How important is mandrel bending in exhaust pipes?

[talon95newb]

I was originally under the impression that only the intake pipes really had to be mandrel bent. I'm asking because I can get a custom 2.5" turbo back for $120, but not mandrel bent. I know most exhaust kits cost a whole lot more than that so do you guys think I should go for this deal or not? Keep in mind I will probably never reach 400whp, my current goal is around 300whp.

 

[Xeiros]

Take a straw and blow through it. Repeat while slightly pinching one section (or use a loose fitting paperclip). Then repeat while while pinching two sections, three...Each added restriction causes increased backpressure to the total flow. This is not scientific but the general principle is there. Draw your own conclusions.

I see where you're going with this, and I agree. The thing is, if there isn't a bunch of restrictions, your overall back pressure shouldn't be very bad, especially if you use larger diameter pipe for those sections.

There are 4 bends on a GT-S section (2 90's and 2 45's). Using the restriction percentage posted earlier for the 45's (20%), if you wanted a 3" catback, and used 3.5" in those two sections, you're diameter would be 2.8. Now yes, I do realize that it is restricted, but it's now only restricted 6.66% instead of 20%. I don't know what the restriction is on a 90, but I'm sure it would be greatly dimished as well (though yes, I know, not totally gone).

There are ways of making a pressbend work more effectively.

 

[Xeiros]

One more thing I wanted to add. I did find a Mandrel vs Pressure bend dyno sheet, and yes mandrel does win. If you don't opt for a larger diameter pipe for your bends when it's pressure bent, you will see more of a loss.

http://www.bobsmuffler.com/dyno.htm

Also, if you do want mandrel bends, there is also a pretty reasonably priced place I found on the intranets as well.

http://www.globaltecheng.com/ProductCart/pc/viewcat_h.asp?idCategory=65

 

[DSMcamaro]

The only possible way you're going to make a profit off of a press bent exhaust system is if you sell it to some idiot who doesn't know what he's buying (and thus, what he should be buying).

So we should all go out and buy this expensive ass mandrel piping and press bent is for idiots? My full 2 1/2" exhaust on my fwd is close to getting me into the 12's with my 14B. I also built my own intercooler piping with press bent exhaust pipe...same car, am I proud of the way it looks, not so much, but it works damn fine and thats all I care about.(like most dsmers) My Camaro with 2 1/4" press bent exhausts runs a 12.6. So now if I had mandrel bent pipe on it I'd probably still run what...... a 12.6? (or lower considering I could spent my money better elsewhere) Will mandrel bent pipe flow better than press bent....duh. Does every tuner on here need mandrel bend, NO.

PS -when I said fine, I was responding to his question of if press bent was good enough to make 300WHP.

 

[DSMunknown]

Something you could do to keep a large restriction from happening is if you're using 3" piping for your exhaust and have to do pressbent, do 3.5" for your bends, that way your restriction is minimal.

Now you're getting the idea.


While adding larger ID sections at the bends will still cause turbulence, there will be much less of a restriction then if one were to stay with the same-sized piping throughout a press bent exhaust system.

Will mandrel bent pipe flow better than press bent....duh.

I rest my case.

 

[DSMcamaro]

Quote:
Originally Posted by DSMcamaro
Will mandrel bent pipe flow better than press bent....duh.

I rest my case.

Funny how that wasn't the original question.

 

[PieEyedPiper]

Not to stirr up the debate, but if someone were to test 2 piping systems, both mandrel bent, but one system had 1/8 of an inch section of piping that was 2.5 while the rest of the system was 3" and the second piping system to have just pure 2.5" piping with no neck downs, and the first piping system was proven to flow more air over a given time at an exact pressure over the second system, would that make you, DSMunknown, wrong?

 

[19Eclipse90]

Not to stirr up the debate, but if someone were to test 2 piping systems, both mandrel bent, but one system had 1/8 of an inch section of piping that was 2.5 while the rest of the system was 3" and the second piping system to have just pure 2.5" piping with no neck downs, and the first piping system was proven to flow more air over a given time at an exact pressure over the second system, would that make you, DSMunknown, wrong?

Interesting. Though technically, would either flow better than the other? I'm gonna have to test this later cause I'm so very interested now. Think of a funnel since it is my easy way of seeing a neckdown. Pouring a liquid in a normal funnel will exit at lets say X mL/sec. Take another funnel that, say, is connected to another funnel end to end (the neckdown part to neckdown part). Pour the same amount of liquid into one end of that concoction and it seems that it will still exit at X mL/sec. Opening it up at the other end will not help it flow more.
Yes I understand that this is a gas we are talking about and that it is very hot and should expand to the shape of it's container, however, the whole time it is running through the exhaust piping it is cooling. The one neckdown should restrict the flow allowed to move through the rest of the pipe because at the point of the neckdown in the pipe, the gas temperature should be fairly fairly close. So while the pipe previous to the neckdown is trying to flow so much air, after the neckdown will not be able to flow the same amount.

Just my thoughts on the subject. Please, proceed......

 

[luvmygst]

Interesting. Though technically, would either flow better than the other? I'm gonna have to test this later cause I'm so very interested now. Think of a funnel since it is my easy way of seeing a neckdown. Pouring a liquid in a normal funnel will exit at lets say X mL/sec. Take another funnel that, say, is connected to another funnel end to end (the neckdown part to neckdown part). Pour the same amount of liquid into one end of that concoction and it seems that it will still exit at X mL/sec. Opening it up at the other end will not help it flow more.
Yes I understand that this is a gas we are talking about and that it is very hot and should expand to the shape of it's container, however, the whole time it is running through the exhaust piping it is cooling. The one neckdown should restrict the flow allowed to move through the rest of the pipe because at the point of the neckdown in the pipe, the gas temperature should be fairly fairly close. So while the pipe previous to the neckdown is trying to flow so much air, after the neckdown will not be able to flow the same amount.

Just my thoughts on the subject. Please, proceed......

If you go strictly by that theory then 2.25" exhuast would be all you ever need. The exit at the o2 housing is not 2.5". Im no expert but the mandrel would be better, but either would make more power than stock.

 

[19Eclipse90]

If you go strictly by that theory then 2.25" exhuast would be all you ever need. The exit at the o2 housing is not 2.5". Im no expert but the mandrel would be better, but either would make more power than stock.

Oh yeah....I forgot to try and make a loop hole or theory for that part....
Again, people who know what's going on since I do not, proceed.

 

[PieEyedPiper]

If you go strictly by that theory then 2.25" exhuast would be all you ever need. The exit at the o2 housing is not 2.5".

^^^ therin lies the problem.


Something only half realted though has also piqued my interest. There is a company, a magazine perhaps? I forget who did it but they have a review of the capability of a stock 99 GSX posted on the web. They experienced a 40whp increase by removing the cat from the stock 2.25" exhaust.

 

[lookinfor400hp]

^^^ therin lies the problem.


Something only half realted though has also piqued my interest. There is a company, a magazine perhaps? I forget who did it but they have a review of the capability of a stock 99 GSX posted on the web. They experienced a 40whp increase by removing the cat from the stock 2.25" exhaust.

Dang it , now my wife is mad at you................

I just spent the last 1/2 hour digging into 10 years worth of magizines.
It was either SSC or Turbo , they were doing step by step modding/dyno runs.
After doing air filter,3" cat back then a 3" Dp , they pulled the cat and gained 30-40 hp.
But I think that was in conjunction with the DP with cat delete.
Still have to find the book , right now I cant locate it

 

[nightspeed87]

I have something to add. A 3in system is supposably good for at least 400whp right?
Since turbo cars dont need backpressure, would it matter then if one were to just get a full 3.5 in exhaust since the diameter is more than youd need anyways but yet where it crushes down it would flow better than a car with a full 3in exhaust with crush downs?

Also to add, what if your running o2 dump into the atmoshere ...
This would also mean at least xx percentage of your exhaust isnt exiting through that
main pipe so your flow demands would be less and the press bent may not matter so
much in that scenario; correct?

 

[1gcrazy]

I have something to add. A 3in system is supposably good for at least 400whp right?
Since turbo cars dont need backpressure, would it matter then if one were to just get a full 3.5 in exhaust since the diameter is more than youd need anyways but yet where it crushes down it would flow better than a car with a full 3in exhaust with crush downs?

Also to add, what if your running o2 dump into the atmoshere ...
This would also mean at least xx percentage of your exhaust isnt exiting through that
main pipe so your flow demands would be less and the press bent may not matter so
much in that scenario; correct?

The prices between a larger pressbent and a mandrel will almost be the same...maybe even more for the pressbent since 3.5 is kinda hard to find.
Also, a mandrel would STILL be better because like someone said above...a restriction like that will cause turbulance...

 

[DSMunknown]

Every time a liquid (aka air) has to change direction or is forced into a smaller diameter, there is a loss of power.

Just to clarify, I actually meant to use the term "fluid" instead of "liquid."

True to an extent. Exhaust pulses much like electricity follow the path of least resistance. Just having a neck down does not negate the whole system, but will make a slight difference.

Sorry for not catching this before. I hope you're not referring to exhaust scavenging. Scavenging has NOTHING to do with turbocharged vehicles. But if that's not what you're referring to when using the term "pulses" when discussing exhaust systems, then please clarify.

There are impedances throughout the whole system though. The exhaust portion coming from the head, and exhaust manifold are not 3", so by your way of logic, we shouldn't bother improving pipe size, when in reality, it improves performance.

You're forgetting an important aspect to exhaust manifolds with a turbocharged system - the four runners are forcing the excess gases through the turbine housing and pass the turbine wheel (and in certain instances, pass the internal/external WG). Thus, you could claim that the turbine housing/wheel/valve are all impeding on the flow of the exhaust gases, and therefore they are a restriction. But of course they are restrictions to this flow, but the results far outweigh the minor backpressure inside the exhaust manifold.

There are 4 bends on a GT-S section (2 90’s and 2 45’s).

I think you mean GS-T (unless you are now discussing the Celica).


Actually, there are three 90 degree sections. You forgot the DP. If you really want to get technical, you could make the argument that there are four 90 degree sections. That is, the gases escape the turbine horizontally, and are usually redirected down towards the ground in a 90 degree fashion. Most people usually see this regarding the O2 housing.

I also built my own intercooler piping with press bent exhaust pipe

...

My Camaro with 2 1/4" press bent exhausts runs a 12.6. So now if I had mandrel bent pipe on it I'd probably still run what...... a 12.6?

First of all, you are now bringing in the issue of piping on the intake side, which doesn't necessarily follow the same exact rules that a discussion on exiting exhaust gases will follow.

What do I mean by this… well, let's go back to something I stated earlier (seen in post # 23) about directional changes. Simply put, the rules of airflow and these directional changes (whether abrupt or subtle) are even more pronounced on the intake side of a turbocharged system than the exhaust side of the same system. This is because the fluid (aka air) is pressurized, and thus SIGNIFICANTLY more dense. Therefore, using press bent tubing for intercooler piping is simply unfathomable to me when considering airflow (and of course, the need to maximize airflow as much as possible).

In addition, bringing in your example of an NA car (assuming that it is NA) has little-to-no bearing on the discussion that is taking place here. As I have already said, we get into the issue of scavenging, which does not apply whatsoever to turbocharged vehicles.

Please keep in mind that my main issue here is airflow, and maximizing its potential. IMHO there is little need to bring in one's 1320 numbers. I'm not particularly interested in what you see at the track. I am interested in maximizing airflow.

Funny how that wasn't the original question.

That's odd, because I thought the original question was something like "How important is mandrel bending in exhaust pipes?"

I think one of the more important questions should be something like "When regarding airflow, how important is keeping the bends and number of bends at a minimum (regardless of the process used)? And, how do I go about maximizing airflow?"

Not to stirr up the debate, but if someone were to test 2 piping system, both mandrel bent, but one system had 1/8 of an inch section of piping that was 2.5 while the rest of the system was 3" and the second piping system to have just pure 2.5" piping with no neck downs, and the first piping system was proven to flow more air over a given time at an exact pressure over the second system, would that make you, DSMunknown, wrong?

Notice that I was fairly careful with the words I used and how I described the situation. In your example, it would depend on where exactly this collapsed section of piping occurred. Right after the O2 housing? Or perhaps after the B-pipe? You can refer to post # 16 and 23 where I briefly touched on this issue.

But you're not pushing the example far enough! You need to attempt to make a case for resonators/silencers! As you might expect from all I have previously stated, resonators are also airflow obstructions. To put it simply, if one must have a neck down of any kind, ideally it should be as far away from the turbine housing as possible (with the example of resonators, you can't get any farther away than that).

Trying to not get too technical, I will provide you with yet another example. Let us take a second generation Eclipse GS-T. Let us also assume that what luvmygst claims is true, that the ID of the O2 housing exiting passage is 2.25 inches in diameter. Now let us assume that we are given two exhaust systems for some special occasion. The first system has an ID of 2.25 inches, and the other has an ID of 2.75 inches. Both systems include a down pipe, test pipe, and cat-back system. The larger of the two systems came with a resonator, and the other one did not. Let us also assume that the resonator has an exit hole diameter of 2.25 inches.

What’s different between these two systems?

Well, one difference is the ID (obviously). But what does the larger system have that the smaller system does not? More room for the exhaust gases to fill. Yes, of course the exhaust gases are hot, and want to expand, but that is not the focus of this example. If we put the resonator on the larger system, this will of course create unwanted backpressure. However, the larger system also has the holding capacity to hold more exhaust gases than the smaller system ever will.

What does this mean? It means that the gases coming through the turbine housing have more space to be pushed in to, and thus more gases it can get rid of.

On a side note, there is also the issue of the exhaust valves opening, and lobe camshaft location, but I'm not fit to discuss that in depth here.

However, with the smaller system, there is no area to expand out of the O2 housing. Yes, the exhaust gases are presumably constantly escaping into the atmosphere at the rear of the car, but there is no relief given to the O2 housing. Thus backpressure is created in the O2 housing and turbine housing.

Give this a thought - imagine purchasing a block-off plate that fits perfectly between the down pipe and the O2 housing. Before the install, you decide to drill a 1 inch hole in the center of the plate. Then you install it. Do you see how it wouldn't matter which exhaust system you used (whether it be OEM or a larger ID system)?

If you go strictly by that theory then 2.25" exhaust would be all you ever need. The exit at the o2 housing is not 2.5". Im no expert but the mandrel would be better, but either would make more power than stock.

There is a lot that happens as the gases are leaving the turbine housing and going through the O2 housing, probably more than you realize.

The issue has become deeper than simply comparing press bent and mandrel bent exhaust systems to OEM. The issue is now airflow.

When I address RJ's question below, it will also pertain to your statement (in part).

I have something to add. A 3in system is supposedly good for at least 400whp right?

The simple answer - not exactly.

Why? Because you specifically asked about "whp".

There are other aspects which you need to keep in mind when stating this. Firstly this is an approximation. Such things as directional changes, the use of a catalytic converter (no matter what kind), mufflers, camshaft lobe location, ignition timing, exhaust velocity etc. all play a role.

Just to be nitpicky, I have a problem with your use of the phrase "at least". I will make another generalization here - a three inch exhaust system is not a flow disturbance until 400 crankshaft horsepower (I am assuming that this 3 inch system has an ID that is generally seen with such systems).

So when you ask about an appropriate exhaust system that will not impede on a turbocharged engine putting out approximately 400whp, you have to remember that the crankshaft hp will probably be somewhere around the 450-500 mark (and of course, I just made another generalization).

Since turbo cars dont need backpressure, would it matter then if one were to just get a full 3.5 in exhaust since the diameter is more than youd need anyways but yet where it crushes down it would flow better than a car with a full 3in exhaust with crush downs?

Also to add, what if your running o2 dump into the atmosphere ...
This would also mean at least xx percentage of your exhaust isnt exiting through that
main pipe so your flow demands would be less and the press bent may not matter so
much in that scenario; correct?

As 1gcrazy said, you also need to take into account the turbulence formed with the neck downs in your example.

As far as excess exhaust exiting through an alternative pipe and the effect it would have on the rest of the exhaust flow after passing the turbine wheel, it would seem that you are correct.

But you are also not pushing the example to the extreme. How about no O2 housing?! It would initially seem that this would be ideal. However, physics shows us otherwise. As one individual put it, theoretically,

the "best" exhaust for the widest range of operating conditions would be a short (6-10 inch long) megaphone-style exhaust tube, that tapers at roughly 10 degrees out from the turbine outlet.... The effect is small, but measurable.

Here is a picture of what is being discussed above:

You must be logged in to view this image or video.

Here are some links that may interest those who want to know more:


http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=48
http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=355
http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=47
http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=309
http://www.ricardo.com/download/pdf/wave_iuc_investigating_exhaust.pdf
http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html
http://members.axion.net/~enrique/pressureratio.html



Yes, some of the links above are focused on NA exhaust systems, but certain sections do apply to every exhaust system.

 

[PieEyedPiper]

Anthony,
I'm glad you put so much energy into that post. It shows you have a real interest in the discussion. However, most of our points and examples were, if Im not mistaken, arguements against your statements. It appears as though, intentional or not, that you have side stepped the main issue and picked apart each of our posts and corrected or elaborated on information that was merely there to help prove a point, rather than the real heart of the issue.

How is it that a catback exhaust system on an otherwise stock DSM has been dyno proven to increase hp and torque? Yet, according to you it would make absolutely no difference because of the 2.25" downpipe and cat. You stated that a portion in the middle of the system, as test pipe in your example, would entirely negate the rest of this 3" catback.

I do agree, however, that placement of this restriction does play a large factor (what you said about back pressure closer to the turbine).
I'm also not so sure about your increased holding capacity theory which seems to alter your orignal suggestion that there would not be any performance or flow improvements if there was any restriction in the exhaust. Once the "resevoir" is full, which would happen at the onset of boost, flow would then drop once the resevoir was fully saturated with exhaust gases, would it not?
Granted, I believe it must play a part as to why, in real life, having a larger catback with a stock downpipe does improve flow and performance, but somehting that should also be considered is that since the exhaust gases are cooling the whole way down the exhaust, the gases should be contracting making for better flow and less backpressure as well.
I guess where I'm going with this is that I'm not sure which side of the debate you're on anymore. So to be clear and have a better understanding of your viewpoint:
Do you believe there are any gains from installing a 3" catback onto an otherwise stock exhaust system?
Do you believe in the megaphone 10* taper theory?
And now after answering those questions, do you believe that a smaller diamter test pipe will ultimately negate the entire system after the test pipe?

Regardless of how off track we've gotten from the original topic, I believe this is what we should have been discussing from the get go.
I think everyone here knows and agrees that:
pressbent is "bad"
neckdowns are "bad"
small resonators are "bad'
silencers are "bad"
and any backpressure in an exhaust system is "bad".

p.s. I'm not in any way trying to be antagonistic, I just want to understand

 

[90 TSI FWD]

Anytime an ID is reduced, you may as well have the rest of the piping system be at the same size as the collapsed section.

For example, if you have a 3" down pipe, a 2.5" test pipe, and a 3" cat-back exhaust system, you might as well have a 2.5" cat-back system. Why? Because the test pipe in this instance is creating such a restriction (aka neck down) that it negates the rest of the system completely. Such restrictions in the piping also create turbulence, as opposed to the smooth flow of the exhaust gases. Every time a liquid (aka air) has to change direction or is forced into a smaller diameter, there is a loss of power.

From what you said here, that would mean you might as well get the same diameter piping as whatever the o2 housing outlet is. thus, if you have the stock o2 housing, stick with the stock exhaust?

How big of a collapse is there on a pressbent 3" system? could it be smaller than 2.5"?

 

[DSMunknown]

From what you said here, that would mean you might as well get the same diameter piping as whatever the o2 housing outlet is. thus, if you have the stock o2 housing, stick with the stock exhaust?

I've already addressed that.

How big of a collapse is there on a pressbent 3" system? could it be smaller than 2.5"?

It depends on the craftmanship of the work, and how severe/subtle the bend is.

 

[DSMunknown]

Anthony,
I'm glad you put so much energy into that post. It shows you have a real interest in the discussion. However, most of our points and examples were, if Im not mistaken, arguements against your statements. It appears as though, intentional or not, that you have side stepped the main issue and picked apart each of our posts and corrected or elaborated on information that was merely there to help prove a point, rather than the real heart of the issue.

I took a fair amount of time last night to try and respond to the best of my ability (and to the best of my knowledge and understanding) the posts that I deemed necessary to reply to.

I appreciate that you noticed (as well as I did last night) that certain posts or examples were made to directly negate my propositions. However, that does not shake my resolve in the statements I have made thus far.

As you noted later on in your post, the heart of the issue has changed. This is a good thing.

How is it that a catback exhaust system on an otherwise stock DSM has been dyno proven to increase hp and torque? Yet, according to you it would make absolutely no difference because of the 2.25" downpipe and cat. You stated that a portion in the middle of the system, as test pipe in your example, would entirely negate the rest of this 3" catback.

And I would still stick by my statements. What I mean by "negating" the rest of the system is simply that it does not matter if it's bolted on or not. I realize that that may be a little confusing. So I will clarify.

What do I mean by this... Take a look at this link. At the present moment, the graph, the numbers, and the claim that the author makes stumps me.

I would claim that you would virtually see no difference between leaving the cat-back exhaust system off the car and bolting on a 3" cat-back exhaust system. For me, the numbers should basically be the same.

I do agree, however, that placement of this restriction does play a large factor (what you said about back pressure closer to the turbine).
I'm also not so sure about your increased holding capacity theory which seems to alter your orignal suggestion that there would not be any performance or flow improvements if there was any restriction in the exhaust. Once the "resevoir" is full, which would happen at the onset of boost, flow would then drop once the resevoir was fully saturated with exhaust gases, would it not?

The theory does not alter my original suggestions. If you see conflicting statements I have made, please point them out to me specifically.

I'm not sure about your question regarding the "reservoir" becoming "full." It may in fact become "backed up", but I think it would help if you explained exactly what you mean before I respond. Hopefully we won't get hung up on terminology.

Granted, I believe it must play a part as to why, in real life, having a larger catback with a stock downpipe does improve flow and performance, but somehting that should also be considered is that since the exhaust gases are cooling the whole way down the exhaust, the gases should be contracting making for better flow and less backpressure as well.

I don't have corroborating data in front of me to support your statement, but it would be interesting to see under "normal" conditions what the temperatures are at certain sections of the exhaust system (notice the emphasis on the term "normal").

I guess where I'm going with this is that I'm not sure which side of the debate you're on anymore. So to be clear and have a better understanding of your viewpoint:
Do you believe there are any gains from installing a 3" catback onto an otherwise stock exhaust system?

For me, theoretically speaking, there would be no difference between leaving your cat-back exhaust system on the side of the highway and installing a 3" system. That does not mean I think there will be no advantages to doing so. I cannot deny the very real fact of performance improvements when installing such a system over an OEM system. That would be just crazy.

What I have in mind when claiming this is less back pressure. And for most of us, as the old adage goes, "Less is more."

Do you believe in the megaphone 10* taper theory?

Yes, I do.

Actually, let me rephrase that. No, I don't believe in the theory, per se. It is proven physics, and certainly I will not deny physics its due respect.

And now after answering those questions, do you believe that a smaller diamter test pipe will ultimately negate the entire system after the test pipe?

Which example are we going with again?

If the example is something like a second generation Eclipse GS-T with a 3" DP, a 1" test pipe, and a 3" cat-back system, then my answer is yes.

Regardless of how off track we've gotten from the original topic, I believe this is what we should have been discussing from the get go.

BINGO.

I think everyone here knows and agrees that:
pressbent is "bad"
neckdowns are "bad"
small resonators are "bad'
silencers are "bad"
and any backpressure in an exhaust system is "bad".

BINGO, BINGO, BINGO!

p.s. I'm not in any way trying to be antagonistic, I just want to understand

I thank you for your honesty and genuine attempt to grasp theories and principles which are by no means simplistic. Certainly I do not have all the answers, but I make calculated assumptions based on other principles which I know to be true.

 

[boostnhard]

That's a fantastic price. Bigger is generally better at any hp level (quicker spool, more TQ) but at that price I would do it.

You forgot to mention boostcreep sometimes with certain turbo setups. mine

 

[nightspeed87]

The simple answer - not exactly.

Why? Because you specifically asked about "whp".

There are other aspects which you need to keep in mind when stating this. Firstly this is an approximation. Such things as directional changes, the use of a catalytic converter (no matter what kind), mufflers, camshaft lobe location, ignition timing, exhaust velocity etc. all play a role.

Just to be nitpicky, I have a problem with your use of the phrase "at least". I will make another generalization here - a three inch exhaust system is not a flow disturbance until 400 crankshaft horsepower (I am assuming that this 3 inch system has an ID that is generally seen with such systems).

So when you ask about an appropriate exhaust system that will not impede on a turbocharged engine putting out approximately 400whp, you have to remember that the crankshaft hp will probably be somewhere around the 450-500 mark (and of course, I just made another generalization).

i shouldve been more specific, and I know a lot of variables change the outcome . As I understand a 3in exhaust isnt a restriction until about 400hp. The part I wasnt exact on was whether that was whp/ or bhp.
Also when I asked about the 02 dumping into the atmosphere relieveing xx percentage of the "wouldve been" mainstream exhaust gases you responded

But you are also not pushing the example to the extreme. How about no O2 housing?! It would initially seem that this would be ideal. However, physics shows us otherwise. As one individual put it, theoretically,

Explain what you meant exactly?

 

[Dorifto]

I'll stick with sectioned-pipe for bends.

Case in point, the intake and downpipe on an MA70-chassis Supra [with 2JZ-GTTE swap], from a member of my forum WanganMidnight.com.

http://pwned.my604.ca/New Folder/Supra Build Body and 2jz swap 175.jpg

http://pwned.my604.ca/New Folder/Supra Build Body and 2jz swap 161.jpg

http://pwned.my604.ca/New Folder/Supra Build Body and 2jz swap 162.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 133.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 127.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 128.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 131.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 132.jpg

Even included some close-ups and inside shots for the nit-pickers. This is how I've built all my custom exhausts, both for my cars, and friends' cars.

 

[DSMunknown]

i shouldve been more specific, and I know a lot of variables change the outcome . As I understand a 3in exhaust isnt a restriction until about 400hp. The part I wasnt exact on was whether that was whp/ or bhp.
Also when I asked about the 02 dumping into the atmosphere relieveing xx percentage of the "wouldve been" mainstream exhaust gases you responded

But you are also not pushing the example to the extreme. How about no O2 housing?! It would initially seem that this would be ideal. However, physics shows us otherwise. As one individual put it, theoretically,

Explain what you meant exactly?

So you're asking "Why did DSMunknown bring up this issue of dropping/negating the O2housing altogether? How did he get from my example to this one?"

Well, sooner or later a Newbie would come along and assume that it would be "ideal" to have a non-existant exhaust system coming off the turbine housing. Heck, perhaps even some fairly knowledgeable individuals may try to argue this. So I thought it necessary to address the issue before false claims or assumptions were made that could possibly confuse others.

Quite simply, I was trying to cover an example that was most likely to appear.

I'll stick with sectioned-pipe for bends.

Case in point, the intake and downpipe on an MA70-chassis Supra [with 2JZ-GTTE swap], from a member of my forum WanganMidnight.com.

http://pwned.my604.ca/New Folder/Supra Build Body and 2jz swap 175.jpg

http://pwned.my604.ca/New Folder/Supra Build Body and 2jz swap 161.jpg

http://pwned.my604.ca/New Folder/Supra Build Body and 2jz swap 162.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 133.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 127.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 128.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 131.jpg

http://pwned.my604.ca/Supra Build Body and 2jz swap 132.jpg

Even included some close-ups and inside shots for the nit-pickers. This is how I've built all my custom exhausts, both for my cars, and friends' cars.

This work is exceptional when regarding airflow. Regarding the cost... that's another story. But again, the emphasis has turned to airflow, regardless of one's wallet size and price range.

It seems in the second photo you shared, the owner decided to slightly widen the angle of the piping where the exhaust gases were leaving the turbine housing. Very nice.

The only comment that I would like to make (regarding piping off the turbine housing on any turbocharged automotive vehicle) is that there are measurable gains to be found when removing or decreasing any and all bends from normal exhaust piping. But do not mistake this notion despite the megaphone-style exhaust theory that I stated earlier. This does not mean the "ideal" exhaust system is no exhaust system whatsoever. From a performance mindset, the "ideal" exhaust system (regarding OEM turbocharged DSMs) would be short piping coming out in front of the driver's side front wheel (or something similar). This is assuming that the turbocharger is placed relatively in its original location, and that the engine is still in its original position (that is, it hasn't been rotated like we see with Brent Rau's Eclipse). While this may be the "performance ideal", this would not pass any normal emissions testing by far.