What fuel for 2CV's?
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    1000+ Posts Bad Bertie's Avatar
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    Default What fuel for 2CV's?

    I now have a early 425 CC 2CV, and one with the 602 cc engine. What is really the best fuel?

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    1000+ Posts Bad Bertie's Avatar
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    Quote Originally Posted by Bad Bertie View Post
    I now have a early 425 CC 2CV, and one with the 602 cc engine. What is really the best fuel?
    Also, My D special will be going on the road soon, fuel suggestion?

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    98 Octane. Preferably from BP or Shell.

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    If you don't have hardened valve seats then consider the use of a "lead replacement" valve seat protection additive like FlashLube (which has an additional merit of being an upper cylinder lubricant).

    Rule of thumb with older engines which don't have knock sensors & computer adjusted timing to accommodate various fuel RON grades is to use the lowest grade fuel which will not knock (lour grades are more energy dense). With most old motors the compression ratio is under 9.5:1 which is about where 98 becomes a good idea.

    If you do use 91 (compression ratio under 8:1 with an old tech motor) then I'd recommend using a fuel system cleaner each service as 91 will create deports on the back of the inlet valves.

    cheers! Peter
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    JBN
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    For the 602 (compression ratio 8.5:1 or 9.0:1) use 98 RON. The 425 (compression ratio 7.5:1) use 91 RON. These are Haynes minimum recommendations, so 98 for either would be OK. On Raids, you use whatever petrol you can get, which is often 91.

    John
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    Hi Bert, I have always used 95 or 98. It goes fine on 95.
    I have never put 91 in but a lady who purchased one that lives up my way (Joe S's old Red one) put 91 in and the car stalled, refused to start and needed to be towed. It started at one point whole engine shuddering, spluttering and shaking. That was at a get together for 2cv folk on the northern beaches.
    Stick with the good fuel. I would assume same for D. Chris M
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    From BP, approx figures for carby engines:
    Highest
    useful
    compression
    ratio

    BP Regular Unleaded 91 8.5 - 9
    BP Regular Unleaded with 10% ethanol (e10) 93 9
    BP Premium Unleaded 95 9 - 9.5
    BP Ultimate 99 9.5-10

    url for source:
    https://www.bp.com/content/dam/bp-co...tane-power.pdf
    Last edited by 4cvg; 9th October 2017 at 11:34 PM.
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    Bertie,
    for what it's worth I run my three Classics on BP Ultimate exclusively. The Mini because I'm running 10.5:1 compression, the 2CV and D-Special because I reckon they benefit from the hotter burning fuel. Just my theory.

    It's entirely possible I'm the (un)witting victim of good marketing of course!

    The limited use these cars get well offsets the extra cost of the 98 octane.

    Cheers, Pottsy (and glad the D is hitting the road)
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    Thank you all guys for your helpful advice.

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    Having been on several raids and only getting 91 octane in the outback the 2cv runs well on 91
    However the higher the octane the better it runs
    I used to buy 100 octane from united and made the 2cv notably more agile



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    avgas!

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    I always thought that higher octagon fuels burned slower and cooler than lower octagon fuels, with the temperature of the burn less critical than the pressure and duration of that pressure on the top of the piston. I understand that temperature and pressure are related of course.
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    But for the 2 CV I reckon you'd get by with lawn mower fuel.

    The good stuff but...
    Daily Drivers: R10, R12, R17T(?) Decouvrable

    In the Shed(s):
    R8 (1.4 motor, 4 shock rear end), Dauphine, Pugeot 404

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    Default High octane fuel !

    Quote Originally Posted by Exfrogger View Post
    I always thought that higher octagon fuels burned slower and cooler than lower octagon fuels, with the temperature of the burn less critical than the pressure and duration of that pressure on the top of the piston. I understand that temperature and pressure are related of course.
    Hi
    I think you people are too influenced by random thoughts bought on by advertising !! Mostly the petrol is just--well --petrol. A mixture of random decomposed trees and stuff. It burns when the spark goes off, hopefully, and if the design and compression ratio is not too high it just burns till it is all gone. If the octane rating is not high enough it pre-ignites and pings or worse and the effect is wasted from there or worse. Why is it hotter or cooler when it burns BS I would say. Slower or faster BS mostly.

    Back in the "good o'l days" when fuel was sourced from different oil fields for the inherent high octane types there may have been differences but now it is just a matter of the chemist tipping in a can of 'stuff' every tanker load.

    If the woman down the street put in 91 and it refused to go then the fuel was crap and the 91 octane had nothing to do with it. It is true that the 95 & 98 should have a better additive package to help with keeping the system cleaner. Part justification for charging so much more than 91, part marketing to get punter to part with more money.

    Years ago I drove an old Toyota Hiace to Darwin and back. It was a leaded engine so needed a higher octane fuel. I set the timing appropriately for the unleaded fuel here. But when fueling up on the long road trip I often had to reset the timing to accomodate the crap fuel i was given sometimes. But i usually put it back again to get the best economy. My BX did the same thing sometimes. The computer has a knock sensor to do the same thing in new cars.
    Cheers Jaahn
    Last edited by jaahn; 11th October 2017 at 09:47 AM.
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    I acknowledge that my choice may well be a result of effective advertsing (and visualise ponytailed onanistic advertisers high fiving each other! ) but it's also sort of based on experience.

    My Mini has a highly strung engine which gets temperamental if not fed with a preferred diet. Part of this is because of the state of tune of course, so it's my fault, but there's nothing much better to bring a smile to the dial than a squirt in a hot Mini. But I digress. I mention the Mini because of an experience with it a few years ago.

    In 2009 I drove it to Sydney to take part in celebrations of the 50 years the Mini has been sold in Australia. I thought I'd run it on the good stuff as droning up the Hume for such an engine is hard work of a different sort. So I religiously only used Shell V-Power for the trip up the map.

    I battled with overheating all the way! After doing all the usual things such as checking fan slippage, removing any and all obstacles to the air flow, even playing with timing a tad, the temperature still sat steadfastly on the scary side of 95 degrees celsius wherever I went.

    After a few days of this I sort of accepted it, until, heading for a fun day at Mt Panorama I filled up with BP Ultimate as a matter of convenience. My passenger that day commented that I shouldn't be using V-power anyway as it was unsuitable for my motor, burns much hotter and would cause it to overheat! He's a factory trained ex BMC mechanic, so I tend to listen to him.

    We drove the car all day at some blistering speeds, including some legal laps of the Mountain, and the temperature stayed under 90. Filling up in Bathurst I decided to test the premise with another tank of Shell and it promptly tried hard to boil the kettle all the way back into Sydney. Theory looking good I reckoned.

    Subsequent tanks of Ultimate saw me back to Melbourne with it hardly raising a sweat, so the empirical finding was that V-Power burned "too hot" for my motor. At the time I was running a bored and stroked motor of 1098cc. I now run a bored 998cc based motor of 1070cc and it runs cool on an exclusive diet of Ultimate. Both engines in a similar state of tune with over 10:1 compression, big valves, lumpy cams and the same twin SU's and extractors.

    OK, my reasons may or may not be sound, and also may or may not be a result of brain washing, but I stick to my premise anyway.

    Such is the stubborn nature of a petrol head.

    Cheers, Pottsy.
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    The Fleet:

    2006 307 Auto 5 Door ("Spike" Mrs P's)
    1974 D Special Manual Sedan ("Moby Dick")
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    1957 Slough 2CV ("Alphonse") Waiting in the wings
    1982 ex UK 2CV6 ("Gaston") On the road! (Woohoo!)
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    JBN
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    I have grave doubts that there is much difference between brands for their equivalent octane ratings. There are no petrol refineries in Sydney anymore as the fuel comes direct from Singapore. I think most difference is in advertising, not what goes in the tank.

    If you want to drive a 2CV the way it should be driven - flat out, then I would use 98 by choice. On long trips, I don't worry about the brand of petrol, I am influenced by the position of the fuel gauge needle.

    I wouldn't mind a bit of avgas. Used to use that in a VW Beetle with dome topped pistons that pinged at the drop of a hat. The best part about avgas is the smell.

    John

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    I think there's more to it than advertising.

    Not it sure you'd want to fly your Cessna from Bathurst to Melbourne on 91 octane fuel.
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    JBN
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    Quote Originally Posted by Exfrogger View Post
    I think there's more to it than advertising.

    Not it sure you'd want to fly your Cessna from Bathurst to Melbourne on 91 octane fuel.
    No, I would use avgas. I flew a Cessna 172 from Albion Park (near Wollongong, my home airport) to Bathurst, Orange, Cowra, Canberra and back to Albion Park on one of my navigation flights to gain my unrestricted PPL.

    From memory (circa 1963) I could get Shell A Racing fluid and some Total equivalent. One was about 145 octane, the other was about 115. I think I used 100 octane mix above 3,000 ft (I lived at Walcha) and 115 at sea level. That VW engine was crap. It started off life as a 1200cc and ended up with 1500 barrels and domed top 1500 S pistons. I think it was around 9.5:1 compression. Dual throat Solex carb. Very expensive on fuel to stop the engine pinging. The stupidity of youth. Once I stopped buying VWs, I started to enjoy cars. I have always wondered why the RAF bombed Berlin where the people lived rather than Wolfburg where the VW factory was. I hope I am safe making that comment on a French car forum as we were on the same side.

    John

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    Fellow Frogger! driven's Avatar
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    Octane and BURN temperature
    As always as good as many
    Octane 101: Autogas vs. avgas | AviationPros.com

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    I know a guy who was in the RAAF in the seventies, he's a mechanic now and he reckons that they knew who was pinching the avgas as the culprits car engines tended to blow up! Might have been connected to driving styles too I guess
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    driven,
    Mr. Szymanski looked to be doing fine until that last sentence, I reckon, when he should have used 'autoignition', rather than simply 'ignition'.

    "Many people think high-octane gasoline is more powerful than low octane gasoline. This is not true. The energy produced from a gallon of high and low octane gasoline is almost the same. Any minor variation depends on what additives are used by refiners and blenders. The key features of high-octane gasoline are a higher ignition temperature and a slower burning rate."


    As regards flame propagation speeds/burning rates, here's what Bruce Hamilton had to say on this topic, back in 1999.
    ( Full text here... Engine knock (Bruce Hamilton) )

    >> Eric Lucas <[email protected]> wrote: The octane number is related to how fast a flame front propagates through the air/fuel mixture.
    From: [email protected] (Bruce Hamilton) Newsgroups: sci.chem Subject: Re: Super Unleaded Petrol Date: Sun, 13 Jun 1999 16:48:10 +1300
    >> No it is not. It is related to the ability of the unburnt end gases ( the hot, turbulent fuel/air mixture that hasn't yet seen the flame front, even though the spark has fired ) to resist autoignition under the conditions in the rating engine.
    .

    Also, later in the same response to Eric...

    "The stoichiometric flame speeds of hydrocarbons under identical conditions don't vary very
    much between similar sized members of the groups found in petrol, such as alkanes, hence flame
    speeds aren't a major parameter for hydrocarbon-air octane ratings."


    Quote Originally Posted by driven View Post
    Octane and BURN temperature
    As always as good as many
    Octane 101: Autogas vs. avgas | AviationPros.com
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    John,
    Australia and Blighty use the same system for octane rating, (RON, or Research Octane Number), so it may be worth commenting that I've found 8.5:1 engines ( and even those with 9.0:1 CR) will run just fine on 95 octane, with a couple of provisos.

    1. The maximum ignition advance should be no more than 34* ( equivalent to just less than 8 flywheel teeth before the static timing point set by Citroen)

    2. With unleaded fuels containing ethanol, it's essential that the carburettor is rejetted to compensate for the 'leaning' effect of the ethanol and other additives which may contain oxygenates.
    For the final version of the 26/35 Solex (with 18 & 26mm venturis) used in A series vehicles and with our current 5% maximum ethanol content, replacing the original 102.5 primary petrol jet with a 107 works with 'normal' induction.
    'Blown' induction, as fitted to Dyanes and Amis, needs the primary petrol jet taking out to 110 for that carb.

    9.0 engines need 98 octane to cope with 34* total ignition advance, but won't lose too much 'go' if the total advance is reduced to 31* when run on 95 octane.
    I've just given the 250,000 mile engine in my old Dyane a rest, after 21 years hard labour and a strict diet of 95 octane.

    As for 91 octane fuel with up to 10% ethanol, you have my deepest sympathy...


    p.s. Re. that reference to flywheel teeth and ignition timing, this may make things clearer.
    https://www.flickr.com/photos/301328...etaken-friend/



    Quote Originally Posted by JBN View Post
    For the 602 (compression ratio 8.5:1 or 9.0:1) use 98 RON. The 425 (compression ratio 7.5:1) use 91 RON. These are Haynes minimum recommendations, so 98 for either would be OK. On Raids, you use whatever petrol you can get, which is often 91.

    John

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    Until the last post (#22), I was wondering why no-one seemed to be commenting on the dreaded ethanol... That I do avoid like the plague.

    I use 91 octane in the Renault 4CV (who knows, it might run on kero when hot), an indisciplined 95 or 98 in the R8 and 98 in the CX. All seem fine. Of course, the R8 presumably spent most of its life on 91 or 95 and has never either overheated nor complained. I guess no-one would call any of those engines highly tuned, although sophisticated enough in their day.
    JohnW

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    Hi JohnW
    My advice is to avoid E10 "like the plague" if you have an old car. You will not know what problems will come up till they do
    I was in PNG in the '80s and cleaned carbys till the gaskets fell apart because of the problems caused when they introduced some locally grown ethanol into the fuel. It cleaned out all the crap in the tanks and storage and ?? and it ended up in the carbys. Also the jelly deposits from the high humidity and water. No thanks not going there again. It eats the brass bits as well and some hoses and diaphrams fall apart !
    Be OK in new cars if they are on the list perhaps but why bother .
    Jaahn
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    JBN
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    Quote Originally Posted by forumnoreason View Post
    I know a guy who was in the RAAF in the seventies, he's a mechanic now and he reckons that they knew who was pinching the avgas as the culprits car engines tended to blow up! Might have been connected to driving styles too I guess
    Remember avgas doesn't contain lead, so it would have been like feeding engines designed for leaded petrol without the vitamins.

    John

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