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Straight Pipe, Back Pressure? Need Help

27592 Views 17 Replies 11 Participants Last post by  Lucan89, 
C
Ok, i know this has probly been discused numerous times allready, and ive researched it a little bit and never really quite found my answer. I got an 04 cummins (bone stock) I noticed it doesn't have a resonator and cat on the exhuast. All i seen is a big mufflor. I want to take my mufflor off and just run a straight pipe to make it louder. Someone told me i shouldn't do this becuase i'll have no back pressure and that diesels need back pressure. This guy also said it would be safer to just put an after market mufflor on it, but becuase of the back pressure difference the after market mufflor would make i would also have to tune it. Is any of this true? I take really good care of my truck and don't want to do any damage to the engine due to mod's on the exhuast becuase of back pressure. Is it safe to run an open straight pipe, like is it harmfull to the engine. All i want is to make it louder but don't want to cause any damage. Any input is highly appreciated.:buttkick:
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ChrBro said:
Ok, i know this has probly been discused numerous times allready, and ive researched it a little bit and never really quite found my answer. I got an 04 cummins (bone stock) I noticed it doesn't have a resonator and cat on the exhuast. All i seen is a big mufflor. I want to take my mufflor off and just run a straight pipe to make it louder. Someone told me i shouldn't do this becuase i'll have no back pressure and that diesels need back pressure. This guy also said it would be safer to just put an after market mufflor on it, but becuase of the back pressure difference the after market mufflor would make i would also have to tune it. Is any of this true? I take really good care of my truck and don't want to do any damage to the engine due to mod's on the exhuast becuase of back pressure. Is it safe to run an open straight pipe, like is it harmfull to the engine. All i want is to make it louder but don't want to cause any damage. Any input is highly appreciated.:buttkick:
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you technically have 2 mufflers already, its called a turbo. yea its safe to run straight pipe dont listen to anyone who says you need back pressure when you have a turbo.
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L
Turbo Charged Diesel's dont need backpressure.
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C
Thank you, i just wanted to hear this from the cummins guys. Straight pipe it is.:headbang:
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SOUTHERN SMOKE
dont need back pressure, dont have to have back pressure, only thing you will notice and its mostly on an automatic, is with a muffler the throttle will feel a little more touchy with the pressure it has... not a noticeable difference unless you are really paying attention...
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A
No kind of engine needs backpressure. Search the internet for exhaust scavenging and learn all about it. People talking about backpressure really makes me mad. So many people believe in this myth its not funny.

Short answer: Turbo means go with the biggest freest exhaust you can stand.
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D
AMEN- Aidan
There are countless engineering papers written on this subject. Engines don't want and don't need backpressure.
During the very early years of development a few gas engine EGR systems relied on backpressure for proper function. I think that is where this misconception got started.
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BSouth
It pisses me off so much when I hear people saying "oh you have to have a muffler".
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ykdave
DocDyno said:
AMEN- Aidan
There are countless engineering papers written on this subject. Engines don't want and don't need backpressure.
During the very early years of development a few gas engine EGR systems relied on backpressure for proper function. I think that is where this misconception got started.
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4 stroke engines do not, but 2 stokes heavily rely on a properly tuned exhaust!

But thats a totally different subject.


Any ammount of restriction after the turbo is only going to increase lag and EGTs, open'er up and let'er breathe!
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A
ykdave said:
4 stroke engines do not, but 2 stokes heavily rely on a properly tuned exhaust!
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Now, I'll be honest, I don't know much about 2-stroke motors but is it backpressure they're relying on when you tune the exhaust? I would imagine its the same scavenging effect you are looking for in a naturally aspirated 4-stroke, just has much more of an effect on the 2-stroke.

You can tune and exhaust on a 4-stroke naturally aspirated motor... heck, I bet you can even do it on a supercharged motor. The problem is that the turbo screws up any effect you could really have on tuning an exhaust so you might as well go as big as possible
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cotharyus
Actually, on a two stroke with a properly tuned pipe, what happens is you have a scavenging stage during the down stroke which aids in getting the new air fuel charge into the cylinder, this is aided by an expanding pipe. Next the pipe closes down, resulting in "return" wave of pressure to keep the new air fuel charge in the cylinder while the piston is coming back up until it rises over the exhaust port in the cylinder. If you really wanna know, I'll go deeper, but yeah, 2-strokes are completely different beasts, and to run right, the DO need "back pressure" but it still != restriction, however it can't happen without some CONstriction - hence, tuned pipe.
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A
Scavenging, exactly what I was talking about. Its just much more noticeable on a 2-stroke motor than a 4-stroke. It does help to tune the scavenging on a 4-stroke as well, just not on a turbocharged one like these diesels. And to be completely accurate, a diesel is not a 4-stroke motor since it is based on the Diesel cycle and not the Otto cycle.
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4wd99cummins
So on my 99 24V i can chop off the redicously large muffler and keep the resonator for drone reasons and ill be fine?? truck is stock
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Lucan89
4wd99cummins said:
So on my 99 24V i can chop off the redicously large muffler and keep the resonator for drone reasons and ill be fine?? truck is stock
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Yep, I did that with my '02 and it was just fine. Sounded pretty good, and let it breathe, but didn't drone at all
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4wd99cummins
Lucan89 said:
Yep, I did that with my '02 and it was just fine. Sounded pretty good, and let it breathe, but didn't drone at all
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is that with no resonator or with a resonator?? Cause i really wanna straight pipe it but dont want drone, ive heard either way it doesnt drone
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Lucan89
With the resonator still on
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4wd99cummins
Lucan89 said:
With the resonator still on
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do you know the size of the pipe thats between the resssy and the muffler, is it 4"??? thanks
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Lucan89
I have no idea
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