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Old 10-17-07, 06:07 AM   #1
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Default Stock Up-pipe - a more serious look

It occurred to me that many folks trying to make good power on their STi tend to overlook doing the up-pipe. The number one reason is because it does not have cat like the older 2.0 liter setups, and folks feel that's good enough and call it a day on that part.

The purpose of this thread is to take a closer look at stock STi up-pipe. We're going to point out what's good, and what's not so good about it.

For reference we have some pics (hey, these are as bad as Clint's normal pics).

Keep track of the numbers of the pics because we'll be referring to them throughout this thread. We'll be breaking it down by top or bottom just to get folks oriented to the pics they see.

Picture 1 - This is the stock STi Up-pipe in all it's glory. It came straight off my car. The heat shields have been removed for two reasons. The first reason is the up-pipe heatshield rattle. The second, and convenient for this thread, reason is so we can see what's under those heat shields.



Picture 2 - This is the bottom half of the up-pipe.



Picture 3 - This is the top half of the up-pipe.


Picture 4 - This is a closeup of the top half. More specifically the transition from the flex joint to the upper flange.


Picture 5 - this is the bottom of the up-pipe looking inside. The tube was lightly ported by me a long time ago to remove the hard edge of the tube.


Picture 6 - this is the top of the up-pipe looking inside. Again the tube was lightly ported by me a long time ago. Even though that edge is "downwind" of the flow by smoothing the hard edge you lessen turbulence, and make the low pressure zone created by that hard edge smaller.


Now, on to our discussion below.

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Old 10-17-07, 06:26 AM   #2
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Default Re: Stock Up-pipe - a more serious look

Lets start with the basics and move from there.

What the up-pipe does
Very simple - the up-pipe is the connector between the headers and the turbo. It's the tube that the exhaust gases go through to get to the tubine side (hot side) of the turbo. The entire purpose is to move exhaust gases easily, and efficiently to the turbo. In summary, it's just a tube that move exhaust from under the engine, to the back upper right side of the engine. That's it.

Why do we need it
Well, real simple, you've got to get those exhaust gases to the turbo somehow. Now, this brings up a question of why the turbo is where it is. That part is also simple - space. There's not a lot of room under the hood to put a fairly sizable chunk of metal like a turbo. This is a package concern.

Yes, the turbo would spool a LOT faster if you put it close to the heads (ie in a DSM or MINI fashion). The problem is you just can't easily do that in this car. The reason is the boxer motor.

The way the motor is layed out the exhaust ports are on the bottom. If you put the turbo down there spool sure would be increased, but that creates a whole other mess of issues. Here are some of them:

A) ground clearance. You can't just stick the turbo under the car and expect to not lose ground clearance. So you've got to stick it somewhere kind of out of the way. Behind the foglight covers, provided you don't have fog lights or ever plan on offering them as an option might seem like a good place, but that causes another concern which is lubing the turbo.

B) Lubing the turbo. While turbos are fed oil under pressure (in our case off the head) the flow of oil out of the turbo doesn't see a lot of pressure. In other words the oil just falls out of the turbo. In the stock location the oil falls out of the bottom of the turbo straight back into the oilpan. You MUST be able to evacuate the oil that is fed to the turbo. Otherwise you get pooling, over heating oil that can begin to press out the seals and will start to coke up on the bearings. In other words, you want flow through there to cool things off. The other rule of thumb is you have a 30* "window" from vertical to have enough slope to allow gravity to evacuate the turbo fast enough. If you were to move the turbo to a location that is lower (ie behind the fog light cover) you need some way to evacuate that oil from the turbo. That means a sump to catch the oil coming out of the center section, and a pump to push it up hill into the pan. This means more parts, more parts that can fail, more parts that have to be maintained, more parts that cost the manufacturer money. Not to mention IC placement, and tubing costs to get it there. Remember, Subaru's goal is to make a car that meets specs, and does it within a budget where when they sell a car is 1) affordable and 2) they make a profit. Hell, you don't have look any further than the cheap plastic dash to realize that.

So, in the end, it's easy to see why putting the turbo where they did is really the best location.

Anyway, back to the up-pipe. We have the location for the turbo, and we need to get the exhaust to it. Thus the up-pipe.

Think about some of the specs that the up-pipe has to meet.

1) min amount of flow to allow turbo to work ok (not great, but just enough to meet sellable specs). In this we're talking tube/port size.

2) must be cheap to make (remember they don't give cars away or sell them at a loss)

3) Longevity of the part

Last edited by Turninconcepts.com; 10-17-07 at 06:30 AM.
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Old 10-17-07, 06:28 AM   #3
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Default Re: Stock Up-pipe - a more serious look

So, to start off on this grand adventure that is the up-pipe lets take a look at some of the pics, and make some general observations about it.

Take a look at pics 1, 2 and 3.

Specifically in pic 1 take a look at the angles of the flanges. These are actually not easy angles. You can't just bend a pipe, slap some flanges on it, and call it a day. It won't work because the flanges sit in two different planes at odd angles to each other.

The stock up-pipe does these angles very well. In fact, it fits so well that if fits like a stock part. Hmmmm.... small wonder there.

Now take a look at pics 2 and 3. Specifically notice the flanges. They're decently thick for a stock part. In fact, the stock ones are just under 10mm thick. Remember this - exhaust flanges must be flat to properly mate up to the gasket and interfacing flange. Exhaust pipes are subject to extreme heating and cooling (heat cycles) over time. These heat cycles can make stressed metal warp. Stress in this case comes from bolting flanges together. Thick flanges stay flat longer than thin flanges. Here is part of where longevity of the part comes into play.

Now, some more on pic 2. Look at the bend. Notice how it's crushed. Why is is crushed? Well, that's also an easy one. It's cheaper to bend tubing that way. Cheaper because the equipment is cheaper, and easier to get. It's still big enough to flow enough exhaust fast enough to make specs, but from the performance aspect this is not the best way. This goes back to that cost factor.

Now take another look at picture 3. The flex section.

We've played with a lot of different up-pipes, and we have come to a conclusion. A flex section in the up-pipe is a good thing. We've tried solid pipes, and we've tried flex pipes. In our book flex pipes win. Now, is this the best flex section for making big power? No, but more on that in a bit.

Hey, as long as we're in the area take another look at pic 3, and perhaps a quick glance a pic 4. Take a look at the tubing reduction into the flange. This is needed because the flex section is basically a high clearance slip fitting, and the top side got the larger OD. They have to neck it down in size to get close to the port size on the tubine inlet. Is this best? No, but it's pretty cheap, and still allows them to meet specs.

Anyway more on the ups and downs in the next couple of posts.

Last edited by Turninconcepts.com; 10-17-07 at 07:00 AM.
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Old 10-17-07, 06:29 AM   #4
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Default Re: Stock Up-pipe - a more serious look

Let's take a look at what the stock up-pipe does well and the parts that are good.

1) Gets exhaust from the manifold to the turbo. (function)
2) Gets that exhaust there fast enough and in enough volume to meet some arbitrary specs set by Subaru. (function)
3) Has thick flanges that will resist warping over time. (longevity)
4) Has a flex section to help account for vibration and heat cycles (longevity)
5) Is pretty cheap to make for Subaru, and free for you since it comes on the car. (cost)
6) No cat. (function, cost, longevity - the trifecta).

Last edited by Turninconcepts.com; 10-17-07 at 07:05 AM.
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Old 10-17-07, 06:30 AM   #5
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Default Re: Stock Up-pipe - a more serious look

Now lets look at the downsides of the stock up-pipe.

1) The heat shields. They suck. Sure they keep the exhaust gases from cooling (hot gas flows faster), but the spot welds break, and you get a rather annoying rattle. Sure the part is still functional, but if you're anything like me it'll drive you bonkers.

2) The bends and necking. Take a look at pic 2. Down toward the bottom on the flange you'll see tube that's not in the crush section. This is the original OD of the pipe. That OD measurement is 44.84mm. Now look at the bend. At it's narrowest point it's 43.04mm. Ok, not too bad at first glance, but here's the thing. You're pipe is only as big as the smallest section. Kind of like the weakest link in a chain.

Here's the other thing to consider - any time you crush or neck down that tube you cause turbulence. Turbulence kills performance. Remember you want to get as much exhaust to the turbo as quickly as possible (within reason - go too big and you kill velocity). Creating turbulence hurts the flow.

3) The flex section. Yes, we feel a flex section is a good thing, but the stock flex section a) sucks for flow and b) sucks for location.

First the flow. Take a look at pics 3, 4 and 6. Check out how it's a slip fitting with an accordion over it. Sure this allows some flex, but you run into a problem. There is a sharp "drop off" from the inner section to the outer section. This causes a low pressure zone causing more turbulence. Remember, that's bad. It gets even worse - the size necks down just before it joins the flange. More turbulence.

Second lets take a look at the position of the flex joint. Through this whole pipe the flex section with its neck down is the worst place in the entire pipe for flow. What makes it even worst is the fact that it's RIGHT BEFORE it enters the turbo. Nothing like stalling the gases before you put them to work. Yuck. Don't get me wrong. I still feel that a flex section is needed, but a better place for it would be down low so the air has a chance to smooth out before entering the turbo.

Last edited by Turninconcepts.com; 10-17-07 at 07:22 AM.
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Old 10-17-07, 06:31 AM   #6
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Default Re: Stock Up-pipe - a more serious look

So, what to look for in an up-pipe when increasing performance is on your mind. Well, here's a list:

1) it fits.

2) Thick (and flat) flanges. I point out flat because there have been some super cheap pipes to hit the market that don't have flat flanges to begin with. If you have access to a stationary belt sander you can flatten them yourself if you need to, but you should not have to do this.

3) A flex section. We feel this one is kind of important. This is based upon our experience from working on these cars. Sure a solid pipe will flow better, but the tradeoff is worth a flex section PROVIDED that flex section is a) a good high quality section that matches the pipe size well, and not one of these crappy slip/accordion stock style flex sections and b) is closer to the bottom on the up-pipe. This will allow flow to smooth out some before entering the turbo.

3) Minimum bends, and if it does have to be bent look for mandrel bends so you have a consistent tube diameter. Additionally, those bends should be as smooth and cover as much distance as possible. Remember, the key is smooth. Whether you're talking about driving, up-pipes or picking up hot chicks things have to be as smooth as possible.

4) The tube ID closely matches the port size on the header and turbo.

Last edited by Turninconcepts.com; 10-17-07 at 08:01 AM.
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Old 10-17-07, 07:07 AM   #7
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Default Re: Stock Up-pipe - a more serious look

THANK YOU! I've lost count on how many up pipe debates I've given my 2c (pros for changing the up pipe) on and gotten vegetables thrown at me... hopefully this will help folks make an educated decision. TIC ROCKS!
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Old 10-17-07, 07:36 AM   #8
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Default Re: Stock Up-pipe - a more serious look

The anticipation of the fourth post is killing me! Do I sense a promo for the P&L ewg coming?

JPW...do you have your up pipe coated and/or wrapped?
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Old 10-17-07, 07:43 AM   #9
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Default Re: Stock Up-pipe - a more serious look

Quote:
Originally Posted by Muffnbluff View Post
The anticipation of the fourth post is killing me! Do I sense a promo for the P&L ewg coming?

JPW...do you have your up pipe coated and/or wrapped?
I see nothing in there about the P&L EWG setup. In fact, EWG setups are a subject for another essay. Will the P&L be mentioned? Probably. Why? Because it's an example of a quality part that works well. Afterall, we don't believe in selling parts that don't work well. Why? Because parts that don't work well suck. Bad parts waste your money, and both of our time.

Last edited by Turninconcepts.com; 10-17-07 at 07:51 AM.
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Old 10-17-07, 07:45 AM   #10
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Default Re: Stock Up-pipe - a more serious look

This is why I ordered the new Grimmspeed uppipe. It only has a single bend, 10mm flanges, the ID is a perfect match to my GT52 (I will port the outlet on the manifold accordingly), and the flex section is at the bottom, minimizing turbulence at the point where the exhaust enters the turbo. I think it's the best piece available right now.
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