Before reading, please note that this is my first vehicle, and I'm not exactly a mechanic, so I what I'm asking may sound a bit silly, my apologies in advance

I'm driving a 2004 F-350, I've got the early engine roaring inside, and I wanted to know if straight piping it is a good idea? I know diesels are supposed to have a lot of back pressure, however I've been told by multiple buddies and family members that I should consider straight piping the thing. Is it both safe to do and a good idea? Im not exactly loaded with money, so if something were to go wrong due to the straight pipe, be it the lower exhaust temp or the lack of back pressure, I'm not in a place where I can buy a replacement part to fix it. I love the idea of straight piping the truck, I've heard a few run, and oh my goodness it sounds incredible, but I figured it a safe bet to consult those who have more experience then myself with this engine.

 

This assumption is not true. No engine, diesel or other wise, needs, wants, or is benefited by back pressure. As far as the turbo diesel goes there is always back pressure because the turbine section of the turbo charger poses a significant restriction to the engine exhaust system resulting in back or more correctly "drive" pressure before the turbo, however after the turbo the smoothest, best flowing exhaust will produce the best results. This doesn't mean a 12" exhaust is best, the exhaust gases exiting the turbo want a smooth non turbulent transition into the exhaust system. The optimum size exhaust pipe depends on the size turbo installed and the max total airflow thru the engine. For your truck I would recommend a 3.5" turbo downpipe with a 4" exhaust system. The primary downside of a straight pipe system is exterior noise and interior drone, if these don't bother you, go for a straight pipe system. If they may bother you, or in my case bother my wife, then a quality high flow muffler will maintain the performance benefits while reducing the exterior noise a bit and the interior drone quite a lot. Magnaflow, MBRP, and Flow Pro among others offer good systems, always remember you get what you pay for. Good Luck, Russ

P.S. some folks will point to a particular engine combination that lost performance when a high flow exhaust system was installed and say "see it didn't have enough back pressure that's why it lost performance" what is actually going on is the engine system or package was tuned for a specific configuration and mass flow through the engine. They altered the configuration and didn't have the package re-tuned for the new configuration and so performance was lost. Remember engines are complex systems and for best results should be modified as a complete system. Randomly bolting on various aftermarket parts creating a completely unique and untested system that is not tuned to work together, may not have the result the owner wanted.

 

How long have you had this truck? Do you have any devices for reading engines sensors or codes?

Before fitting a new exhaust, make sure the engine is healthy. Check to make the oil cooler is working, you have adequate fuel pressure, change fuel filters, use the correct oil filter. Check if any codes are present.

Just make sure there is nothing else lurking unseen that needs attention if your money is tight. Fix stuff that is broken before swapping out properly functioning systems.

 

You could always save the old exhaust system and bolt it back on if you don't like anything about the new system. I don't know your state smog laws but it wouldn't be legal here in Ca. Also some beach communities are clamping down on noisy exhaust.

 

Kinda sorta legal here in Ca. My 01 is smog exempt and is straight piped, totally legal. My 03 has a cat and muffler that if you were to remove those it would not pass smog, thus illegal.

 

"No engine, diesel or other wise, needs, wants, or is benefited by back pressure."
That statement is not accurate,
Link: http://scholar.google.com/scholar?q=...s=1&oi=scholar

 

Stop polluting our air.

 

Exhaust scavenging is not exhaust back pressure. A properly designed free flowing exhaust system will have excellent exhaust scavenging. Back pressure is a measurement of exhaust system pressure created by the resistance the flow of exhaust. Russ

 

"No engine, diesel or other wise, needs, wants, or is benefited by back pressure."
Do you have any references that can validate your statement ?
There have been several examples on this forum of guys putting 4 inch plus exhaust on trucks and performance is degraded "turbo lag" the sweet spot seems to be 3.5 inch systems for a 6.0
I can state my first hand experience that on a motorcycle on the race track or anywhere else for that matter and had a clamp or weld fail and muffler falls off performance goes to shat as a direct result of the loss of backpressure the muffler / exhaust system creates. Been there done that a few times regretfully. Seen the same thing happen on dyno runs.
But that is the great thing about this forum everyone can voice there opinion.......

 

The truck I am not driving right now because of a bad engine issue has a MBRP system on it.
Not too loud and still sounds nice. It has the kat still in place and what is more or less a glass pack resonator.
It is a 3.5 down and 4" kat back system. I picked it up from Ed at FICMrepair. >>> https://www.ficmrepair.com
Just give them a call and talk to then. They also carry real Ford parts with the real Ford warrantee.

One BIG helpful item is to use the band clamp and not the crush type muffler clamps.
For the larger pipe they are a lot larger but are so nice when making changes.
Also they temd to have sharp edges to put on gloves or use some sand paper to take the sharp ends down a tiny bit.

https://youtu.be/UB8tXN9Uo8Y


https://youtu.be/lVAE6orimMo