I thought that the problem with lower octane fuel was that it would ignite itself when too hot (ie, run a performance engine hard, the fuel gets really hot when compressed, and it self-ignites before it's supposed to) - is that not right? Pulling the timing means lighting (with the spark plugs) the fuel later doesn't it? So I must have misunderstood something along the way.
GR86 The GR86 : Time for a reality check
- Thread starter Silver Fox
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Nearly. "Pulling timing" is a term which means igniting the fuel earlier, not later, than it should . You are right, that lower octane fuels might suffer pre-ignition, where the air/fuel mixture ignites before the spark plug fires. By "pulling timing", what we mean is the engine detects this using the knock sensor, and "pulls" the ignition timing back, and fires the spark plug earlier, to prevent the pre-ignition. However, this means you lose some power and efficiency, as the air/fuel mixture has not been compressed as much as a higher octane fuel could be.
But essentially you are right - higher octane fuels are more resistant to pre-igniting = they can be squashed more = they can make a bigger bang. So yes, the GT and GR86 can run on 95RON, but they will just be a little less powerful and efficient when they do so. But as I said, whether you'd notice or not is questionable. I've always run mine on 98RON as it's recommended, but a couple of times i used 95RON in my GT and didn't notice any difference really, except maybe a bit of a dip in economy.
Disclaimer - I am by no means an expert, so the above might all be bobbins.
Alistair31
Totally Hooked
Test drove one this morning, only 1.5 hours but unaccompanied over some fine Scottish country roads, lots of fun.
ShootinJack
Obsessed member
There are some things I think could have been done better:
Online ordering (say no more)
Upgraded speakers
More exhaust noise from factory or at least a factory fit option
And that's it, throttle / gear changes have taken a little getting used to at slower speeds. When traveling 'with purpose' I love the quick gear changes. Car handles great and makes me smile when I start driving it properly.
When I gave my wife a few pointers (lecture as she put it) about the clutch and throttle before she took it out for her first drive, she wondered what I was talking about as she says they are both fine.
She loves it too.
Online ordering (say no more)
Upgraded speakers
More exhaust noise from factory or at least a factory fit option
And that's it, throttle / gear changes have taken a little getting used to at slower speeds. When traveling 'with purpose' I love the quick gear changes. Car handles great and makes me smile when I start driving it properly.
When I gave my wife a few pointers (lecture as she put it) about the clutch and throttle before she took it out for her first drive, she wondered what I was talking about as she says they are both fine.
She loves it too.
Hachi-roku
Totally Hooked
- Oct 8, 2022
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If anyone else feels like running the car on 95, or 2 stroke mix or cooking oil and octane booster I’m happy to be an observer and see what the outcome is. I’ll be sticking with 98 or better, I don’t see the point in quibbling over a few pence a litre. I’ll concede it likely represents less of an expense for me as I’m running it as a fun weekend car not a daily.
That can't be right? That would basically mean you're deliberately making it pre-detonate, and blow up the engine.
Ok good, got that bit.
It prevents pre-ignition by making even worse pre-ignition - that doesn't make sense to me.
But the pistons will complete their cycle and continue compressing the fuel/air regardless, and if you ignite the fuel earlier it will blow while the pistons continue their compression stroke.
I thought (and I'm probably wrong) that you could just get more fuel in so that you can get a bigger bang, because the pistons are going to do the full compression stroke regardless.
Hopefully someone can help me get my head around it - but now, Saturday night calls, and I'm going to pretend I'm not old.
Guitar spark
New member
- Dec 15, 2022
- 17
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Decided to use 95 for the running in period on my GR Yaris as I wasnt using full throttle or taking it past 5K revs
Didnt notice much loosening up after the first hundred miles or so, but did notice a reluctance to pull from much below 2500 revs. When I finally completed the running in this week its was on fumes and I filled it with Tesco 99 and noticed a big improvement in low end pulling with no problems from 1800rpm now and it was noticeably running both smoother and quieter
Didnt notice much loosening up after the first hundred miles or so, but did notice a reluctance to pull from much below 2500 revs. When I finally completed the running in this week its was on fumes and I filled it with Tesco 99 and noticed a big improvement in low end pulling with no problems from 1800rpm now and it was noticeably running both smoother and quieter
Pre-ignition really only happens with *really* crappy fuel or with the cylinder running lean (malfunctioning injector) making everything too hot giving a alternative ignition hot surfaces. On boosted engines there is also LSPI, a different subject matter. Also oil drops or carbon deposits can cause it.
Higher octane doesn't give more power by injecting more fuel. That just makes the AFR lower and 'fatter', usually lowering power by additional cooling effect.
Higher octane allows for a cleaner ignition without other areas of the mixture igniting causing knock. This allows to ignite the mixture sooner, thus prolonging the power stroke and rendering more power.
(edit: much more can be said but in essence, if I'm wrong I'd like to hear it
)
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So Conscript says for lower octane fuel, the timing is pulled, meaning you ignite the fuel earlier, and Onehp says with higher octane you ignite earlier. This is confusing.
Moving on from the technical details for a second, what we need to know if how often the ecu adjusts for different quality fuel. I think in my old Impreza it was done over a fair period of time, so if you switched from 95 to 98 you wouldn't get a benefit straight away (although mine was an import, so I always ran it on 98). But reading a few posts here gives the impression it switches really quickly, so you could change to cheaper fuel if you needed with no real problem.
Thanks - I'm the same. Thought I understood it, but there's more to it than I realised. I'll have a good read tomorrow.
North of the Border in Scotland it doesn’t matter whether it’s 95,98 or 99 Octane as they are all E10 by decree of our leaders in Edinburgh. Should I wish to buy fuel with less (or even zero) Ethanol in it, I’d have to drive South the 2-3 hours each way to find it. I just use Tesco Momentum for the most part as it’s local but again, it’s still E10. I blame Covid… and Brexit… and the Cost of Living Crisis… [insert others here] 
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.Does the E rating make any difference to the engine?
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I'm in Sweden and I *add* E85 to 98 in my cars to mix up to E30. My GT86 was remapped to run E85 straight.North of the Border in Scotland it doesn’t matter whether it’s 95,98 or 99 Octane as they are all E10 by decree of our leaders in Edinburgh. Should I wish to buy fuel with less (or even zero) Ethanol in it, I’d have to drive South the 2-3 hours each way to find it. I just use Tesco Momentum for the most part as it’s local but again, it’s still E10. I blame Covid… and Brexit… and the Cost of Living Crisis… [insert others here]
Ethanol has much higher octane and burns cooler and 'bigger' giving some extra power. So if the 99 is good quality, I see absolutely no issue in it being E10, rather the opposite...
Silver Fox
Totally Hooked
- May 7, 2022
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A brief update from me with three quick points, if I may:
1. My original post might seem harsh on the GR86. I'd like to clarify that I absolutely love (almost) everything about mine and I have had some wonderful, memorable drives in it already.
2. Not all items listed in the intital post will be an issue for you. These items were gathered from a mixture of my own experience and accounts gleaned from some of our more credible and trusted comrades on here. (For example, I know some have been irritated by the throttle response but it hasn't bothered me personally at all).
3. Do we need a dedicated super or standard unleaded thread? All this talk of detonation confuses me (but does raise my anticipation for my Friday morning showing of the no doubt excellent film Oppenheimer).
Have a pleasant Sunday all. ¡Buena suerte Alcaraz!
1. My original post might seem harsh on the GR86. I'd like to clarify that I absolutely love (almost) everything about mine and I have had some wonderful, memorable drives in it already.
2. Not all items listed in the intital post will be an issue for you. These items were gathered from a mixture of my own experience and accounts gleaned from some of our more credible and trusted comrades on here. (For example, I know some have been irritated by the throttle response but it hasn't bothered me personally at all).
3. Do we need a dedicated super or standard unleaded thread? All this talk of detonation confuses me (but does raise my anticipation for my Friday morning showing of the no doubt excellent film Oppenheimer).
Have a pleasant Sunday all. ¡Buena suerte Alcaraz!
It's alright, we can read each point and see if we think they'd apply to, or bother us.
We probably should, if we don't already. Not so much for the technical aspects, just for whether it matters to the car. Sorry for posting off topic, although I figured the thread already had everything we need regarding the possible negatives of owning a sports car.
E10 (10% Ethanol) is slightly less efficient than E5 (5% Ethanol) but its use is said to reduce CO2 emissions, which is why the SNP+Greens coalition decreed that all fuel sold in Scotland would be E10. One issue with Ethanol though is that it is very hygroscopic, so if a vehicle is stored for several months the fuel can start to draw moisture - one way to mitigate this is to add a fuel preservative (sta-bil, fuel fit, POR15 etc) which helps maintain the chemical balance. Another issue with Ethanol is that it is corrosive to certain seals and plastics; we witnessed this with plastic fuel tanks on some Ducati motorcycles which became swollen and warped during Winter storage.
In general use though, the use of E10 is absolutely fine in modern engines and all new cars from 2011 had to be compatible with it. Just don't fill up your E-type Jag and leave it in storage for 2 years as it might not work very well
Silver Fox
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- May 7, 2022
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No problem - fuel use is definitely on topic (like you say, an important aspect/factor of GR86 ownership), but as a discrete, technical subject it might serve the contributors and readers better being separate.
I just put Shell V Power in mine!
KobayashiMaru86
Totally Hooked
Since I only run Super Unleaded in mine, longer runs need planning. When I did Scotland and back I had to pre-plan where I expected to get fuel. Range was better than expected so go to Fort William with some to spare. Then coming back I could skip one stop and get one further on.
This isn't exclusively an 86 issue but is if you only want to run the good stuff.
This isn't exclusively an 86 issue but is if you only want to run the good stuff.
