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Thread: A poser for the turbo experts...

  1. #21
    Guest EvilScotsman's Avatar
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    lol, im pissed too but never too pissed for physics haha

    Interesting point tho eh?

    I think the extra fuel is un-needed, hence a fuelling computer fixes the problem, that shouldnt exist in the first place, cos some tech at nissan decided it would be better to add fuel when the throttle shuts, for air that hasnt gone into the engine yet.......
    Last edited by EvilScotsman; 03-01-2010 at 22:02.

  2. #22
    South West Rep Evilchap's Avatar
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    Scottish person, having a rant, getting backs up and recently registed? Maddog isn't back is he?

    I do not really grasp this arguement. I see where you're coming from, but the experience and sound reasoning of everybody here, including somebody with a gauge that tells them what's going on, is saying one thing, and you're still going the other way?

    I hope you've changed your fuel pump and not got any boost leaks, as they're the next two favourite issues of people fairly new to the 200

  3. #23
    Guest EvilScotsman's Avatar
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    Nothing wrong with being Scottish, and its a scientific discussion, not a rant. Its only a rant of you completely misunderstand the others intentions.

    And no, ive not changed my fuel pump, why should i have? and no, I dont have any boost leaks.

    I might be new to the 200, but I've had plenty of turbo cars and im not a noob in the traditional sense, if thats what your getting at.

    Riled englishman there i think

    And i have no idea who maddog is, but it was a genuine discussion.

  4. #24
    South West Rep Evilchap's Avatar
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    Boost leaks and fuel pump failures are the next 2 most common questions after DV discussions for people new to 200s. If you dont believe me, scroll through S14 tech and you'll see something about 1 of the 3 on every page

    I wasn't having a go, well, wasn't meaning to, I just must have (mis)read your posts as a bit of a rant against the norm.

    Maddog was somebody who liked to argue really a lot, and was from North of the border. I did not mean to stereotype

  5. #25
    Guest EvilScotsman's Avatar
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    ok fair enough mate

    Nah, I was just questioning the rightness of how harmfull it is to use a VTA DV on the SR20DET motor, nothing else.

    Honestly, I am a professional engineer in the plant industry, I have designed many things which still work to this day, including disc turbine sludge pumps, automatic safety systems, GPS & Gyro combined steering systems for rocket motors, gas turbines, and the rest.

    I do not subscribe to the belief that if the DV is missing, the resultant overfuelling is harmful. End of.

  6. #26
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    Its nice to see someone trying to talk facts and physics. There is soo much hear-say on here that its refreshing to read something different.

    As you say when the throttle is closed then the air isn't going to enter the engine anyhow and any fuel thats going to be injected will do so no matter where its vented to. One thing that has come up on here though is does the air back-out through the AFM with no DV?

    Maybe we're looking at this wrong though, maybe its not the instant that you close the throttle thats made richer, but the point in which you open it again? If the ECU expects the intake pipework to be full of oxygen then surely its possible that the fuel will be injected too early/much.

    And something else to consider is the throttle body doesn't seal the intake off. So not ALL the air would be pushed away and under compression I would have thought that a fair amount of air would be pushed through?

    Bit of a random post but just typed as the thoughts come to my mind

  7. #27
    South West Rep Evilchap's Avatar
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    I think depending on the extent of it of course, there are worries of bore wash, which is harmful I believe.

    It's also wasteful and inefficient, which some people dont like, but others find the flames cool, and like the extra pops and bangs, and the hiss on gearchange, so fit VTA DVs for that reason.

    It's personal preference really, but has been shown over and over that recirc is the best option if you're running a MAF. If you're on a MAP sensor then it wont be an issue, but that's a story for another thread

  8. #28
    Guest clive's Avatar
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    Quote Originally Posted by EvilScotsman View Post
    Nothing wrong with being Scottish, and its a scientific discussion, not a rant. Its only a rant of you completely misunderstand the others intentions.

    And no, ive not changed my fuel pump, why should i have? and no, I dont have any boost leaks.

    I might be new to the 200, but I've had plenty of turbo cars and im not a noob in the traditional sense, if thats what your getting at.

    Riled englishman there i think

    And i have no idea who maddog is, but it was a genuine discussion.
    because it will fail soon for sure

  9. #29
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    Just fit MAP engine management then it won't matter a **** anyway

  10. #30
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    Quote Originally Posted by drifter View Post
    Just fit MAP engine management then it won't matter a **** anyway
    d-jetro power fc ftw

  11. #31
    Guest EvilScotsman's Avatar
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    Dan-T - Very good post and spot on mate.

    The pressure on the closed throttle plate is still boost yeah, but just like when your cold tap is shut at the sink, the pressure is still there, but there is no flow.

    Idle air is a tiny amount - just enough to prevent stall, and due to closed loop operation when warm, never exceeds stoich ratio.

    You have the gist of my argument there on the button. How and when is fuel added for this extra small volume of air in bypass? Likely when the throttle next opens....but, what if its switched off with no further throttle movement? Does the ecu chuck that extra fuel in next time you start the car?

    Its a tiny burst of extra fuel for a few miliseconds between gears.

    Hardly borewash.

    And unless you have a chinese turbo made of chocolate, a bit of extra resistance is nothing. Manufacturers didnt want people saying "whats that weird noise it makes?" LOL

  12. #32
    Banned sideways14a's Avatar
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    I dont get how this is still going on, it doesnt matter where the air goes when the throttle shuts except for the fact most of it doesnt reach the combustion chambers where the ecu has already asked the injectors to put fuel in for...

    Its also not great for your Cat if you still have one, all that unburnt fuel and explosions generated give the kitties a good all kicking so not a good idea.

    VTA dv's are for chavs, they attract attention for the "look at me" crowd and on the SR at least do little to improve (but plenty to fk up) the running of the engine.

    Also if you dont see the need to replace a fuel pump on the sx (especially if its modded) then you have not read enough posts on this forum.. They are a liability even when standard on stock cars.

  13. #33
    Guest EvilScotsman's Avatar
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    If its circulating round the bypass path how can extra fuel be injected till the air is actually sucked into the engine to be used???

    Why would the engine inject fuel into the cylinder for air thats still not been drawn in yet????

    It cant reach the cylinders if the throttle is shut!

    It can only run rich for a split second on next throttle opening until it catches up with the next analogue scan of the maf input.
    Last edited by EvilScotsman; 03-01-2010 at 22:35.

  14. #34
    Guest clive's Avatar
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    Quote Originally Posted by EvilScotsman View Post
    If its circulating round the bypass path how can extra fuel be injected till the air is actually sucked into the engine to be used???

    Why would the engine inject fuel into the cylinder for air thats still not been drawn in yet????

    It cant reach the cylinders if the throttle is shut!
    right im out

  15. #35
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    Quote Originally Posted by Sideways14a View Post
    I dont get how this is still going on, it doesnt matter where the air goes when the throttle shuts except for the fact most of it doesnt reach the combustion chambers where the ecu has already asked the injectors to put fuel in for...
    Exactly... so why has the ECU Injecting this fuel?

  16. #36
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    BTW... do look at getting a fuel pump ready for a spare though. I've had two just die on me in the past in two different cars.

  17. #37
    Banned sideways14a's Avatar
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    Help..ma...bob...

    The ecu instructs the injectors to open at enough duty to send in fuel that the AFM registered away back when it metered it.
    The air doesnt go in but the fuel does....because the afm told it to when the air was sucked in at first..

  18. #38
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    So what happens differently when its re-circed to when its vented?

  19. #39
    Guest EvilScotsman's Avatar
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    So it would run rich on the recirc dv if that was the case! Think about what your saying.



    The air doesnt go in but the fuel does
    So the extra fuel goes in anyway, even if the air it was metered for is stuck outside in the bypass pipe???

    Or just vented to atmosphere...

    When the throttle shuts, the ecu should know it is shut. And drop to idle fuelling.

    The ecu decides fuelling based on load, and air mass. And 10:1 is only 2% more fuel by mass than perfect stoichometric ratio, well 1.9% to be exact, check the figures anywhere you like.

    Bring the maths!

    And before anyone says its lower than 10:1 in reality, 1:1 is 50% fuel, 50% air.

    So even 5:1 would be just 20% more fuel than perfect burn ratio, and extra fuel is just used up as coolant, since vapourisation occurs beyond 70oC in petrol, causing a drop in enthalpic energy in the hydrocarbon mix. Saturation occurs around 51% fuel to air by mass.

    If you disagree, post the maths to prove it, instead of blindly believing what has been said before.

    Post what percentage of fuel to air ratio by mass causes borewash or any other problems.

    And never mind fuel pump problems or boost leaks, we are talking about normal operation
    Last edited by EvilScotsman; 03-01-2010 at 23:01.

  20. #40
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    tell you what.... anyone got a bit of pipe about 1m in length with a I/D of 28mm they want to lend me...

    ill do a video of my afr gauge with my HKS ssqv (yeap im a " gav"... still admit it over fuels like a bitch on lift off)

    i will put this pipe on along with my stock dv (modified ) and do an after video....

    think it will solve this for once and for all!!!!!!!!!
    Last edited by Clive; 03-01-2010 at 22:48.

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