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Thread: DCOE jets/spares for dyno session

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    Bodger wxneypar's Avatar

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    DCOE jets/spares for dyno session

    Hi, good morning!

    I have a 1978 MK2 Escort Historic Racing Car (if you a curious, here's some onboard of the last free practice https://www.youtube.com/watch?v=CEn2sa1pinc)
    Currently the engine spec is:
    1600 Xflow
    40/34mm valves on stage 1 head
    10.5:1 CR
    Electronic ignition with custom springs and counterweights
    32/36 DGV
    4 into 1 manifold with short exhaust pipe (1.5meters, under driver door)
    Iskenderian Cam ( .387 VALVE LIFT----290 DEG ADVERTISED DURATION--252 DEG @ 050 DURATION ON A 108 LOBE CENTER)

    The engine is doing a good 112hp @710 0 RPM at the flywheel based on the last dyno session, but I need around 10hp more to get closer to the rest of the cars.
    So I build a pair of DCOE with this jetting: 32mm chokes, 125 mains, 180 air correctors, F11 tubes and 50f9 idles just to start with, and I'm planning on fitting them during this week and go to the dyno for the fine tuning.

    I'm used to tune the DGAV so I have spares for that carb, but not for the DCOE's.
    What should I buy to take with me to the session? Some smaller and bigger mains and air correctors is OK, or is there's something I'm missing? What do you DCOE guys use to carry with you to the dyno?
    Thanks in advance,
    Peter

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    Re: DCOE jets/spares for dyno session

    Just make sure the carbs are in good working order.
    Float levels set, needle valves not sticking, gaskets not leaking, synchronise carbs and take enough petrol with you.

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    Bodger wxneypar's Avatar

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    Re: DCOE jets/spares for dyno session

    Thank you! So beyond that, just taking a size more and and size less of mains and air correctors is a good guess or not?
    Or should I take even more jets?
    Thanks!

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    Re: DCOE jets/spares for dyno session

    Quote Originally Posted by wxneypar View Post
    Thank you! So beyond that, just taking a size more and and size less of mains and air correctors is a good guess or not?
    Or should I take even more jets?
    Thanks!
    you really should be going somewhere which has a stock of jets, as you could spend a fortune buying jets and still find you dont have what the engine wants

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    Bodger wxneypar's Avatar

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    Re: DCOE jets/spares for dyno session

    I would, but there are only 4 dyno's here in Uruguay, and none of them also sells carb spares.
    I have a pair of every main jet for the dgav from 130 to 170, but it is not that easy for the DCOE's and hence my question.
    How far off can my jetting be with that spec (I know it is a guess, and I am welcome to "guesstimate" answers)
    Thanks!

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    Re: DCOE jets/spares for dyno session

    Think your jetting will not be far of.
    Take 120, 130, 135 main jets, 170 and 160 air and F9 tubes.
    Idle jets can be more work to get right.
    On ebay there are sets of jets for sale especially put together for rolling road sessions or contact Anthony at Fastroadcars for jets and other spares.

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    Bodger wxneypar's Avatar

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    Re: DCOE jets/spares for dyno session

    That is great advice, exactly what I was looking for, thank you.
    One last question that is related and probably difficult to answer, what can I see on the dyno or afr readings that can tell me that the f11 are not right?
    Thanks again

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    Re: DCOE jets/spares for dyno session

    Dont bother buying lots of jets, buy jet drills,

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    Re: DCOE jets/spares for dyno session

    Quote Originally Posted by Erikmex View Post
    Dont bother buying lots of jets, buy jet drills,
    Couldn't disagree more !

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    Re: DCOE jets/spares for dyno session

    Why? you only need the middle size jets ie. the 0.05mm increments, you can start with a small jet and drill out in steps of 0.1mm easily, saves lots of money, even jets that are too large you just braze them up and re-drill, saves a fortune, ive been doing it for years with bike and car carbs.

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    Re: DCOE jets/spares for dyno session

    with drilling you ruin the venturi of the jet

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    Re: DCOE jets/spares for dyno session

    Seem to remember Dave Walker drilling jets years ago in CCC magazine.

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    DCOE jets/spares for dyno session

    Quote Originally Posted by daniele View Post
    with drilling you ruin the venturi of the jet
    That's the chokes.

    I think Leon's reasoning will be that you loose the accuracy of the original sets.


    Sent from my iPhone using Tapatalk

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    Re: DCOE jets/spares for dyno session

    Main jets, idle jets and air correctors are parallel, provided you drill them straight and accurately with jet drills there’s no issue, lots of people do it, when you buy the various sizes they are drilled anyway, no reason why you can’t do it yourself

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    Bodger wxneypar's Avatar

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    Re: DCOE jets/spares for dyno session

    I know lots of people who drill the jets while testing on the dyno and then buy new ones with the size they found work best.
    As I said yesterday, one last question that is related and probably difficult to answer, what can I see on the dyno or afr readings that can tell me that the f11 are not right?
    Cheers,
    Peter

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    Re: DCOE jets/spares for dyno session

    re the F11 tubes you wont see in with afr as such, but if you can only get the afr right at say medium or high revs the tubes are probably not suiting your setup

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    Re: DCOE jets/spares for dyno session

    Drilles jets are never the same, soldering them back up then drilling them again is alot of hassle, you can never rely on the engraved size and when you file the size off the jet you always have to check them again, and again ..
    If I come across a drilled jet I throw them away.
    With today's prices you can get a range of jets for almost nothing.

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    Re: DCOE jets/spares for dyno session

    It’s worked fine for me and when I check with jet pilots the drilled and new jets are always the same.

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    Re: DCOE jets/spares for dyno session

    i know in theory drilled jets are bad and may not flow exactly the same as a factory fresh jet, but my experience, it doesnt matter, if the engine gets the fuel it wants does not matter whether the jet is a 140 or really a 142. but i would go as far as to say i dont mix virgin and drilled jets, if i drill a jet i also grind the number off it

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    Bodger wxneypar's Avatar

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    Re: DCOE jets/spares for dyno session

    Thank you all, had my dyno session yesterday, and just had to increase the mains from 125 to 135 to get the AFR right, and for security ended up with 140 because the car is a race car and in the last races it tends to go leaner on circuit conditions than what it shows on the rolling road. Power Plot on the correct section of the forum

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    Re: DCOE jets/spares for dyno session

    What AFR did you aim for?

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    Re: DCOE jets/spares for dyno session

    Around 12

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    Re: DCOE jets/spares for dyno session

    Quote Originally Posted by wxneypar View Post
    Around 12
    That's quite rich for NA! Are you at altitude or near sea level? I know about rich dyno / lean track but a shift of 1-1.5 AFR points would be a lot.
    Track AFR for max power 13.5 - 13.2 IMO. From your other thread I know max power is not what you want but if the cam is working there the other option is down cam - improve the torque and run less revs but pull higher gears?

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    Bodger wxneypar's Avatar

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    Re: DCOE jets/spares for dyno session

    I will quote your reply on the other thread so we don't go off topic here, but let's follow up there cause I really like the discussion!

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