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Catalytic Converter Install

Old 06-08-2019, 10:12 AM
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Catalytic Converter Install

I have a desmogged 1985 22R, Weber 32/36. I currently do not have a catalytic converter. There is a pacesetter header, 2" pipe and a flowmaster raptor muffler that terminates above the rear axle. I would love to replace the entire exhaust with nicer headers and larger pipe, but that is not in the budget at this time. My goal is to reduce tail pipe emissions.

What do you all think about installing a free flow cat? I can cut the pipe near the transfercase and install it before the muffler. Pros? Cons? Worth it for a desmogged engine?

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Old 06-09-2019, 08:56 PM
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I think it is worth installing a free flow catalytic converter.

You should be able to install it right in the section you have pictured.

Make sure the engine is tuned correctly to minimize unburned fuel entering the exhaust.

You may or may not need to add some heat shielding under the cab right above the catalytic converter. They can get hot!

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Old 06-10-2019, 10:42 AM
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With no other emissions components? I would not run one. If you do not have an air injection system, or a way to monitor rich lean or adjust for that matter, you would risk overheating the cat. Which would not be a huge issue, until the catalyst inside melts and plugs up. I think you would be wasting your time and money. Maybe try and tune the carb a little better. Adjust for idle with a vacuum gauge installed on the manifold. adjust for max vacuum.
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Old 06-10-2019, 11:06 AM
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Originally Posted by SENOR NOODLES View Post
With no other emissions components? I would not run one. If you do not have an air injection system, or a way to monitor rich lean or adjust for that matter, you would risk overheating the cat. Which would not be a huge issue, until the catalyst inside melts and plugs up. I think you would be wasting your time and money. Maybe try and tune the carb a little better. Adjust for idle with a vacuum gauge installed on the manifold. adjust for max vacuum.
Can you elaborate on adjusting for max vacuum? I have a vac gauge. I have not used it to tune the carb. Perhaps there is already a write up somewhere?
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Old 06-10-2019, 12:57 PM
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Adjust idle adjustment screw. Screw it in as far as possible while still allowing it to run. Unscrew it until the vacuum rises as high as possible. idle mixture will be set. idle speed will just me a mechanical adjustment after that. This process is usually with most new holleys and edelbrocks. I use the same process with stock Toyota carbs, and have always had the truck pass smog with very low hc's, co, and nox.
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Old 06-11-2019, 06:11 AM
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Originally Posted by SENOR NOODLES View Post
Adjust idle adjustment screw. Screw it in as far as possible while still allowing it to run. Unscrew it until the vacuum rises as high as possible. idle mixture will be set. idle speed will just me a mechanical adjustment after that. This process is usually with most new holleys and edelbrocks. I use the same process with stock Toyota carbs, and have always had the truck pass smog with very low hc's, co, and nox.
Good stuff, thank you. I presume it will be similar with a weber 32/36. I'll get the gauge out and see what I can do.
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Old 06-12-2019, 02:12 PM
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Had a few minutes to play around with vacuum gauge and carb. I started at just shy of 20 and got it up to 21 inHg by slightly unscrewing the idle mixture screw. The valves got noisier but perhaps my valve cover is too tight. Tailpipe emissions smell better. I think I will go through and reset my timing and idle as well. Thanks senor noodles, learn something new everyday!


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