Kind of petrol

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maremmamara, Aug 13, 6:01am
I just got a second hand car and I saw that it says 98 only unleaded. My friend is saying that I can also use 91. your suggestions? VW touran 2005
Cheers
franc123, Aug 13, 6:06am
So your friend knows better than the.manufacturer do they? Like hell you use 91, 95 if you have to, otherwise 98 only.
sw20, Aug 13, 6:13am
You use 98.

Jazz will be along soon with some information that will scare you into only filling it up with 98.
carclan, Aug 13, 6:18am
It will be a Euro with that kind of statement.
sw20, Aug 13, 6:18am
Clearly it is, when they explain what car they have in the original post.
monaro17, Aug 13, 7:02am
Never ever run it on 91, with all due respect to your friend they are obviously out of their depth.
melonhead1, Aug 13, 8:19am
It will run like crap on 91. Give it a try if you don't believe anyone on here.
tamarillo, Aug 13, 9:05am
I Suggest 95 will be adequate, I say that cause we can't get 98 down here so al these cars speced for 98 get 95 and are fine. 91 isn't though.
bryshaw, Aug 13, 11:06am
I have 'discovered' 95 and my Honda Civic and even non fuel injected Corolla run better.
maremmamara, Aug 13, 11:13am
I believe that you can't that is why I asked here
ianab, Aug 13, 11:18am
It's to do with the compression ratios of those engines. They run 11:5 or 12:1 compression. Way too high for regular octane petrol.

Use the higher grade and your engine will thank you.
sharchew, Aug 15, 1:45am
You guys are full of shit
kazbanz, Aug 15, 1:55am
Only run it on 95-98
monaro17, Aug 15, 2:30am
Are you implying 91 is fine? If so please explain your Un educated statement
networkguy, Aug 15, 10:28pm
No they aren't, do you know what octane is? Its not a measure of the amount of energy in the fuel or anything like that, roughly speaking its the amount of compression the fuel can undertake before detonating. You don't want it to detonate on its own, you want it to detonate when the spark plug fires so it happens at the right time, otherwise you risk a premature explosion that tries to push the piston down when the piston needs to go up still, basically causing that cylinder to try and rotate in the opposite direction to the other cylinders. This is called knocking and is usually harmless if the premature ignition is close to the spark anyway. But if your octane is too low, it can happen too early and cause major damage. Like the guy further above points out, these engines run higher compression, so they need the higher octane fuel so that they won't ignite under the higher compression like 91 does.

You shouldn't give dangerous advice on a something you know nothing about, the different fuels aren't just a money making scheme

ETA: Yes its a waste to put higher octane in a vehicle that only needs 91, but not the other way round
kazbanz, Aug 15, 10:35pm
Actually on this exact subject.
If you bought a euro car and were advised by the yard that sold it to you to run it on 91 how upset would you be to get a mechanics bill a few months later to fix a clogged up engine?
bumfacingdown, Aug 15, 10:44pm
About as upset as the carsalesman when he sees you coming back waiving that bill at him
cjdnzl, Aug 16, 1:07am
I run my older Primera Camino on 98, smoother, more power and better mileage than 95. I wouldn't have believed it, but seeing's believing. Try a tankful and see. BP98
jesus2000, Aug 16, 2:51am
I realise you were only roughly speaking to give the general idea, but technically the knock most cars experience is 'end-gas detonation'. That is the spark plug has already ignited the combustion chamber, but as the flame front propagates out, areas of gas at the edge of the combustion chamber ignite due to the increasing heat and pressure rather than from the controlled burn of the advancing flame front.

The end-gas detonation causes a pressure spike and knock. Usually at higher loads at a lower RPM.
kazbanz, Aug 16, 3:14am
I think the yard owner will be puckering
ignition328, Aug 16, 3:19am
I'm sorry that you think that your 5 series and a base model mitzi colt is evidence of the great NZ octane conspiracy.

I will now ask everyone in this thread to apologize and accept your in depth well researched opinion as fact.
intrade, Aug 16, 8:03am
nothing runs well on 91. i almost did not make it up to whakapapa with my corolla while i had a large amount of 91 in the tank. its quite complex to explain and most of you probably wont even understand why you should not use 91 octane at all , here in taumarunui they got 98 so i filled 40$ 98 in it and then it made it a bit better up the hill .
there is 2 problems the corolla is a map engine so absolut pressure is what it calculates the amount of fuel to inject and there is quite a lot less air pressure up in whakapapa ski field car park then at see level,
thats one reason and 98 octane is slower burning then 91 octane.
it took me a long time to understand why fuel that burns less intense is giving more power. there is a few factors , but a petrol engine is just slapping the top of the piston with the explosions , unlike diesel whom are pumping the pistons , that is basically what you need to understand and the whole injection of fuel is 20 millisecounds , so if its got less pressure it probably reduces that to 15 millisecound as there is not enough air going in the engine up the mountain combined that with 91 octane fuel whom burns way to fast off is slapping the piston less then a slower burning fuel like 98 octane

now having said this timing has also to do with what fuel a engine can burn. Like on Rover of all cars you can programm the engine managment to set the timing so its optimised for 91 octane fuel ,
with the oem factory scanner "rover mems"
i have a youtube video demonstrating what my corolla does do on 91 octane fuel when you snap the throttle is how you get a engine whom runs on wrong fuel to pink or ping. The video shows how the timing retards by -10° and my scantol shows knock detected . now if my corolla did not have a working knock sensor it would be history since ages
because if it dont retards timing it will bash the piston backwards by igniting fuel before the piston travels down again .,destroyting the crank-bigend bearing , so the knock sensor saved the engine and the result is reduced power if the engine constantly has to retard the timing
less forcfull explosions can slap the piston= less power and throttle needs to be pushed further to the floor to add more air and more fuel to try and make the same force as with higher octane fuels who dont preignite and cause pinking .
networkguy, Aug 16, 7:47pm
Nothing to do with the octane rating though and everything to do with the additives they put in the more expensive fuels - thats why you see all the marketing about it cleaning your engine and whatnot. Theres more to the 98 than just raised octane, and you might not get the same results with another blend of 98 from Gull for instance
networkguy, Aug 16, 8:00pm
Too many factual errors to even go into here. The first sentence is the worst though "Nothing runs well on 91" - absolutely incorrect. You are saying that you know better than all of these vehicle manufacturers recommending 91 octane fuel for their brand new vehicles? You are dreaming lol.
rodeorunch, Aug 16, 8:09pm
Following this
So what octane should I be running a v6 Toyota
Prado on my litres per 100 kms seems a bit high