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Thread: 505 turbo

  1. #1
    Fellow Frogger! 505 to the max's Avatar
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    Default 505 turbo

    The motor in my GTi turbo is getting a little bit smokey on start up. It had the head reconditioned including new valve stem seals about 18 months ago (covered about 20 000k's since) and the smoke tends to diminish once the motor gets up to operating temp. It has only 'breather' type filters on the tappet cover, all factory ventilation has been removed. Does anyone know if this would be causing a build up of oil vapour under the tappet cover, forcing it to pass by the valve stems and into the motor?
    I am also looking into rebuilding it in the not too distant future. Any ideas on replacement pistons which would be better suited to boost than the OEM items (ZDJL motor), as I intend to ditch the T25 for something in the 250 - 300hp range so the motor will need some work...
    PM me if you are trying to sell a GT25 or T28.
    Chris.

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  2. #2
    Contented Peugeot Driver addo's Avatar
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    Isn't it possible to fit some form of PCV? You might get better ring seal when it's up to temp, too. What made you discard it (crankcase evacuation) to start with?

    Adam.

  3. #3
    Fellow Frogger! 505 to the max's Avatar
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    Default 505

    When I dropped the motor in (it's a GR body) I 'simplified' it to reduce engine bay clutter, which didn't seem a problem at the time as I switched to an aftermarket ECU. Also because it's got positive manifold pressure (see also boost) I had nowhere to run a vacuum line from the tappet/rocker cover (until recently it had a pod filter straight off the front of the turbo). The biggest 'sticking point' i've realised since noticing the smoke on start up is that the hose going from the block just above the sump on the dist. side to the rocker cover is no longer fitted. Is this the absent hose which may be causing problems? I'm guessing that this hose vents crankcase pressure and is supposed to be vented into the top of the motor, and subsequently released through the inlet setup? Is this correct?
    Any ideas on pistons anyone?
    Please keep the advice coming, it's very much appreciated!

  4. #4
    Contented Peugeot Driver addo's Avatar
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    You'll always have the opportunity for vacuum between the filter and the compressor wheel.

    Vacuum pumps are common on some high-performance motors, and drag cars use the scavenging effect of their tuned extractors to suck crankcase gases out (looks weird to see the exhaust plumbed up to the crankcase but it's totally proven).

    Not familiar with the hose you describe but it sounds like fitting it back would be one good step, then plumbing with a well-baffled PCV to the inlet side of your turbo. Or do the bong-style PCV/inlet hookup where there's an intermediate canister that traps a modest amount of inducted oil vapour.

    As a result of plumbing in the crankcase gases, you'll possibly show rich on the AF meter and need to tweak the tune a little.

    Pistons - hypereutectics are generally the way to go (good enough for the current Falcon turbo and that has some stick) but not sure if ACL do a set. If your bore wear is within spec, could always look at the rings. Many people are using old tech ideas and new rings; the result is they aren't bedding (smoke and indifferent performance are two outcomes). ACL have a good part in their PDF on pistons/rings/liners catalogue about break-in for new bores and rings. Worth a read if you can stand the catalogue download time.

    Regards, Adam.

  5. #5
    Fellow Frogger! 505 to the max's Avatar
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    Default 505

    Is a bong-style PCV the same principle as a catch can? I have a catch can which I bought ages ago but shoved it under a pile of old parts and forgot about it until I went digging last week. Any ideas on how it's meant to be fitted? It's got two hose connections and a threaded plug (I assume that's so you can empty oil from it), all on the upper part of the cannister. I was never sure of what was supposed connect to which breather/vacuum lines, or weather it was meant to vent back into the induction setup.
    Any links for potential piston manufacturers?

  6. #6
    Contented Peugeot Driver addo's Avatar
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    Bong-style trap is the same deal. Basically this catch can will do it for you in conjunction with the PCV. If it has a threaded plug or tap fitting one end, this is for draining and normally goes downwards. The hoses go in the top. Because it breaks continuity of airflow, it's a chance for some of the oil to condense in the canister.

    The PCV has a weak spring closing a ball or shuttle valve - the vacuum overpowers its spring and then airflow keeps it open. As I mentioned - you need to baffle it or there is a good chance of snorting up too much oil mist and messing up the intakes. The rocker cover is probably baffled anyhow.

    No recommendations on the pistons, I'm sorry. ACL don't do them (odd, since they do a few Renault parts) and my French is too limited to surf the country of origin. Try one thing at a time, though - you may need nothing besides crankcase evacuation, or only a ring job.

    Cheers, Adam.

  7. #7
    Fellow Frogger! 505 to the max's Avatar
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    Thanks for the advice Addo. I intend to freshen up the motor regardless of the outcome of PCV experimentation due to wanting more power from a bigger, more efficient turbo. At present the T25 is working fairly hard to provide a decent torque curve. Awesome midrange but it runs out just short of 5000rpm. With a bigger turbo I think that 150rwkw is quite easy (currently peaking at 150rwhp on 8 psi @ 4600rpm).
    This will mean more boost so improved pistons, or OEM pistons (somehow treated for additional strength) are a must as I don't want to mince the internals.
    I'll do some searching and let you know how I go.
    Chris.

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