Engine/Transmission (1998.5 - 2002) Hot exhaust valves

[Ramtough]

I read today a newspaper aritle in the "Tom & Ray" column about mufflers. The article related to gasoline engines but I am interested in the principle raised. Tom & Ray were advising a writer to repair a faulty muffler because the loss of exhaust backpressure could cause exhause valves to overheat, particularly on a long interstate cruise.



Many TDR members, including me have eliminated mufflers, increased exhaust system size and performed other modifications to hopefully favorably impact performance.



Now for the question - what is the risk, if any of exhaust system modification to causing other unanticipated problems in the engine?



I have never heard of lower exhaust backpressure causing valves to 'melt' as stated in the newspaper article.

 

[Whitmore]

Exhaust back pressure is important to gas motors but on a diesel the less back pressur the better



cheers, Kevin

 

[WestTN]

bad muffler?

It sounds like Tom and Ray had that one backwards. A clogged muffler will cause the engine to retain more heat because the exhaust gasses are not purged from the cylinder. A rotted out muffler would cause the engine to run cooler. A carburated non-computer engine will lean out slightly with lower exhaust back pressure and thereby run a little hotter peak combustion temperature, but this effect would be more than nullified by more exhaust heat being scavenged from the cylinder, resulting in a net heat loss. Higher back pressure would cause this engine to richen the mixture and reduce the combustion temperature, but more exhaust heat would be retained for the reason stated above. Burned out mufflers are a lot more common than clogged ones.



On a fuel injected engine, the mixture is regulated by the computer based on input from the oxygen sensor, so there would be no lean out. Computer controlled carburated engines would respond the same as fuel injected.

 

[bmoeller]

The turbo creates some back pressure. After the turbo you want to get rid of it. So running a larger exhaust won't hurt anything, only help. Less back pressure after the turbo also helps it spool faster and lower exhaust temps.