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Discussion Starter #1 (Edited)
I just bought a stage 2 STI forester- mods listed below.

I have a new 18g turbo, that I'm either thinking of upgrading to or selling. So.. three questions.

1. What kind of HP / torque increase can I expect with the upgrade?

2. what do I need to do besides take off the vf43 and put on the 18g?

3. If I decide to sell the 18G, what is it worth (its new) or what is the vf43 worht? (only 5-10K on it).

STI tmic/vf43/STI ecu/AP v2
Walbro 255 pump
Maddad whisper turbo back
Cobb uppipe
Ported manifolds w/crossover pipe
Cobb Access Port with Cobb map running currently

Thanks!
 

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2007 Forester XT Limited
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653 Posts
1. Depends on what support mods you have. 300whp on a normal reading dyno is possible.
2. I would upgrade injectors to at least 650cc, walbro fuel pump, APS CAI, larger intercooler, and turboback exhaust (stage 2 means you at least already have downpipe).
3. In this economy, hard to say, should be able to fetch at least $600 bucks with low mileage. Assume it's 8cm.
 

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Discussion Starter #3
1. Depends on what support mods you have. 300whp on a normal reading dyno is possible.
2. I would upgrade injectors to at least 650cc, walbro fuel pump, APS CAI, larger intercooler, and turboback exhaust (stage 2 means you at least already have downpipe).
3. In this economy, hard to say, should be able to fetch at least $600 bucks with low mileage. Assume it's 8cm.
I'm assuming the Maddad, includes the downpipe, correct?
 

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BLUE WASABI, (#2 Info Provider)
2008 SG Model D
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9,224 Posts
I just bought a stage 2 STI forester- mods listed below.

I have a new 18g turbo, that I'm either thinking of upgrading to or selling. So.. three questions.

1. What kind of HP / torque increase can I expect with the upgrade?

2. what do I need to do besides take off the vf43 and put on the 18g?

3. If I decide to sell the 18G, what is it worth (its new) or what is the vf43 worht? (only 5-10K on it).

STI tmic/vf43/STI ecu/AP v2
Walbro 255 pump
Maddad whisper turbo back
Cobb uppipe
Ported manifolds w/crossover pipe
Cobb Access Port with Cobb map running currently

Thanks!
I am assuming you mean a protuned forester XT running a VF43 and not an actual JDM FSTi running a VF43 w/ an aftermarket TBE, correct? (Pretty sure it is not the latter due to you running the COBB AP.)

Depending on the full specs of the 18G, how hard it was pushed/run, and its state will determine how much you could get.

I have 300WHP/300TQ running a VF43 right now on stock pump and injectors for my '08 Forester. I do have the STi TMIC, APS CAI, and supporting TBE (3" DP to 2.5" catback).

What year is your forester?
Is it MT or AT?

FYI, I decided not to install my brand new 18G b/c it was easier to start w/ the brand new VF43 b/c of the COBB map for my car (protuner was a good distance away and our schedules kept conflicting...if it wasn't for that, I would have gone w/ the 18G). Once I got a protune, I hit the power range I wanted and the car feels great! You won't see a huge gain over the VF43 if you swapped in the 18G but it will hold power up top better. If you just started off needing to upgrade the stock TD04 turbo, I would recommend the 18G over the VF43 b/c it is a slightly better turbo, but if you already have the VF43 in, it isn't worth it IMHO unless .
 

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Discussion Starter #5
Not protuned (yet). But yeah, upgraded 04' with 6 spd swap.

I am assuming you mean a protuned forester XT running a VF43 and not an actual JDM FSTi running a VF43 w/ an aftermarket TBE, correct? (Pretty sure it is not the latter due to you running the COBB AP.)

Depending on the full specs of the 18G, how hard you pushed, and its state will determine how much you could get.

I have 300WHP/300TQ running a VF43 right now on stock pump and injectors for my '08 Forester. I do have the STi TMIC, APS CAI, and supporting TBE (3" DP to 2.5" catback).

What year is your forester?
Is it MT or AT?

FYI, I decided not to install my brand new 18G b/c it was easier to start w/ the brand new VF43 b/c of the COBB map for my car (protuner was a good distance away and our schedules kept conflicting...if it wasn't for that, I would have gone w/ the 18G). Once I got a protune, I hit the power range I wanted and the car feels great! You won't see a huge gain over the VF43 if you swapped in the 18G but it will hold power up top better. If you just started off needing to upgrade the stock TD04 turbo, I would recommend the 18G over the VF43 b/c it is a slightly better turbo, but if you already have the VF43 in, it isn't worth it IMHO unless .
 

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2007 Sports XT 4EAT
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2,502 Posts
It just depends on what you want to spend. First and foremost hopefully you have a good quality 18g (and not all of them are). You would probably want to do several supporting mods. Injectors for sure, and you might want to do an intake and a bigger TMIC, plus you'd HAVE to get a protune (the AP obviously has no standard maps for an 18g).

With the 18g the overall power delivery should be smoother than the VF43 and you will see more power up top. The 18g is a bigger turbo and a good match for our 2.5 liter engines.

All in all, the gains might not be HUGE, but if you are willing to shell out some cash, you will have a faster car. If you want to keep it more simple, I'd just get a protune for your VF43.
 

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Official sf.org decal guy
2006 FXT
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12,516 Posts
It just depends on what you want to spend. First and foremost hopefully you have a good quality 18g (and not all of them are). You would probably want to do several supporting mods. Injectors for sure, and you might want to do an intake and a bigger TMIC, plus you'd HAVE to get a protune (the AP obviously has no standard maps for an 18g).

With the 18g the overall power delivery should be smoother than the VF43 and you will see more power up top. The 18g is a bigger turbo and a good match for our 2.5 liter engines.

All in all, the gains might not be HUGE, but if you are willing to shell out some cash, you will have a faster car. If you want to keep it more simple, I'd just get a protune for your VF43.

What 18g is it? There are different ones that will have different specs.

Regardless, if you want to get the most out of the 18g you're going to need bigger injectors and a bigger intercooler. I am running a Blouch 18g-8cm with Diechmenderingtonshememondieter 740cc injectors, STi exhaust manifold, STi TMIC, and turbo back exhaust. At 18.5psi I came out with ~305whp and ~310wlb/ft. I have maxed out the intercooler and need to go bigger before the boost can be turned up.
 

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Official sf.org decal guy
2006 FXT
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12,516 Posts
What indicates a TMIC is "maxed out"

My tuner telling me that he's not going to turn the boost up any higher til I get a bigger intercooler. :biggrin:

He said that the IC could no longer effectively cool the charge and I risked knock. This is coming from Jorge at P&L so I took his word for it.
 

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2004 Subaru FXT MT
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1,853 Posts
My tuner telling me that he's not going to turn the boost up any higher til I get a bigger intercooler. :biggrin:

He said that the IC could no longer effectively cool the charge and I risked knock. This is coming from Jorge at P&L so I took his word for it.
Was this based on temperature and pressure measurements that he took on your car or someone else's?

Your IC might be "maxed" out, but there are measurements to be taken otherwise you are making decisions blind and by the seat of the pants...

Many tuners operate on intuition, and while I won't discount good intuition, this is an area you simply don't have to guess.
 

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Official sf.org decal guy
2006 FXT
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12,516 Posts
Was this based on temperature and pressure measurements that he took on your car or someone else's?

Your IC might be "maxed" out, but there are measurements to be taken otherwise you are making decisions blind and by the seat of the pants...

Many tuners operate on intuition, and while I won't discount good intuition, this is an area you simply don't have to guess.
Honestly i'm not sure what he was going on. He's been tuning long enough that I assumed he just "knew". Or else there were other indicators that made him come to that conclusion.

In the end I was much more willing to go with a safe tune even if in fact the IC wasn't "maxed".
 

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BLUE WASABI, (#2 Info Provider)
2008 SG Model D
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9,224 Posts
Honestly i'm not sure what he was going on. He's been tuning long enough that I assumed he just "knew". Or else there were other indicators that made him come to that conclusion.

In the end I was much more willing to go with a safe tune even if in fact the IC wasn't "maxed".
Jorge from P&L knows from the real time measurements as he is tuning on the dyno along with all his experience from dealing with it all the time. I trust him and that is why I waited for only him to tune my car. :icon_wink: The STI TMIC can flow fine, it is just the cooling that you have to deal with. A larger bar and plate core will flow but will cool a lot better. The STi TMIC is just a cheaper option that works perfectly fine for lower power levels.
 

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2004 XT
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3,205 Posts
if you are doing the labor yourself do the swap, and the sell the vf43 and use the money towards a protune. but as others have said slightly bigger injectors and better tmic are necessary. what i would recommend is just drive the car and enjoy it for now since it is probably faster than what you were driving before(just guessing) and then once you get bored then upgrade
 

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Official sf.org decal guy
2006 FXT
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12,516 Posts
Right now your injectors are going to be the limiting factor. And you'll have no problem maxing out the stock injectors with the VF43. So if you're installing the 18g with hopes of going for bigger power larger injectors will be required. Should you go with the injectors, the intercooler will be next in line as the limiting factor. You can go with a Spearco or TurboXS TMIC.

I'm hoping to go with an 08 STi IC or some type of FMIC and then get a new tune. That should keep me happy for a little while. Especially since going for higher power will just throw me into a money pit i'm likely never to get out of.... A prime example is VinnyD :biggrin:

Oh, and don't forget about your transmission. I was able to break 5th gear with the power i'm making. I have since started downshifting to 4th.
 

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The Sub kit guy
2005 Forester X & XT VF39
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13,100 Posts
He has an STi 6 speed, so his tranny can handle the power.

The reason I went with a VF39 over an 18G was mainly because I did not want to have to replace the injectors and find a larger TMIC. I was also worried that my tranny wouldn't last long.
 

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2004 XT
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3,205 Posts
upgraded 04' with 6 spd swap.
Oh, and don't forget about your transmission. I was able to break 5th gear with the power i'm making. I have since started downshifting to 4th.
I may have a money pit of a car but at least I can read:chair:

Protuned 18/20g with supporting mods and a 6 speed would be the perfect daily driver imho. enough power to have fun with but not enough to worry about breaking a clutch or engine
 

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The Sub kit guy
2005 Forester X & XT VF39
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13,100 Posts
Since you have a 6 speed, already have the 18G turbo and need a protune anyway, maybe you should upgrade to it. Selling the VF43 will pay for some 740cc injectors, and you can run the STi TMIC with that setup if your not ready to buy a bigger TMIC.
 

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2004 Subaru FXT MT
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1,853 Posts
A larger bar and plate core will flow but will cool a lot better.
Sorry, you have that backward. All else equal, a tube fin has higher thermal efficencies but also higher backpressure. Bar-plate has low back pressure but lower thermal efficencies...

Pick your poison in other words when you are dealing with air-to-air.

Since I always like to have my cake and eat it too, I choose bar-plate air-to-water as my weapon of choice (I think I just let you know what I'm working on):biggrin:
 
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