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Preface: There’s a story of someone who had been instructed to stuff a rag into their tailpipe either fully blocking or partially blocking their tailpipe to prevent the vehicle from stalling / sputtering. This was a late 1996 Saturn vehicle. To keep things relevant to this site, I will say this backstory may be true or false.

Question: From the mechanical perspective of a vehicle, is there any logical reason where restricting the airflow of your tailpipe with an object (i.e. a rag stuffed in it) would somehow prevent your engine from stalling / sputtering or somehow keep an older vehicle running? Possibly due to changes in airflow?

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No, there is no logical reason to ever restrict the exhaust for any engine performance gain. I'm assuming your back story was to play a joke with someone.

This clip from the movie Beverly Hills Cop has proven that a restricted exhaust is in no way beneficial ;) - https://youtu.be/a_1OVYsLqMU

All joking aside, the following might be a very far fetched scenario where an exhaust restriction might cover up a stalling condition. But lets go over a couple things first.

  1. A 1996 Saturn has a speed density fuel injection system, and has no Mass Air Flow sensor. So a lower vacuum at an idle equals a richer condition.

  2. A restricted exhaust will cause lower engine vacuum - https://youtu.be/d-jp1IIJVVk

So let's say the fuel pump was getting a little weak, or there was a higher concentration of ethanol in the fuel causing a lean condition (note that it would have to be running just lean enough to stall the engine now and again).

Theoretically the rag in the exhaust trick may bump up the MAP reading just enough to keep it from stalling. (A rise in MAP equals an increase in injector pulse width). I'm pretty sure that any sputter would still be present.

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There is a difference between severely restricting the exhaust flow and normal backpressure caused by the mufflers and the tailpipe itself. In general, all naturally aspirated (eg. non-turbo) engines benefit from a limited amount exhaust backpressure because it actually improves airflow in the cylinder head. Removing the backpressure altogether (like removing the exhaust manifold) will harm engine performance.

However stuffing a rag in the exhaust and severely limiting flow doesn't do anything good at all. If the engine starts running better the fuel mixture is probably way too lean like Milson already mentioned.

  • I knew a guy who filled a neighbors kid noisy muffler with expanding foam just to prevent the kid from disturbing the peace at at night,. It blew a 6 inch hole in the muffler when he tried to start in the morning,,,too much back pressure.....LOL – Old_Fossil Jun 8 '18 at 8:53

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