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Old 03-21-2018, 04:32 PM   #1
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Is it just for show?

My wide ranging but feeble old brain came up with a question the other day that I don't have an answer for so I'm hoping you all can shed some light on something for me.

I see diesel pickups from the Big 3 automakers and they all seem to have HUGE exhaust systems. I'm talking REALLY big, like 8" in diameter.

Now these diesel engines for pickups generally are around 6.0L to 6.9L so they're similar in size, albeit a little bigger than their gas counterparts. The diesel pickup engines also don't run at higher rpm's than gas engines so they're not pushing higher amounts of air/exhaust through the engines. .

So why the big exhaust systems? Are they just for show; designed to give a he-man diesel truck owner a shot of testosterone every time he climbs into his he-man truck? Is this just a marketing ploy or does that big exhaust system really serve a purpose. They seem to be a recent addition to the trucks and something you did not see on the trucks from 15 years ago or longer.

Now before you answer, I'm well aware that the diesels supply significantly more torque and use higher compression ratios to accomplish that, but does that figure into the picture?
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Old 03-21-2018, 04:50 PM   #2
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All diesel pickup trucks and all marine engines built from the same engines- Dodge/Cummins have diesel engines with high compression ratio turbochargers that push the air through at up to three times the volume of a normally aspirated engine. That is why they need big exhausts.

A Cummins 5.9 or 6.7 liter marine engine requires a 6" exhaust, sometimes 5". That is because the exhaust temp has been reduced by raw water injection, which reduces the actual flow rate and therefore the pressure drop which is really what you are trying to acheive. Trucks exhaust at turbo exhaust temps with no cooling which can be hundreds of degrees hotter.

So two reasons why modern pickup diesels have bigger exhausts than gassers as well as marine versions: high output diesels use high compression ratio turbos which increases exhaust output and marine engines benefit from raw water injection which reduce the flow rate.

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Old 03-21-2018, 04:54 PM   #3
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When I owned a 1991 Dodge/Cummins pickup, I changed the exhaust from 3 inch to 4 inch.
It made a noticeable difference in power, and it set me up to make further "power enhancements".

A diesel does not like any restrictions to the exhaust flow.
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Old 03-21-2018, 05:00 PM   #4
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I am the same as Jay, on my Duramax I added a 5 level chip for power to pull a large fifth wheel trailer and in doing so needed to up the exhaust size to maintain EGT at a safe level. It is quite amazing to watch the EGT go quickly up when climbing a mountain with a large load unlike a boat.
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Old 03-21-2018, 06:09 PM   #5
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I knew you guys would come through for me. Thanks.
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Old 03-21-2018, 08:44 PM   #6
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Greetings,
Mr. GFC. While all gave the performance reason for larger pipes, I'm sure there is still that "he man" segment of truck owners. Most probably a similar physiological demographic as those who drive older small imports with "race mufflers" (we call them fart cans around here).

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Old 03-21-2018, 09:34 PM   #7
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I think you want those big stacks so you can do some "rolling coal" too. A good bit of over-fueling is, I suppose, how they do it.
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Old 03-22-2018, 03:03 AM   #8
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Also the joke about the big large loud exhaust pipes is too compensate for undersize male equipment or the Corvettee equals short guy syndrome.

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Old 03-22-2018, 10:58 AM   #9
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Another reason for the bigger pipes is the EPA. I have an 2009 Ford and they have a catalytic converter like cars. The difference in my model is the manufacturer injects raw fuel into the converter sets it on fire to burn off the particulates. This drove down MPG and created a lot of smoke.

Today they use a urea mixture that does the same thing but doesn't create a lot of smoke.
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Old 03-22-2018, 01:17 PM   #10
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Quote:
Originally Posted by BaltimoreLurker View Post
I think you want those big stacks so you can do some "rolling coal" too. A good bit of over-fueling is, I suppose, how they do it.
I had a guy (well, I'd say arsehole but that's not allowed on here) with a diesel powered Ford who had a more traditional exhaust that came out the sides of the truck behind the rear axle.

I was driving my car on a nice day with the top down, stopped next to him at a light. When the light changed he did that black smoke thing with his exhaust when he accelerated. Needless to say it didn't smell or taste very good!

A**hole!
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Old 03-22-2018, 02:25 PM   #11
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Quote:
Originally Posted by GFC View Post
I had a guy (well, I'd say arsehole but that's not allowed on here) with a diesel powered Ford who had a more traditional exhaust that came out the sides of the truck behind the rear axle.

I was driving my car on a nice day with the top down, stopped next to him at a light. When the light changed he did that black smoke thing with his exhaust when he accelerated. Needless to say it didn't smell or taste very good!

A**hole!

Were you driving a Prius or another hybrid? Apparently, they are favorite targets of Rolling Coal. And bicyclists and liberal protestors too. I didn't know this was a "thing" until there was an attempt to pass a law outlawing it in MD.
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Old 03-23-2018, 09:40 AM   #12
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"Rolling Coal."

A great name for an enviro buggy!!!If charged at night its Coal powered.

Electric cars are popular among the car mfg as there expensive , so 30% of $100K is lots more fun than 30% of $18,500.

The really demented ride Hogs with megaphone exhausts to prove what real men they are.
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Old 03-23-2018, 10:44 AM   #13
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Quote:
Originally Posted by GFC View Post
I had a guy (well, I'd say arsehole but that's not allowed on here) with a diesel powered Ford who had a more traditional exhaust that came out the sides of the truck behind the rear axle.

I was driving my car on a nice day with the top down, stopped next to him at a light. When the light changed he did that black smoke thing with his exhaust when he accelerated. Needless to say it didn't smell or taste very good!

A**hole!
Mine blows grey/white smoke. I have sat at a light and the EPA thing running and when I pulled away from the light, well let say there were no more insects..

I actually had a guy chase me down and told me there was a good injector repair place down the road. I told him he could thank the EPA and my truck was operating normally.
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Old 03-23-2018, 11:49 AM   #14
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"I told him he could thank the EPA and my truck was operating normally."

When VW attempted to make sweet running cars that were efficient and didn't pour fuel down the exhaust , the Air Police found out and it cost VW over a Billion bucks for making what the customers wanted.
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Old 03-23-2018, 11:57 AM   #15
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Were you driving a Prius or another hybrid?
BMW 330 convertible. My baby. The top goes down about the first of April and stays down until some time in September, except for the infrequent rainy day.
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