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Mostly Harmless
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Discussion Starter #1
I'm starting this just to avoid further cluttering invert's GB thread.

...and advance warning: I'm a newb to the whole IRTB game, so you've been forewarned.

In said thread, there are several mentions of IRTB setups simply not being able to pass smog. Yes, they require plenty of accurate tuning. Yes, they require some tinkering, resyncing, etc. What would keep such a setup from passing a smog test? Is this strictly in reference to a visual inspection in Cali or other such states...or is there something in the basic setup of these that totally screws us as related to emissions?

I simply don't get how, in TX for example, simply changing the method of intake would so drastically alter the exhaust gases that our locals couldn't pass a sniffer test on an inspection dyno. This really just sounds dumb to me considering those cars that have them stock, as well as those on this site with Fuji, Aizawa or other kits.

Granted, that might just be because I don't have such a setup, haven't looked into the tuning methods, etc. But would someone please be kind enough to spell it out to me? I want to know if I'd just be wasting $$ fitting these bits to my '90 (no EGR anyway) or '94 only to later find that "won't pass smog" really means the emissions are gonna kill me come inspection time.
 

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If there is no visual inspection in Texas, which I assume there still isn't, you may be able to pass. The issue is less of the ITB's and more of the motor's internals and tune. Typically one who has ITB's also has higher compression pistons, larger cams, etc. I would imagine a stock motor and ITB's would pass with a good tune, but do you really want a stock or stockish motor and ITB's?
 

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Garage Quinn Motors - GQM
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2,847 Posts
I'm starting this just to avoid further cluttering invert's GB thread.

...and advance warning: I'm a newb to the whole IRTB game, so you've been forewarned.

In said thread, there are several mentions of IRTB setups simply not being able to pass smog. Yes, they require plenty of accurate tuning. Yes, they require some tinkering, resyncing, etc. What would keep such a setup from passing a smog test? Is this strictly in reference to a visual inspection in Cali or other such states...or is there something in the basic setup of these that totally screws us as related to emissions?

I simply don't get how, in TX for example, simply changing the method of intake would so drastically alter the exhaust gases that our locals couldn't pass a sniffer test on an inspection dyno. This really just sounds dumb to me considering those cars that have them stock, as well as those on this site with Fuji, Aizawa or other kits.

Granted, that might just be because I don't have such a setup, haven't looked into the tuning methods, etc. But would someone please be kind enough to spell it out to me? I want to know if I'd just be wasting $$ fitting these bits to my '90 (no EGR anyway) or '94 only to later find that "won't pass smog" really means the emissions are gonna kill me come inspection time.
I can't speak for much on your state's visible inspection, as CT only looks for a catalytic converter. There seems to be a lot of misconceptions about ITB's. First, not all ITB's require synching and fiddling. TWM's units come pre-synchronized from the factory and all linkages are torqued. If for some reason they are changed, TWM will re-synch them for free. Also, I have travelled through various elevations since my car was tuned and have not noticed any difference in performance or driveability.

Unless your state has some sort of visible inspection for the engine, then ITB's will not immediately disqualify you. If your Miata is a 90-95, then it is OBD-I. All you need is a catalytic converter and a tune that you can load onto the ECU for emissions. This is what I do for my turbocharged 91 running a Megasquirt PNP. If your Miata is a 96+, then you have OBD-II, which is a whole other ball park. OBD-II vehicles are tested via the OBD-II port, not by using the sniffer test for the older cars. The reason that ITB's will disqualify you is because you are removing the MAF sensor, you replace the stock TPS with the TPS for the ITB manifold, the EGR is completely eliminated, and because you need to run a standalone ECU. Therefore, when they plug into the OBD-II port nothing is going to happen. The stock ECU can't run the car without the MAF or an aftermarket TPS. No EGR will throw check engine lights that will most likely cause a failure also.

Since both of your cars in questions are OBD-I. You will have no issues passing the sniffer test for emissions with a cat and an emissions map. That is all. Run a standalone ECU and feel free to remove / change whatever sensors you want, build your engine to whatever spec you want, etc. You just have to find out what your state's requirements are for visible inspection.

I hope this helps clear up some of the confusion and will eliminate some of the false bullshit that is strewn around the internet.
 

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Mostly Harmless
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Discussion Starter #4
Thank you for the input guys! Very helpful info.

Quinn, given that you have ITBs on your '99, your thoughts are definitely what I was looking to read. Thank you again.
But given my current car situation, I'd likely end up with said setup on the '94. grrrr
Need to chat with Travis @ Boundary to see if I can swap my 90-93 Adaptronic harness for a 94-95 version. Might serve me better.

I have more reading and selling to do.
 

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Steve, in a couple years the "90 can be tagged as an antique.
No emissions, in fact, No inspection at all.
That opens up so many possibilities for the early Miata owners.
 

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Mostly Harmless
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Discussion Starter #6
Oooh, good call, Stevan! Thank you for that reminder. 25 years, right?
Is it the antique or classic tag that restricts the annual mileage?

...and I will see you on Saturday, good sir. :)
 

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Antique, but no one checks.
Classic is unrestricted but also has inspections.
I'm not sure about emissions though, mine have always been to old for emissions.
 

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brontosaurus
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If you dont have visual, and can pass with a standalone, you should be fine with itbs for smog. Its all in the tune at this point. Standalones do not have oboII ports so if you need one come smog time you are SOL. Hopefully you have an awesome tune. I'd imagine getting the idle values right will be the toughest part while under the sniffer.
 

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Mostly Harmless
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Discussion Starter #9
Our sniffer tests consist of 15mph and 25mph runs at a given rpm (range) for some set amount of time. As such, I'd guess idle values wouldn't be of much concern.
 

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Premium Member
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I've only just started having issues passing emissions this year in GA. Previous 4 years passed either on the first try or on a retry after pulling some timing.

It really helps to have a competent tuner work with the car for a bit to get things dialed in. You can save yourself some time by getting a good baseline tune made up before you get on the rollers so they can jump right in. Having a wideband is key here as it will not only let you tune the car yourself much easier but also give feedback to your ECU to let it make small adjustments on the fly based on your AFR readings.
 

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If it's not a strange question (or hasn't been answered before), why do the standalone ecu manufacturers not supply a unit with an OBD II port so then it just becomes a tune issue?
 

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brontosaurus
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If it's not a strange question (or hasn't been answered before), why do the standalone ecu manufacturers not supply a unit with an OBD II port so then it just becomes a tune issue?
Probably development costs. Its one thing to make a new harness for every application, it would be a huge project to make every standalone act like the oem ECU. Probably wouldnt be much of a market for a $4,000+ ecu. I guess if you wired a standalone in parallel, you might be able to get around this issue, if you could find a way to not trigger a cel.

A couple companies offer reflashes of the stock ecu, but that wont help in the case of itbs since the method of air metering is totally different.
 

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I went to get a smog test and failed. Ill post up my numbers once I get the chance. The tech said a new catalytic is the culprit. Is there a difference between a $150 catalytic or $250? Can I just get whatever cheap one I can find?
 

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Google me.
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I can pass OBD2 with my ITB rig, as far as the plug-in and cat in place rules go. Since I use MAF and the stock ECU this is much easier.
 
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