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Discussion Starter · #1 ·
I’m always mulling Ecoboost related stuff in my head, but I was just wondering if a downpipe actually matters. Maybe this is a stupid question, but maybe someone can answer.

So what I mean by does a downpipe matter, is, so when you tune, let’s say a tuning company says, 60hp increase to stock truck. Then how big of a difference does an aftermarket downpipe have compared to stock? Like will you make 70hp increase with an aftermarket downpipe?
Those of you who have dyno’d probably know, but I suppose this could apply to intake, or any other mod.
 

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Engine is an air pump. Always remember this and then ask yourself, is "xyz" a restriction? If the answer is yes, then increasing size will generally allow more power to be made. If the answer is no, then its not going to help until you make enough power to where it becomes a restriction.

This is the same with all components to an engine. Intake, throttle body, intake manifold and runner size, valve size, exhaust port size, exhaust itself etc. At some point, they all become a restriction, the question is where?

For a stock truck, the downpipes are not much of a restriction. You can consider them a supporting mod that will help more as you build more and more power. Just dont expect them to make 20+whp on their own.
 

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@Boostking I emailed back and forth a while back with a guy from MPT, who told me that downpipes do absolutely nothing. Point blank said they do not recommend anyone upgrade them because they make zero additional power. I've seen others say the same. I've also seen countless folks say they should be the FIRST mod you make, best bang for your buck, etc etc.
I'm guessing you fall somewhere in the middle of these two sides? I'd really love someone to put up some dyno runs before and after, with all else being exactly the same. None of this "stock vs. downpipe WITH tune" garbage that doesn't actually clear anything up.

EDIT: The emails with the MPT guy was after giving him a rundown of all my mods - I wasn't asking him about downpipes on a stock truck at any point.
 
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Tuxedo Black 2012 F150 SCrew XLT EcoBoost
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To caveat what @Boostking said, I heard it described like this:

Try blowing through a stirring straw.
Now blow through a 3" PVC pipe.
Now blow through a McDonald's straw.


The stirring straw is way too small for the force your lungs are capable of producing. It bottle-necks in your mouth and comes out as fast as it can.
The PVC pipe is way too large. All the air leaves your lungs at once with absolutely no force behind it (back pressure in an engine).
The McDonald's straw represents finding the right exhaust for the amount of horsepower your car is making.
 

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Discussion Starter · #5 ·
Engine is an air pump. Always remember this and then ask yourself, is "xyz" a restriction? If the answer is yes, then increasing size will generally allow more power to be made. If the answer is no, then its not going to help until you make enough power to where it becomes a restriction.

This is the same with all components to an engine. Intake, throttle body, intake manifold and runner size, valve size, exhaust port size, exhaust itself etc. At some point, they all become a restriction, the question is where?

For a stock truck, the downpipes are not much of a restriction. You can consider them a supporting mod that will help more as you build more and more power. Just dont expect them to make 20+whp on their own.
That makes sense. So in other words, if my engine was making 600 crank hp then the stock downpipe would probably be a restriction because it’s not big enough for that engine to breathe.
In my opinion, the stock intake tubes are a bottle neck, they are so tiny up to the turbos.
I see what you’re saying, restrictions will slow down the flow, which in turn makes less hp. But at some point, like if you did a 5inch exhaust from the turbos back, it would be like blowing through a 3” pvc pipe, (@EB150) your lungs can’t put enough force through it.
 
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Discussion Starter · #6 ·
@Boostking I emailed back and forth a while back with a guy from MPT, who told me that downpipes do absolutely nothing. Point blank said they do not recommend anyone upgrade them because they make zero additional power. I've seen others say the same. I've also seen countless folks say they should be the FIRST mod you make, best bang for your buck, etc etc.
I'm guessing you fall somewhere in the middle of these two sides? I'd really love someone to put up some dyno runs before and after, with all else being exactly the same. None of this "stock vs. downpipe WITH tune" garbage that doesn't actually clear anything up.

EDIT: The emails with the MPT guy was after giving him a rundown of all my mods - I wasn't asking him about downpipes on a stock truck at any point.
I know what you mean, they’re always like, “here’s what it made after a tune and downpipes” and it’s like, dude, I want to see what it made on the dyno without a tune, stock to downpipe comparison.

Well, even if I won’t gain 20hp from the downpipes, it was worth it just for the sound. 😝
 
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There is no such thing as to little back pressure in a turbo engine.

The lack of backpressure blowing through the 3” pvc pipe just means your lungs and throat are the restriction and those are the next thing you need to upgrade
 

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If you’re seeing your wgdc max out then thats a good sign you could use a downpipe. Its also a good sign that you need more turbo too though.
 
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Downpipes are not a good first mod, or good "bang for your buck".

Tune and Intercooler are the two best, and in my opinion, first upgrades you should do. After that, it's all minimal if any gains until turbos and other things that make big airflow improvements are made. Or if you can run a better fuel to allow more timing.
 

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If you’re seeing your wgdc max out then thats a good sign you could use a downpipe. Its also a good sign that you need more turbo too though.
That’s one PID I never pay attention to that I should take a look at on my next drive. Never had it displayed on the NGauge since I tuned it.

EDIT: I don’t want to hijack boostkingmatt’s thread here but maybe this can be answered quickly and easily. Is there a healthy or otherwise ”normal” range I should see my WGDC in at any particular point in the rev range? Or if I need to be more specific, on a WOT run at peak boost do I want to see 100%?
 

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That’s one PID I never pay attention to that I should take a look at on my next drive. Never had it displayed on the NGauge since I tuned it.

EDIT: I don’t want to hijack boostkingmatt’s thread here but maybe this can be answered quickly and easily. Is there a healthy or otherwise ”normal” range I should see my WGDC in at any particular point in the rev range? Or if I need to be more specific, on a WOT run at peak boost do I want to see 100%?
100% means your current setup has nothing left to give and your wastegates are likely blowing open due to the exhaust manifold pressure. The pcm is trying to force the turbos to make more airflow but they cannot.
 

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Discussion Starter · #12 ·
Downpipes are not a good first mod, or good "bang for your buck".

Tune and Intercooler are the two best, and in my opinion, first upgrades you should do. After that, it's all minimal if any gains until turbos and other things that make big airflow improvements are made. Or if you can run a better fuel to allow more timing.
And that’s from the tuning expert. Well,
Downpipes are not a good first mod, or good "bang for your buck".

Tune and Intercooler are the two best, and in my opinion, first upgrades you should do. After that, it's all minimal if any gains until turbos and other things that make big airflow improvements are made. Or if you can run a better fuel to allow more timing.
Well, that answers my question for sure. Not exactly what I thought, but, now I know. Like I said, I don’t really care if the downpipe adds power or not, it was worth it just for the sound. And, later on when I get turbos, it will be better.
 
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