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Old 01-11-2014, 10:02 PM   #1
cards6142
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Default big turbo build questions.

May be the wrong thread I apologize if it is. But I'm interested in finding out if anyone has experience with running a precision 6768 on a built sti. What numbers did you make? How was spool? Worth the funds? Ect.
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Old 01-11-2014, 11:38 PM   #2
jdpsearcher
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Find Matt Kincaid....I think he is running a turbo that size....

My build isn't done yet but I am a little bit bigger with a 72mm turbo....

What questions do you have besides worth it....
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Old 01-12-2014, 03:03 PM   #3
cards6142
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Is it worth it? Is a lot of fabricating needed? How's the spool? It'll be run on a built motor, big injectors, stock heads, killer b header set up. Just trying to get a feel for what I'm gunna be looking at. Also stock tranny. 05 sti.
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Old 01-12-2014, 03:33 PM   #4
Shortpersonbk
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Why go through all the work to setup a large turbo and run stock heads?
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Old 01-12-2014, 04:03 PM   #5
cards6142
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I'm debating on honestly, she's been sitting for a while and I'm just wanting her back, I'm not planning for the full potential of the 6768 I wanna run decent boost for a while till she's good and broke in. Then I was planning on picking up a set of heads, and a new tune for the full potential.
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Old 01-12-2014, 04:14 PM   #6
BmoreSti
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To me a 6768 is too large for a Subaru and the 2.5 displacement. Powerband>peak power. To utilize a 6788 you will need to be on a race fuel, or E85. It will be worthless to have stock heads on that large frame turbo. You are going to hit full boost 5500K+rpms and shift at what 7200 range? Why not go with a 626X sized turbo, built motor with head work on E85. Full boost a lot sooner and a fun ride. Why do all that work and not use its full potential? Raise the compression on the built motor, cosworth intake manifold, port the heads, springs, retainers, ect with a mild cams on 6264.
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Old 01-12-2014, 05:03 PM   #7
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If your budget is too small to do all of the supporting mods, including +1mm oversized heads that flow, get a smaller turbo that you will enjoy. No point in making 500 HP for a 500 RPM power band, you would have more fun with a 450 HP car that makes it for 3000 RPM. The bigger the turbo, the further the powerband is going to shift to the right on the RPM scale. I have all of the supporting mods, and I am making over 500 and peaking at about 580 on my street tune 93+meth from 4700-8200. Much more enjoyable. Powerband is key. You want to make enough power that you don't drop out of your power band from gear to gear. I bought the Cosworth heads, and that really made a huge difference over the last build with stock sized valves.
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Old 01-12-2014, 05:05 PM   #8
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I'm pretty sure you'll want to build the motor (including heads) for a redline of 8500 at least. Swapping heads on Subarus is enough of a hassle that I would want it done while the motor is out for the build.

I only have a GT30R and the powerband is narrow enough to be an annoyance. It comes on around 4k in 3rd gear, so have I have about 3k left before I need to shift. Tolerable, but just barely. A powerband that starts above 5k and still ends at 7k sounds like you will never get a chance to take your hand off the shifter.
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Old 01-12-2014, 06:27 PM   #9
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6466 will work for 90% of the guys building these cars. Spools good and can make over 800whp
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Old 01-12-2014, 06:54 PM   #10
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The big question is how much are you willing to do with the engine to support the air flow? We're talking all hardware here. Every single piece the air and fuel touches has to be resized to the new operating parameters. Plus you need to rev out the engine more to make use of the operating power band with this comparatively small engine. You might also consider stroking the engine and boring the engine out to gain displacement. I'm actually curious how you intend to use that much are flow, or are you simply shooting for peak efficiency and sizing a turbo to that. A 2.7 stroked engine revving to 8500 at 30psi will get you into that ballpark (~85lb/min). I assume this will be a dedicated drag car. Any reason not to drop in an EG33 in and start there?
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Old 01-13-2014, 01:30 AM   #11
jdpsearcher
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Cards.....Tapout and Juniour have hit it....Stay with a smaller turbo, especially with stock heads....You will have fun

Is the big turbo worth it, for me it is, worth the build and all that is associated with it...

Lag....LOL BLOW ME....Downshift and get that bitch on the pipe and NOTHING feels that good.....Hayabusa bike acceleration in 3rd - 5th....Yeah I will take that....
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Old 01-13-2014, 01:50 AM   #12
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I think it's useful to define build goals first. You should lay out a solid plan of action with all parameters defined. For example, you may say you want 500ft-lbs and 800hp to the wheels. Then you have to lay down basic principles. Identify necessary air flow, fuel flow, engine size, fuel type, and boost level necessary for such numbers. Then start piecing together parts that meet those requirements. Identify off the shelf solutions and any places that will require custom fabrication. Plan it out. Once you're done with the engine, start identifying supporting mods. What will you need to do to the drivetrain? The clutch, transmission/gears, diff, axles, etc. all need to support the output. You will also need to upgrade bushings and possibly need to stiffen up some parts of the chassis.

It all comes down to what you want to do and how far you're willing to go. Maybe you're willing to build a car that will run on straight alcohol and live at 35+ psi. I don't know. Maybe that's its purpose, just pure drag. I just know that for the size of turbo you're looking at, there won't be much left that's stock through the entire power train system. There is nothing oem speced to support that output.

You're rather new to the forum still and likely to Subarus. I don't know what your previous cars were nor your previous builds. I don't know what base knowledge you have on building up a high hp system. I also don't know your expectations nor how far you are willing to go to achieve X goal, whatever that may be. All I know is you're looking at a damn big turbo that has very little reason to be on a tiny 2.5L engine that isn't very specifically getting built as a drag car. A turbo half the size you're looking at is a "good" fit for these engines that are near stock to medium modified.
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Old 01-13-2014, 09:44 AM   #13
02WRX2.5
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Do stuff outside the box! Stay away from what everyone tell you they do or have seen done. Keep it simple. Big turbo with no restrictions is what makes power with these cars from my experience. Twin scroll turbo and big cams with no restrictions in flow will give you a great combo.
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