Exhaust backpressure good or bad

[LandCruiserPhil]

I wanted to test my catalytic converter to see if it had any restriction. I drilled a hole in the exhaust in front of the CC and one behind. I used a 15lb new pressure gauge and I came up with no readable backpressure. I did get about ½ lb at 1500 rpms but no noticeable difference in front or behind the CC. I think I'm safe to assume that my CC is not clogged. I wanted to test it because I run a single small CC. Is this a bad thing or should I just be happy with little to no backpressure.

 

[Romer]

Do you run a stock muffler? I have an aftermarket muffler thats louder, but provides no backpressure to the motor. I was told, it allows the engine to run cooler. Don't know if thats true.

 

[IdahoDoug]

Backpressure per se is an energy drain, but engines are designed around a certain amount of it for proper cylinder scavenging, etc. I've *heard* you could lop the exhaust pipe off at the ex. manifold and end up overheating the exhaust valves.

As for Phil's finding, I can find nothing to say bad about it. CC's tend to increase backpressure with clogging over time, so provided it's not totally blown internally (I'm assuming you know the history or actually installed it) low BP is a good thing. Even a straight pipe to the rear bumper provides back pressure, so you have enough to be within the mfrs intended range IMHO.

DougM

 

[LandCruiserPhil]

Romer - Flowmaster muffler, large resonator(sp?), peanut cat, and 2" off the manifold into 3' pipe makes up the exhaust system.

Doug - The exhaust runs all the way to the rear and as RPM increases I see the gauge moving a little. If the cat was blown the OBDII should code due to the two O2 sensor.

So for now I will call it good and off to Moab on Tuesday.

 

[Gold Finger]

Engines are tuned to run with the stock exhaust to achieve good running that is also within emission regulations removing part of it or putting a less restrictive exhaust on while it may well reduce the back pressure which will effect the amount of scavenging in the cylinders and usually results in a leaner mixture hence more heat and often less power and more noise. To optimise performance exhausts should be tuned to length and bore as there is a relationship with the power curve and the fuelling ought to be adjusted preferably on a dynamiter to achieve the best results..

 

[LandCruiserPhil]

Engines are tuned to run with the stock exhaust to achieve good running that is also within emission regulations removing part of it or putting a less restrictive exhaust on while it may well reduce the back pressure which will effect the amount of scavenging in the cylinders and usually results in a leaner mixture hence more heat and often less power and more noise. To optimise performance exhausts should be tuned to length and bore as there is a relationship with the power curve and the fuelling ought to be adjusted preferably on a dynamiter to achieve the best results..

Is it also true on forced induction motors?