RON95 or RON98

[Mucus72]

Morning POBC,

i have been reading previous posts (that stretch a long way back!) regarding fuel type. 

I'm a day away from filling up properly for the first time prior to a rolling road running in session and IVA on the new build Duratec. 

And via email with a few mates we have been having a debate about how common 98RON will be across forecourts in the highlands as we plan a touring holiday up there, and one of  the other cars needs it.

It appears that if Duratecs have a knock sensor then there is some merit to using 98, and it should improve both performance and mpg. It may also be better for the engine long term (cleaning properties). These are the 3 factors I have gleaned from the old posts.

Do you guys know if current factory ECU Duratecs are set up in such a way that makes 98 worthwhile please?

thanks

marcus

[john milner]

I don't know but right or wrong someone will say 98 or higher is great. If they do and you take their advice I suggest you try half a tank and see what happens. If it mutes performance it means the ECU can't handle it but no harm done and if it doesn't mute then you may get slightly better mpg but unlikely enough to outweigh the cost. I can't see a marginal increase in performance being of use on the road. I also have doubts about the cleaning hype as I can't say I have noticed Asda 95 causing me any problems.

If one of the cars is tuned to "need" 98 then 95 would cause big problems. Basically safe to go up but lethal to go below the minimum required.

[Jonathan Kay]

Just checked the Assembly Guide and Handbook and can't find any specifications or advice... what does the factory say?

Agree with John, but sceptical about being able to detect any difference in performance even if it exists, because of uncontrolled variables and all those cognitive biases.... unless it's done blinded. And travelling with others offers you the perfect chance to do that. They toss a coin to decide what goes in, and you write down your findings without knowing what it was. Then on your last evening you break the code.

Jonathan

[nigelpugh]

As a comparison my previous R500 was 99% of the time filled with Shell Optimax, and always ran fine.

On one trip to Northern France, where a lot of the gas stations were closed on the Sunday, we were forced to fill from empty at the only open Total garage we could find, and they only had standard unleaded.

My car ran like a complete dog all that day, including flatspots, stalling and taking an age to start.

When we got back to Dover, I immediately stopped and filled up with She'll Optimax, and after a few miles of running the problems all went away.

Of course it could have been poor quality, or dirty fuel, but I never went back to standard unleaded again.

Once you car is on the road Marcus it would be worth a quick test with half a tank of 95 to see what happens as the guys have suggested.

[Jonathan Kay]

Of course it could have been poor quality, or dirty fuel, but I never went back to standard unleaded again.

What does the factory say for your engine? Once we know how could we persuade you to rerun that experiment, but with 95 RON fuel from a high turnover supply in the UK?

£5 wager that it doesn't run as badly as it did that time, takings to NtL?

Jonathan

PS: Following that interesting discussion about Ricardo, here's a photo (I don't have a schematic diagram) of the E-35 variable compression test engine that helped him unlock the problem of fuel quality, and his own thoughts:

http://www-g.eng.cam.ac.uk/millennium/achievements/ricardo/images/th-R34.jpg

During the 1914-18 War, I came into contact with Sir Robert Waley-Cohen, of the Shell Company, who, at that time, was chairman of a committee dealing with fuel supplies. To him I told of my experiments on detonation, of the very great importance I attached to it, and of my belief that it was largely a function of the fuel. He immediately sent me samples of a wide range of fuels of different origin, which I tried out on my supercharging engine, and I was able to show him very great differences in their behaviour as regards detonation. Of these sample fuels, by far the best was one hailing from Borneo. He told me to my amazement, that hundreds of thousands of tons of this particular petrol were being burnt to waste in the Borneo jungle merely because it did not comply with the existing specification as to specific gravity. On the strength of these observations, he invited me to undertake, as soon as the war was over, a comprehensive research into the behaviour of liquid fuels. This, then, formed the first piece of large-scale research undertaken at our new laboratory at Shoreham."

[ScottR400D]

I tend to put Shell 98 in my R400 but have on several occasions not been able to get it and have run it on a branded 95. I can't say I've noticed any difference.

My owners manual says 95.

[Golf Juliet Tango]

I'll use 98RON fuel if it is available, if not I'll use whatever petrol is needed. The ECU on the 21 was set up for 98, for the the Crossflow, I have been recommended to use 98 but the differences are marginal, in my experience on the road. On track, possibly some would notice. I have certainly experienced bad fuel and the poor running from a tankful but these haven't correlated to the grade of fuel in my cars. Other set ups probably differ.

[jimh]

In the Caterham manual only the 620 is down as requiring 98 ron all the rest say 95.

Has anyone tried a 620 on 95?

[JNC]

When I had my Duratec on the rr with the two Steves big Steve told me to fill up with 98 and he said not to use Shell !, I have used 95 since when 98 was not available and not noticed any great difference . I have noted fresh Petrol  and Diesel  from the pump always seems more responsive has any one else noticed that ?.

[Mark w]

I have used 95 in my 620R on the odd occasion 98 wasn't available , i cannot say i have noticed a lot of difference but i wouldnt make a habit of it .

When i had my R400 mapped  the two Steves suggested mapping on 95 to give some headroom on the track ( when i always used 98 or 97 .) 

A few pence more per L doesn't really make any difference in ownership costs .

[Brian Deacon]

My K series 1.6 runs okay with either 95 or 98, so I save on 95 !

[SM25T]

Duplicate post.

[SM25T]

My k-series is set up for 95. However ..... touring in Europe ... the 95 is 10% vegetables or bio ethanol .... which doesn't like rubber hoses .... so I always use 98 or higher when across the water.

[Paul McKenzie]

If you have a tuned engine (higher CR, ported, wilder cams etc) then it will have been set up on a rolling road or dyno with a certain amount of ignition advance, using a fuel that will maximise power without detonation - it is unlikely to be 95.

[ChrisC]

Hi Marcus

My take on 95 98 question is from a different angle.  98 has less bio ethanol, which from my understanding attracts moisture, and is known to damage aluminium fuel tank when stored.  I know this is over simplify the ethanol in fuel issue, but I just err on the side of caution.

I toured to Germany, and found no problem getting 98 in any country on the way,  but while in Germany it was rude not to use the 105 that was on offer ;-)

Chris

[Jonathan Kay]

I toured to Germany, and found no problem getting 98 in any country on the way,  but while in Germany it was rude not to use the 105 that was on offer

Do you think it made any difference?

Jonathan

[Mucus72]

All interesting and inconclusive stuff. I was at Northampton Motorsport this morning whilst "working from home" and Troy (top bloke) ran my new car through a 2 hr rolling road cycle for running in purposes. Got a good power and torque trace too, which was nice. There isn't a knock sensor on Duratecs by default. He said that 95 is fine unless you have had your car specifically mapped for 98.  Which is the rough opinion on here too. I will play around over time and see if I notice any difference, it's obviously a dark art. ;)

i have just checked the owners manual and it does say 95. Today's first fill was from a motorway BP garage. 

My car recorded 204bhp max and 152lbft torque. Which is apparently spot on for a brand new tight 420R on a warm day. He then talked about a Duratec Westfield running a supercharger kit that gave a driveable 430bhp. Yikes! 

[SM25T]

You found 105 ?? I like the 102 at Aral stations in Germany. And yes .... it feels great. Better mpg .... more go from less throttle input.

[sjmmarsh]

I saw 110 Octane on one of the pumps when I filled up at Lake Havasu in the US. Never knew you could go that high before I saw it. I presume is is mainly used for the powerboats on the lake. 

Steve

[Smiffy69]

Can't add anything to the above other than say mine is Duratec with the standard CC Map for the stage 2 upgrade to 225 BHP.  I run on 98 where available and 95 when not and have never experienced any poor running on the 95.  

[Jonathan Kay]

I saw 110 Octane on one of the pumps when I filled up at Lake Havasu in the US. Never knew you could go that high before I saw it. I presume is is mainly used for the powerboats on the lake. 

The availability of high octane fuel and the understanding of how to make it was a major part of the development of aircraft engines. And different countries took very different approaches up to 1945. There's an excellent description of this in Setright's "Power to Fly: History of the Piston Engine in Aviation".

Highly recommended.

Jonathan

PS: Yes, of course there's lot about the Merlin.

[Jonathan Kay]

In case anyone's puzzled by the engineering, chemistry and physics underlying this discussion, and its previous versions, here's an attempt at a summary, corrections and additions welcome:

• Premature detonation is a problem in piston engines.
• Compression ratio is one of the determinants and limiting factors of thermodynamic efficiency.
• For a given octane number or similar, and other things being equal, there's a limit to the achievable compression ratio before premature detonation occurs. A higher octane number allows a higher compression ratio.
• Some engines detect premature detonation and change things if it occurs. (Has anyone established whether any factory Caterham engines have knock sensors?)
• But fuels with higher octane ratings don't necessarily* have any more usable energy per unit volume or per unit mass.
• Fuels with higher octane ratings are more expensive per unit volume.

After that it gets difficult and might be controversial:

1. There's a shortage of evidence that higher octane ratings than needed to avoid premature detonation give greater power, economy, or any other benefits.
2. There's a shortage of evidence that any fuels keep engines cleaner than any others.

Can anyone provide more on 1 and 2? (And why aren't there lots of studies out there? They aren't hard to do on eg fleets and could easily be done double-blinded.)

* It's probably worth adding that it's not implausible that the composition of some fuels that have higher octane ratings coincidentally do have more usable energy, but I haven't seen that any studies of that for ordinary road fuels as opposed to trick fuels used for records and racing, see Setright above.

Jonathan

[prangerman]

JK - the sourcing of additives to increase the octane of fuel for the Merlin engine shortly before hostilities is an often overlooked and underestimated critical factor in Battle of Britain. It's very unlikely that the Hurricanes and especially the Spitfires tangling with the Bf109s would have been able to hold their own without the power boost the higher octane delivered. I have the story somewhere in my military history library... Peter

[Mucus72]

Jonathan,

Troy, who runs Northampton Motorsport told me that there are no knock sensors in factory Caterham Duratecs. 

[Jonathan Kay]

Mmmm... data.

Thanks

Jonathan