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  • Exhaust Return

    Problem. I did the NA2T swap and couldn't clear the transmission with the pipe that runs from the downpipe to the AIV(?). What options do I have? The car runs, but it runs slightly rich and damn sure won't pass emissions. Let me know.

  • #2
    MaximumQ wrote: Problem. I did the NA2T swap and couldn't clear the transmission with the pipe that runs from the downpipe to the AIV(?). What options do I have? The car runs, but it runs slightly rich and damn sure won't pass emissions. Let me know.
    you will have to make a splice of somkind I would think. Maybe somone else has run into this but I think a splice would work fine, Not a lot of heat if you do it at least 18-24" away from the down pipe.
    85 Z31 6.0 LSX turbo 766whp/792wtq
    04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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    • #3
      aiv blows fresh air into the exhaust, as such it is only heated by the metal's conductivity, you'll find the tube doesn't get that hot far from the downpipe

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      • #4
        as Satan stated, you can either adapt a patch into the original AIV pipe to the AIV on your downpipe - you probably cut the AIV pipe fairly close to the downpipe though, in which case heat could be a continuous problem. My 86na had been patched with a heater hose (i kid you not). It worked fine, but once a year or so it would disintegrate and I would just stick another one on it.

        If your visual inspections for emissions are not too tough, you can delete the AIV altogether, just remove it and plug up the intake hose where it was plugged in. There are a couple ways to seal off the downpipe, best is to remove the AIV fitting and replace it with a plug. I have never seen anyone actually able to remove one of these as they are always rusted in severely. What most people end up doing is cutting off the AIV pipe about 3" from the down pipe then using a vice crush the AIV pipe closed, then fold it over a couple times on itself. This will seal it up nice and costs nothing. I have done this to a couple z's, mine included and have had no problems.
        "If you don't hold it....you don't own it"

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        • #5
          G-E wrote: aiv blows fresh air into the exhaust, as such it is only heated by the metal's conductivity, you'll find the tube doesn't get that hot far from the downpipe
          Right, thats why I was saying about 18" to 24" since thats roughly what they recomend doing if you are measuring exhaust pressure from manifolds. The 18-24 was just to be on the safe side.
          85 Z31 6.0 LSX turbo 766whp/792wtq
          04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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          • #6
            Couldn't he do what the earlier cars do and run a line from the intake to the aiv?

            Terrible idea putting those wheels on...

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            • #7
              MrwassmanNA2T wrote: Couldn't he do what the earlier cars do and run a line from the intake to the aiv?
              Huh? He still has to have the line from the aiv to the down pipe though. This was his problem. Unless he just deletes it all together.
              85 Z31 6.0 LSX turbo 766whp/792wtq
              04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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              • #8
                Can't delete it or plug it, since I still need to pass emissions.

                The visual inspection won't be too tough, but without the AIV connected, I'm a dead man at the smog test.

                Here's my idea, let me know what you think: The port on the downpipe is temp plugged, so I will permanently plug it, probably with a weld. I'll have a fitting screwed into the downpipe on the opposite side, and run a custom hardpipe (or the original, if it fits) up to the AIV the way it was supposed to be run.

                Let me know.

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                • #9
                  Hey, I am in L.A. also, but I don't register my car here

                  The AIV won't affect passing emissions. If they even look, as long as they see the AIV unit there and the pipe from up top, I think you are good to go. Just block it off at the downpipe and find some way to secure the hard pipe so its not flopping around.

                  Or just make a pipe like you said. I have another VG engined car that I do get smogged, and they look from the top for egr, pcv and evap can. The guy was cool and let me see exactly what he was looking for, he didn't even look at the AIV. The only time they looked under the car was to shoot the cat with the gun thing they use to measure the heat at the cat to prove its real/working. Then they just check that timing is relatively spec for the test and run it.
                  "If you don't hold it....you don't own it"

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                  • #10
                    AIV is just for warm up isn't it? If he just set it up the same as on my 85, wouldn't it pass? (Tubue right after maf, then it goes around the back of the plenum to the valve right?)

                    This thread is the first i heard of it being hooked to the downpipe. So i am assuming it uses the warm exhaust to help speed the warm up process up?


                    Terrible idea putting those wheels on...

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                    • #11
                      I put a question mark after AIV because there are two almost identical devices...I'm not sure that's where the hard line from the downpipe connects but I think it IS the AIV.

                      It's not the visual inspection that I'm worried about......I had a small emissions problem to begin with that I was addressing by replacing the catalytic converter. Now, my numbers are twice as bad with the AIV(?) hardline disconnected.

                      I'm trying to find a good time now to get the line installed, and unless someone has additional suggestions, will let you know how it turns out.

                      But apparently it's not just for warmup.....the car was well into operating temperature and still threw horrible numbers.

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                      • #12
                        I strongly doubt that your AIV is any cause of your problem passing. Post your test results and lets work from there. I assume you have done the most obvious (EGR) test prior to replacing the cat. The next thing to look at before replacing the cat is the o2 sensor and related systems. You seem to be on the ball so we are assuming you have checked your codes a long time ago to find any problems they may indicate and have a properly tuned and timed car. You can bench test your o2 sensor to see if it's working right using a meter, power source and propane torch.

                        Also, you are taking the car to the smog shop nice and hot right? Z31 are notorious for failing emission if you don't run it under load for a while prior to the test. If you just drop the car off overnight and they warm it up for a few minutes, it's not as likely that your cat will be fully functioning (hot) as it would be if someone drove it around for 20 minutes right before the test.
                        "If you don't hold it....you don't own it"

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                        • #13
                          Yes, car should pass without the aiv. There are tricks to make it pass, but we need to know what it is failing and by how much. So far, there has not been a car that I was not able to make it pass emmissions.
                          Chuck Stong
                          300+ Parts and Performance owner
                          http://www.300-plus.com
                          2002 ZCOT president and always active member

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                          • #14
                            I thought the only hard line was the EGR? Dude, if that is disconnected you will definetly fail.

                            Terrible idea putting those wheels on...

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                            • #15
                              MrwassmanNA2T wrote: I thought the only hard line was the EGR? Dude, if that is disconnected you will definetly fail.
                              Egr is not the only hardline. But not all cars have an aiv. Egr is the one that is on the passenger side exhaust manifold to the plenum and is short. The aiv hardline is much longer and runs under the engine from the exhaust to near the driver side headlight.
                              Chuck Stong
                              300+ Parts and Performance owner
                              http://www.300-plus.com
                              2002 ZCOT president and always active member

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