back pressure question - Diesel Truck Forum -
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post #1 of 6 (permalink) Old 07-21-2007, 07:04 AM Thread Starter
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back pressure question

ok my buddy decided that he wanted to cut off his muffler and just run a strait pipe ive herd them they sound great so i said alrite we can jus do it right here at my house so we go to the parts house to pick up a new exhaut hanger and a little pipe extension and we got to talkin to one of the guys that work their and he said that cuttin off the muffler was a bad idea because u have no back pressure and u will loose lots of low end torque, is that true cuz ive never herd that b4
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post #2 of 6 (permalink) Old 07-21-2007, 12:51 PM
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your engine will have enough back pressure threw your turbo. If i remeber right in school desiel engine needs some thing like 4lb of back pressure and a gas engine needs something like 13lb.
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post #3 of 6 (permalink) Old 07-21-2007, 12:54 PM
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The turbo provides enough back pressure, so cutting the muffler out will not harm a thing. Iíve done it to every diesel Iíve owned and never had a problem. The only thing I ever noticed was the truck would roll down a hill a tad bit faster in first gear .
Also think about how many other people on this site have straight piped there trucks, you never herd of a problem have you? Do a search.
I say straight pipe it and let her sing and enjoy the music.
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post #4 of 6 (permalink) Old 07-21-2007, 02:08 PM
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On a turbodiesel, the less back pressure, the better. Remember, any pressure on the exhaust side of the turbo means you need more pressure in the exhaust manifold to spin the turbine. Look at it this way:

P1 = the pressure on the downtube side
P2 = the pressure in the exhaust manifold
DP = P2-P1

The spin rate of the turbine is proportional to DP. If you increase back pressure (means P1 gets bigger), then you have a smaller DP, or, to get the same DP, you need higher manifold pressure, which will likely mean higher EGT's. Lower backpressure will normally have lower EGT's. That is why the bigger (4" and above) turbo-back exhausts reduce EGT's.


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post #5 of 6 (permalink) Old 07-21-2007, 02:57 PM
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Where I think you here about the need for back pressure is in the non turboed gasers. They need back pressure because when the piston gets to TDC between exhaust and intake stroke. All the valves are open for a short time peroid producing what is call the "Scavenging effect". If you don't have enough backpressure it'll send fresh air and fuel threw the combustion chamber and right out of the exhaust.

I think it goes something like that.
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post #6 of 6 (permalink) Old 07-21-2007, 11:17 PM Thread Starter
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see thats exactly what i told him i said nearly every truck like this here has a strait pipe that doesnt make any sense my dad drives 4 different 1 tons but he's never put any exhaust on em preciate it yall
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