower octane fuel , without ethanol , would make more power per unit than higher octane stuff - if you could avoid detonation .

Older Subaru engines , EAs , have dark ages tech combustion chambers and with turbo versions ditto with piston crown designs so they don't need much to make them ping .
Computer controlled ignition timing makes a huge difference because it can do things that a mechanical/manifold pressure distributor can't . The mechanical system is reasonably simple and reliable but cannot follow as closely what the engine requires timing wise to give best drivability / consumption / emissions .

A .

[2nd Hand Yank]

98 i shigher octane= better explosion or bigger bang... treat your engine like a male the bigger the bang the happier it is

But I thought higher octane is just a rating for when a mixture will ignite.
Though I do know that rating is based on temp and pressure.

I've heard motors designed for the lowest grade fuel do not gain power on the higher grades
and perhaps lose economy slightly if not all the mixture gets burnt. (too delayed igniting?)

So if my EA82 is giving better response on 98,
the does that mean it was tuned for it?
Or motors not in tune respond better to 98? (hahahahaha)

[2nd Hand Yank]

Octane is ONLY an advantage if an engine is detonating - it does nothing else .

The reason high octane fuel works in some circumstances is its harder to ignite which makes it less likely to "auto" ignite in the chambers .

Unknown fact that lower octane fuel , without ethanol , would make more power per unit than higher octane stuff - if you could avoid detonation .

Older Subaru engines , EAs , have dark ages tech combustion chambers and with turbo versions ditto with piston crown designs so they don't need much to make them ping .
Computer controlled ignition timing makes a huge difference because it can do things that a mechanical/manifold pressure distributor can't . The mechanical system is reasonably simple and reliable but cannot follow as closely what the engine requires timing wise to give best drivability / consumption / emissions .

A .

Exactly what I was suspecting.
But even as I switched to 95 octane, I hear a bit of mild detonation when I start to roll sometimes, in moderate-high load situations.

So it's because it doesn't have a computer, a mechanical system probably works better on the higher octane?

[Tweety]

I own a new Jumbuck ute with 10,000kms on it

I've swapped from 91 to 95 to 98 and back many times already and find that on 98 it runs best with a low 6.6 L/100kms compared to 7.5 L/100kms. This means regardless of the extra price it is worth the higher octane and yes, your foot has less "down" on the accelerator to maintain the same speed and towing makes a big difference.

[revmax]

I'm with Tweety Bird on this one.
I don't realy care what yas think or reckon or what yas read in a book.
Fact is I/we (my wife) get better fuel economy on 98 in her 09 Camry, my 00 Outback and the lil old Brumby. Enough to warrent using it all the time.

[mud_king91]

i paid 149.9 a litre today for 91oct theres a fine excuse for not running 98... iv always been for the better bang and cleaner fuel and iv never been one to care about fuel prices but even im starting ti think these prices are becoming ridiculous my merc has a 70ish litre tank and HAS to run on 98 @1.60- 1.70 a litre you do the maths i no longer find the point to high octane its cheaper to use low grade and octane booster

[Brumby Kid]

Whats octane booster like?

[mud_king91]

depends on the type you use i find the ones with NOT FOR STREET USE written on them work best BUT do exactly as the instructions say or you,ll blow your engine to hell

[2nd Hand Yank]

i paid 149.9 a litre today for 91oct theres a fine excuse for not running 98... iv always been for the better bang and cleaner fuel and iv never been one to care about fuel prices but even im starting ti think these prices are becoming ridiculous my merc has a 70ish litre tank and HAS to run on 98 @1.60- 1.70 a litre you do the maths i no longer find the point to high octane its cheaper to use low grade and octane booster

Do you recommend any octane boosters?

I've only bought a single tank of 98, and I'm still trying it out.

Our fuel prices are better though: $155.4/L for 98 octane at BP yesterday.
Still I could save more buying 91 octane and boosting it, if you are already saving money that way.

[2nd Hand Yank]

I own a new Jumbuck ute with 10,000kms on it

I've swapped from 91 to 95 to 98 and back many times already and find that on 98 it runs best with a low 6.6 L/100kms compared to 7.5 L/100kms. This means regardless of the extra price it is worth the higher octane and yes, your foot has less "down" on the accelerator to maintain the same speed and towing makes a big difference.

Makes sense.

I was only using the cheap stuff because I never compared it with other fuel.
I think if it runs better in an obvious way, I "should" use it, even if all it means is a little less wear on the motor.
It's only a bonus that there's added power and economy...
Though I didn't notice an economy improvement switching from 91 to 95.
95 had a little bit more bottom end punch though,
which is obvious because if it's actually firing instead of detonating,
power can be put to the crank instead of just making engine noises.

[mud_king91]

have a shop around i had a NOS one i think it was idk it was a clear bottle but i cant find it in S.A it was $20 and covered 4 tanks had a dramatic change on a 89 mazda 323 till i put to much in and totalled the head

[Silverbullet]

have a shop around i had a NOS one i think it was idk it was a clear bottle but i cant find it in S.A it was $20 and covered 4 tanks had a dramatic change on a 89 mazda 323 till i put to much in and totalled the head

I'm confused, it actually DID something? Some tv show in the UK tested about 6 types of octane booster on a dyno and found between a 3% and -2% difference to normal fuel...dunno if they were being non-biased or not though...

[mud_king91]

nah it definitly worked i could make it spin to 2nd usually id be lucky if it chirped 1st

[sven '2']

I topped up a tank that probably had 5 Litres of 95 left in it with 10 Litres of 98 octane, since that's all one service station had.

I don't know if I was imagining things, but wow!
My motor sings a lot better, a lot smoother and seems to rev more easily.
I drove the rest of the way home a bit throttle-happy.

I have no idea why my old L Series is liking the higher octane fuel since it wasn't designed for it...

We told you so - 46 posts for, and 1 against can't be wrong.

You car WAS designed for better fuel than the AUDM variety.

[2nd Hand Yank]

We told you so - 46 posts for, and 1 against can't be wrong.

You car WAS designed for better fuel than the AUDM variety.

Well partly I didn't know where to get it (I now know BP has it) and the other was I thought it was worth trying out the 95 first.

95 Octane I thought was a 90% improvement, but maybe it's more like 75% improvement.

On 98, my motor has an eerie quietness and smoothness about it, allowing it to rev sooooo much easier than before.

I remember talking to RSR 555 about me losing some grunt after I rinsed under my bonnet,
maybe it's because I have a front bearing dying now,
but even without fixing anything, I have (compared to before) impressive throttle response.

I don't know if I'll be able to tell if it's better on economy,
because I'm getting throttle-happy a little too easily.
Burping the throttle's fun.
Donk's laughing too.

[mud_king91]

you can get it at every servo they just give it different names

[2nd Hand Yank]

you can get it at every servo they just give it different names

Is that "octane boost" you can find at every servo?