How much Compression for turbo
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  1. #1
    Tadpole Gonzo404's Avatar
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    Icon5 How much Compression for turbo

    Hi everyone,

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    I've done a few things on my peugeot 404, i've modified the camshaft, polished ports, a twin 36mm weber carburettor, but right now Im triying to put a turbo on my 404, i've already got the turbo (garret T25) and the intercooler (of some chevrolet diesel pickup), but the problem is that all the mechanics i've asked have very different views on how much compression ratio should be lowered, some say i don't need to lower it, other say that i've got to lower it more, so i was wondering if anyone know how much it should be lowered. the compression ratio is now about 7.6:1 (original). And if so, how can i do it.

    Thank you all
    Gonzo

  2. #2
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    Quote Originally Posted by Gonzo404
    Hi everyone,

    I've done a few things on my peugeot 404, i've modified the camshaft, polished ports, a twin 36mm weber carburettor, but right now Im triying to put a turbo on my 404, i've already got the turbo (garret T25) and the intercooler (of some chevrolet diesel pickup), but the problem is that all the mechanics i've asked have very different views on how much compression ratio should be lowered, some say i don't need to lower it, other say that i've got to lower it more, so i was wondering if anyone know how much it should be lowered. the compression ratio is now about 7.6:1 (original). And if so, how can i do it.

    Thank you all
    Gonzo
    What octane fuel do you have in your country?
    7.6 to 1 sounds fine unless you can't get 95 to 98 RON fuel.
    To lower the compression machine the tops of the pistons.
    Graham

  3. #3
    Tadpole Gonzo404's Avatar
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    Here you can find 87-92 RON fuels.
    How much can i machine from the top of the pistons, for not leaving them too weak?.
    Last edited by Gonzo404; 27th April 2005 at 02:54 PM.
    Peugeot 404
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  4. #4
    1000+ Posts alan moore's Avatar
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    Given only 92 RON fuel, I would leave the compression standard and only run a moderate 7 Pounds or 0.5 Bar of boost. The intercooler will certainly help. Are you fuel injecting the motor, or doing a blow through carburettor job?
    '56 Renault 750 (16TS Power)
    '62 Renault Dauphine Gordini
    '89 Renault Alpine GTA V6 Turbo
    '08 Renault Megane sedan

  5. #5
    Tadpole Gonzo404's Avatar
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    Sorry for the avobe, here you can get higher RON fuels, the gas dealer near my house told me that the gas they sell is 95 RON.
    I think that would help.
    Im doing it with the carburettor a twin Weber 36mm. I've been told it's very good for turbo applications.

    And another cuestion, can i put more boost in case I go to the dragway? how much will it be "safe boost" with avgas (130 RON)?

    Thank you all
    Peugeot 404
    It's Hard to make a good pug here.
    Colombia Rules
    Gonzo404

  6. #6
    1000+ Posts alan moore's Avatar
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    When you do a blow through on the Weber you need to use plastic floats as the brass ones will crush. With 95 RON fuel and standard compression 10 pounds would be plenty, although when on boost you really need to have a system of reducing the ignition advance, or suffer poor performance when not on boost if the ignition is specifically set up for boost.

    Avgas 100/130 is actually only about 107 octane and certainly will reduce the detonation, but to change over to it for drag racing would also require more ignition advance, as its' flame front burns slower, or of course you can add more boost, but I think I would be worried about what standard pistons and such can take before destruction, in such an old style engine.
    '56 Renault 750 (16TS Power)
    '62 Renault Dauphine Gordini
    '89 Renault Alpine GTA V6 Turbo
    '08 Renault Megane sedan

  7. #7
    Tadpole Gonzo404's Avatar
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    Thanks Alan,

    You've been very helpful, wich system can i use for reducing the ignition advance?
    and can i get the plastic floats for te weber in a store, or do i have to get it made?

    Thanks
    Peugeot 404
    It's Hard to make a good pug here.
    Colombia Rules
    Gonzo404

  8. #8
    1000+ Posts alan moore's Avatar
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    The distributors for this have a diaphragm on the side a bit like a vacuum advance but made to work both ways. Just try out what what you have got and see how you go. At lower amounts of boost the floats may be fine.

    The blow through single barrel carb (Solex?) that is used on the Renault 5 Turbo front wheel drive, would set up and work much nicer than a carb not built for boost.
    '56 Renault 750 (16TS Power)
    '62 Renault Dauphine Gordini
    '89 Renault Alpine GTA V6 Turbo
    '08 Renault Megane sedan

  9. #9
    Tadpole Gonzo404's Avatar
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    Oh, i tought that vaccum only worked one way.

    I still have got mi old single barrel (solex) carb, But i don't know the measurements, would that one work fine?

    Thanks
    Peugeot 404
    It's Hard to make a good pug here.
    Colombia Rules
    Gonzo404

  10. #10
    1000+ Posts alan moore's Avatar
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    The device on the distributor I was talking of, gives advance with vacuum and retard with boost. The R5 Turbo Solex I mentioned is special. The Fuego Turbo has a similar carb. Most standard type carbs do not like to have boost applied to them. These Solexes should be available quite cheaply off old Renault 5 turbos from England

    Modification like this is always going to be difficult, and costly unless you can do it yourself. Maybe you are taking too big a step.

    A 504 2 Litre motor modified would give adequate power in a 404, a lot easier than trying your turbo experiment, and you can build it while still driving your car, with your current engine.
    '56 Renault 750 (16TS Power)
    '62 Renault Dauphine Gordini
    '89 Renault Alpine GTA V6 Turbo
    '08 Renault Megane sedan

  11. #11
    Tadpole
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    Some A##hole in south australia got my brothers 2.2 set up for turbo, including turbo and gas-research throttle body which would suit you perfectly.
    If you could get him to the pay the $1000.00 he owes my brother - after 4 months of excuses, then you could buy it off him.

  12. #12
    Fellow Frogger! jarrods's Avatar
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    Another thing worth considering is lack of parts available for 404 motors. It might be worth putting the effort into a 2L motor as parts are still available. If you start to push the boundarys you will end up breaking something sooner or later. Power is very addictive and people always look for more. Everyone I know that has undertaken projects such as this has had a few failures. The only way of potentially avoiding this is to buy a complete setup from someone that has been tried and tested (and don't change anything). Unfortunately setups like this are few and far between.

    Good luck

    Jarrod

  13. #13
    Tadpole Gonzo404's Avatar
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    Oh, i wish i coud get the 2L engine but here those engines parts are as same as hard to get as mine, so it wouldn't be a lot of change to be done here.

    And about the mod i'm going to do it myself, i know it's a big step but i like the challenge.

    Sorry 'bout the "vaccum" in last thread, the thing is that here it's called that way.

    What i'm worried about now is the diaphragm, then how can i manage the advance of the ignition?

    And i've seen a lot of these weber in turbo setups, and the owners told me they worked great, i think the solex setup is very hard to be done beacuse of the shipping cost from there, and here i'm sure i won't find it. But anyway i'm going to look for it nearby.

    Thanks
    Peugeot 404
    It's Hard to make a good pug here.
    Colombia Rules
    Gonzo404

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