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05 FXT 4 speed
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4 Posts
Discussion Starter · #1 ·
Having never owned an automatic I hope this makes sense. I may be getting a 05 forester xt that is stock and having owned an 04 STI I'm sure I'll be looking for more power my question is since it's an auto which turbo would best match the shift pattern of the auto trans as far as torque curve and such. Since an auto spends a lot of time within a certain RPM does it makes sense to match it to a turbo and if any are better than others? I may have the 04 STI TMIC and a COBB cat less DP to get me started and had an accessport on the STI that was sold but I am familiar with it.
 

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2008 FSXT 4EAT
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4,143 Posts
I have an '08 FSXT auto, and I've had the following turbo setups:

1. Stock turbo & exhaust
2. Stock turbo + Cobb down pipe
3. VF39 + full exhaust + external wastegate + STi TMIC
4. AMR T60R + tons of supporting mods

Here's the dyno plot for setup #3 (VF39 @ 17 psi)



Here's the dyno plot for setup #4 (T60R @ 19 psi)



The two setups couldn't be more different. The VF39 (flows 38ish? lb/min) is a great choice for neck (& tranny) snapping torque, whereas the T60R (flows 60 lb/min) is laggy but great for drag racing. Another way to look at it is a smaller turbo will be better for city driving, and a bigger turbo will be better for racing & long highway pulls.

Honestly, the VF39 setup was more fun, because of the instant spool and external wastegate, even though it's slower than my current setup.

That said, a VF48 or slightly larger (40-45 lb/min) @ 17-19 psi would be a good choice if you're just trying to make some more power without risking a blown tranny or shortblock. Hope this helps.
 

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2008 FSXT 4EAT
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4,143 Posts
A few more thoughts...

-04/05 FXTs have a catted up-pipe; you'll want to replace it or gut it when you swap turbos. You don't want a cat going through the hot side of your turbo.

-Big turbo automatic cars can be a hoot, because they maintain full boost between gear changes. This also means the power delivery will be smooth, which should (theoretically) be easier on the tranny.

-Regardless of what turbo you choose, think of "D" as an overdrive gear and keep the tranny in "3" until you're on the highway. This will prevent the tranny from hunting, and you'll enjoy the car more.
 

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2004 Forester XTi 4EAT
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1,430 Posts
I have an 04 with..
vf43
3inch catless dp
stock midpipe
prodrive axleback
catless up-pipe
sti tmic
and a road tune (17.5psi).

Alot of it comes down to the tune,the cobb maps will leave you yearing for more if you took a ride in a car that was custom tuned.

I've had my share of highway fun,ppl get angry when the car walks away from them lol.
Lastest victim was a 6spd evoX with some bolt-ons :)
 

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05 FXT 4 speed
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4 Posts
Discussion Starter · #5 ·
Thanks for the info, I was hoping someone understood what I was trying to get at. So would a P&P on the vf39 help it spool quicker and keep the tourqe curve somewhat flat across the RPM's as I am looking for the head snapping feel you get in the low end. So will the VF 39 still pin your head to the seat when you steep on it at a 70 Mph roll? Or does it usually have to drop a gear? And while I'm at it, does the accessport change the profile of the trans at all? By say holding the gear longer or making the gear changes quicker? Thanks for the helpful info!
 

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2004 Forester XTi 4EAT
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1,430 Posts
Thanks for the info, I was hoping someone understood what I was trying to get at. So would a P&P on the vf39 help it spool quicker and keep the tourqe curve somewhat flat across the RPM's as I am looking for the head snapping feel you get in the low end. So will the VF 39 still pin your head to the seat when you steep on it at a 70 Mph roll? Or does it usually have to drop a gear? And while I'm at it, does the accessport change the profile of the trans at all? By say holding the gear longer or making the gear changes quicker? Thanks for the helpful info!
VF39's tend to have boost spikes so start with a VF43 at least, crusing at 60-65..if i punch it the car will still dart off like nobody's business. I've never used an AP but I dont think it changes anything regarding the transmission. P&P may help but you probably wont be able to tell. If you really want to P&P, then do it in every area possible area. The catless up-pipe will help with spool, or just go straight to an EWG set-up. As I said before thought, find a good tuner..it's the most important piece to making everything work in harmony.
 

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05 FXT 4 speed
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Discussion Starter · #7 · (Edited)
Tuning should be easy for my area with andrewtech and turboxs less than 10 miles away. So stick with a VFXX or would a TD05-18g do what I want but better without doing injectors? Fuel pump I can handle.
 

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2004 Forester XTi 4EAT
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Those turbos are a definite step up in the right way from the Vfxx. More than a few guys here are using them, do a search in the motorbuild and member journal sections and see whats going on with the bigger turbos.
 

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2008 FSXT 4EAT
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4,143 Posts
You shouldn't need to do injectors or fuel pump on a VFxx build, unless you do E85 or want some conservatism in your setup.

A starting point for a 260-280whp setup would be:

VFxx turbo
STi TMIC
Downpipe
Catless Up-pipe
Tune (15-18 psi)
 

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05 FXT 4 speed
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Discussion Starter · #10 ·
Cobb ap, ecu reflash or some other em? I had an Cobb ap on my STI and never swapped the maps around just flashed it once. There's a couple shops around here with awd dynos that tune which would be the best while still being reliable? Thanks for the help been out of the car world for a couple years.
 

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2008 FSXT 4EAT
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4,143 Posts
Your two best options are Cobb AccessPort or Open Source via Rom Raider. A lot of tuners nowadays only use AccessPort, but I'm not sure who's in your area.
 
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