XN modifications
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  1. #1
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    XN modifications

    I know someone has posted the answer to this question before--but my search has found nothing...

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    With 8.8:1 pistons, what would the compression ratio of an XN be if the head was shaved a max safe amount. And, what is a max safe amount of material to remove? Shop manual says 6 thousandths I think--is this a good number or is Peugeot playing it safe?

    I saw a pic on Dave's site of a 504 TN motor--those long header tubes got my imagination going, again. I go through an XN-tuning phase every year or so...

    -Joe

  2. #2
    Guru davemcbean's Avatar
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    Joe,

    The shop manual plays it very safe. I know of heads with 0.060" shaved off which brings the compression up to around 10:1, in conjunction with 8.8:1 pistons.

    From my calculations, each millimeter (0.040") off the head raises the compression by approx 0.8 of a ratio point.

    I have a head lying in my fathers shed, which has spacers between the rocker gear and the head. The spacers would be to allow standard length pushrods to be used on a head with alot of material shaved off it (you can run out of tappet adjustment otherwise). I have encountered one engine where the tappets used to hit the rocker cover. It was an XM (1796cc) with a very shaved XC (1618cc)head and rocker cover. I put the XM rocker cover on and it was OK. So I assume there must have been a slight difference in the depth of the covers. This would be something to watch out for with a shaved head and a wilder cam. The best policy in that case would be to shorten the pushrods or custom make some pushrods. I know of people who have custom made pushrods for their 504 engines from titanium rod.

    Dave
    NZ Fleet
    1976 504 Ti
    1984 205 GT twin carb
    1991 205 SI 1.6GTI motor
    1994 106 Xsi
    1996 Mondeo V6
    Aus Fleet
    1955 203C
    1997 Civic Cxi (great allrounder- revy, flexible, nimble, comfortable , economical, simple and durable )

  3. #3
    Guru davemcbean's Avatar
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    I forgot to mention that shaving 0.060" off the head seems to work OK with standard pushrods and no spacers under the rocker gear (I know of one or two engines like this). This leads me to assume that if you fit the spacers (or shorten the pushrods) you can shave quite a bit more off. There certainly appears to be plenty of material there to machine. Beyond a certain point you would find that the grinding stone hits the inlet valve seat insert (or the valve, if it's in place). This may mean the valve seat has to be cut back further, which would reduce the tension on the valve spring. This would mean that a spacer under the spring would probably be a good idea. The heal of the valve would also have to be ground a little (or alternatively you could shorten the pushrods further).

    Dave
    NZ Fleet
    1976 504 Ti
    1984 205 GT twin carb
    1991 205 SI 1.6GTI motor
    1994 106 Xsi
    1996 Mondeo V6
    Aus Fleet
    1955 203C
    1997 Civic Cxi (great allrounder- revy, flexible, nimble, comfortable , economical, simple and durable )

  4. #4
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    Watch the rocker angle, however. As the rocker moves in the arc, when the valve is open the rocker will put more side force on the valve.
    Doug

  5. #5
    Guru davemcbean's Avatar
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    Doug,

    Very true. That is an important consideration, especially for a performance engine.

    This means that shortening the pushrods would be the best policy, rather than spacers under the rocker gear. If the inlet valves are seated in further then it would probably be best to take some material off the heal of the valves AND shorten the pushrods slightly, to maintain the correct angle geometry on the rockers.

    Dave
    NZ Fleet
    1976 504 Ti
    1984 205 GT twin carb
    1991 205 SI 1.6GTI motor
    1994 106 Xsi
    1996 Mondeo V6
    Aus Fleet
    1955 203C
    1997 Civic Cxi (great allrounder- revy, flexible, nimble, comfortable , economical, simple and durable )

  6. #6
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    Okay... Sweet!

    Here's another inquiry. Does anyone have any good specs on the Australian spec XN6? I wonder if it was identical to the US spec version.

    More obscure a question, does anyone know which air flow sensor the Australian XN6 used (60 or 80mm)?

    For the record, the US spec car had 8.35:1 compression and used a 60mm air flow sensor. We also had the 4-2-1 type manifold but the twin downpipes are pretty short--like 25cm maybe.

    It'd be great if you guys had 80mm air flow sensors, 8.8:1 pistons, and a different exhaust setup--it would be less work for me to just use those parts instead of adapting and experimenting, if you know what I mean...

    -Joe

  7. #7
    1000+ Posts Rod Hagen's Avatar
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    Don't have the other specs to hand Joe, but the Australian XN6 (1986 and 1987 models) had an 8.35:1 compression ration too.

    Emission control equipment fitted as standard includes:

    over-run emission control
    vacuum advance over-run solenoid
    lambda sensor & cat

    It was installed primarily to meet the need for an engine that would meet the then new Australian unleaded petrol requirements.

    The full engine designation is 136Y (XN6)

    One of the interesting things about the Australian 1986 / 1987 SLi wagons is that most I have seen have a French body build date of 1985, but Australian compliance plates of 86 or 87.

    Cheers

    Rod

    [ 22 January 2002: Message edited by: Rod Hagen ]</p>
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