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Old 09-22-2010, 09:29 AM   #1
MM'S STI
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Default Max Boost on STI stock turbo?

hi there, what is the max boost u can push out of a stock turbo safely? and how much horsepower does that make?
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Old 09-22-2010, 09:37 AM   #2
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you will get various responses to this question. i personally run 20psi, which is still out of this turbos efficiency range. I have seen people run 25psi etc. As for horsepower it depends on what mods your running and fuel (91,93,100 e85 etc) also depends alot on your tuner and engine management. The question you asked will get you such a broad response.
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Old 09-22-2010, 09:38 AM   #3
Candor
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Which turbo; VF39, VF43, VF48?
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Old 09-22-2010, 09:44 AM   #4
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I'd say the OP's got a VF39 considering his profile says he's got an 05 STi.
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Old 09-22-2010, 09:46 AM   #5
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I think once you start running them above 20-ish psi they start producing gobs of heat. I'm not sure where the cutoff is between overheated air and boost creating power though. I'm tuned at 20 psi as well.

HP is ok on these but you'll really have fun with the torque, they spool quick but die off towards redline.
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Old 09-22-2010, 10:12 AM   #6
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ive heard of 27psi on a vf39. not sure if this is legit though. i wouldnt want to run much past 25psi on one though. i was just a cobb stage 2 (i think thats 19psi?)
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Old 09-22-2010, 01:29 PM   #7
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ok thanks! and ya its a vf-39.
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Old 09-22-2010, 01:37 PM   #8
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Mine is running at 19.5 lbs and it spools pretty f'in quick.... and thats pretty safe from what chris at efilogics said.
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Old 09-22-2010, 01:39 PM   #9
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sweet thanks! do u have any clue how much horsepower ur making?
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Old 09-22-2010, 01:43 PM   #10
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Quote:
Originally Posted by MM'S STI View Post
sweet thanks! do u have any clue how much horsepower ur making?
right now its 295hp 330 ft lbs

the torque is amazing! i could care less about hp.
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Old 09-22-2010, 02:14 PM   #11
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Quote:
Originally Posted by evoeater8 View Post
right now its 295hp 330 ft lbs

the torque is amazing! i could care less about hp.
330 ft lbs? Isn't that like 50 ft lbs more than stock?
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Old 09-22-2010, 10:22 PM   #12
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thats awesome. evoeater8 is that with everything stock setup except higher boost?
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Old 09-22-2010, 11:40 PM   #13
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Quote:
Originally Posted by istayaway View Post
330 ft lbs? Isn't that like 50 ft lbs more than stock?
Closer to 100 lb-ft's over stock actually. Don't forget, the factory numbers are measured at the crank and the numbers you hear about modified cars putting down are almost always at the wheels.

There are a lot of variables that come with an answer to your question. It's possible to up the boost over 20psi, but the higher boost you run the less efficient the turbo becomes and the more heat it starts producing... as heat goes up, power goes down and the potential for engine knock increases. Big power is less about trying to max out peak boost pressure from your turbo and more about trying to max out it's efficiency.

Also, a vf39 doesn't flow enough air to hold your peak psi in the higher rpm range. Your boost pressure will (typically) peak in the middle of your revband and then gradually fall as you close in on redline... since peak horsepower usually occurs closer to redline where boost pressure is tapering down, peak psi usually has little correlation to peak horsepower...
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Old 09-22-2010, 11:41 PM   #14
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Quote:
Originally Posted by MM'S STI View Post
thats awesome. evoeater8 is that with everything stock setup except higher boost?
Those numbers sound like typical stage 2 numbers... probably a tune with a turboback.
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Old 09-25-2010, 12:05 AM   #15
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I've pushed mine up to 22 psi on my 08 STI, but there isn't much gain to be made above 20 psi with it. There is slightly measurably greater torque when it peaks that high, but it's mostly between 3600-4000 RPM, which is nice, but goes by very quickly, and you won't spend much time there if you're seriously trying to haul ass. With 22 psi mine made 304 Hp and 343 Tq using the Airboy road dyno... that said... that was on a cold (FL wise) 41* day. On our usual 89* 89% humidity swampy hell, I probably make closer to 270 measured the same way.

My 07 STI, for whatever reason, would become a knock prone, timing pulling wimp at anything above 20 psi. After pulling enough timing to keep it from knocking, there were no gains to be had.

I have a suspicion that every car, even with identical equipment, will have slightly different capabilities. That said, most seem to make close to 300 WHp (using Airboy's spreadsheet) on 93 octane around sea level with whichever variety of STI turbo on them at or around 20 psi. Want to run higher on a stock turbo? water/meth injection or E85 seem to be the best alternatives.
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Old 09-25-2010, 12:12 AM   #16
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Quote:
Originally Posted by kyledupreez View Post
ive heard of 27psi on a vf39. not sure if this is legit though. i wouldnt want to run much past 25psi on one though. i was just a cobb stage 2 (i think thats 19psi?)
17.5.
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Old 09-25-2010, 12:12 AM   #17
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Old 09-25-2010, 12:49 AM   #18
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330whp/390wtq on The Shops Dyno Dynamics.
port and polish EVERYTHING. the vf series turbos love torque but will never net you high horsy powahs.

20 psi, when I don't overboost 25 by accident
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Old 09-25-2010, 02:51 AM   #19
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Quote:
Originally Posted by istayaway View Post
330 ft lbs? Isn't that like 50 ft lbs more than stock?


Not on that dyno it isn't.

In fact I dont know of any dyno, anywhere that a stock STI will put down anything even close to 280ft/lbs.
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Old 09-25-2010, 07:36 PM   #20
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Quote:
Originally Posted by Davenow View Post
Not on that dyno it isn't.

In fact I dont know of any dyno, anywhere that a stock STI will put down anything even close to 280ft/lbs.
I'm assuming you mean on a stock tune, not just a stock turbo!

I'm sure someone out there could force a dyno to come up with that number... but it doesn't really matter anyway. That's why I like to reference the Airboy road dyno, because anyone (who can log) can run the numbers themselves and come up with a reasonably similar reading measurement.

My 08 was a stout 285 WHp at stage 1 on a dyno dynamics, a few month ago it put out 265 at stage 2 on a Mustang dyno... Number's are just numbers. I'm not into racing much, but it ran 13.6 at stage 1 and 13.1 at stage 2. With less "power" at stage 2. Meh.

But the whole dyno thing is another thread altogether! What's your take on max useful boost (assuming 93 octane gasoline)?
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Old 12-07-2010, 08:07 PM   #21
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I deff trying to figure out about the stock wrx's, can you boost your stock turbo in be safe with it , or I need to spend some money!?
somebody know the psi on the wrx turbo!
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Old 12-07-2010, 08:13 PM   #22
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I could be off a little but I believe stock WRXs (2.0 w/TD04) run about 12.5psi peak. My protuned bugeye peaked at 19psi tapering to ~12psi at redline. This was with only a catted 3" TBE, UP, intake and EBCS.
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