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Thread: removing smog, need assistance

  1. #1
    Formerly known as Koalia Reverend's Avatar
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    Default removing smog, need assistance

    My friend has a 1973 240Z with smog equipment, and he decieded to get rid of it. I just wonder what is the purpose of these pipes, my -72 does not have them. One goes to heater hose that comes from manifold and other goes to exhaust manifold?? Is there any grand purpose for these items, will they affect on anything if removed? We are planning to put E41 balance tube (euro) but it seems we have to modify the throttle lever as well..



    btw. what is that small pipe that attachs to brake booster outlet?
    -72 240Z "Goldie"

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    Boat Anchor Repairman Captain Obvious's Avatar
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    That's the EGR control valve. (EGR started in 73 which is why your 72 didn't have this device.)

    The purpose of the EGR system is to reduce oxides of nitrogen (NOx) from being released into the atmosphere which is a good think for the next generation.

    There isn't really any performance reason to remove it. It's only active at light cruise and is disabled at higher throttle positions. Looks better without it, but no reason to do so for performance.

    I'm assuming he's still running the original carbs? Because if not, I'm not sure where he's going to hook up the ported control vacuum signal...

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    Formerly known as Koalia Reverend's Avatar
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    He has similar-ish carbs as i did in my 72, "regular" SU's. Yeah it will look way better without all those. So we'll just have to find a proper plugs for the exhaust manifold outlet and water hose. Ported control vacuum? is it the small black hose in the picture? Whats the purpose of it?


    Just realised that its the choke wire... lol. Too long since i had SU's..
    Last edited by Reverend; 10-21-2014 at 10:28 PM.
    -72 240Z "Goldie"

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    Boat Anchor Repairman Captain Obvious's Avatar
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    I can't see the control signal tubing at all. I suspect it's been removed and disabled ever since he swapped in the older SU's.

    There is a vacuum port on the original rear flat top carb that is a ported signal. "Ported" such that there is no vacuum at idle or at WOT but only at a point between the two at "light cruise". That signal is what was originally used to control the amount of EGR.

    The round top SU's have no such vacuum connection on them at all, so I assume that control line is simply capped off rendering the whole EGR system inert.

    There's a small electric solenoid valve between the EGR control valve and the valve cover. Can't see it in your pic because it's tucked behind the device you were curious about. That's also part of the system.

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    Registered User Stanley's Avatar
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    "what is that small pipe that attachs to brake booster outlet?"

    That goes to the AT modulator. You need that for the AT to function properly. There's another short curved hose that connects the steel pipe to the trans. It can slip off the modulator when the brake booster fitting is removed. I'd replace that short hose - a newer piece of vac hose is less likely to come off. Much easier when the car is on a rack or ramps.

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    Formerly known as Koalia Reverend's Avatar
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    BTW is there any proper way to get that air galley off the exhaust manifold?
    -72 240Z "Goldie"

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    Registered User LeonV's Avatar
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    Quote Originally Posted by Reverend View Post
    BTW is there any proper way to get that air galley off the exhaust manifold?
    I've done it and it wasn't easy. I ended up drilling out a couple of fittings to get the job done but it worked out in the end. Soak the fittings in good rust penetrant and use flare wrenches so you don't round them off. You may get lucky and have them all pop loose.
    2/74 260Z

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