Q&A: How does fuel octane rating effect performance driving?
It’s a cardinal sin to use regular unleaded petrol in your performance car at the track, right? Let’s talk about that…
QUESTION
Hi John,
I’ve enjoyed your channel for a while now. Love how you ‘fuel up’ on the haters.
Seeking a bit of reassurance on most appropriate fuel for the Stinger GT 3.3TT. [Full review here >> ]
The manual is bewildering and fuel cap fails to confirm.
Many on social media pay-out on owners ‘silly enough’ to only use RON 91 in these engines.
Several boast they’re happy to waste money by putting no less than RON 95 or the expensive 98 in their Stinger GTs. I still can’t justify the price difference for the claimed improved economy.
I do a weekly Hume freeway journey Albury to Melbourne so it’s easy to do comparative runs too.
Even though Europe gets its own mention in the manual, the terminology is pretty similar to sans-Europe, and so Aussies defaulting to running at least 95 RON is understandable.
I’ve run 98 when enjoying ‘spirited driving’ on track days because I was reviving it hard and so, it seemed a good idea.
I didn’t want to ask the dealer staff. Too many opinions there.
As for E10, owner/member posted they regularly commit to filling with E10, which brought on howls of opposition, so it’s apparently a cardinal sin. Why is E10 so pilloried? I’ve never been game to try it.
The Kia service supplement (in the manual) finally answered the question, but I had to be committed to carefully reading to find this though. It wasn’t indexed either.
Who are writers for these manuals anyway? Granted, not many owners ever read these through; they’ll never make the best-seller list.
Thanks for your help
- Stuu
ANSWER
Stuu,
You’re not in Europe, so I’d forget that. The reason they’re saying 95 RON in Europe is because it’s the lowest RON available over there. 91 is fine here.
Also, e10 is also fine. It gives you roughly a 3% reduction in fuel efficiency; about 94 RON.
As for the manuals, people don’t buy a car because of the beautiful manual mate.
And those forum members - in particular the most prolific commentators, are typically fuckwits. So there’s your answer there.
Pro tip: Your lap times on 91 and your lap times on 98 will be identical (especially if they’re blind tests). What’s limiting your lap times is not engine performance, even if you’re a decent performance driver. It’s typically driving technique - in particular brake application, which is very hard to get right.
As for RON and track performance, the keyword in relation to performance reduction is: ‘Slight’.
‘Unleaded fuel only’ is required by law. If a car needs a minimum of 95 RON it says ‘Premium unleaded only’ and if it needs 98 minimum is says ’98 RON premium unleaded only’.
As for engine health at 6600rpm, the fuel doesn’t matter. Engines have knock sensors (acoustic microphones tuned to hear knock). They advance the timing to the point of knock, then back off, and repeat. It’s all they do, regardless of the fuel.
So on 98 you get slightly more ignition advance before knock, and hence slightly more torque at the crank. Because the engine is also turning, that means slightly more power - slight - you’d never feel it.
The fuel doesn’t make a contribution to engine health because the engine protects itself from knock. That’s how this works.
If an engine is tuned for 98 the overall compression (static compression + turbo boost) is too great for fuels less than 98, and hence no amount of retarding the timing will help, and you’ll always get knock at high RPM and high throttle inputs (which is the kind of knock that destroys engines). The Stinger engine is not tuned like that - happily enough.
Handy links:
Talking tyres - performance, handling, braking, longevity >>
Are you still holding the steering wheel wrong? Stop it now >>
REPLY
Thanks for getting back to me. The Europe RON explanation helps, and the fuel decal explained. It’s what is not written that causes me trouble.
I accept the subtle / no change in times due to 98 RON fuel but with it revving up to 6600rpm or so I thought it wise to at least use the higher octane as a token contribution toward engine health.
It’s also great driving this car in and around the mountainous drives of Hotham, Falls Ck, Bright, etc, on the usual fuel.
You’re right about braking. I did run off the end of the pit straight at Winton once, leaving it a tad too late to brake. Steered it off instead of sliding etc. Much less embarrassing that way and no panels harmed either.
The drive days are great to enjoy more of the car, pretty cheap, very safe, without attracting the constabulary.
Managed to get the pedal quite spongy by day’s end too, after completing about 30 laps with 24 of them having a go. Kia dealer was a bit surprised though!
