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exhaust back pressure
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Jakob
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I want to twin stack my truck and run the NAPA mufflers. With the non-turbo engine, will it suffer if I put a larger exhaust on it? I plan on upgrading to a turbo in the future, so if it's not a huge difference, I'll take the loss on it now so I won't have to do the exhaust again in the future. I couldn't find anything about modding the exhaust on a non-turbo truck. This seems like the best post for my answer.
russ81
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I have found several posts that list the NAPA muffler part number, but none of them seem to be correct. Do any of you have what you believe is the correct part number?
Thanks
Thanks
BillIdaho
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I have read numerous studies about exhaust, mufflers, temps, etc. The general agreement is that you want to keep the gases as HOT as possible and not attempt to cool them off. Formula cars, Nascar, road racing, etc (except drag racing) usually wraps the header/pipes with that metalized tape. The idea is to hold the heat in the pipe as much as possible, as physics says hot gases flow better/easier than cold gases do. If you can keep the heat in the pipe longer, that alone will help the system flow. Years ago, an old genuis named Smokey Yunick experimented with that logic in the earlier years of Nascar. He kept it secret, for the always-wanted edge over the competition. The better he could keep the heat in, the faster he went. When the press and the other racers saw what he was doing, he said it was to keep the engine compartment cooler, saving stress on the other stuff. They bought the excuse but they also figured he was wasting his time. Little did they know he was on to something.
Diesels, especially ones with "hairdriers" (a slang term for a turbocharger I picked up while drag racing) are very particular in regards to back pressure. A gasoline engine will produce more torque with a certain amount of resistance/back-pressure, but will produce more out and out horsepower with a straight through system, BUT usually ONLY at wide open throttle and the very top end of the RPM band. Kids put loud mufflers on their cars, and since they SOUND faster, they think they GO faster. Rarely are they right. A diesel engine cannot operate as well if it has to overcome any back-pressure, in this case other than what the hairdrier provides. Putting a flow through muffler, usually called a "Cherry Bomb" inside the pipe of an existing system will work relatively good, until the inside of the engine decides its had all the fun it can stand, and start to self-destruct. In a hurry.
I own a multi-fuel 5 ton, and yeah, it's loud. I don't really drive except to shows, parades, etc, and wear substantial hearing protection, (earplugs AND earmuffs.) I never really desired to try to quiet it down. BUT if I was,
I would attempt to run a larger pipe down out off of the windshield area, and find a route underneath to simply re-route where the noise is going to come out.
That being said, there is a design of muffler for gas engines that does in fact quiet things down a bunch, yet provides hardly any back-pressure. Go to a muffler shop and ask to see a "Flow-Master" muffler. Most shops that carry those will also have a display cut-a-way model that shows how they place the baffles inside. The idea is that when one pulse of exhaust gas is "pushed" into the muffler, it has to go around the first baffle, but then as it goes by it, the second baffle causes a scavenging effect, clearing the way for the next pulse of gas. By the time you multiply that effect several times with a handful of baffles, you have quieted things down, but really haven't created the usual related back-pressure in doing so.
(The problem with Flow Master showing off how they make their mufflers makes it easy for someone to replicate it. I have built about 20 different similar mufflers for a whole bunch of different vehicles , ALL with positive results.However, I must say I have never tried to put one on a diesel.)
Diesels, especially ones with "hairdriers" (a slang term for a turbocharger I picked up while drag racing) are very particular in regards to back pressure. A gasoline engine will produce more torque with a certain amount of resistance/back-pressure, but will produce more out and out horsepower with a straight through system, BUT usually ONLY at wide open throttle and the very top end of the RPM band. Kids put loud mufflers on their cars, and since they SOUND faster, they think they GO faster. Rarely are they right. A diesel engine cannot operate as well if it has to overcome any back-pressure, in this case other than what the hairdrier provides. Putting a flow through muffler, usually called a "Cherry Bomb" inside the pipe of an existing system will work relatively good, until the inside of the engine decides its had all the fun it can stand, and start to self-destruct. In a hurry.
I own a multi-fuel 5 ton, and yeah, it's loud. I don't really drive except to shows, parades, etc, and wear substantial hearing protection, (earplugs AND earmuffs.) I never really desired to try to quiet it down. BUT if I was,
I would attempt to run a larger pipe down out off of the windshield area, and find a route underneath to simply re-route where the noise is going to come out.
That being said, there is a design of muffler for gas engines that does in fact quiet things down a bunch, yet provides hardly any back-pressure. Go to a muffler shop and ask to see a "Flow-Master" muffler. Most shops that carry those will also have a display cut-a-way model that shows how they place the baffles inside. The idea is that when one pulse of exhaust gas is "pushed" into the muffler, it has to go around the first baffle, but then as it goes by it, the second baffle causes a scavenging effect, clearing the way for the next pulse of gas. By the time you multiply that effect several times with a handful of baffles, you have quieted things down, but really haven't created the usual related back-pressure in doing so.
(The problem with Flow Master showing off how they make their mufflers makes it easy for someone to replicate it. I have built about 20 different similar mufflers for a whole bunch of different vehicles , ALL with positive results.However, I must say I have never tried to put one on a diesel.)
bottleworks
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The "main" muffler thread has the NAPA part number listed on the first page. Yes it is the correct part number. It is NAPA part #21470.russ81 said:
See:
http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=viewtopic&t=1868&postdays=0&postorder=asc
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russ81
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Thanks Bottleworks,
I tried that number at NAPA'a on line store, and couldn't get any results. I will try again.
I tried that number at NAPA'a on line store, and couldn't get any results. I will try again.
Unforgiven
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Jones,
I've read the opposite is true. You want the exhaust gasses to stay hot until they exit. It keeps the flow laminar, thereby reducing back pressure. Likewise, going from small diameter to large diameter pipe can (I repeat can, not will) cause non-laminar flow.
Pittsburgh Power has a lot of info on their website. They suggest wrapping the exhaust with header wrap for a few feet after the turbo. Supposedly this keeps the air flowing smoothly and actually decreases back pressure. They also claim this will actually keep the turbo cooler, as the hot exhaust gasses carry the heat away instead of dispersing it nearby.
After a recent trip where I forgot my ear muffs, I think you know where this is heading ...
mudguppy
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there are several inter-twined points in this discussion and they are getting mixed up in their relationship to one another.
however, the discussion about backpressure in relation to exhaust pipe diameter is not the same. no internal combustion engine likes backpressure; an engine is a mechanism that performs work by moving gases. therefore, the easier the engine can move the gases, the more efficient the process becomes.
diesel engines don't 'like' backpressure and turbos don't 'need' backpressure to operate. however, since it is not practical to let the exhaust simply exit the turbo, some piping is required.
an ideal exhaust system would be one that utilizes the same internal diameter as the turbine outlet, is completely straight or very smooth full diameter bends, and rejects heat completely. however, even then it has a limit to it's length; backpressure will start to build due to frictional losses and will eventually reach 'choke flow' if left long enough.
what was the point again?
i agree with this statement.
however, the discussion about backpressure in relation to exhaust pipe diameter is not the same. no internal combustion engine likes backpressure; an engine is a mechanism that performs work by moving gases. therefore, the easier the engine can move the gases, the more efficient the process becomes.
diesel engines don't 'like' backpressure and turbos don't 'need' backpressure to operate. however, since it is not practical to let the exhaust simply exit the turbo, some piping is required.
an ideal exhaust system would be one that utilizes the same internal diameter as the turbine outlet, is completely straight or very smooth full diameter bends, and rejects heat completely. however, even then it has a limit to it's length; backpressure will start to build due to frictional losses and will eventually reach 'choke flow' if left long enough.
what was the point again?
- diesels need backpressure - myth
- bigger pipes lower backpressure - depends; could cause turbulence, but could also reduce system restrictions
- keeping exhaust hot helps flow - true
Unforgiven
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I'm sorry what did you say? 
When I got to GL yesterday I couldn't understand what anyone was saying. The base security guy looked at me like I was crazy. His lips were moving, but all I could hear was GGGRRRRRRRRRRRRRRRRR. So I just nodded my head and handed him my license. It lasted for a good 10 minutes.
I'm off to the world of online shopping right now. Resonators, adapters, clamps, and mufflers are calling my debit card.
What kind of stack tip would you suggest? I'm going to keep the stock exhaust location & add a muffler. Should I get one of those bent tips & point it out or towards the back? Or should I get a straight tip with one of those flapper thingies?
When I got to GL yesterday I couldn't understand what anyone was saying. The base security guy looked at me like I was crazy. His lips were moving, but all I could hear was GGGRRRRRRRRRRRRRRRRR. So I just nodded my head and handed him my license. It lasted for a good 10 minutes.
I'm off to the world of online shopping right now. Resonators, adapters, clamps, and mufflers are calling my debit card.
What kind of stack tip would you suggest? I'm going to keep the stock exhaust location & add a muffler. Should I get one of those bent tips & point it out or towards the back? Or should I get a straight tip with one of those flapper thingies?
mudguppy
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dunno. i re-oriented my turn-out to almost 90° out to the side of the truck - it really didn't seem to effect the sound level much.
but other folks on here have said that the straight-up tip seemed to help?
so i dunno. i still have a bullet muff in my stack; the 5.9 is slightly louder than the MF, but the tone is much deeper. i'm happy with my setup for now, but will likely build a 4" stack when i change turbos and i'm pondering what method of tip and orientation i should use.
Unforgiven
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Pre-muffler resonator and supposedly super quiet muffler are on the way.
I'm debating whether to add a pyrometer/boost gauge just to see what happens pre-muffler vs. post-muffler. Any back pressure should be noticeable on the pyro/boost. I'm not sure if it's worth the expense though.
I wonder if Fry's has a cheap dB meter so I can run a proper experiment?
I'm debating whether to add a pyrometer/boost gauge just to see what happens pre-muffler vs. post-muffler. Any back pressure should be noticeable on the pyro/boost. I'm not sure if it's worth the expense though.
I wonder if Fry's has a cheap dB meter so I can run a proper experiment?
mudguppy
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unless the back pressure is significant, i doubt that you would notice anything within the accuracy of a pyro/boost gauge.
dB meter would be cool.
dB meter would be cool.
Unforgiven
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Okay,
I ordered a Pittsburgh muffler, an FTE resonator with a 3.5" adapter, and a $100 Japanese dB meter (Nagasaki or something like that).
The muffler cuts down overall noise. The resonator cuts down the constant droning GGGGRRRRRRR. The dB meter is just for curiosity.
I'm planning to cut the stock stack above the fender. I still need to get an exhaust tip & probably a small section of straight pipe to get everything welded together. Plus I'll need vertical hangers w/supports b/c the muffler is a little more heavy than the stock straight pipe.
I'll post results in a couple of weeks. Man, I love experiments!
I ordered a Pittsburgh muffler, an FTE resonator with a 3.5" adapter, and a $100 Japanese dB meter (Nagasaki or something like that).
The muffler cuts down overall noise. The resonator cuts down the constant droning GGGGRRRRRRR. The dB meter is just for curiosity.
I'm planning to cut the stock stack above the fender. I still need to get an exhaust tip & probably a small section of straight pipe to get everything welded together. Plus I'll need vertical hangers w/supports b/c the muffler is a little more heavy than the stock straight pipe.
I'll post results in a couple of weeks. Man, I love experiments!