Catalytic Converter for THDP and ATR Exhaust

[mgmshar]

Need some help from those in the know...

I just moved back to Indiana after spending 14 years in Michigan. One of the downsides is that Lake County, IN requires emissions testing. My car have never had a catalytic converter on it, so now it's time to install one.

The car currently has a 3" THDP, a cut-out pipe that's about 12" long, and an ATR 2.5" stainless steel exhaust. I need a converter that will fit in place of the cut-out. So, it needs to have a 3" inlet, an outlet that will fit the ATR system, and be about 12" long. If I remember, the ATR flange that bolts to the converter is the same as the stock flange.

Does anyone know of someone selling a converter that will fit? Vendor, board member, whatever.

EDIT: Since Indiana checks for NOX, it would be better if the converter has a three-way catalyst, not a two-way catalyst.

Thanks,

 

[johnplogii]

I have one that came with the Terry Houston downpipe when I bought it. I did run it for a couple hundred miles. $50 plus freight if you want it.

 

[83ttypecooled]

converter

Hi,
That's a great price the guy offered you,I'd accept that deal. The aftermarket converters are not all that great,and fail with regularity under duress,but what the hey! It should get you emissions legal, anyway.

 

[mgmshar]

I have one that came with the Terry Houston downpipe when I bought it. I did run it for a couple hundred miles. $50 plus freight if you want it.

Can you confirm if it's a two-way or three-way cat? If it's a three-way, I'll take it.

Let me know. Thanks!

 

[johnplogii]

What's the difference? I don't know anything about catalytic converters.

 

[Roc87]

That's a GREAT price for a cat with the 4 bolt flange that should allow you to bolt it right in regardless of 2 or 3 way. I ordered one from Reds a few years ago that was about $150, Pretty sure it's a 2 way, It has passed emissions every time by a good margin for NOX. Just drive it a bit before having it tested to make sure cat is up on temp, and use an emissions chip for that day you have to pass.

 

[TurboDave]

Can you confirm if it's a two-way or three-way cat? If it's a three-way, I'll take it.

Let me know. Thanks!

A three way cat uses air injection. Our cars do not have that provision so why require three way?

 

[johnplogii]

Well, mine does have an extra port on the side that is capped off. Don't think about it too long or I will just take it to the scrappers, It is worth that much or more for the platinum in it.

 

[mgmshar]

John: Sent you a PM.

Others: Three-way cats do not necessarily have air injection. Air injection was used on older cars to help get the cat up to temperature more quickly. All modern cars have three-way cats, but practically none of them have a cat with air injection.

Below is the best description I've seen for the difference between a two-way and three-way cat. The big difference: three-way cats help control NOx in addition to unburnt hydrocarbons and carbon monoxide.

Reference: Wikipedia.com (this description is accurate)...

Two-way
A two-way catalytic converter has two simultaneous tasks:

Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
Oxidation of unburnt hydrocarbons (unburnt and partially-burnt fuel) to carbon dioxide and water: CxH2x+2 + [(3x+1)/2] O2 → xCO2 + (x+1) H2O (a combustion reaction)
This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. They were also used on spark ignition (gasoline) engines in USA market automobiles through 1981, when the two-way converter's inability to control NOx led to its supersession by three-way converters.

Three-way
Since 1981, three-way catalytic converters have been used in vehicle emission control systems in North America and many other countries on roadgoing vehicles. A three-way catalytic converter has three simultaneous tasks:

Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2
Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + [(3x+1)/2]O2 → xCO2 + (x+1)H2O

Thanks Again,

 

[TurboDave]

Learn something new every day!! :biggrin:

And simultaniously answered your own question. Must be a three way.

 

[mgmshar]

Learn something new every day!! :biggrin:

And simultaniously answered your own question. Must be a three way.

...not necessarily. According to my research, the catalytic converters that were originally sold with the THDP's were found to be two-way catalysts. Many of the aftermarket cats out there are two-way. So, you don't really know unless you can contact the source, or if the person who originally purchased it remembers what it is.

 

[TurboDave]

...not necessarily. According to my research, the catalytic converters that were originally sold with the THDP's were found to be two-way catalysts. Many of the aftermarket cats out there are two-way. So, you don't really know unless you can contact the source, or if the person who originally purchased it remembers what it is.

Interesting.....

I can add however, that I have one of those THDP cats, and had to use it when I was in CA to get through their smog checks, which as many may know are some of the tightest in the country. It must be a 3 way because it got me through several years of CA smog checks.

 

[mgmshar]

It's hard to say for sure what the story on the THDP cats are. I can only go by what others were saying. Maybe both two-ways and three-ways were offered, depending on who sold the DP and when.

One thing about NOx - it forms during the combustion event right at the moment of highest peak temperature and pressure. So, the higher your compression ratio and the more vigorous the combustion, the more NOx will form. That is why EGR (Exhaust Gas Recirculation) is used on most engines (but not all in today's world). Exhaust gas is "inert", meaning it doesn't have the ability to burn (since it already burned once). So, if you mix exhaust gas back into the cylinders through the intake manifold, the peak combustion temperature will be lower. Thus, less NOx is formed during combustion. The whole purpose of the EGR valve is to control the amount of exhaust gas going back into the intake manifold. In simplest terms, you want zero EGR at idle (to prevent misfires), you want more and more EGR as you increase the throttle, but then you want to go back to zero EGR at full throttle (to maximize power). So, at part throttle, say when you are cruising down the highway, the percentage of exhaust gas being sent back into the intake manifold through the EGR valve is pretty high to prevent NOx formation. At idle and full throttle, the EGR valve closes, and no EGR is going back into the intake manifold. The above is a bit of a simplification, but it's basically what's going on with the EGR valve.

Now, my point: Our cars' engines have a low compression ratio (8 to 1 from memory). So, at part throttle, our engines probably don't generate a whole lot of NOx, anyway. Just having a functioning EGR valve might be enough to pass an emissions test (i.e. a three-way catalyst might not be needed).

In my case, I don't want to take a chance. I want a three-way cat to clean up any NOx and ensure that I pass the first time.

Hope this helps...

 

[mgmshar]

...just to close the loop on this thread.

I purchased the cat offered by Southeast Turbo Performance after I confirmed that it was, in fact, a three-way cat. Southeast sent me the full specs on it, so I was sure. I ordered the cat that is designed for fit on the back end of the THDP.

The cat fit like a glove - it took me longer to hoist the car then to swap-in the cat. I then passed the Indiana emissions test (HC, CO, and NOx) with flyling colors. My car's emissions were about 1% of what the limits allow.

I did make some other tweaks to the car to help it pass, but I'm sure that the cat was 90% of the reason why it did so well.

Regards,