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Old 03-17-2015, 03:30 PM   #1
GrimmSpeed
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Default 2015 WRX Downpipe/J-Pipe - Any Interest?


GrimmSpeed 2015 Subaru WRX Downpipe/J-Pipe

Latest Update - 4.8.15 - CAD Models and Tube Routing


If you’ve been around the Subaru world for long, you’re probably well aware that GrimmSpeed has become a leader in high-end exhaust componentry for the WRX and STI markets. We haven’t yet () dipped into the catback market, as we don’t consider that to present quite the same challenges as the other pieces of most Subaru exhaust systems. We’ve seen time and time again that the care that we take during the development stage pays off with efficient manufacturing, perfect fitment and outstanding quality. When we first became aware of the new downpipe/j-pipe configuration, we got excited. Having decided to delay tackling the 2015 WRX a bit until we were finished with a few other major projects, we kept a close eye on what became available for as time went on. To our surprise, almost a year later, we still see a great opportunity for a product that sets itself apart from the rest.

If you aren’t familiar with our other exhaust offerings, you might enjoy taking a quick look at our downpipes and external wastegate up-pipes. These two products show a wide range of engineering challenges as well as a variety of manufacturing techniques. You’ll also get a glimpse at the quality and craftsmanship that you can expect from GrimmSpeed.





In this thread, we’ll document those observations and how we converted them into system requirements for development. In the interest of full disclosure, at the time of writing this, we do already have a pre-production prototype on our 2015 WRX for testing. The design is still flexible, but it’s important to us that we get many miles on these components before going into production, to ensure that there’s no chance of unforeseen issues during use, given the new chassis and engine configuration.

Requirements

The first thing that we always need to do is establish a set of primary design requirements. Here’s what we came up with. Of course, we have many other requirements as part of every product that we develop, but here are the heavy hitters on this particular project.
  1. The GrimmSpeed J-Pipe must fit all other factory systems without modification (retain grounding point and all other factory hardware).
  2. The GrimmSpeed J-Pipe must be made of extremely durable, high-quality, American materials.
  3. The GrimmSpeed J-Pipe must be offered with and without high-flow cat and thermal dispersant coating.
  4. The GrimmSpeed J-Pipe must utilize the smallest number of bends and be made from a single piece of tubing.
  5. The GrimmSpeed J-Pipe must make very careful use of space to maximize ground clearance.
  6. The GrimmSpeed J-Pipe must not require the use of a flex section to facilitate fitment and tubes must enter flanges at a 90deg angle (no 'cheating' bends).
  7. The GrimmSpeed J-Pipe must include three O2 sensor bungs with plugs for potentially unused bungs.
  8. Your suggestion goes here.
Other requirements that are typical of any GrimmSpeed product involve material selection and sourcing (locally, when possible), quality, visual appeal, innovation, etc.

Here’s where you guys come in. Share some of your experiences with other exhaust components. What do you like, what do you dislike? What features would you like to see?

One of the first things we noticed was how difficult removing the factory J-Pipe can be without the right tools and procedure. Even then, we had some trouble. We also noticed that the factory locking nuts can cause some serious trouble, even after you’ve cracked them loose the first time. Luckily, we’re experienced in machining custom stainless studs, as we provide them with our up-pipes, so that will be something that we’ll definitely be including. We do not recommend reusing the stock nuts if at all possible and if your studs can be easily removed, replacement would be wise. One of ours was quite stubborn, so we left it in.

Initial Design Considerations and Measurement

The first step in the design of this J-pipe is two-fold. We’ve dug into our 2015 WRX to 3D scan the factory exhaust system as well as the entire underside of the car. This will give us the critical points where the J-Pipe interfaces with the turbo, catback and mounting tab. From here, we can bring that data into CAD and start to get an idea of our routing options.
At the same time, we began working on flanges and exhaust gaskets. Each of our exhaust components ships with GrimmSpeed Multi-layer Stainless gaskets to ensure that a cheap gasket doesn’t ruin the experience of an otherwise great product. The same goes for hardware.

Flanges

These flanges aren’t really anything tricky, although with the other support brackets involved, fitment of a ” thick turbo flange will be a bit of a challenge. We’ve got some ideas there, so no worries. We love our ” thick flanges for a few reasons. First, they allow us to weld without having to worry so much about warping the flanges with the heat. We also have some super-secret methods of eliminating that warpage. In most cases, manufacturers seem to hope that the action of bolting the flange to the turbo will flatten it enough to create a seal. A lot of times, that’s true initially, but over time, that gasket will tend to fail or the heat and fatigue of operation will cause the flange to pull and warp even more, sometimes breaking exhaust studs (do we have any Chevy truck owners here?). One reason we'll be extra sensitive to this is that the turbo to downpipe flange does need to have a pretty small cross-sectional area in a couple spots in order to fit and those areas will be especially prone to warping.

Tubing

Finally, the tubing. We’ll use our standard 3” tubing with a flare at the end to meet the 3.5” outlet of the turbine housing. Experimenting in flow simulation will let us know if we need to be terribly concerned with the angle of that transition or not, so stay tuned. Our primary goal here is to make the entire J-Pipe from a single length of tubing. There are a few reasons for that.
  • Less welded joints means more efficient manufacturing (lower cost)
  • Less welded joints means even lower risk of failure
  • Less welded joints means less concern for ‘pulling’ during the final welding process, which means more accurate fit
Based on our previous experiences with bent tube components and from what we’re seeing in CAD, here’s why we believe there aren’t many (any?) others doing the same thing. This pipe is actually quite difficult to bend in a single shot. There’s a bend at the top that’s over 90deg, followed by a few bends to get back to the catback, and there has to be a certain minimum distance between each bend in order to be manufactured. So the greatest challenge in designing this component as a single piece is making it possible to bend while minimizing the amount and angles of the bends you have to make. All the while doing so without sacrificing ground clearance as well as clearance with the car, cross members, swaybar, suspension pick up points and bolts. Does it sound easy? It might. But if it were actually easy you would see more of these created out of a single bent tube as opposed to cut and welded, or welded to flanges and joined. Without the engineering equipment and experience that we have, we’d need to err on the safe side where fitment is concerned, which requires additional bends or decreased ground clearance. We've seen others take the easy route, and we're passing them by as we take the clever route.

What’s Next?

We’re working on compiling a few screenshots of our current CAD model to show some of the areas where we’ve had fitment concerns and some of the areas where we think ‘aggressive’ design will really enhance the product (primarily where ground clearance is concerned).
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Last edited by GrimmSpeed; 04-08-2015 at 11:52 AM.
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Old 03-17-2015, 03:30 PM   #2
GrimmSpeed
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Join Date: Jan 2007
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2015 WRX, 2012 WRX,
2013 BRZ, 2006 STI

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Last edited by GrimmSpeed; 04-08-2015 at 11:54 AM.
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Old 03-17-2015, 03:30 PM   #3
GrimmSpeed
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Last edited by GrimmSpeed; 04-08-2015 at 11:55 AM.
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Old 03-17-2015, 05:33 PM   #4
On_Thy_Edge1
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Mmmm keep me posted. Cause I only live 30mins from you and would love to jump on this as soon as you make them available.
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Old 03-17-2015, 06:06 PM   #5
GrimmSpeed
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Originally Posted by On_Thy_Edge1 View Post
Mmmm keep me posted. Cause I only live 30mins from you and would love to jump on this as soon as you make them available.
Will do! What do you drive? I've been seeing more and more 2015's around!

Matt Beenen
Engineering
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Old 03-17-2015, 09:02 PM   #6
WRX YNZ
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Do you guys have an idea on price?

I want one coated and catted. TAKE MY MONEY!
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Old 03-18-2015, 12:04 AM   #7
On_Thy_Edge1
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Originally Posted by GrimmSpeed View Post
Will do! What do you drive? I've been seeing more and more 2015's around!

Matt Beenen
Engineering
2015 WRX WRB just pick it up last week in feb. So, most likely ur j pipe will be my first mod. Must ask the President of the house hold aka wife. But She can't say no cause she has here 11' Forester XT to race around.
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Old 03-18-2015, 12:30 AM   #8
ryager
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Grimmspeed, I do not want to throw anyone under the bus, however Mishimoto did the same thing with the questions for an exhaust. I would suggest going over to that thread and reading some of those suggestions and see if anything pops out at you guys. One of the main things were keeping factory locations, being able to keep the grounding wire, keeping 02 sensor in factory location and also adding in a wideband bung that can be plugged, which you guys seem to have already hit up. I would say to utilize quality bolts also, many companies seem to make some great stuff and then the hardware is half-assed and rusts all the time and things like that. The bolts and studs are just as important as the main unit. The cat can fit in the factory location, Cobb has already done this however other manufactures are saying it cannot be done. I just got a custom TBE put on and he has the cat in the factory location. I like how you guys already hit up that it needs to be able to connect with the factory cat-back portion, a flange going from 3" to factory size would be awesome. Also people like when the j-pipes come with extra bolts and studs incase they are broken or stripped in the process, this happens often. I am pretty sure at this time that Mishimoto is the only ones that give the extra hardware with their j-pipe. Other than this, which you hit up most of it, it sounds like you guys are ready to go. I cannot think of anything else, nor can I think of anybody else's gripes and complaints when it comes to exhausts. Do you guys think you will be making a cat-back at some point? If so I know one of the biggest complaints with that is highway drone.
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Old 03-18-2015, 12:04 PM   #9
GrimmSpeed
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Originally Posted by ryager View Post
Grimmspeed, I do not want to throw anyone under the bus, however Mishimoto did the same thing with the questions for an exhaust. I would suggest going over to that thread and reading some of those suggestions and see if anything pops out at you guys. One of the main things were keeping factory locations, being able to keep the grounding wire, keeping 02 sensor in factory location and also adding in a wideband bung that can be plugged, which you guys seem to have already hit up. I would say to utilize quality bolts also, many companies seem to make some great stuff and then the hardware is half-assed and rusts all the time and things like that. The bolts and studs are just as important as the main unit. The cat can fit in the factory location, Cobb has already done this however other manufactures are saying it cannot be done. I just got a custom TBE put on and he has the cat in the factory location. I like how you guys already hit up that it needs to be able to connect with the factory cat-back portion, a flange going from 3" to factory size would be awesome. Also people like when the j-pipes come with extra bolts and studs incase they are broken or stripped in the process, this happens often. I am pretty sure at this time that Mishimoto is the only ones that give the extra hardware with their j-pipe. Other than this, which you hit up most of it, it sounds like you guys are ready to go. I cannot think of anything else, nor can I think of anybody else's gripes and complaints when it comes to exhausts. Do you guys think you will be making a cat-back at some point? If so I know one of the biggest complaints with that is highway drone.
Regarding your very first comment, I feel obligated to point out that this method of community involved product development is something that we've been doing for a very long time and has been (in my opinion, poorly) replicated by others as of late. Check out our 16 month, 1000 post development thread for our latest TMIC engineering cycle. It's also important to note that the difference is that we're doing this in real time, rather than after the product has been fully developed and is in production, so your answers to our questions can have a real impact on the design of the product. Lastly, most of what you've mentioned are features that are standard for us. We've been including a complete set of high-end, American made hardware with all of our exhaust components since 2007, even machining custom stainless hardware when we're not satisfied with what's available (our uppipe studs, for example). The same goes for our multi-layer stainless steel exhaust gaskets.

We're looking for the community feedback to spark something new and interesting. Our engineering, development and manufacturing capabilities are unique and I strongly suspect that if you've had a chance to handle and install our products, you're well aware of that. It's not our style to enter a market and simply provide an 'alternative'. We insist on offering something that sets itself apart, either by it's design, materials, manufacturing, quality, performance or a combination of factors. Like we mentioned, we've already identified a couple of areas where there's definite improvement to be made.

To clarify the first post, and I think this might be how you got on the hardware topic, my comment regarding hardware is that we won't require that you modify other parts of the car to fit the exhaust. For what we can tell, a couple of manufacturers include additional low profile bolts that replace OEM suspension hardware in order to buy themselves more clearance in certain areas. We aren't seeing that this is necessary unless the design of the tube must pass through that space. We're always very cautious when it comes to replacing OEM hardware, particularly when a critical vehicle system (like suspension) is concerned.

Regarding the cat placement, do you know what the importance of having the cat in the factory location is? In our experience, placing it at the end of the straight tube greatly reduces the effect that is has on the exhaust gas velocities through the downpipe. Is the concern that you wont have the heat to light it off? On the GD/GR Subaru, we place our cat much further from the exhaust ports and it still functions very well. The only reasons that we can think of to try and force the cat into it's original location are to keep it in the same spot if you happen to have regulations in a racing series that require that or if you want to try and trick the ECU into not throwing a code (which you would just disable during the tuning process anyway). One concern with that location is that with the larger tube and cat, you can't mange that amount of heat properly. The factory pipe has a very nicely made series of heatshields to protect your belt and water pump. Putting a high flow cat right there makes me a little bit nervous, to be honest.

In any case, your feedback is greatly appreciated. Do you mind if I ask why you opted for a one-off TBE rather than one of the existing options? Have you uninstalled it and reinstalled it yet?

Matt Beenen
Engineering

Last edited by GrimmSpeed; 03-18-2015 at 12:14 PM.
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Old 03-18-2015, 12:17 PM   #10
GrimmSpeed
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Quote:
Originally Posted by WRX YNZ View Post
Do you guys have an idea on price?

I want one coated and catted. TAKE MY MONEY!
Nothing firm yet, but you can expect that it will be very competitive with the rest of the market!
Quote:
Originally Posted by On_Thy_Edge1 View Post
2015 WRX WRB just pick it up last week in feb. So, most likely ur j pipe will be my first mod. Must ask the President of the house hold aka wife. But She can't say no cause she has here 11' Forester XT to race around.
Nice! 6spd or CVT?

Keep an eye on our facebook. We just moved into our new headquarters a few months ago and will be planning on open house/GTG soon. I'd love to see a big group of 2015's!

Matt Beenen
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Old 03-18-2015, 12:25 PM   #11
On_Thy_Edge1
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Oh of course 6MT. The only way I would get a CVT is for the wife. I will be bare stock most likely on your opener. Due to 30th birthday is in September and rolling down to subiefest and with some cash in the pocket. Unless some really good deals come up by then.

Last edited by On_Thy_Edge1; 03-18-2015 at 12:33 PM.
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Old 03-18-2015, 03:33 PM   #12
GrimmSpeed
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Quote:
Originally Posted by On_Thy_Edge1 View Post
Oh of course 6MT. The only way I would get a CVT is for the wife. I will be bare stock most likely on your opener. Due to 30th birthday is in September and rolling down to subiefest and with some cash in the pocket. Unless some really good deals come up by then.
Good man! Nothing wrong with stock! We will definitely have the J-Pipe available before subiefest and between the group buy and our local club discount, you'll have a couple opportunities at really great pricing.

Matt Beenen
Engineering
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Old 03-18-2015, 03:40 PM   #13
ryager
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Quote:
Originally Posted by GrimmSpeed View Post
Regarding your very first comment, I feel obligated to point out that this method of community involved product development is something that we've been doing for a very long time and has been (in my opinion, poorly) replicated by others as of late. Check out our 16 month, 1000 post development thread for our latest TMIC engineering cycle. It's also important to note that the difference is that we're doing this in real time, rather than after the product has been fully developed and is in production, so your answers to our questions can have a real impact on the design of the product. Lastly, most of what you've mentioned are features that are standard for us. We've been including a complete set of high-end, American made hardware with all of our exhaust components since 2007, even machining custom stainless hardware when we're not satisfied with what's available (our uppipe studs, for example). The same goes for our multi-layer stainless steel exhaust gaskets.

We're looking for the community feedback to spark something new and interesting. Our engineering, development and manufacturing capabilities are unique and I strongly suspect that if you've had a chance to handle and install our products, you're well aware of that. It's not our style to enter a market and simply provide an 'alternative'. We insist on offering something that sets itself apart, either by it's design, materials, manufacturing, quality, performance or a combination of factors. Like we mentioned, we've already identified a couple of areas where there's definite improvement to be made.

To clarify the first post, and I think this might be how you got on the hardware topic, my comment regarding hardware is that we won't require that you modify other parts of the car to fit the exhaust. For what we can tell, a couple of manufacturers include additional low profile bolts that replace OEM suspension hardware in order to buy themselves more clearance in certain areas. We aren't seeing that this is necessary unless the design of the tube must pass through that space. We're always very cautious when it comes to replacing OEM hardware, particularly when a critical vehicle system (like suspension) is concerned.

Regarding the cat placement, do you know what the importance of having the cat in the factory location is? In our experience, placing it at the end of the straight tube greatly reduces the effect that is has on the exhaust gas velocities through the downpipe. Is the concern that you wont have the heat to light it off? On the GD/GR Subaru, we place our cat much further from the exhaust ports and it still functions very well. The only reasons that we can think of to try and force the cat into it's original location are to keep it in the same spot if you happen to have regulations in a racing series that require that or if you want to try and trick the ECU into not throwing a code (which you would just disable during the tuning process anyway). One concern with that location is that with the larger tube and cat, you can't mange that amount of heat properly. The factory pipe has a very nicely made series of heatshields to protect your belt and water pump. Putting a high flow cat right there makes me a little bit nervous, to be honest.

In any case, your feedback is greatly appreciated. Do you mind if I ask why you opted for a one-off TBE rather than one of the existing options? Have you uninstalled it and reinstalled it yet?

Matt Beenen
Engineering
Awesome thread that you posted a lot of great information. For the cat I know that there was a huge thing about it does/doesn't fit, just wanted to give the information if need be. I think the main reason was to not throw a code as you guys stated. I also do not understand what your saying about one-off? I do have a tbe it is a custom one, however I want to see how yours turns out, mostly because I have owned grimmspeed products on my 08 wrx amd they were amazing, great build and always bringing the most to the table.
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Old 03-18-2015, 04:12 PM   #14
GrimmSpeed
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Originally Posted by ryager View Post
Awesome thread that you posted a lot of great information. For the cat I know that there was a huge thing about it does/doesn't fit, just wanted to give the information if need be. I think the main reason was to not throw a code as you guys stated. I also do not understand what your saying about one-off? I do have a tbe it is a custom one, however I want to see how yours turns out, mostly because I have owned grimmspeed products on my 08 wrx amd they were amazing, great build and always bringing the most to the table.
Awesome, glad to hear our products have treated you well in the past! What I meant by one-off was I think the same as you're describing - custom. As opposed to buying an existing j-pipe and catback. That's all!

Matt Beenen
Engineering
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Old 03-18-2015, 04:29 PM   #15
On_Thy_Edge1
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Originally Posted by GrimmSpeed View Post
Good man! Nothing wrong with stock! We will definitely have the J-Pipe available before subiefest and between the group buy and our local club discount, you'll have a couple opportunities at really great pricing.

Matt Beenen
Engineering
Sounds great can't wait to pick one up then.
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Old 03-18-2015, 06:50 PM   #16
ryager
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Originally Posted by GrimmSpeed View Post
Awesome, glad to hear our products have treated you well in the past! What I meant by one-off was I think the same as you're describing - custom. As opposed to buying an existing j-pipe and catback. That's all!

Matt Beenen
Engineering
I did get a custom, couple reasons. A lot of the tbe were very expensive. I know what you are thinking you get what you pay for, however the shop I went to has not done a tbe for the 2015 yet and when they were done realized how much more labor intensive it was then older models. So the price was awesome, they said they would not do another for that price, lol. Secondly I wanted something that was different then everybody else. It seems like everybody has the Q300 catback or the nameless axel back exhaust. I wanted something that did not sound the same as everyone else. The cobb ots map has been great with the exhaust also so I couldn't complain. The shop also brought me outside to show their progress and how everything was going along so again could not complain about the customer service. I am excited to see how your exhaust turns out and will definitely get an ebcs from you guys.
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Old 03-26-2015, 11:21 AM   #17
Scooby11WRX
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GrimmSpeed, first off thanks for supporting the 2015 WRX platform. I've owned several of your products in the past and they've been nothing but top-quality.

As the day I take that plunge and buy a J-Pipe is getting closer, I am starting to nitpick every detail on the options out there and would like your thoughts. Where the J-Pipe comes off of the turbo housing, I've seen company A/B/C/D all do it very differently in terms of the 3.5 to 3.0in transition. Some drop immediately to 3.0, some gradually taper within 3-4 inches, others keep 3.5 until the bend for approximately 8 inches. Can you weigh in on this? Are there measureable benefits to be had by having a more "stretched out" transition? Or is this purely a marketing tactic?

Thanks!
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Old 03-26-2015, 11:23 AM   #18
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Glad to come across the info about catalyst location. That has been a concern of mine when debating an aftermarket J-pipe. Seeing your(Grimmspeed's) reasoning on moving the cat downstream makes me feel better about potentially buying a J-pipe with a cat in that location. Initially I thought it may be a bad idea because of the ECU and O2 sensors not working right due to no cat in the factory location. Excited to see what you come up with GS. In my experience, which is limited, your parts are Top Of The Line!!
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Old 03-26-2015, 03:15 PM   #19
GrimmSpeed
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Originally Posted by Scooby11WRX View Post
GrimmSpeed, first off thanks for supporting the 2015 WRX platform. I've owned several of your products in the past and they've been nothing but top-quality.

As the day I take that plunge and buy a J-Pipe is getting closer, I am starting to nitpick every detail on the options out there and would like your thoughts. Where the J-Pipe comes off of the turbo housing, I've seen company A/B/C/D all do it very differently in terms of the 3.5 to 3.0in transition. Some drop immediately to 3.0, some gradually taper within 3-4 inches, others keep 3.5 until the bend for approximately 8 inches. Can you weigh in on this? Are there measureable benefits to be had by having a more "stretched out" transition? Or is this purely a marketing tactic?

Thanks!
Thank you we appreciate the kind words. We aim for the highest quality in everything we do, and I honestly never get tired of hearing people such as yourself reminding us that we're still doing our jobs!

This is an outstanding question, and I'm glad you asked. There is a LOT of thought that goes into making a design decision like this. Some of them are based on practice and theory, and some of these designs are based on "hey, if it looks like it works and does what their marketing guy says, it must, right?"

Since this exhaust part is after the turbo, we want to see as little back pressure as possible in order to minimize the pressure differential across the turbine to increase the efficiency of the system. The exhaust gasses coming out of the turbo are still very hot, and as soon as they exit the turbo they are still expanding rapidly as they cool. This expansion is increasing velocity of the exhaust gas which is already moving VERY fast (think a couple hundred miles per hour). Also, remember according to the Ideal Gas law that for a given pressure, when you decrease the diameter of a pipe you end up increasing the velocity of the gas moving through it. So we have lots of molecules moving very fast, and they start to fight for space as their flow rate increases (increased RPMs). If the pipe isn't of sufficient size we will start to see an increase in back pressure.

So why not just have no transition at all? A 3.5in J-Pipe. Well, for the amount of exhaust gas that these turbos can move, the benefit in top end power vs a 3in pipe is already pretty negligible. The negatives being increased weight, cost, diminished ground clearance, and increased loudness. So we'll choose a 3in pipe, and since the outlet on the turbo is about 3.5in in diameter, we'll have some sort of transition. There are a few ways to accomplish this, so lets talk ideas:

Screw it, flat flange, 3in outlet, let 'er buck... Well, it's not ideal. In a 3in diameter pipe with about 500 CFM at it's entrance the difference between a blunt flat entrance and even a small flared entrance is around 1.5 to 2 inches of water (about 0.07 psi) of restriction. As horsepower increases so will exhaust CFM, and since the rates of increased restriction are exponential, at high rates of flow this restriction can start to turn into a problem. But to be fair, for this difference in flared vs blunt entrance to even become a 1 psi difference between each other's given restriction, you would need to be making a significant amount of power, a lot more than you will on the stock location turbo.

So with that said, now that we know the worst case scenario and some real numbers to go with them, we can better grasp how much there is to gain with the "long stretched gradual transition." If the difference between a flat blunt entrance and a slight flare is only 0.07 psi restriction, then the difference between that slight flare and a long gradual flare is going to be a nearly insignificant difference. I believe it is safe to say that the difference would most likely measured in fractions of an inch of water. But there HAS to be a reason for it, right? I mean, a nice smooth transition is going to be less turbulent and better flowing. Well, these are 1300 deg F exhaust gasses traveling over 350 feet per minute, laminar flow went out the window SO long ago that there is nothing but turbulent flow, so it doesn't make nearly as big of a difference as you'd think. So this is going to be a case of "if it looks like it works, it must work, right?" Don't fall for it anymore.

Okay, maintaining the 3.5in straight section for about 8 inches before the bend, go! Seems like a good idea, right? Larger pipe diameter = increased volume = decreased back pressure. Giving the turbo a little room to breathe... But you've only increased that diameter for a very short distance until you're back to the same old back pressure you'd have been at if it were a quick 3in transition. So the additional benefit, until proven otherwise, is VERY small if any. In fact, now since you've added an abrupt change in area you're going to add a reflective pressure wave. This wave can actually help or hurt performance by timing it with the length of pipe before the other volume change (the turbo itself). If it's timed wrong you're going to end up with a pressure wave "pushing" back on the turbo's outlet (extra back pressure), or you can end up with the wave actually helping to "pull" the exhaust through the turbo's outlet (reduced back pressure). Unfortunately this effect cannot be constant and changes with rate of exhaust flow, so sometimes it'll help, and sometimes it'll hurt, but most of the time it'll do absolutely nothing. However, the short length of pipe and small diameter change makes the effect here pretty small.

Tons and tons of theory here, but you've almost answered your own question before you even finished asking it: "Are there measurable benefits... or is this purely a marketing tactic?" I'm going to answer that question with another question, and let you infer what the answer is: Have ANY of the companies that made these "other" design decisions showed you any measurable benefits to their design choices, or do they just say they work?

We honestly explored all these ideas and more (things like machining the transition into the flange, etc) and using our real world knowledge about what the real gains are of each design decision we ended up choosing the flared tube design. Not only that, but we choose to do the diameter reduction immediately after the flange to keep the flow expanding as evenly as possible. We know we have to have a change from the turbo outlet to the J pipe, so why not just make it once, instead of multiple times? All the while since we're using only a single pipe we have less welds, and thus less points of failure than others who are welding on their transitions or their different diameter tube. This is honestly why we believe we've made the best design decisions on this J pipe. The only sacrifice, being a slightly longer transition that would most likely equate to a reduction in back pressure of less than 0.01 Psi. And since creating the tooling to make an "ideal transition" is very expensive, we decided that a reduction in back pressure of one hundredth of a Psi, or increasing the cost to you, was an easy decision.

Quote:
Originally Posted by Bryan82 View Post
Glad to come across the info about catalyst location. That has been a concern of mine when debating an aftermarket J-pipe. Seeing your(Grimmspeed's) reasoning on moving the cat downstream makes me feel better about potentially buying a J-pipe with a cat in that location. Initially I thought it may be a bad idea because of the ECU and O2 sensors not working right due to no cat in the factory location. Excited to see what you come up with GS. In my experience, which is limited, your parts are Top Of The Line!!
Thanks Bryan, we appreciate that! Just so we're super clear: the secondary O2 sensor won't work right with the removal of the stock location cat. It'll think it has a cat efficiency problem and throw a code. However, since if you're going to add a J pipe you should get a tune anyways, you can disable the rear 02, and there will be no problem at all. You can try to fool the rear O2 with spacers as well if you didn't want to get a tune, but we will be firmly suggesting a tune (for maximum benefit if nothing else) over this option.

Chase
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Old 03-30-2015, 05:35 PM   #20
sway162
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Thank you for all the information you provided on here. I am looking forward to mounting this onto my FXT. Subscribed
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Old 04-08-2015, 11:51 AM   #21
GrimmSpeed
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Updates! The tube routing has been finalized. As we mentioned before, the original J-Pipe and the underside of our WRX were 3D scanned for fitment data. From there, we created a CAD model with the most efficient tube routing possible. Knowing that we had extremely accurate fitment data, we were able to achieve the routing with four bends and without 'cheating' the either of the flanges (having the tube enter a flange at anything but perfectly perpendicular).

This is a screenshot of what we end up with after our initial 3D scanning. In 2D like this, it can sometimes look like just a blob, but it's actually a 3D point cloud and when you're manipulating the model, it really comes to life.



Next is a screenshot showing the critical portions of the under car scan along with the CAD model of the tube that we worked up based on the scan above. This is where our engineering process sets itself apart from most. Instead of confining ourselves to the working envelope of the factory J-Pipe (above), we're able to make our own design decisions based on clearances and manufacturing tolerances that we're comfortable with. This is the reason that we're able to provide such perfect and consistent fitment without pigeonholing ourselves into the factory routing. With that, we're able to bend this tube in a single part, which achieves one of our major goals!



From there, we used our model to quickly mock up a prototype part to confirm what we were seeing on the screen. We cut a few flanges on the waterjet and got to work!



Fit was great and with that, we were ready to move forward and finalize some production details. I'm working on putting together some photos and screenshots of what we have in store for the flanges. We're pretty excited about having some features that will really set this J-Pipe apart, so stay tuned.

Matt Beenen
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Old 04-08-2015, 02:01 PM   #22
On_Thy_Edge1
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Can't wait to see what is to come. Ugh Hurry up and take my money for this. But shhh don't tell my wife lol.
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Old 05-09-2015, 03:22 PM   #23
Bryan82
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Any updates Grimmspeed?
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Old 05-10-2015, 01:32 AM   #24
danoz
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Hi grimmspeed. You have a good looking product there! I can see a lot of planning and consultation has gone into its production. Obviously you will have a CVT and 6MT version, but will you have a catted version?
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Old 05-12-2015, 08:17 PM   #25
1sikRX
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Hi Grimmspeed I was wondering how long the highflow catted version will last? I mean I know cats don't last forever, how long can we expect it to function?
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