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2008 FXT
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128 Posts
Discussion Starter #1
I am in the market for an automatic Forester XT and am selling my 03 WRX. My WRX has a VF34 and all the other goodies so i am planning on swapping most of the stuff into the Forester. I have a couple questions...

1. Is it remotely safe to run the VF39 AccessPORT map with the VF34 turbo?
2. I assume the answer to 1 is no... so i would have to run a custom tune as soon as i put on the VF34. Is there any noticeable difference between a car with a 39 vs a 34 either while driving or on the dyno?

Thanks!
 

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Official sf.org decal guy
2006 FXT
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12,516 Posts
I am in the market for an automatic Forester XT and am selling my 03 WRX. My WRX has a VF34 and all the other goodies so i am planning on swapping most of the stuff into the Forester. I have a couple questions...

1. Is it remotely safe to run the VF39 AccessPORT map with the VF34 turbo?
2. I assume the answer to 1 is no... so i would have to run a custom tune as soon as i put on the VF34. Is there any noticeable difference between a car with a 39 vs a 34 either while driving or on the dyno?

Thanks!
Hmmm... that's a good question (#1). They are nearly identical. I wonder what kind of issues, if any, you would having using a vf39 map with a vf34. Wanna try it and let us know?

I would actually think the opposite with #2. I went with a vf34 because I felt that I would get better results. What sold me on the vf34 was the ball bearings as opposed to the roller bearing of the vf39 (oh and the whole cracking case did not sit well). I would say if you already have a vf34 you can swwap over do it!! OTC maps usually suck because they are so conservative. Soooo... seeing as how you would most likley need a tune for either, I vote, emphatically, for the vf34.

Definitely get a higher capacity fuel pump too.
 

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2007 Sports XT 4EAT
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2,503 Posts
I wouldn't run a VF39 map with the VF34. As noted above it's a ball bearing turbo and it's also has a larger hot side than the 39 IIRC. I haven't ridden in a car with a 34; from what I have read it both spools faster and has a higher potential than the 39 but I don't know how that translates to the street.
 

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2017 VW Golf SportWagen 5MT
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I wouldn't risk running a VF34 with OTS maps either. And, Cobb maps aren't conservative at all in my experience, too much boost target. Local Subaru shop really likes VF34s on a 2 liter, should be nice on the FXT as well.

Stan
 

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Official sf.org decal guy
2006 FXT
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Now, I don't know if it's because they aren't as readily available as the vf39 but try searching for blown-up turbos on NASIOC. I guarentee you'll be hard pressed to find a vf34 that went bad. The vf39....well... that's going to be pretty easily. And if you count the whole hot-side cracking (which I know people say is not a big deal blah blah blah) then forget about it.
 

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2008 FXT
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128 Posts
Discussion Starter #7
Well, looks like everyone definitely reinforced what i was thinking, thanks! I'm going to keep the 34 but now i gotta figure out the best way to get the tune, i'd rather not have the shop install the turbo so how do i get it from my place to the shop(20 miles) for the tune?? I'm not planning on buying an accessport so i won't be able to load any sort of basic tune to drive it there.
 

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Honestly I wouldn't even run the OTS VF39 map on a VF39. A custom tune is always the way to go. The VF39 map would probalby work to get you to a tuner though (even the stock map probably would if you kept out of boost though).
 

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2005 FXT 5-spd
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282 Posts
Talk to your tuner. They should be able to send you a limp map to get you to the shop for a tune. Otherwise you should be able to drive the stock map and just not boost at all.
 
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