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Looking at exhaust systems and trying to decide whether I should go 4" or 5".

In a turbo application back pressure /scavanging is not really a concern.

Does it really come down to a sound preference? 5" can lower EGT's a bit more correct?

Thanks,
Rascal
 

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Usually larger pipes will lower egts. You can go too big though, the velocity of the exhaust gasses are important too. What do you have done to your truck? Do you have future upgrade plans?
 

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No you cant go "too big" on an exhaust. The bigger the better. Deeper sound, louder turbo, more responsive turbo, lower egt's. This is exacerbated with more modifications, also.
 

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5" and LUVIT....and yes you can go to big but 5 is not too big
 

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and yes you can go to big but 5 is not too big
Maybe in your opinion of the sound quality, but in terms of technicalities, there is no "too big".
 

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Discussion Starter #7
Usually larger pipes will lower egts. You can go too big though, the velocity of the exhaust gasses are important too. What do you have done to your truck? Do you have future upgrade plans?
Nothing really yet. When I got the truck it was bone stock minus someone cutting th muffler out and replacing with straight pipe.

I plan to do some intake/exhaust/intercooler mods to help her breathe better. Maybe one day I will upgrade turbo/injectors/valve train but for now I want to keep her as dependable as possible.

Thanks,
Rascal
 

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Maybe in your opinion of the sound quality, but in terms of technicalities, there is no "too big".
Yes you can go to big technically. You seem to spread a lot of info that is just hear say or bad.

If the pipe is too big, the air inside will get lazy (slow down) and actually create resistance. This is why "velocity" was mentioned.
 

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Yes you can go to big technically. You seem to spread a lot of info that is just hear say or bad.

If the pipe is too big, the air inside will get lazy (slow down) and actually create resistance. This is why "velocity" was mentioned.
Really? So what size is "too big" then, where the numbers begin to reflect upon your statement?

A turbo diesel doesn't need "velocity"... theres a fat ****ing garrett turbo pushing the exhaust out :thumb:


A turbo wants the least amount of resistance and restriction in the path of the intake and exhaust. Why do you think sled pullers run a filter clamped to the turbo and the biggest exhaust they can fit with the shortest path routed?


Here's a nice little article written by a former Garrett development engineer, on how scavenging and velocity theory goes out the window with a turbo:
http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html






Next time think twice before you attempt to slander somebody :thumb:
 

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I can't give you an exact size because I don't know the math and it would depend on a lot of other factors.

Pulling trucks are a very different senerio! They are forcing a ton more air through the engine so they NEED larger exhaust to vent it all. Also, as you mentioned, these "pulling" exhaust are as short as possible. If you understood fluid dynamics you would also understand that the length of the pipe largely impacts flow velocity.

I didn't read your article so I don't know what was talked about. I am talking about velocity after the turbo.
 

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I didn't read your article so I don't know what was talked about. I am talking about velocity after the turbo.
Ok and if you had read the article, you would have noted that a turbocharger development engineer from Garrett had wrote it, and noted that "Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine".

read the article. It reinforces turbo theory in great depth, and it's not that long of a read.

My knowledge of fluid dynamics means nothing if your knowledge of turbocharging dynamics is low :thumb:
 

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Back to topic... Your stock exhaust, minus the muffler, is sufficient until you upgrade your turbo. If you going to go bigger 4" will work better for you, 5" if you have a BB turbo and big injectors.

I plan to do some intake/exhaust/intercooler mods to help her breathe better
You won't need to upgrade our intercooler until you upgrade our turbo. While your intake shopping, look for a dry filter setup. Easier to properly maintain an just as much flow as wet filters.
 

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Iv had both 4 and 5 ( currently running 5 inch diamond eye to single 8 inch miter cut ) love it wouldn't go back to 4 if I had to do it all over would have got 5 and not even messed with 4
 

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I belive this might be considered to big :laugh: On a side note if you have stacks up draft is created like in a chimmney which also helps exhaust flow.


 

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Yea I ran with stack and with out. On my 5 inch
 

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Dont have any technical input , but i have a 4" downpipe that goes into 6" under the passengers front seat ( by there feet) that runs all the way bac , no cat or muffler.. Sounds good to me , but sure is a pain in the *** to work around when you hve to get on the side of the transmission... If i had to do it over id go with a 4" all the way through
 
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