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Thread: NA Cosworth 12.5:1 pistons - what fuel?

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    Spanner Monkey glenn666's Avatar

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    NA Cosworth 12.5:1 pistons - what fuel?

    I have a fairly mildly tuned N/A YB here using Wossner 12.5:1 pistons. The heads been ported and is running Newman cams but otherwise the engine is mostly standard.

    It wouldn't start on ordinary fuel and I've been told to run race fuel mix in it. It runs OK on the race fuel mix but is there any possibility of safely tuning it to run on road fuel? It's on 45 DCOEs if that makes any difference.

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    Running super unleaded may be possible with a shed load of reduced timing. What you need is octane and pump piss just don't have enough. You could use aviation gas which is either unleaded or low lead and 100+ octane but not really convenient on a road trip LOL! Whatever you use, the timing will need setting for the fuel - a decompression plate may be a better option?

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    whether its on low octane, super unleaded race or rocket fuel, it should still start, theres something else wrong other than fuel quality

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    Spanner Monkey glenn666's Avatar

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    Appreciate the replies lads. Do you think with carbs jetted to suit & timing adjusted correctly, would it be safe to run on super & octane booster maybe?

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    i would of thought so

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    i run an n/a engine with a 12.5-1 cr and i run shells V-Power Nitro+ as that is what i mapped the car to. i have done loads of track days and road mileage in the car and it is great. it doesn't like 'lesser' fuels at all which is a shame as v power costs a bomb. But if you want the full bang lout of an engine you have to run decent fuel. I could have went down the octane booster route as well but cost would start getting out of hand then.

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    If the engine won't start on normal pump then there's something fundamentally wrong. Start with checking fuel, spark and ignition timing before going out and buying expensive high octane fuel. We ran these type of engines in the late 80's and early 90's and they were one of the best starting engines we have had. You have a problem somewhere and it's not the grade of your fuel.

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    Quote Originally Posted by Forest_rallying View Post
    If the engine won't start on normal pump then there's something fundamentally wrong. Start with checking fuel, spark and ignition timing before going out and buying expensive high octane fuel. We ran these type of engines in the late 80's and early 90's and they were one of the best starting engines we have had. You have a problem somewhere and it's not the grade of your fuel.
    spot on, you just said it better than i did

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    Spanner Monkey glenn666's Avatar

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    Quote Originally Posted by freddy686868 View Post
    i run an n/a engine with a 12.5-1 cr and i run shells V-Power Nitro+ as that is what i mapped the car to. i have done loads of track days and road mileage in the car and it is great. it doesn't like 'lesser' fuels at all which is a shame as v power costs a bomb. But if you want the full bang lout of an engine you have to run decent fuel. I could have went down the octane booster route as well but cost would start getting out of hand then.
    There is no fuel available in Ireland apart from standard pump fuel unfortunately.


    Thanks for the info lads. I did talk to one well renowned tuner over here who said it wouldn't be possible to run on road fuel but I will have a look around see if I can find anyone more capable or interested in sorting it out.

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    Quote Originally Posted by glenn666 View Post
    There is no fuel available in Ireland apart from standard pump fuel unfortunately.


    Thanks for the info lads. I did talk to one well renowned tuner over here who said it wouldn't be possible to run on road fuel but I will have a look around see if I can find anyone more capable or interested in sorting it out.
    damn that's a shame. what about a 75% road fuel to 25% race fuel? one of the boys just bought a stage car from Ireland and is running that in his.

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    it wouldnt be that difficult to machine a bit off the pistons to drop the compression, and/or simply use a thick head gasket
    Last edited by Graham; 18-05-2017 at 19:25.

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    also have a cossy N/A, run on wossner, 98 octane belgian fuel, mapped for that. No issue.
    Not used for competition, so not really need V-power or something like that, plus don't want to bring such fuel from Germany !

    Engine was mapped before for 99 UK fuel, and started with our bad belgian fuel. The ignition timing was reduced from UK map to use our fuel when rebuild occured.
    Last edited by Mkdu; 18-05-2017 at 20:35.

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    Re: NA Cosworth 12.5:1 pistons - what fuel?

    When I go to Ireland I run std unleaded with a bottle of Millers Oils CVL Turbo in every jerry can (20l)
    This is on a N/A cossie with 12:1 compression

    In the UK I use Shell V-Power
    GavinR

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