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Any issues using a Turbo cat on an N/A car? 900

I'm not trying to be fancy here. The Monroe shop that did the exhaust on my '95 940 for the previous owner did a hideous job. Apart from welding the cat to the front muffler (at a weird angle, no less), and leaving off the center muffler hanger, I've just discovered they used a cat intended for a Turbo car (which this car is not). They chopped a couple of inches from the slip joint on the muffler, and maybe the end of the cat. Then butt welded the two (badly), as the diameters are the same. I realized the cat was the wrong diameter, and too long for the car while trying to install a new Starla system.

So I can buy a new correct cat, but would have to wait, pay money, wait, and waste a low milage part. Did I mention I'll have to wait. Other option is that I can shorten the turbo cat by cutting between the cat and the three bolt flange (there's four or more inches there, unlike any other aftermarket cat I've seen). I can then weld a length of the correct diameter pipe (2 1/8"?) to the other end, and slip my new system on. I could have the car back on the road tomorrow. Shortening my brand new exhaust is not a desirable option for me. I'd rather pay and wait.

So that's the back story. My question is, am I losing torque by having this slightly larger diameter catalytic converter on my car? It basically has no power until you hit about 3k, but I figured that's normal for an N/A wagon. But if I'm losing even a smidgen of power, I'll pay and wait to get the correct part on there.

Thanks for bearing with my long winded diatribe.








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    Any issues using a Turbo cat on an N/A car? 900

    Dear allrounderco,

    Hope you're well and stay so. I stood aside in the hope that someone - who had tackled this problem - would offer experience-based insights.

    I don't have those. But it seems to me that a wider-bore catalytic converter than that factory-supplied is not likely to be a problem. Turbo engines' exhaust is at higher pressures than is exhaust from non-turbo engines. So, a wider-diameter exhaust pipe is needed to prevent back-pressure.

    On a non-turbo engine, the wider exhaust pipe would do no harm. On your car, only the catalytic converter has a larger diameter than its input and output pipes. There's nothing that restricts the exhaust stream.

    I don't know whether a catalytic converter for a turbo-equipped engine has a larger block of reactive material, than is found in a non-turbo catalytic converter. Catalytic converters are not meant to be opened - except for end-of-life recycling: there's no obvious way to ascertain the size of the reactive material block.

    Even if the turbo-compatible catalytic converter has more reactive material than is found in a non-turbo-compatible unit, that can do no harm. The exhaust from a non-turbo-equipped engine will be a tad cleaner.

    Hope this helps.

    Yours faithfully,

    Spook








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      Any issues using a Turbo cat on an N/A car? 900

      Thanks for that. I admit I was over thinking this. A chain is as strong as it's weakest link, and the overall flow would obviously not change in any meaningful amount given the rest of the exhaust is the correct diameter.

      Truth be told, my real intention was to try to find a reason to NOT modify my existing cat to work. In the end, however, I did just that. I shortened the pipe between the inlet flange and front of converter by two inches, and hacked the last four off the end, replacing it with a length of the correct diameter. Now it fits fine. The rest of the exhaust is loosely fitted, and I'll get it all buttoned up tomorrow, unless my five year old, who was looking under the weather this evening, has to stay home from school.







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