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2014 Forester MT
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91 Posts
Discussion Starter #1
Can someone explain to me how an aftermarket charge pipe improves engine performance?

I can see that the aftermarket ones are larger in diameter in diameter than the stock ones, and u can say better airflow. However, if we look at the system as a whole, the intercooler inlet and outlet are certain diameter so regardless if the charge pipe diameter, no additional air can go inside the engine in one shot... Hope someone can clarify this.

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2017 XT
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169 Posts
For the turbo models it supposedly gains power by 'smoothing out' the airflow. Think I saw that from Perrin somewhere.

But you are correct, the inlet/outlet diameters are still the same. So how do you quantify an improvement if inlet/outlet diameters don't change??! You think it wouldn't, but it does. Albeit marginally. I've seen similar flow bench testing on this same principal with improvements over stock.

So that's prob what nets you the +5 to 10hp increase.
 

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Premium Member
2015 Forester XT Touring Stock Cooler/Heater Hardlines Deleted Custom 19 Row Cooler with -6AN Lines Directly Ported to CVT
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395 Posts
Ok this is going to a little long but feel like my personal experiences would shed some light on this upgrade.

First let's talk about designs and explanations:
1: the upgrades no matter the style.
Single pipe, single pipe with custom molded silicone turbo outlet with stock BOV location retained, two pipe systems with the same coupler like the one I previously stated with or without two different diameter pipes, etc.
The stock systems have accordion style fittings with different diameters and a pinched main tube going to the intercooler.
The aftermarket systems create a smoother more free flowing system from the turbo.
2. These designs also help to remove the back pressure on the turbo. Meaning it allows you to spin up the turbo faster and smoother.
3. These systems were designed for the WRX which runs a more aggressive tune, hotter cams, and a higher rev limit. In short the HP gains are found in the higher boost, higher rpm ranges.
4. They do seem to work well on the FXT under the following conditions. Stock air box with upgraded filter and the stock intercooler. Or a true stage 2 with a modified stock turbo or a Steamspeed STX-67 or similar.

My personal experiences having used two different manufacturers charge pipe kits with the same results:
(I didn't like the fiment of the first kit.)

On my stage 1 pro tune I installed an upgraded TMIC afterwards. My new TMIC reduced the back pressure on the the turbo from 3-3.5lbs on the stock TMIC to around .5 lbs. Throttle and turbo response we're night and day it was like a new and different car!.

When I started my stage 2 upgrades I did the charge pipe first and that feeling went away. I actually was just having a discussion with my mechanic about it right now. (He's a race mechanic and fabricator specializes in EJ Subarus and Porsche race motors and gear boxes) because I had already relieved the max amount of back pressure on the turbo it actually was working harder at day to day driving rpms and boost to fill up the bigger interior of the charge pipe. When I completed my stage 2 and brought back to my tuner I expected to get that response back and I didn't. I did get a bump in top end boost hp but I wasn't really happy with the response it was like I had to time the spool up of the turbo and then the thing exploded with power my Tuner even made a comment about on a test drive/tune when I did the TGV deletes.

Now fast forward about a month I was still having weird DAM issues on my stage 2. Then something super strange happened on the freeway with my fuel pump or it's relay clicking very loudly. Long story short it fried my turbo. Which ended up dumping oil into my intake tract components. I decided to put it back to mostly stock. Since whatever the car did not have anything to do with my mods and my dealer already knew about the stage 1.
The first half I did my self which started with the charge pipe .
Well guess what happened to my throttle response? It went back to being super responsive. This was with my stage 2 tune, the turbo blowing oil into the intake under any boost, and my J-Pipe kit still installed.
I had my mechanic put the exhaust components back to stock and re-flashed the ECU back to factory. Everything on the car was CARB legal and stock ECU compatible.
It turns out what used to be a super tuner friendly dealership changed when they moved to their new location.
Long story short on that the called SOA almost immediately and now my car is flagged by them. They said the wouldn't warranty the just for having an AEM intake on the car.
Ok sorry rant off...

Back to the good and potentially bad about the charge pipe and changes to the I take system. I stand by what I stated earlier on when and why you may want one.
You probably gain more with an AEM intake a 3 port EBCS an upgraded TMIC and a pro tune. These parts mated with an Accessport netted me the great percentage of who/wtq gains of all my mods my torque went up astronomically!

If you want to run the stock airbox with an upgraded air cleaner and the stock TMIC it will make a noticable increase but nothing compared to what I stated above.

If you do the upgrade on the stock turbo, which is basically a little bigger billet exhaust side compressor wheel, or if you decide to install an STX-67 then the charge pipe kit will really work as advertised. The first mod flows about 10-15% more air and the Steamspeed flows around 25-30% more air than stock.

My car is now at my mechanics back from the dealership. Everyone's consensus is the Turbo has a blown seal and the motor is fine. I contemplated the STX-67 and decided on a rebuilt stock unit with a warranty. I'm keeping my stock charge pipe, TGV's, and OEM crank pulley. I added a Perrin header and their EBCS.

I only want 15- 20 more whp/wtq from where I was. And I want a daily Econ tune again hence the TGV's staying.

I am also doing some drivetrain safety/performance stuff. Oil cooler with the stock water to oil heater/cooler deleted. A lower degree thermostat, 1.3 bar radiator cap, and performance synthetic coolant.
And an AOS system. After my mechanic cleans my valves and intake tract I never want to do it again!

Welp I told you it was going to be a long read. If you scrolled down to the bottom of this just read the beginning with the 1-4 section. All the answers to the OP are located there. 😋

Sent from my Nexus 6P using Tapatalk
 

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2006 FXT 5MT
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548 Posts
Charge pipe? Are we talking about the turbo inlet? If so, they don't even require a tune, which tells me they do nothing other than provide a better seal to the turbo (If you're using aftermarket) and can be replaced, with patience, without removing the intake manifold.
 

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Premium Member
2015 Forester XT Touring Stock Cooler/Heater Hardlines Deleted Custom 19 Row Cooler with -6AN Lines Directly Ported to CVT
Joined
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395 Posts
Charge pipe? Are we talking about the turbo inlet? If so, they don't even require a tune, which tells me they do nothing other than provide a better seal to the turbo (If you're using aftermarket) and can be replaced, with patience, without removing the intake manifold.
I believe you would consider it an uppipe?

It's the NA/Recirculating BOV/Charged Air Turbo Outlet to Intercooler Intake Pipe.
 

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2006 FXT 5MT
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548 Posts
Ah, I'd call that the turbo to intercooler pipe, not sure if it's got another name. My understanding is that it provides smoother airflow from the turbo to intercooler, resulting in some more HP. The intercooler then chops that air right back into pieces and stuffs it into the throttle body in the most turbulent fashion possible. The main reason I replaced mine with silicone is because of oil degradation of the factory rubber parts. With a 2015, you probably don't have that issue yet, and with the expense of silicone parts, I doubt you'd notice any gains that you can feel.

The uppipe is from the exhaust manifold up to the turbo's hotside.
 

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2004 Sube slushy
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567 Posts
Soo, for someone considering this gen Xt from an 04 XT, There's not as much gain in up/down pipes as in the old gen car?

Just the gain from up/down pipes on '1st' gen xt 's is enormous, like from 215hp to 240-250. My accessport added another 10-15 (maybe 30 in premature stage 2 settings!) and then the street tune(4eat) must have brought it all together (done by Metric in NY) to about 260ish. Still fun at 14y.o., 12 yrs under my stewardship(soon FS).
 

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Registered
2015 Forester XT
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18 Posts
Ok this is going to a little long but feel like my personal experiences would shed some light on this upgrade.

First let's talk about designs and explanations:
1: the upgrades no matter the style.
Single pipe, single pipe with custom molded silicone turbo outlet with stock BOV location retained, two pipe systems with the same coupler like the one I previously stated with or without two different diameter pipes, etc.
The stock systems have accordion style fittings with different diameters and a pinched main tube going to the intercooler.
The aftermarket systems create a smoother more free flowing system from the turbo.
2. These designs also help to remove the back pressure on the turbo. Meaning it allows you to spin up the turbo faster and smoother.
3. These systems were designed for the WRX which runs a more aggressive tune, hotter cams, and a higher rev limit. In short the HP gains are found in the higher boost, higher rpm ranges.
4. They do seem to work well on the FXT under the following conditions. Stock air box with upgraded filter and the stock intercooler. Or a true stage 2 with a modified stock turbo or a Steamspeed STX-67 or similar.

My personal experiences having used two different manufacturers charge pipe kits with the same results:
(I didn't like the fiment of the first kit.)

On my stage 1 pro tune I installed an upgraded TMIC afterwards. My new TMIC reduced the back pressure on the the turbo from 3-3.5lbs on the stock TMIC to around .5 lbs. Throttle and turbo response we're night and day it was like a new and different car!.

When I started my stage 2 upgrades I did the charge pipe first and that feeling went away. I actually was just having a discussion with my mechanic about it right now. (He's a race mechanic and fabricator specializes in EJ Subarus and Porsche race motors and gear boxes) because I had already relieved the max amount of back pressure on the turbo it actually was working harder at day to day driving rpms and boost to fill up the bigger interior of the charge pipe. When I completed my stage 2 and brought back to my tuner I expected to get that response back and I didn't. I did get a bump in top end boost hp but I wasn't really happy with the response it was like I had to time the spool up of the turbo and then the thing exploded with power my Tuner even made a comment about on a test drive/tune when I did the TGV deletes.

Now fast forward about a month I was still having weird DAM issues on my stage 2. Then something super strange happened on the freeway with my fuel pump or it's relay clicking very loudly. Long story short it fried my turbo. Which ended up dumping oil into my intake tract components. I decided to put it back to mostly stock. Since whatever the car did not have anything to do with my mods and my dealer already knew about the stage 1.
The first half I did my self which started with the charge pipe .
Well guess what happened to my throttle response? It went back to being super responsive. This was with my stage 2 tune, the turbo blowing oil into the intake under any boost, and my J-Pipe kit still installed.
I had my mechanic put the exhaust components back to stock and re-flashed the ECU back to factory. Everything on the car was CARB legal and stock ECU compatible.
It turns out what used to be a super tuner friendly dealership changed when they moved to their new location.
Long story short on that the called SOA almost immediately and now my car is flagged by them. They said the wouldn't warranty the just for having an AEM intake on the car.
Ok sorry rant off...

Back to the good and potentially bad about the charge pipe and changes to the I take system. I stand by what I stated earlier on when and why you may want one.
You probably gain more with an AEM intake a 3 port EBCS an upgraded TMIC and a pro tune. These parts mated with an Accessport netted me the great percentage of who/wtq gains of all my mods my torque went up astronomically!

If you want to run the stock airbox with an upgraded air cleaner and the stock TMIC it will make a noticable increase but nothing compared to what I stated above.

If you do the upgrade on the stock turbo, which is basically a little bigger billet exhaust side compressor wheel, or if you decide to install an STX-67 then the charge pipe kit will really work as advertised. The first mod flows about 10-15% more air and the Steamspeed flows around 25-30% more air than stock.

My car is now at my mechanics back from the dealership. Everyone's consensus is the Turbo has a blown seal and the motor is fine. I contemplated the STX-67 and decided on a rebuilt stock unit with a warranty. I'm keeping my stock charge pipe, TGV's, and OEM crank pulley. I added a Perrin header and their EBCS.

I only want 15- 20 more whp/wtq from where I was. And I want a daily Econ tune again hence the TGV's staying.

I am also doing some drivetrain safety/performance stuff. Oil cooler with the stock water to oil heater/cooler deleted. A lower degree thermostat, 1.3 bar radiator cap, and performance synthetic coolant.
And an AOS system. After my mechanic cleans my valves and intake tract I never want to do it again!

Welp I told you it was going to be a long read. If you scrolled down to the bottom of this just read the beginning with the 1-4 section. All the answers to the OP are located there. 😋

Sent from my Nexus 6P using Tapatalk
Interesting feedback, I always had a charge pipe on my list of mods to do however I forgot that a larger/more free flowing charge pipe (hot pipe) will cause a reduction in throttle response. It improves mid-high rpm power and boost response so for lots of people there are enough pros to outweigh the cons. But that con is very rarely mentioned. Thanks!

A larger intercooler can have the same reduction in throttle response.
 

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2017 ForesterXT Vespa
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105 Posts
Soo, for someone considering this gen Xt from an 04 XT, There's not as much gain in up/down pipes as in the old gen car?

Just the gain from up/down pipes on '1st' gen xt 's is enormous, like from 215hp to 240-250. My accessport added another 10-15 (maybe 30 in premature stage 2 settings!) and then the street tune(4eat) must have brought it all together (done by Metric in NY) to about 260ish. Still fun at 14y.o., 12 yrs under my stewardship(soon FS).
It's a totally different thing (pipe)! We're talking post-turbo/pre IC here.
 

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Hi
just to share...
After changing intercooler without change in Charge Pipe, but with a tune, I was having very good throttle response.
Then I changed my charge pipe, but without another tune, the throttle responsiveness went away.
Then I did something different. I installed an old throttle controller (Pivot 3-drive) to my car...and the responsiveness of the throttle came back when i upped the settings...so you can overcome the delayed throttle response with a throttle controller.
 

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Registered
2017 Forester XT
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180 Posts
Hi
just to share...
After changing intercooler without change in Charge Pipe, but with a tune, I was having very good throttle response.
Then I changed my charge pipe, but without another tune, the throttle responsiveness went away.
Then I did something different. I installed an old throttle controller (Pivot 3-drive) to my car...and the responsiveness of the throttle came back when i upped the settings...so you can overcome the delayed throttle response with a throttle controller.
Just curious, why didn’t you go for re-tune after installing the charge pipe? You will probably net more gains and it will be safer for the engine
 

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2015 Forester XT
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4 Posts
"Long story short on that the called SOA almost immediately and now my car is flagged by them. They said the wouldn't warranty the just for having an AEM intake on the car."

I keep seeing stuff like this, but it's just not true. The Magnuson–Moss Warranty Act would cover this. It would REQUIRE SOA to prove that your modifications DIRECTLY caused the issue. They cannot require you to use OEM parts, cannot require you to use the dealer for routine maintenance, and without direct proof that a Cobb Accessport, or aftermarket pipe directly caused the issue, cannot deny a valid warranty claim.

Warrantees in the US are not required, but if provided are heavily regulated.
 

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2017 Forester XT
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76 Posts
they have to prove that the aftermarket parts damaged the part of the car that is being warrinted. a air filter has nothing to do with a problem with a transmission. they can NOT use a blacket void warrinty just because of that. SEMA would love to hear about that.
 
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