Hmm, interesting stuff! Unfortunately I cannot buy 98ron fuel in Ireland due to stupid taxes being imposed so nobody sells it anymore. I have however used E5 in mine, along with using standard 95ron and 95ron + a fuel booster. I seem to have the best high end power with the E5 oddly, but not economy. I have stopped using the fuel additive for now as I suspect it might be increasing oil usage (possibly attacking oil lining on cylinders?). It did however still give me a bit more top end over the standard fuel IMO. Have no conclusive tests to prove any of that though, just my 2 cents! On the plus side I will be hheading back to the UK next month so will enjoy soaking up a bit of V-power!

E5 paddy? is that the bio stuff? thats higher RON right?

Ethanol got 104 octane so the more "E" you mix in, the higher octane-rating you will get.

However, E5 was something new... thought it would be E10?

It will give you more top end as more ignition advance ECU can dial in => more poowwaaah!

Ethanol has much higher knock resitance than gasoline but has 34% lower energy content so economy suffers.

When you pottering around and staying within lower rev ranges RON95 is better fuel to use economy wise

When you do drive "enthusiastically" then the top you are after and RON98 would be better for you.

E5 and E10 (5% and 10% Ethanol additive to straight petrol) is not going to give you massive difference really and your driving style will be of much higher significance by far.

One thing which is rarely mentioned is that Ethanol is highly hygroscopic (sucks water from the air) giving you even more knock resitance ( water-meth injection systems for example) but can create "water slugs/bubbles" in fuel line causing engine to stall and lowers energy content of the fuel even further. Then there is corrosion problem as Ethanol attacks corrosion protection films on metals.

To top it all off it causes cold start problems as it has very low vapour pressure at low temps.

Biobuthanol is the answer really (straight petrol replacement) but it gets awfully political then...

Ethanol is used in many racing series. They run insane compression ratios with silly ignition advances and AFR's to cause a heart attack .

A couple of nice links

http://www.greenbiologics.com/biobutanol-fuel.php

www.napier.ac.uk/randkt/rktcentres/bfrc/bbp/events/Documents/Biobutanol.pdf

So if I might chime in here, the conclusion from this thread is that if you intend on "pootling" around with regular driving and sub 4k rev range, you're better of with 95 RON fuel because the mpg difference is negligible. However, if it's the performance at the top end you're after, go for the higher octane fuels. Is this about right?

Also, at the top of this page, how does a completely stock ford focus RS generate 450 HP?

The car will run fine on 95 i have to run it on this because i cannot get hold of anything else.

She still pulls well upto 120mph, economy is alright

Pulled plugs after 15000(ish) and very slight build up.

She seems to be a bit slow somedays but then otherdays she pulls like a train

So if I might chime in here, the conclusion from this thread is that if you intend on "pootling" around with regular driving and sub 4k rev range, you're better of with 95 RON fuel because the mpg difference is negligible. However, if it's the performance at the top end you're after, go for the higher octane fuels. Is this about right?

Also, at the top of this page, how does a completely stock ford focus RS generate 450 HP?

It doesn't develop 450 hp, it's 450 nm . The "lesser" one off the graphs is HP, the other one is NM .

So if I might chime in here, the conclusion from this thread is that if you intend on "pootling" around with regular driving and sub 4k rev range, you're better of with 95 RON fuel because the mpg difference is negligible. However, if it's the performance at the top end you're after, go for the higher octane fuels. Is this about right?

Also, at the top of this page, how does a completely stock ford focus RS generate 450 HP?

I found the economy advantage with VPower gave a marginal cost advantage over 95RON despite the higher price. So I exclusively use super unleaded now, taking into account the manufacturers recommendation too.

Running with 95RON doesn't save me money, as the MPG drops noticeably.

I mostly just pootle around too.

I agree with that teebs, I found 3mpg advantage under controlled test with super over 95

I agree with that teebs, I found 3mpg advantage under controlled test with super over 95

Yep I found price per mile is equal to or very slightly better on super. So may as well use it for all the other benefits (performance / cleaning properties / double Shell points etc)

'Tesco Momentum 99' might well give the same extra and costs 5 pence a litre less than Shell V Power Nitro.

I will always use it rather than Shell & would even if it cost the same as the Shell fuel.

(I do use it and will continue to since any problem with the wrong stuff in a Filling Station tanks and i will get better treatment from

Tesco than many get from Shell & Independent station owners.)

'Sainsburys Super Unleaded' works nicely instead of using 95 RON from other places and may not cost you any more.

Nectar Points with that & worth try it out and see how well the cars runs on it.

george

I work for a rival supermarket to tesco so don't want to give them more profit Also not sure they'd be impressed with all my business mile receipts being from a competitor, unfortunately my company doesn't offer super hence the use of shell.

I wonder if the accountants would rather have it as £2 less a tank for business miles being spent @ Tesco,

rather than Royal Dutch Shell profiting

on their over expensive (To cover advertising) fuel.

george

I must admit I never run my vRS on anything but TESCO's Momentum99. I will have to run a test with 4-6 tank fulls to see what the difference might be.

E5 paddy? is that the bio stuff? thats higher RON right?

Yeh E5 is 5% bio-ehtanol. According to the magic of the internet E10 is actually used as a substitute for lower OCtance (93RON or thereabouts?) though I may stand corrected. There are no quoted RON figures on the pumps at the E5 station which is annoying. As has been pointed out to me before it depends on the quality of the petrol to begin with, if it was 95 to start with, adding some ethanol would raise it up above the 95 mark, but it could be crap fuel before that and having just enough to bring it to 95RON. Does seem to help at te top end though, and yes economy isnt quite as good, but I can live with it. The manual says its approved to use E5 but not E10 I think.

Tesco's Momentum99 is an E5 fuel...

Tesco's Momentum99 is an E5 fuel...

Interesting... didn't know that! Its a shame they don't say on the pumps here what the Octane is, just guesswork really! Still, the trip this month to the UK will be a good chance to try proper fuels again :P

I wish we had fuels without that pathetic, lip service type of a token gesture of adding 5% of alcohol into the fuels. It is actualy detrimental to the environment as fuel economy suffers ...