Hate my 3" thermal exhaust

[TMac]

Not sure what the OP is talking about regarding it being slower - but I can say that on a TURBO vehicle, the larger the exhaust (especially starting at the turbo), the better. This talk of a dual 3" exhaust making the vehicle slower is silly. If one wants to argue that it's not any faster, then okay, I'd potentially agree to that. But to say it's slower...no. This is not a naturally aspirated engine where exhaust scavenging is a thing. Turbos love big open exhausts. Full stop.

Backpressure, scavenging, pipe diameter and velocity - all that stuff matters...on a N/A engine. Once a turbo is added to the mix, all that other stuff ceases to be a thing. Because the exhaust is no longer necessary to help suck fumes out of the cylinders. We have good 'ol forced induction pushing it out for us. And the turbo turbine, in order to spool free and happy, wants as little restriction as possible after the turbine housing..

Rather than just do this debate again, read this thread, especially these three posts:
https://www.explorerst.org/threads/...-a-performance-exhaust-system.2775/post-33847
https://www.explorerst.org/threads/...-a-performance-exhaust-system.2775/post-43705
https://www.explorerst.org/threads/...-a-performance-exhaust-system.2775/post-60497

 

[mcglsr2]

Rather than just do this debate again, read this thread, especially these three posts:
https://www.explorerst.org/threads/...-a-performance-exhaust-system.2775/post-33847
https://www.explorerst.org/threads/...-a-performance-exhaust-system.2775/post-43705
https://www.explorerst.org/threads/...-a-performance-exhaust-system.2775/post-60497

Yup, I read all those. Your theory is sound; I felt like I was reading Corky Bell's Maximum Boost again, specifically the section on Exhaust Systems (section 11) - completely sound...for a NON-TURBO engine. Turbos work very differently from superchargers (even though the net result - producing boost - is the same), and obviously very differently from N/A engines. The conventional thinking - which is what Mr. Bell explains (albeit in a turbo book), and what you describe - are specifically for naturally aspirated motors. And to an extent, supercharger motors, since the supercharger is explicitly not driven from the exhaust.

Look, I'm not criticizing your understanding of conventional exhaust theory. And Corky (though he was mistaken) agreed with it as well, so there's that. But a turbo exhaust is completely contrary to a non-turbo exhaust. Your lack of appreciation of this implies to me that you don't really have a solid understanding of how a turbo works. You can think of a turbo as a pressure differential device. High on the upstream side (exhaust manifold), low on the downstream side (exhaust). This is what promotes fast spool.

I know I said Corky (and you) are wrong. Who am I to say that? I'm nobody. I'm not turbo engineer or anything, so what I am saying here may not be worth all that much to you (but I DO intimately understand how turbos work). Instead, here's a link for you to read, from a Turbo Engineer for Garrett: Turbo Exhaust Theory (tercelreference.com) . He knows exactly what he is talking about. And he does a great job of explaining exactly why the turbo exhaust is different, and that a "conventional" exhaust approach - what you keep pushing - is NOT applicable to turbo cars. He refutes everything you are saying - FOR TURBO ENGINES. So I get it if you don't want to take my word for it, but will you take the word of a Turbo Engineer from Garrett?

I will be happy to go into more detail on why everything you said regarding exhaust is completely applicable to non-turbo engines but NOT turbo engines if you would like (and for what it's worth, I won't just regurgitate what that link says - I already had the understanding in mind, and when I read that link it just solidified it even further.)

Now. The only thing I'm willing to agree with you on is that a bigger exhaust may not make MORE power on a car. I absolutely refute any statement, though, that a bigger exhaust will HURT performance. Again, ONLY for a turbo engine. The general rule of thumb when doing mods (and this of course varies by vehicle), is that for N/A vehicles, the 1st thing you do is intake. You must get more air into the motor. The 1st thing you do on a turbo vehicle is EXHAUST. You must free it up so the turbo can do its job better.

Lastly, I'll leave you with some real-world examples. I encourage you to go to a drag strip. A test and tune night - nothing too Pro, but something where people have a decent of amount of money invested in their Hondas, Corvettes, etc. Look at all the cars that are turbos! (Most will be turbo'd). And then look at the exhaust. Many will have the exhaust exit right from the engine bay. And it will be a big ol' sewer pipe (your term). If velocity and pipe size and all that stuff mattered, these people with some money to burn, would have titanium exhausts built to the specs you list. But they don't. Think about that. There's a reason they don't, and it's not because they are "misinformed" about turbo exhaust theory.

Look, if you want to be happy with the OEM exhaust, go for it. That doesn't bother me at all. In fact, I have one sitting in my garage, I'll sell it to you for a good price. Again, your theory is sound for NA engines (and even supercharged engines, though to a slightly lesser extent). But it absolutely is NOT sound when applied to turbo engines.

 

[mcglsr2]

Oh, furthermore, the ST OEM exhaust is 2.25" in diameter. It does not "neck down" to 2.25" in one spot as I've seen mentioned. It is 2.25" all the way through. I know this, because my OEM exhaust (cat back all the way to the tips) is sitting in my garage and I literally just measured it.

The only places where it's larger than 2.25" is when the dual pipes come together into a single, such as entering and exiting the mid resonator. The mid pipes (cat back section with flex pipe), the portion before the resonator, the portion after the resonator leading to the mufflers - ALL 2.25".

Of course, this is OEM exhaust from a 2020 ST. I suppose Ford could have changed pipe diameter in later years; however, the performance numbers haven't changed and I seriously doubt Ford would have spent the money to fab up a larger exhaust...for the same performance numbers. So I'm decently confident the exhaust on all model years to date are also 2.25". I could be wrong of course.

 

[Greywolf]

Oh, furthermore, the ST OEM exhaust is 2.25" in diameter. It does not "neck down" to 2.25" in one spot as I've seen mentioned. It is 2.25" all the way through. I know this, because my OEM exhaust (cat back all the way to the tips) is sitting in my garage and I literally just measured it.

The only places where it's larger than 2.25" is when the dual pipes come together into a single, such as entering and exiting the mid resonator. The mid pipes (cat back section with flex pipe), the portion before the resonator, the portion after the resonator leading to the mufflers - ALL 2.25".

Absolutely great info and great reading. I’m an old timer of the days of nonturbo. And I can tell you larger was definitely not better. In simple terms at a very small portion of time. An engine cylinder is both filling with fuel and trying to dump its exhaust. Therefore, both the intake and exhaust valves are open at the tiniest slight bit at the same time, if you were dumping exhaust too fast, it was literally suck out the air gas mixture from that cylinder leaving you to think I must’ve lost my engine somewhere back the last mile.

 

[mcglsr2]

Absolutely great info and great reading. I’m an old timer of the days of nonturbo. And I can tell you larger was definitely not better. In simple terms at a very small portion of time. An engine cylinder is both filling with fuel and trying to dump its exhaust. Therefore, both the intake and exhaust valves are open at the tiniest slight bit at the same time, if you were dumping exhaust too fast, it was literally suck out the air gas mixture from that cylinder leaving you to think I must’ve lost my engine somewhere back the last mile.

Yup. And what @TMac is saying in his threads with regard to pipe diameter, velocity, all that stuff is super, super important on non-turbo'd engines. You are 100% correct in that larger was not better, and the area calcs that TMac talked about regarding dual pipes vs single, all relevant. What he (I'm assuming it's a he, please forgive me TMac if I'm mistaken) is saying is event relevant to supercharged engines - solely because a supercharger has nothing to do with the exhaust stream and is mechanically driven off the crank, making the motor just act like the same, but bigger, motor. However, there is still some discrepancy because we are now talking about forced induction, so the cam should be set up correctly to ensure the boost isn't getting blown out the exhaust valves by accident.

And it all goes out the window when a turbo is added on. Turbos do funny things to the exhaust flow by nature of how they work. The exhaust exiting a turbo does NOT look like the exhaust exiting a N/A engine.

Additionally, speaking to your mentioning of valve overlap (intake vs exhaust), that's also why turbo motors have cams with different profiles from non-turbo cars. A turbo cam on a non-turbo engine will be terrible, just as a non-turbo cam on a turbo engine wouldn't be great (though not as bad as the former).

 

[TMac]

It seems interesting that you would include info from Corky Bell only to say "he was mistaken", but look up a 30 year old post from a Garrett engineer on a (Tercel?) site that you think agrees with you.

I would totally agree with the Garret engineer's post (and you) that a turbo exhaust is different than an N/A or Supercharged exhaust, and I said as much. But only to the extent that we have to deal with exhaust post turbine differently. I would also agree that we have a steady supply of exhaust energy entering the turbine, so the lower the pressure post turbine the more rapidly that energy can traverse the turbine.

But you seem to think that having velocity in a supercharged engine or N/A engine either in the headers or exhaust is important because it lowers the pressure, but not in a turbocharged engine. I can't imagine the logic behind that statement.

To quote another thing you say "Turbos do funny things to the exhaust flow by nature of how they work. The exhaust exiting a turbo does NOT look like the exhaust exiting a N/A engine". You are absolutely right, and I made exactly that same point.

However the information from the "garrett" poster doesn't in any way, other than by just increasing the size of the piping, address how to create a lower pressure post turbine. That "paper" does not address converting the downside of the turbine to laminar flow since he doesn't address the helical (spinnng) nature of the exhaust post turbine. It also doesn't address having velocity downstream of the turbine to help with throttle transitions and shifting.

If you were as knowledgeable about turbocharging as you claim, you wouldn't have posted this: "I know I said Corky (and you) are wrong. Who am I to say that? I'm nobody. I'm not turbo engineer or anything, so what I am saying here may not be worth all that much to you (but I DO intimately understand how turbos work).

If you "intimately understand how turbos work, why, oh why would you have posted this: "Because the exhaust is no longer necessary to help suck fumes out of the cylinders. We have good 'ol forced induction pushing it out for us".

It doesn't matter whether you're N/A, turbocharged, or supercharged, the intake pressure is not "pushing" out exhaust. People have to remember that an N/A engine has a supercharger- powered by 60 miles of atmosphere being acted upon by gravity. The fact that it's fixed to ambient air pressure doesn't change that, it just affects the density of the air and thus the potential HP. A belt driven supercharger or turbocharger just magnifies the air density.

It is certainly true that camshaft design (overlap- when both the exhaust valve and intake valve are open) will affect the V/E of the engine- and must be configured differently depending on the expected charge and exhaust pressure. As the exhaust valve begins to close on the exhaust stroke, a very well tuned exhaust system at a certain RPM range can create a low pressure area that can be used to "tug" a bit more air into the intake on the intake stroke increasing V/E. But we're certainly not using the intake pressure to force out the exhaust. Even if that were true (it's not), it would reek havoc on a MAF or speed-density in terms of A/F ratios.

As far as anecdotal evidence about drag racing, etc, using far larger than necessary exhausts, I'd just say I have spent 40 years around racing and have seen all sorts of things that people pass on as "lore" that doesn't make their car go any faster. I mean, if all you need is a dump pipe out the fender or through the hood, we' re really not talking about an "exhaust" in any sort of apples-to-apples measurement.

Here's something that isn't anecdotal. We have dyno results on this site that show tuned STs on e50 with the stock exhaust at or over 500 WHP (about 560 crank) and that's about the limits of the stock turbos and fuel system.

 

[bosephbarking]

It seems interesting that you would include info from Corky Bell only to say "he was mistaken", but look up a 30 year old post from a Garrett engineer on a (Tercel?) site that you think agrees with you.

I would totally agree with the Garret engineer's post (and you) that a turbo exhaust is different than an N/A or Supercharged exhaust, and I said as much. But only to the extent that we have to deal with exhaust post turbine differently. I would also agree that we have a steady supply of exhaust energy entering the turbine, so the lower the pressure post turbine the more rapidly that energy can traverse the turbine.

But you seem to think that having velocity in a supercharged engine or N/A engine either in the headers or exhaust is important because it lowers the pressure, but not in a turbocharged engine. I can't imagine the logic behind that statement.

To quote another thing you say "Turbos do funny things to the exhaust flow by nature of how they work. The exhaust exiting a turbo does NOT look like the exhaust exiting a N/A engine". You are absolutely right, and I made exactly that same point.

However the information from the "garrett" poster doesn't in any way, other than by just increasing the size of the piping, address how to create a lower pressure post turbine. That "paper" does not address converting the downside of the turbine to laminar flow since he doesn't address the helical (spinnng) nature of the exhaust post turbine. It also doesn't address having velocity downstream of the turbine to help with throttle transitions and shifting.

If you were as knowledgeable about turbocharging as you claim, you wouldn't have posted this: "Because the exhaust is no longer necessary to help suck fumes out of the cylinders. We have good 'ol forced induction pushing it out for us".

It doesn't matter whether you're N/A, turbocharged, or supercharged, the intake pressure is not "pushing" out exhaust. People have to remember that an N/A engine has a supercharger- powered by 60 miles of atmosphere being acted upon by gravity. The fact that it's fixed to ambient air pressure doesn't change that, it just affects the density of the air and thus the potential HP. A belt driven supercharger or turbocharger just magnifies the air density.

It is certainly true that camshaft design (overlap- when both the exhaust valve and intake valve are open) will affect the V/E of the engine- and must be configured differently depending on the expected charge and exhaust pressure. As the exhaust valve begins to close on the exhaust stroke, a very well tuned exhaust system at a certain RPM range can create a low pressure area that can be used to "tug" a bit more air into the intake on the intake stroke increasing V/E. But we're certainly not using the intake pressure to force out the exhaust. Even if that were true (it's not), it would reek havoc on a MAF or speed-density in terms of A/F ratios.

As far as anecdotal evidence about drag racing, etc, using far larger than necessary exhausts, I'd just say I have spent 40 years around racing and have seen all sorts of things that people pass on as "lore" that doesn't make their car go any faster. I mean, if all you need is a dump pipe out the fender or through the hood, we' re really not talking about an "exhaust" in any sort of apples-to-apples measurement.

Here's something that isn't anecdotal. We have dyno results on this site that show tuned STs on e50 with the stock exhaust at or over 500 WHP (about 560 crank) and that's about the limits of the stock turbos and fuel system.

TMAC you Are a treasure.

 

[mcglsr2]

It seems interesting that you would include info from Corky Bell only to say "he was mistaken", but look up a 30 year old post from a Garrett engineer on a (Tercel?) site that you think agrees with you.

I would totally agree with the Garret engineer's post (and you) that a turbo exhaust is different than an N/A or Supercharged exhaust, and I said as much. But only to the extent that we have to deal with exhaust post turbine differently. I would also agree that we have a steady supply of exhaust energy entering the turbine, so the lower the pressure post turbine the more rapidly that energy can traverse the turbine.

But you seem to think that having velocity in a supercharged engine or N/A engine either in the headers or exhaust is important because it lowers the pressure, but not in a turbocharged engine. I can't imagine the logic behind that statement.

To quote another thing you say "Turbos do funny things to the exhaust flow by nature of how they work. The exhaust exiting a turbo does NOT look like the exhaust exiting a N/A engine". You are absolutely right, and I made exactly that same point.

However the information from the "garrett" poster doesn't in any way, other than by just increasing the size of the piping, address how to create a lower pressure post turbine. That "paper" does not address converting the downside of the turbine to laminar flow since he doesn't address the helical (spinnng) nature of the exhaust post turbine. It also doesn't address having velocity downstream of the turbine to help with throttle transitions and shifting.

If you were as knowledgeable about turbocharging as you claim, you wouldn't have posted this: "I know I said Corky (and you) are wrong. Who am I to say that? I'm nobody. I'm not turbo engineer or anything, so what I am saying here may not be worth all that much to you (but I DO intimately understand how turbos work).

If you "intimately understand how turbos work, why, oh why would you have posted this: "Because the exhaust is no longer necessary to help suck fumes out of the cylinders. We have good 'ol forced induction pushing it out for us".

It doesn't matter whether you're N/A, turbocharged, or supercharged, the intake pressure is not "pushing" out exhaust. People have to remember that an N/A engine has a supercharger- powered by 60 miles of atmosphere being acted upon by gravity. The fact that it's fixed to ambient air pressure doesn't change that, it just affects the density of the air and thus the potential HP. A belt driven supercharger or turbocharger just magnifies the air density.

It is certainly true that camshaft design (overlap- when both the exhaust valve and intake valve are open) will affect the V/E of the engine- and must be configured differently depending on the expected charge and exhaust pressure. As the exhaust valve begins to close on the exhaust stroke, a very well tuned exhaust system at a certain RPM range can create a low pressure area that can be used to "tug" a bit more air into the intake on the intake stroke increasing V/E. But we're certainly not using the intake pressure to force out the exhaust. Even if that were true (it's not), it would reek havoc on a MAF or speed-density in terms of A/F ratios.

As far as anecdotal evidence about drag racing, etc, using far larger than necessary exhausts, I'd just say I have spent 40 years around racing and have seen all sorts of things that people pass on as "lore" that doesn't make their car go any faster. I mean, if all you need is a dump pipe out the fender or through the hood, we' re really not talking about an "exhaust" in any sort of apples-to-apples measurement.

Here's something that isn't anecdotal. We have dyno results on this site that show tuned STs on e50 with the stock exhaust at or over 500 WHP (about 560 crank) and that's about the limits of the stock turbos and fuel system.

I had this big thing typed out, addressing the various points in what you said above, but I scrapped it. It's just too much, and I'm not trying to pick a fight. So here's my responses in bullet form:

• Corky Bell is a smart guy. But he can be wrong. And there are a number of books on turbocharging specifically I have sitting here on my bookshelf (along with his) that say contrary to what he does regarding exhaust design. I'll bet you a dollar Corky came from NA cars before getting into turbos. Because he applies NA downstream exhaust design to turbo motors. I don't care how smart Corky is. This is wrong.
• I misspoke when I said the charge air forces the exhaust out. This is wrong, and you are right to call me on it. Sorry about that, I was thinking ahead while typing and not paying attention. The piston is what pushes the exhaust gases out. If the car is NA, and has a properly designed exhaust system, you might get lucky and have some scavenging to help draw the exhaust gas out as well. I apologize for my misrepresentation.
• Having velocity downstream in an exhaust system on a turbo engine is BAD. It generates backpressure. There is absolutely no scavenging happening downstream of a turbo. It just does work that way. So designing an exhaust system downstream of a turbo to have velocity means you will have to neck down, or use smaller pipe or something similar, and this will create backpressure. We want LOW pressure on the turbine exit. Backpressure is the opposite of LOW pressure.
• If you think velocity is required downstream in a turbo engine, STOP. This is patently wrong.
• N/A cars are not supercharged. If they are designed for ram air, and with some induction tuning, they can get close to or maybe slightly above 100% VE. Calling them "supercharged" though is misleading, as actual forced induction is capable of generating VE's well in excess of 100%
• My drag race example is absolutely apples to apples. These are turbo'd engines. Not too dissimilar from what we have in the ST. They absolutely have the option of running a full exhaust, with all kinds of downstream velocity and (non-existent) scavenging. BUT THEY DO NOT. It's "not apples-oranges" because they don't have an exhaust, it's 100% apples because they CHOSE not to have an exhaust. Why? Because it's NOT AS PERFORMANT. That is the ultimate "bigger." You can't get any bigger than running hardly any exhaust at all.
• As for your example, that's great. Good for them. What boost pressure? How much strain on the turbos? I can go get a small straw, and blow super hard through it, and make lots of air. I can also get a bigger straw, blow not as hard, and make just as much air. I will bet money that same vehicle, keeping everything else the same, but swapping for a larger, freer flowing exhaust will make the same power numbers (if not more) at LOWER boost, and SOONER in the RPM range. Your anecdotal evidence doesn't prove anything other than you can force air through a small straw. But if you could run a bigger straw, and it would put less strain on the components...why in the world would you not?

Here's the bottom line: there is NO scavenging downstream of a turbo. Do you think otherwise?

Additionally, I would argue that the OEM 2.25" dual exhaust is the minimum for 400 CRANK hp. Which makes sense: Ford would have designed exactly to the power output of the engine and no larger, because larger means more cost for little to no benefit. But the second one starts going over 400 chp, 2.25" is too small. So with mild bolt-ons and a tune, the 2.25" is no longer an acceptable diameter.

Okay. With that said, what, ultimately is your point? Are you trying to say that people don't need to upgrade their exhaust because the OEM one is good enough? Is that what you are saying?

 

[bosephbarking]

Mcglsr2 you are a bit off sir. The ST has a dual 2.25" exhaust from the factory. 3 cylinders with a turbo are not maxing out the flow rate of a 2.25" pipe. A single 2.25" pipe, sure, but that's not what we have.

The second piece you seem to be missing is the stock downpipe. It isn't 3" piping. Replacing shit after it means nothing when the pipe diameter right out of the turbo is smaller.

Another piece for you, these are not twin scroll, ceramic ball bearing turbos like the vehicles you mentioned. The very turbos you speak of are extremely different and have a 3" or larger hot side. There is a reason to have a little restriction right out the gate. That's due to SIZE of your turbo and its compressor mapping. Your turbo is designed to flow a specific amount of air, its a concert with a ballroom dance happening at the same time. If the dancers and players are not on the same page shit gets fucked up.

To put this succinctly, your turbo outlet and downpipes don't change in size for most people modding here. A cat back exhaust does jack crap to reduce backpressure because it's a dual exhaust already. A single 3" exhaust flows less than the dual 2.25" exhaust we have.

Thank you and have a good day.

 

[mcglsr2]

Mcglsr2 you are a bit off sir. The ST has a dual 2.25" exhaust from the factory. 3 cylinders with a turbo are not maxing out the flow rate of a 2.25" pipe. A single 2.25" pipe, sure, but that's not what we have.

...but that is what we have. If you are going to split the engine in half and say it's only 3 cylinders, you can't then follow that up with "but we have a dual 2.25" exhaust." If you split the engine, you split the exhaust. So if you want to say half is a 3 cylinder with a turbo, with a single 2.25" exhaust...then yes, I agree. You can't just throw in the dual exhaust at the end there because it suits you, the other 3 cylinders and turbo don't just disappear. Now, I'm willing to concede that 2.25" is the acceptable minimum for 3 cylinders and a turbo. Additionally, to just say "3 cylinders", that is potentially misleading, because what it comes down to is flow. We could be talking about 4 tiny pistons (half of a 3.0L v8) vs 3 larger pistons (half of a 3.0L V6). So the number of cylinders isn't nearly as important as the exhaust flow that is produced.

The second piece you seem to be missing is the stock downpipe. It isn't 3" piping. Replacing shit after it means nothing when the pipe diameter right out of the turbo is smaller.

Am I, though? What size do you think the stock downpipe is? Would you be surprised if I told you it were 2.5", NOT 2.25"? Though I do completely agree with you that any change downstream of a small downpipe is diminishing returns, especially the further away from the turbo you go (however, doing a downpipe-back is NOT meaningless - if the replacement exhaust reduces backpressure, that's a benefit; it's not ideal, but it's also not necessarily meaningless). In this case, though, the OEM exhaust "necks down" to 2.25" from the downpipe. So, while one could argue that a 3" exhaust is wasted, it kind of isn't, as it is still stepping up the OEM exhaust to at least match the downpipe. And if one plans to do more mods later anyway, who wants to buy an exhaust twice? But I will agree that part of those "mods to do later" must include 3" downpipes to get the full benefit of a 3" exhaust. Actually, an even bigger downpipe would be better, but likely won't fit in the space there.

Another piece for you, these are not twin scroll, ceramic ball bearing turbos like the vehicles you mentioned. The very turbos you speak of are extremely different and have a 3" or larger hot side.

You are making my points for me. Exactly, those cars are using turbos designed to spool as easily and quickly as possible - in other words, the exhaust has less impact on the spool, as the turbos are "better." So those cars could run a slightly worse exhaust and maybe still get great performance. Because the turbo compensates. We do not have that luxury with our journal bearing turbos. So it makes even more sense for us to do whatever we can to help our turbos out - like install bigger exhausts. Furthermore, just because they are using better turbos does not change the fact that they are still turbos, and will work just like the ones we have in the ST. "Better" does not mean they violate the laws of physics.

There is a reason to have a little restriction right out the gate. That's due to SIZE of your turbo and its compressor mapping. Your turbo is designed to flow a specific amount of air, its a concert with a ballroom dance happening at the same time. If the dancers and players are not on the same page shit gets fucked up.

No, no and no. That is a myth that keeps getting perpetuated, and it just will not die. Restriction is BAD. Full stop. Period. End of statement. Turbos do not need nor do they like backpressure. They do not want "restriction". This is literally the absolute opposite of what a turbo wants, is backwards thinking, and comes from people who have knowledge of NA cars but not turbo cars. They keep pushing this. Yes, the turbo is designed to flow a certain amount of air. The compressor map describes what this flow is and how efficient the turbo is at doing it (the islands). And if the turbo starts to flow too much air, do you know what happens? The wastegate opens up, keeping the rotation in check. To have one say that the exhaust is the thing that is supposed to keep the rotational rpm of a turbo in check is simply asinine, and flat out wrong. Backpressure is a byproduct of restriction - it's not there because it's desired, it's there because the components used do a piss poor job of eliminating it.

To put this succinctly, your turbo outlet and downpipes don't change in size for most people modding here. A cat back exhaust does jack crap to reduce backpressure because it's a dual exhaust already. A single 3" exhaust flows less than the dual 2.25" exhaust we have.

Yup, and the downpipes are 2.5". Which means, at a minimum, you could step up to a 2.5" exhaust and see benefit. Furthermore, you are incorrect regarding the backpressure statement. TMac does this too, he keeps trotting out the cross-sectional area of the pipes, saying that dual 2.25" is larger than 3" and that super powerful cars are running 3" and they make gobs of power, etc. etc. And he's not wrong. But he is misrepresenting the situation. If we were talking about a piece of straight pipe, then yes, everything he says regarding the area is true. But we aren't talking about straight pipe. We are talking about an OEM exhaust, with resonators and mufflers (i.e. restrictions) designed to keep the EPA happy and the exhaust note quiet. Those 3" pipes he's talking about on other cars, those are AFTERMARKET designs, with the singular purpose of increasing flow at the expense of all else. Do you really think our OEM exhaust is a super free-flowing exhaust? Really? It's got a resonator (is it high-flowing?), those mufflers (are those big ass boxes high flowing?), crush bends (not even mandrel bent - which means that one could correctly argue that the exhaust is even smaller than 2.25" in a couple places), all that stuff. To simply state that 2.25" dual has more cross-sectional surface area than a 3" is leaving many, many details out of the equation.

For the life of me, I genuinely don't understand where you guys are coming from. And I'm honestly trying. I'm not a fan of modding just for modding-sake, so I'm not coming from there. I'm not a fan of wasting money. So if you aren't either, I get that. But there are literally thousands upon thousands of dynos out there, across many makes and models, that show gains on turbo motors stepping up to larger exhausts (and yes, especially with larger downpipes when necessary). So I really don't understand the push-back here. If you guys are trying to say that the OEM exhaust "is good enough" for a stock ST, then okay. I'm willing to concede that. But if you then want to follow that with "a larger exhaust is not necessary" then no, that is not a true statement. It is absolutely not true.

At the end of the day, a turbo exhaust section is a pressure differential device (not unlike a fuel injector in a boosted application, if you understand how they work). High pressure on the upstream side (pre turbine wheel), low pressure on the downstream (post turbine wheel). ANYTHING that increases pressure on the downstream side, without a complimentary increase on the high side, will hurt performance. It's as simple as that.

Thank you and have a good day.

You are welcome and I'm trying my best!

 

[bosephbarking]

You good dude?

 

[TMac]

"Additionally, I would argue that the OEM 2.25" dual exhaust is the minimum for 400 CRANK hp. Which makes sense: Ford would have designed exactly to the power output of the engine and no larger, because larger means more cost for little to no benefit. But the second one starts going over 400 chp, 2.25" is too small. So with mild bolt-ons and a tune, the 2.25" is no longer an acceptable diameter."

I don't think you even bother to read anyone's post but your own! I already replied in post (#46) we have actual dyno charts on-site at 560 crank HP on the stock exhaust- in fact stock EVERYTHING except a ZFG tune..

I also provided you three links in post (#41) that provided additional info- you either didn't read them or didn't understand them.

You made a very nice DIY thread on your audio build- you should stick to that.

 

[mcglsr2]

You good dude?

Really? That's your response? Of course I am good. Is there a reason I shouldn't be?

"Additionally, I would argue that the OEM 2.25" dual exhaust is the minimum for 400 CRANK hp. Which makes sense: Ford would have designed exactly to the power output of the engine and no larger, because larger means more cost for little to no benefit. But the second one starts going over 400 chp, 2.25" is too small. So with mild bolt-ons and a tune, the 2.25" is no longer an acceptable diameter."

I don't think you even bother to read anyone's post but your own! I already replied in post (#46) we have actual dyno charts on-site at 560 crank HP on the stock exhaust- in fact stock EVERYTHING except a ZFG tune..

Yup, I saw that. I replied to it in post #48, in the last bullet point. I don't think you even bother to read anyone's post but your own!

I also provided you three links in post (#41) that provided additional info- you either didn't read them or didn't understand them.

Oh I assure you, I both read and understood them.

You made a very nice DIY thread on your audio build- you should stick to that.

Really? Putting me in my place, huh? Because I called you out for being wrong about something? So rather than actually addressing any of it (for example, do you believe that scavenging happens downstream of a turbo? You didn't answer that.), you just keep pointing to the same posts that I explicitly said don't apply because you are making some incorrect assumptions. And now you are telling me that it's not my place to talk about this stuff because it goes against what you say. Really...? Hey, that's okay. I'm new here. But I'm learning. And I see you. Quite clearly now. I think we are done here.

Anyway, sorry OP that you hate your exhaust. I'm sure there are plenty of people that will gladly take it off your hands. I have a stock exhaust sitting in my garage, with about 25K miles on it, I'll sell it you for a good price in case you already got rid of yours. Florida truck, so no salty winters to wear and tear on it. Local pick up only.

 

[bosephbarking]

Really? That's your response? Of course I am good. Is there a reason I shouldn't be?

I don't bother responding when people try to put words in my mouth. Plus the fact that you think 2 pipes to 3 cylinders and a turbo each somehow doesn't mean you half the exhaust flow. 100% of the exhaust doesn't come out each side half of it does. So yes my logic is sound.

If you split the engine, you split the exhaust. So if you want to say half is a 3 cylinder with a turbo, with a single 2.25" exhaust...then yes, I agree. You can't just throw in the dual exhaust at the end there because it suits you, the other 3 cylinders and turbo don't just disappear.

It literally goes out the other pipe. Only one pipe is flowing an entire turbos worth of energy. So yes I can ignore the other turbo when halfing the exhaust gases produced because they go out the other side. So in reality the volume of 2.25" exhaust for the entire engine is doubled. You can't say yes we have dual exhaust then ignore simple math. You want so badly to be right I'm willing to bet you are foaming at the mouth right now.

Link to support my claims that 2 pipes are better than one.

https://garage.grumpysperformance.c...calculating-required-exhaust-pipe-size.11552/

Added a screenshot here since you'll try to gloss over it too. I can't wait to see how you attempt to twist this.

I'm asking if you are good because this clearly bothers you. Look dude you go be right, I don't need to beat my chest and measure with you. Do you boo. Hope you can get past whatever it is that makes you so agitated.

PS. I'm done with your games. Take an anger management class.

 

[mcglsr2]

Mcglsr2 you are a bit off sir. The ST has a dual 2.25" exhaust from the factory. 3 cylinders with a turbo are not maxing out the flow rate of a 2.25" pipe. A single 2.25" pipe, sure, but that's not what we have.

I dunno man. I read that like 5 times. I guess I read it wrong, and there was some other way to read it. My bad I guess.

So let me get this straight. You say stuff that just isn't right. I call you on it. You then act like I'm all pissed about it. This was literally our conversation:

You: "the sky is red."
Me: "No, the sky is blue."
You: "Woah dude, calm down, you are clearly getting pissed over this."

Am I really the one that so badly wants to be right? Are you sure?

PS. I'm not playing any games. I'm just saying you are wrong. And rather than opening your mind to that possiblity, you change the topic to now me having anger management issues. Which you apparently were able to suss out from a couple posts on the internet. Are you sure it's me?

So I got your hero TMac over here telling me to STFU and learn my place because I speak against him how dare I, and you telling me I have anger management issues. Okie dokes, boo.

 

[bosephbarking]

I dunno man. I read that like 5 times. I guess I read it wrong, and there was some other way to read it. My bad I guess.

So let me get this straight. You say stuff that just isn't right. I call you on it. You then act like I'm all pissed about it. This was literally our conversation:

You: "the sky is red."
Me: "No, the sky is blue."
You: "Woah dude, calm down, you are clearly getting pissed over this."

Am I really the one that so badly wants to be right? Are you sure?

PS. I'm not playing any games. I'm just saying you are wrong. And rather than opening your mind to that possiblity, you change the topic to now me having anger management issues. Which you apparently were able to suss out from a couple posts on the internet. Are you sure it's me?

So I got your hero TMac over here telling me to STFU and learn my place because I speak against him how dare I, and you telling me I have anger management issues. Okie dokes, boo.

And there it is. Ignore factual evidence in your face. The world isn't round it's FLAT mcglsr2 exclaimed.

Look at the link. Look at the stuff your presented. Respond to it or keep digging your hole. I stayed on topic and you went to a new one but. Troll 101 distract, accuse, insult and lie. You play the game nicely bud.

 

[TMac]

I dunno man. I read that like 5 times. I guess I read it wrong, and there was some other way to read it. My bad I guess.

So let me get this straight. You say stuff that just isn't right. I call you on it. You then act like I'm all pissed about it. This was literally our conversation:

You: "the sky is red."
Me: "No, the sky is blue."
You: "Woah dude, calm down, you are clearly getting pissed over this."

Am I really the one that so badly wants to be right? Are you sure?

PS. I'm not playing any games. I'm just saying you are wrong. And rather than opening your mind to that possiblity, you change the topic to now me having anger management issues. Which you apparently were able to suss out from a couple posts on the internet. Are you sure it's me?

So I got your hero TMac over here telling me to STFU and learn my place because I speak against him how dare I, and you telling me I have anger management issues. Okie dokes, boo.

Well, that wouldn't "literally" be the conversation. And I didn't tell you to STFU. Since @bosephbarking only just joined and I don't know him, I doubt I've had time to become his hero, so don't bring me into this. Have you heard of the psychological term "projection"? I don't want to get involved in something personal, I deal with technical things. If you're incorrect, I'm going to point it out, but it's not personal. When you make it personal you're going to lose credibility. You only recently joined. Intelligent people know when to quit digging.

 

[bosephbarking]

Sigh

 

[mcglsr2]

And there it is. Ignore factual evidence in your face. The world isn't round it's FLAT mcglsr2 exclaimed.

Look at the link. Look at the stuff your presented. Respond to it or keep digging your hole. I stayed on topic and you went to a new one but. Troll 101 distract, accuse, insult and lie. You play the game nicely bud.

You edited your post with the links AFTER I already replied. I can't address something that isn't was there in the first place. But now that it is...let's take a look at it.

For that link, I followed it. Guess what. All they talk about are NA engines. They even talk about carbs (because that's applicable to our engine). Oh, and it talks about cylinder scavenging - which is totally a thing for NA engines but not boosted ones. I even followed the links from inside that link. They are still talking about NA engines. I feel like you are trolling me.

As for the image, let's take a look. Okay. Look at that. Horsepower: 250 to 550. Well, ours is 400. So that's the only range listed there that it fits in. And we look across to the dual pipe entry...huh. 2.5" to 3". Well shit. That wasn't what you were expecting.

But wait! Our displacement is 183 ci. True, true. Okay. Let's look at that line. Horsepower...100 to 150. Wait. Well that isn't right. So here's the thing. This chart, it's for non-turbo engines. I will bet you a dollar. The power numbers for displacement are way off for a boosted engine.

But you know what? I went ahead and followed that link listed for exhaustvideos.com on how to calculate muffler size, and I read it (despite that you guys think I don't). As they are setting up the parameters for their calculation, they list this:

2) To calculate the volume of air the engine takes in, we multiply the displacement of the engine by the engine RPM and then divide by two (it takes two full revolutions for the engine to exhaust it’s entire air volume). We then convert that to volume to mass.

That, right there, is for a NA engine. Not a boosted one. So the image is wrong, and the link that does the calcs in that image...is basing it off of a NA engine. So it's wrong. I don't know how many different ways I can say it.

Look, if you want to call me angry, or say that I have issues, or call me boo, whatever man. I honestly don't care. But you are wrong. And you are spreading wrong information. I could have not said anything. But that's not the point of these forums. People come here to learn. I come here to learn. I'm absolutely not saying that you have nothing to offer. But I do care when people spread incorrect things. And how a person responds to being told they are wrong speaks volumes to that person. You have not responded well. You just assume I'm an angry idiot with some agenda or chip on his shoulder, and that I don't know what I am talking about. And I dunno, maybe that's my fault. Maybe I presented the info wrong somehow. I'll think on that. But I have not been angry. I have been patient. And you keep putting data in front of me for NA engines (which we do not have), and just wash your hands of me because I won't accept that. If that's how you want to go, okay. No hard feelings man. I don't have to convince you. But I will keep telling you you're wrong. So, there's that.


And just in case it disappears, I'll repost the image you added in after the fact.

 

[mcglsr2]

If you're incorrect, I'm going to point it out, but it's not personal. When you make it personal you're going to lose credibility.

You made a very nice DIY thread on your audio build- you should stick to that.

Yah. Okay. You are incorrect about something. I pointed it out to you. It's not personal for me. The data you are using is for NA engines, dude. I'm not the one making it personal here. I didn't say you should stay out of any certain topics. I didn't tell you that you made a nice post over in the tire section and maybe you should stick to that - the obvious implication being because you don't belong here. I even said that all the stuff you said was solid and sound (for NA engines). And yet, you put it back on me. You tell me I'm projecting. You tell me I don't want to read. I ask you direct, specific questions, you ignore them. And then tell me I'm losing credibility. And that I'm the one making it personal. Whatever man. I've read other posts from you. You've got a brain. So I'm at a loss as to why, when I said you were wrong, your response was "no I'm not," rather than "hmm, let's talk about this." You aren't here to learn. You are here to tell. Like I said. I see you.

TMAC you Are a treasure.

And I was just going off what he said. I don't know if you know each other. It's the internet, we're all anonymous keyboard warriors!