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Hello, 1951 Comet- and what are your suggestions for additives to the petrol ?

Philip Smith

Website User
VOC Member
For a 1951 Comet with BTH mag. what would you suggest as octane booster ? Where I am in Northern Ireland the petrol supply is limited to Octane 95, with ethanol at 5%- this will change to E10 in September. What brand of additive, and how much to add to the standard size of tank- 15 litres. To get 97 grade petrol is a 45- 50 mile round trip. Thank you.....
 

oexing

Well Known and Active Website User
VOC Member
Catalytic converters are not a big thing in classics and tax concerns should not be a point as avgas, at least in my country , is higher taxed than auto fuel. So the government would not be worse from having it in your classic - but it is not worth the effort mostly . . .
Ahmm, what´s alkylate ? You get this from the pharmacy ?

Vic
 

ClassicBiker

Well Known and Active Website User
VOC Member
I think a more interesting question is if E10 needs slightly larger main and pilot jets due to less energy content. Also corrosion problems and effect on rubber and plastic parts. My main concern about ethanol containing fuel is it's short service life. Petrol suppliers here says E5 95 has to be used in six months.
The ethanol free alkylate fuel (95 octane) I use for chain saws, lawn movers and the old sidevalve Norton is still usable after 5 years. The race bikes are fed with 98 octane alkylate, except the Manx which drinks 102 octane alkylate. The road bikes gets alkylate last two fillings before winter hibernation to prevent tanks from rusting.
Fuel stabilizer will extend shelf life to 24 months. You are correct, ethanol does contain less energy that gasoline, I think it is 1/3 less by volume. I haven't bothered changing the main or pilot because of 10% ethanol though. I can't speak to race bikes as I haven't any. My lawn mower gets fed 89 octane with stabilizer. I've had it for 20 years now.
Catalytic converters are not a big thing in classics and tax concerns should not be a point as avgas, at least in my country , is higher taxed than auto fuel. So the government would not be worse from having it in your classic - but it is not worth the effort mostly . . .
Ahmm, what´s alkylate ? You get this from the pharmacy ?

Vic
Avgas doesn't have state level road tax here, just sales tax and doesn't have as high of a federal tax as fuel sold for bikes and cars. So the gov't doesn't like it when it lands up in cars and bikes, particularly new ones that have catalytic converters. Just like fuel sold at boat docks isn't supposed to put in cars and bikes here. Different tax rate, it's much lower. It's called recgas, for recreational gas, it's only to be used in off road applications.
 

vibrac

Well Known and Active Website User
VOC Member
My strimmer drove me mad until I bought some Aspen 2 stroke works a treat I would but Aspen 4 stroke for the racer and hang the price but its low (ish) octane
What we need is a simple device for reducing ethanol content in 10% petrol perhaps add water,agitate and pump into your tank via a centrifuge spin from a pump as the SG would then be wildly different
 

Mike 40M

Well Known and Active Website User
VOC Member
Here in Sweden, Aspen 4 (95RON) is £2/litre, Aspen+ (98RON) is £3 and Aspen R (102RON) is £3.40
Sadly it seems you've only got the low octane grade in the UK.
Edit: Seems + and R is sold in Germany too.
 
Last edited:

LoneStar

Well Known and Active Website User
VOC Member
Here in Sweden, Aspen 4 (95RON) is £2/litre, Aspen+ (98RON) is £3 and Aspen R (102RON) is £3.40
Sadly it seems you've only got the low octane grade in the UK.

US premium is 93 octane at best, which sounds sad but the metric is R+M/2 (research and motor octane ratings). Per Wikipedia, "Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON". So US premium would have an RON rating, as used in Europe, of c. 98 - middle of the Swedish pack.

On the bright side, here in Texas premium fuel can be had for around $3.50 per US gallon; doing the conversions, about £.67/liter.
 

Martyn Goodwin

Well Known and Active Website User
VOC Member
US premium is 93 octane at best, which sounds sad but the metric is R+M/2 (research and motor octane ratings). Per Wikipedia, "Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON". So US premium would have an RON rating, as used in Europe, of c. 98 - middle of the Swedish pack.

On the bright side, here in Texas premium fuel can be had for around $3.50 per US gallon; doing the conversions, about £.67/liter.
Cripes - today in Melbourne, Australia 91 octane is A$1.70 per litre, 98 octane is A$2.05 per litre!
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
For a 1951 Comet with BTH mag. what would you suggest as octane booster ? Where I am in Northern Ireland the petrol supply is limited to Octane 95, with ethanol at 5%- this will change to E10 in September. What brand of additive, and how much to add to the standard size of tank- 15 litres. To get 97 grade petrol is a 45- 50 mile round trip. Thank you.....
Dear Phillip,
Why do you want an octane booster?
Are you getting pinking with your Comet as if the engine is standard the state of tune is quite low and most Vincent engines should not have trouble running on the premium fuel? I always use the cheapest fuel (albeit in Rapide twin) and it runs fine. It has the BT-H magneto fitted and previously had 7:1 pistons and following a rebore now 8:1.
What is the specification of your engine? With more information forum members will be able to better answer your question.
 

Martyn Goodwin

Well Known and Active Website User
VOC Member
sounds like your ignition is way too advanced. Forget what the 70 year old riders handbook or the 60 year old KTB says. With a Vincent in bog standard state with todays excuse for petrol you want no more full advance than 34 degrees before top dead centre. I find that 31 is ideal.

Give it a try, you may be pleasantly surprised
 

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