Talk Morgan Forums Morgan Sports Cars Morgan Plus Four, Supersport & Plus Six (CX & CXV Generation Vehicles) Fuel 95 RON or 98 RON?

I read about MOT problems with 95 RON and no MOT problems with 98 RON. Discussing this with my son (pistonhead) he told me that filling the Plus Four always with RON98 would be a good idea. So i asked AI what they think about it:
Fuel choice is especially important with a B48 (BMW's 2.0 turbo 4-cylinder).

The B48 is designed for a minimum of 95 RON, but it's fully compatible with 98 RON (Super Plus). It automatically adjusts via knock sensors and engine management.

Below are the real pros and cons — without the marketing nonsense 😉

✅ Advantages of always using 98 RON

1️⃣ Better knock resistance (more safety under load)

98 has a higher octane rating → less chance of knocking/pinging under:

High turbo pressure

Warm engine

Sporty driving

Autobahn/full load

The B48 can therefore:

provide slightly more ignition advance

deliver more stable power

➡ Especially useful if you often drive hard.

2️⃣ Slightly better performance (but limited)

The gain is small, but measurable:

Slightly smoother throttle response

Possibly a 2–5 hp difference

Slightly more consistent performance in warm weather

You'll hardly notice this during normal, relaxed driving.

3️⃣ Possibly slightly cleaner combustion

In many countries, 98 contains:

Less ethanol (often E5)

Sometimes more additives

This can:

Provide slightly less fouling of injectors

Provide slightly more stable combustion

However: the difference isn't dramatic.

❌ Disadvantages of always using 98
1️⃣ Higher cost

In Belgium/the Netherlands, usually:

8–15 cents more expensive per liter

Over the year, this can be €150–€300 extra, depending on your mileage.

2️⃣ No significant benefit during normal use

If you:

drive calmly

don't have any tuning

don't put a heavy load on it

then the B48 will run perfectly at 95 and you'll hardly notice any difference.

3️⃣ No "extra power" without tuning

The ECU of a standard B48 isn't aggressively tuned.
98 doesn't provide "magical extra power" unless:

you have Stage 1 tuning

or a performance map

🔧 When is 98 really recommended?

✔ Sporty driving
✔ Long highway journeys at high speed
✔ Hot summer days
✔ Tuned engine
✔ If you want maximum engine safety

📊 Summary
Use Best choice
Quiet commuting 95 is sufficient
Mixed use 95 or 98
Sporty / Autobahn 98 recommended
Tuned Always 98
🎯 My technical opinion

The B48 is a modern turbo with high compression (11:1).
It runs a little "happier" at 98, but it's not essential.

If you plan to keep the car for a long time and the price difference doesn't bother you → 98 is never a bad idea.
But 95 definitely doesn't harm the engine.

Agreed. I always use E5, which (I'm told) often doesn't contain any ethanol as the '5' part is the maximum allowable. 15 cents per litre more expensive to create Euro 300 extra annual cost implies 2000 litres per annum, which for most of us is probably way more than we would likely use. At 5,000 miles per year, 45 mpg, that's around 110 gallons, say 550 litres, 15 cents difference would be less than Euro 100, a small cost to help protect the engine.

E5 in both our Morgan's all the time.

Not quite. The 5 in E% stands for 5% ethanol,


Not really. It all works out. The benefits of using high octane are multiple (though I have no patience with ethanol). I find that blocks that have been
blessed with high octane petrol, have pristine innards. If the blocks are old ones, they have become "seasoned" as well. The American propane variants
are quite amazing, though I have never owned one.

In any event, I figure Morgans are a hobby car, not A-B transportation. Fuel mileage should be irrelevant. I have been astonished at the difference
fuel quality makes from country to country.. Canada is lucky. it's rating system is the minimum average of RON & MON while the USA is the average

In the UK E5 is 'up to a maximum of 5%'

There are still some fuels out there that are marked as E5 but have little to no ethanol, although this can vary by location. (Esso Synergy Supreme +99. Tesco Momentum 99 and Shell V Power 99)

My post said 15 cents per litre because that's what the OP stated, in the UK E5 is probably around that premium against E10, I've never been that bothered to check. My point was that even if it is more expensive to the average Mog owner it's not going to break the bank, particularly as the E5 sold in the UK is usually marketed as having other benefits ("Shell V-Power unleaded contains three times more cleaning and protection molecules than our regular fuel F, helping remove performance-robbing deposits. [Shell web pages])

Interested to know your thoughts on "how it all works out", and also how my 15 cents per litre got changed to 1.5 cents per litre in your post? Perhaps the difference between 95 RON and 98 RON in the US is that small? If so, I'd agree that's peanuts.

Based on UK government, industry, and motoring organization reports, E5 petrol (the "super" grade 97+ octane) does not currently have a fixed, officially announced end-of-sale date, but it is under review to potentially cease or be reduced further in 2026.

Initial 5-Year Plan: When E10 became the standard 95-octane petrol on September 1, 2021, the government mandated that E5 remain available as a "protection grade" (specifically in 97+ octane super unleaded) for older vehicles. This protection grade was guaranteed for at least 5 years, making the initial review period September 2026.
Likely Future: While some reports suggest a potential ban or phase-out of E5 starting in 2026, it is considered highly likely that a version of it will remain available for longer to support classic and older vehicles, though it may become more expensive or harder to find in rural areas.
While there are no immediate, finalized plans to roll out E15 petrol (15% ethanol) across the UK, it is currently under review by the government. Following the adoption of E10 as the standard grade in 2021, moving to E15 is considered a potential next step to meet long-term decarbonisation goals.

Here are the key points regarding the potential introduction of E15 in the UK:

Official Review: The Department for Transport (DfT) confirmed in June 2025 that a move to E15 is being reviewed.

Industry Support: There is lobbying from within the industry to increase the ethanol blend limit to E15 or even E20 to boost demand for lower-carbon fuels, particularly as biofuel manufacturers look for stronger market support.

Compatibility Concerns: While most vehicles built after 2011 can run on E10, a shift to E15 (15% ethanol) raises questions about the compatibility of a wider range of older vehicles, potential damage to fuel system components, and the need for new public information campaigns.
Environmental Goals: The UK aims to cut carbon emissions by 78% by 2035, and increasing renewable fuel blends is part of this strategy.

While E15 is common in parts of the USA, the UK is currently focusing on embedding the use of E10, which already reduced CO2 emissions from transport.


So it will be interesting to see how long E5 will continue to be available

Personally, I alternate between E5 and E10, but will bear in mind when filling up before the next MOT to use E5 whilst it is still available.

Looking forward to a short trip to the Fatherland a bit later this year so I can once more put the Indigo girl into her happy zone , 110mph 2,950rpm and 16mpg of E5 of course.

She will cruise at this indefinitely between fuel stops and settles down into a very relaxed pace of cruising, roof up or the wind break effect kicks in and economy drops + you get even deafer.

Unfortunately the rough surfaces on the Motorways including the monotony of the joins detracts a little from the experience but overall way better than our Nannying 70mph limit poorly surfaced and HGV grooved roads.


Enjoy your miles today - don't wait

I run the MGB on E10 all year round - don't have any bad effects, and average about 28-30mpg. With the Morgan and Harley I tend to stick a tank or so of E5 in at the start of the season, then run on E10 but try and overwinter with E5.

Contrary to a certain opinion several posts above, Fuel mileage is important - if I ran the MG on superunleaded it would be an extra £20 or so a month. I rather spend that money down the pub. It's also one of the reasons I went for a 4/4 originally - I wanted to be able to drive it all year, any distance without worrying too much about the cost of fuel. (I get about 38mpg).

My driving is pretty unsophisticated, so wouldn't really notice any performance difference between E5 and E10

The BMW B48 like all modern engines has comprehensive control over injection/ignition/valve timing with knock sensor(s) forming a key part of the control system. Without all this, these engines could not run reliably at the kind of compression ratios needed for power/emissions. Legally they have to be homologated on 95 octane but most will adjust themselves and run better on 98-100. The key issue with E10 is storage life...it goes off...and absorption of water...corrosion.