Lotus Elan

99 Octane fuel

PostPost by: david.g.chapman » Thu May 03, 2018 3:37 pm

I thought this was a thing of the past and the best you could get in the UK was 97 Octane, but I noticed that Tesco sell something called "Momentum 99".

Maybe I am the only one who does not know about it - but I thought I would post it anyway.

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PostPost by: Maulden7 » Thu May 03, 2018 4:22 pm

All the main UK suppliers sell "super" - high RON - petrol, but the Tesco Momentum blend contains 9% ethanol (most of the others contain 5% or none at all)

Some rubber & plastic parts in the fuel systems of older cars do not respond well to continued exposure to high levels of ethanol, but there are additives that can be used to minimise this detrioration. Ethanol also absorbs water, & with low mileage cars fuel tank corrosion can occur.

The FBHVC web site is a good source of reliable information regarding this subject & the following link is a good summary of the potential issues :-

http://www.joc.org.uk/images/forum/Etha ... ummary.pdf
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PostPost by: david.g.chapman » Thu May 03, 2018 5:54 pm

Thanks for that Maulden,

My fuel lines and fuel tank should be ethanol proof - I have lined the tank with POR-15 tank sealer, and use R9 rated fuel pipes. However I am not so sure about components in my Stromberg carbs.

Further digging on the internet suggests that Shell V-Power is a better bet. It also has a RON of 99 and is supposed to clean the engine better than Momentum, according to internet chit-chat.

There is a Shell garage near me so I might go there. No Tesco clubcard points though :(

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PostPost by: elanman999 » Thu May 03, 2018 8:21 pm

From the Tesco web site:-
"Under UK legislation large fuel producers have a mandatory obligation to use a certain percentage of fuel from renewable sources. The renewable fuel used in petrol is ethanol, typically produced from sugar or starch crops such as sugar cane and maize. Dependent on location and supplier, UK petrol contains between 0 and 5 percent ethanol (produced in compliance to BS EN 288:2012)."
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PostPost by: Maulden7 » Fri May 04, 2018 8:23 am

A recent statement issued by Tesco in response to an enquiry states that their Momentum fuel contains 9% ethanol (made up of two different ethanol type chemicals)

As far as I am aware (from info published by the FBHVC some time ago) the 5% limit applies to 97 RON fuel, but there is no such comparable figure for 99 RON fuel. The suppliers are wanting to raise this limit to 10% for all fuels (as is allowed on mainland Europe where pumps are marked E5 & E10 with all the higher RON fuels I have found being served from pumps marked E10) & the Tesco "super" petrol has had ethanol content around this level for some time

The FBHVC research also found that 99 RON fuel from different suppliers also contained different levels of ethanol, ranging from zero to 9%. There was also some indication that regional variations also occurred, & that the ethanol content of the same brand varied from place to place

Personally I've stuck to the Shell high RON petrol (now called V Power - was Optimax) as far as possible in my Elan (with no special mods to anything in the fuel system) plus the occasional tank of the BP equivalent, & with no adverse effects so far (I do add an octane booster - Millers CVL - but this has no ethanol protecting properties)

From a friend who works for Ford on engine development, they are already developing engines designed to work at an E20 limit - it is coming!
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PostPost by: jono » Fri May 04, 2018 11:53 am

...just filled up my Subaru Legacy with Momentum 99 this morning and it now has a hesitation at low RPM.

They are known to be octane sensitive but I'd expected better running not worse.

I definately won't be trying any in the Elan!

Shell V Power next time.
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PostPost by: nmauduit » Fri May 04, 2018 12:04 pm

jono wrote:...just filled up my Subaru Legacy with Momentum 99 this morning and it now has a hesitation at low RPM.

They are known to be octane sensitive but I'd expected better running not worse.

I definately won't be trying any in the Elan!

Shell V Power next time.


octane ratio is one thing (esp. if one's engine CR makes it prone to detonation - and methanol content does increase octane ratio as it ignites less easily, which incidentally favors its use in dragsters with huge CR) but there are other dimensions characterizing a fuel for a given carbs settings - methanol burning energy is lower than that of gasoline for instance...
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PostPost by: rgh0 » Fri May 04, 2018 12:06 pm

It will be retuning itself to the different fuel density..... give it a day or two to get itself right assuming the change is within the range of adjustment the fuel injection system can handle which it should be if its a post 2000 car.

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PostPost by: Stevie-Heathie » Sat May 05, 2018 6:28 am

The Pistonheads forums seem to conclude that Shell V Power is the UK’s Petrol of choice for performance cars.
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PostPost by: richardcox_lotus » Sat May 05, 2018 7:24 am

How much of a timing change is recommended if moving from 97 octane to 99?
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PostPost by: nomad » Sat May 05, 2018 3:09 pm

Here in the states there has been soooo much misinformation concerning ethanol blended fuel over the years.

First of all, blended fuels affinity for water is a good thing. Unless there is too much water in your system the water will be combined with your fuel and carried out of the system. In the cold climate I live in we used to have to add a product called Heet to our gas every fall to get the water out of our tanks and lines. If we didn't the chance of gas line freeze up was a very dangerous likely hood. No longer necessary with blended fuel.

A note of caution....It will tend to clean out your fuel system and plug fuel filters when you first start using it.

Also, please avoid the snake oil salesmen that will want to sell you what ever they can concerning ethanol fuel.

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PostPost by: denicholls2 » Mon May 07, 2018 4:05 pm

Certainly not snake oil based on my own experience, both with small (snowblower, lawnmower) engines and (Vintage Honda) motorcycle engines. With high-alcohol fuels you can expect:

    - Dramatically more tar buildup inside the carburetor
    - Severe shrinkage of any "rubber" components inside the carburetor, including O rings, fuel shutoff valve seal, float seals. A carb may work OK as it sits, but these components are not reusable once you take it apart. (and in my world, a lot of them are really hard to find replacements for).
    - Greater presence of rust within all interior fuel system components.
    - Washing loose of 'dormant' rust particles in the gas tank.

Had I a reasonable choice, I would not use modern fuels in a vintage engine. Yes, most of these issues have solutions, but generally speaking, the vintage parts market has not yet moved to make them available to owners.
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PostPost by: nomad » Tue May 08, 2018 5:29 am

Ahhh, the debate could begin but I'm not getting involved! :D

I'm just saying avoid all the additives that are supposed to save your engine and fuel system from certain destruction caused by blended fuels. IMO they aren't that bad.

In the early days of conveyances powered by internal combustion engines ethyl alcohol was a major competitor with gasoline for fuel.

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PostPost by: USA64 » Tue May 08, 2018 12:46 pm

My old SU book has a table for methanol use. Twice as much is needed so the needles are sized differently. I wonder if the blended makes the engine run lean? That is of course the idea, to avoid HC emissions but the CD run rich normally. USA engines, back when one tuned them, were leaned out until a misfire then backed up a turn. CD carbs were just the opposite, rich until miss then back. I suspect that and things like -backward- cylinder numbering, and earthing wires caused much of the reputation.
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