RCF - Normal Unleaded (RON95) or Super Unleaded (RON98)

[ronaldo]

Living in Northern Ireland, we have no access to Super Unleaded. I've being doing some research into the usual performance car suspects with regards to their ability to run on RON95 fuel.

In looking at one of the other forums, I've seen a photo from the user manual of a Merc C63 stating that RON 98 should always be used except for emergencies - when RON95 could be used but gives the following warning:

Quote

This may reduce engine performance and increase fuel consumption. You must avoid driving at full throttle.

Even if RON95 runs fine (anyone running a C63 in Ireland must be running on it), I'd be uncomfortable using it given the above warnings.

I've seen reference on this forum about a lot of IS-F owners using RON95 without issue - and believe that may be what's asked for in the user manual for that car anyway.

What do you RC-F owners use and, if you don't mind, could you have a look at either what the manual asks for or whether the inside of the fuel cap specifies such information? Thanks in advance :)

[Linas.P]

The difference between 95 and 98 are very minimal, that is 98 has more additives to increase fuel resistance to detonation and sometimes has additional additives which slow down accumulation of various gunk. Super/Premium Unleaded is not necessary RON98, unless specifically stated - it is more to do with additives, than RON rating. Fuel RON can be improved by using additives, so it is completely possible to run C63 and RC-F in Ireland even if you don't have RON98 at the stations. You fill up the tank with RON95 and add a certain amount of additives which enhances fuel resistance to detonation and you have tank full of RON98.

Generally, I believe we need to explain why MB recommends using premium fuel... because it will slow down wear of the engine. Now why they recommend RON98 puzzles me - generally it is important on turbo engines because turbo increases the risk of knock, but M156 as well as 2UR-GSE are NA engines, so running them on RON98 is more for sake of it than any actual benefit. It would be wise to mention that both engines have high compression ratio which would explain why RON98 is beneficial, but for example, 4GR-FSE in IS250 has an even higher compression ratio, yet it is fine to run it on RON95.

Overall, it is true using RON95 can reduce engine power, but only if it starts knocking, it is not true it will increase fuel consumption.

[NemesisUK]

Modern engines, certainly from the German marques, all have knock sensors and can automatically adjust the ignition timing to account for the different RON. 

My CLS55 always ran better on V-Power, though the handbook didn't require it.

The only benefit for N/A engines running 98RON would be the additional detergent and cleansers.

Running 95RON will be perfectly ok

[Linas.P]

Same for Lexus... all engines have knock sensors - hence running Premium fuel might result in slightly more power, though it doesn't mean it won't run on RON95.

[wendle]

I use standard unleaded, runs perfectly ok, I only do short trips ( 2500 miles p/a ), the last two tanks I did put in shell V power, only because I got an offer on it I haven't noticed and difference in power or mpg. As I only do short trips I may use V power for a couple of fill ups just to help keep the engine clean. Red X costs around £5 for two tank fills, so it's no more expensive to use the premium fuel

[Linas.P]

... I would say that is kind of expected. As well good point about Red X, I have mentioned in another post where I got 1L bottle for £3, which then works out cheaper as premium fuel (as it cover 8 tanks), but overall that is true - Premium fuel from the pump would work out cheaper than, standard fuel + red x. There is one more thing to mention - there are different types of red X and not all improve RON. When I said adding additive I have specifically "octane booster" in mind.

[MNMJ]

Shell V Power all the way for me, both on the RC-F and the IS-F, and all my fast Subarus before.

After completely unscientific testing I decided it improved fuel consumption enough to offset the cost. It also makes cars faster. So basically its a free power boost...

....or the placebo effect.

In any case, when depreciation is £500-2000 a month, an extra £5-20 a month on fuel is not worth fretting about

 

 

[Big Rat]

On 28/03/2017 at 1:22 PM, ronaldo said:

Living in Northern Ireland, we have no access to Super Unleaded. I've being doing some research into the usual performance car suspects with regards to their ability to run on RON95 fuel.

In looking at one of the other forums, I've seen a photo from the user manual of a Merc C63 stating that RON 98 should always be used except for emergencies - when RON95 could be used but gives the following warning:

Even if RON95 runs fine (anyone running a C63 in Ireland must be running on it), I'd be uncomfortable using it given the above warnings.

I've seen reference on this forum about a lot of IS-F owners using RON95 without issue - and believe that may be what's asked for in the user manual for that car anyway.

What do you RC-F owners use and, if you don't mind, could you have a look at either what the manual asks for or whether the inside of the fuel cap specifies such information? Thanks in advance :)

@ronaldo It's all down to personal preferences really as long as knock sensors are fitted, which they are then just plant your foot down harder for the extra performance on the lesser fuel😏

Any way it's a petrol engine so they all ' Suck Squeeze, Bang and Blow' !

Big Rat

[Rabbers]

In a previous thread on this topic in the IS Forum (see Premium Fuel, started by mpls, 19 November 2015), the consensus was that

the benefits of higher-octane fuel are minimal or non-existent.   My own opinion with regard to the IS300h was that "I used to think

that Shell V-Power or similar brands of high-octane fuel might yield a combination of better economy and performance but have never

found objective proof of it...."   

 

I mainly based this conclusion on comparisons of non-stop drives of approx. 900km over exactly the same route with tankfuls of 

RON95 or RON98 V-Power.  After hoping to get a few extra km with the latter, I had recently been disappointed - though not especially

surprised - to find myself pulling in to the same services as I customarily did with RON95 after the appearance of the fuel-reserve

warning some 15-20km earlier.  I thus concluded that higher-octane fuel was not worth its premium price.  And nor, in more normal

motoring situations over the years, had I ever been able to detect significant improvements in punch and acceleration in any car,

including the IS's non-hybrid predecessors, attributable to the use of V-Power or any of several other brands of RON98> fuels.

 

However, on one other occasion since then (actually on the same route but in the opposite direction), I got a much better result which,

if I manage to duplicate it later this year (with due allowance for the fact that I will be driving an RC and not a somewhat more economic

IS), may cause me to revise my opinion.   Instead of starting out with the usual tankful of RON95, I this time filled up with V-Power and,

to my surprise, not only proceeded past the services where I expected to stop but finally saw an increase in range of close to 7%.   My

reason for choosing V-Power despite my earlier thinking was that Shell in Denmark, where I filled up for the journey, were running a

campaign promising it gave you "up to 3% more km".   This was in itself no big deal but it impressed me because I had never before

seen an oil company make so specifically and precisely quantified a claim for its fuel - or, as it turned out, such a conservative one.

 

I can offer no explanation for this event since I recall no great variations from previous drives in terms of weather, traffic, roadworks,

queues, amount of luggage etc.   Maybe Shell uses some particularly miraculous additive for the Scandinavian market, but I have

found no online mention of it.

[Linas.P]

5 hours ago, Rabbers said:

My own opinion with regard to the IS300h was that "I used to think

that Shell V-Power or similar brands of high-octane fuel might yield a combination of better economy and performance but have never

found objective proof of it...."   

 

I don't think it is opinion - it is more like fact. The difference between RON98 and RON95 is so small that nobody ever could objectively feel it. In terms of power engine would start knocking at very high RPMs, so there will be ultimately 1-2HP loss of power on RON95, but it will be at very end of hp curve and would not affect driving, acceleration etc. It is more like a number to boast about, but otherwise it is meaningless. E85 would have better RON than both 98 and 95... if you really that conserned.

In terms of fuel consumption, it would be against the physics that car use less RON98 - after all consumption is defined by energy stored in liquid, for that reason cars burn more ethanol like E85, because it has less energy per volume. When it comes to comparing RON98 and RON95 both have nearly identical amount of energy, in fact RON95 has slightly more energy, because in RON98 fuel is replaced with additives which adds no energy at all. Anyway difference in consumption is so small that it would not be possible to measure it.

Only benefit of Premium fuel is the additives which contrary to some beliefs doesn't clean engine, doesn't even prevents dirt build-up. What they do - they slow down build-up and in result they increase engine life. In long run they as well improve engine efficiency and indirectly fuel efficiency... but that is after maybe 20-30k miles, it is not like you fill with RON98 Shell V power and you going to gain 0.5MPG - no it doesn't work this way. 

Because of that I have decided not to run premium fuel, but instead every year or every second year have my engine cleaned with hydrogen or terraclean - because that actually cleans.That is decision one needs to make when picking up new car from the showroom - run it on RON95 and clean engine every 2 years, or run it on RON98 and clean engine every 4-5 years. Ultimately, both will accumulate gunk and both will need cleaning. When it comes to used car it only makes sense to use RON98 after cleaning engine and only if you plan to keep car for another 4-5 years, otherwise it is just waste of money.

When it comes to RC-F or IS-F I would personally use premium fuel if available, just for sake of it and knowledge that I can get all claimed power at 6800RPM, but I would not worry at all if premium fuel isn't available where I live, it won't damage the car and it won't reduce power to the level where I would be able to feel it.

[Linas.P]

6 hours ago, Rabbers said:

However, on one other occasion...

4

To specifically address this point - fuel consumption depends on may factors e.g. temperature, wind direction, tires, tires pressure, tires wear etc.

So that you get 7% more mileage on one occasion doesn't really count. Similar to what you said I have tried comparing MPG on different fuels and found no correlation between increased mileage and premium fuel, much more correlation between tires pressure, tires wear and time of the year (weather temperature).

[Rabbers]

On 3/30/2017 at 6:03 PM, Linas.P said:

To specifically address this point - fuel consumption depends on may factors e.g. temperature, wind direction, tires, tires pressure, tires wear etc. So that you get 7% more mileage on one occasion doesn't really count......

Agreed.  One swallow does not make a summer, and I am inclined to view the unexpectedly good economy obtained on that particular

drive as something of a freak occurrence.  Which is not to say that the car's ability to perform on that occasion is likely to have differed

too much from past ones since, for peace of mind, I never embark on long trips away from home without checking vital components,

let alone undertake long autobahn drives without checking tyres for wear and pressure.   Still, the single easily identifiable variation in

respect of past experiences on that route was my choice of a type of fuel that claimed superior economy.  I should record, purely

anecdotally, that this reversal of my previous thinking about premium-priced fuels was more whimsical than rational insofar as it

reflected my gratitude towards Shell's Danish copywriters for not crassly exploiting the connotations of steroid-laden muscularity

and potency as would locally derive from any suggestion that the "V" in the name of their product stands for "Viking".