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Old 10-06-2007, 11:14 AM   #1
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Default Do I need a 3" DP?

Hey guys,

I am wanting to buy a DP before starting the install.

What are todays best options?

I am thinking of a 3" DP and 3" back with a magnaflow.


Is it worth it using 3" or are there other bottle necks with the Greddy that cancel the benefits? (such as manifold etc)
Should I just go with 2.5"?


Thanks
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Old 10-06-2007, 11:29 AM   #2
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A three inch downpipe is a great idea if it fits. The turbo placement might make this size a little difficult on a greddy kit.
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Old 10-06-2007, 11:33 AM   #3
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Word is that the tubing "donuts" make the tight bends needed to get the downpipe going down help immensely.
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Old 10-06-2007, 01:00 PM   #4
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Go for it. It may not make more power for the lil' greddy, but you know it's there and ready if you ever want to go crazy.

Last edited by Al Hounos; 10-06-2007 at 01:12 PM.
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Old 10-06-2007, 01:14 PM   #5
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Agreed ^^^
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Old 10-06-2007, 08:43 PM   #6
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Yes, it's always worth it.
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Old 10-06-2007, 09:20 PM   #7
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I think the turbine outlet is only 2"
I'd match and swage. A 3" would be tough.
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Old 10-06-2007, 09:25 PM   #8
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I betcha Corky would recommend against it.

match and swage is just as benefitial for flow/velocity.
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Old 10-07-2007, 01:34 PM   #9
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Quote:
Originally Posted by Ben View Post
I think the turbine outlet is only 2"
I'd match and swage. A 3" would be tough.
I think you are right the outlet is probably ~2"
what do you mean by match and swage?
2" seems kind of small though.
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Old 10-07-2007, 03:11 PM   #10
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start at something like 2.25" or 2.5" and step it up to 3"

like for example, my t3 has a 2.25" turbine exit, my DP is 2.5" and then steps up to 2.75". My cat and exhaust is 3".
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Old 10-07-2007, 07:29 PM   #11
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Quote:
Originally Posted by Braineack View Post
start at something like 2.25" or 2.5" and step it up to 3"

like for example, my t3 has a 2.25" turbine exit, my DP is 2.5" and then steps up to 2.75". My cat and exhaust is 3".
Yah step it up. Big right at the turbo flange isn't ideal if the turbine outlet is comparitively tiny.

But all things considered i'd go as big as you can fit. Wo hoo
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Old 10-08-2007, 06:42 PM   #12
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3" exhaust is the same as vagina
whether you need is arguable
whether you want it is obvious
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Old 10-08-2007, 08:46 PM   #13
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I betcha next time I dyno will make you think twice about a 3"
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Old 10-08-2007, 09:25 PM   #14
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with your new breathing mods, let's shoot for 10 psi at idle
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Old 10-08-2007, 09:49 PM   #15
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10psi at idle would mean a .5" exhaust and tons of backpressure.

lets shoot for 10psi at 2000RPM
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Old 10-09-2007, 12:40 PM   #16
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10 psi @ 2K.....that would be very boner inducing
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Old 10-09-2007, 12:56 PM   #17
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Quote:
Originally Posted by whaaamx5 View Post
10 psi @ 2K.....that would be very boner inducing
Seeing 12psi @ 3800RPM with my turbo vs 4200RPM is pretty close.
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Old 10-09-2007, 01:09 PM   #18
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indeed...what size is your DP/exhaust?
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Old 10-09-2007, 02:14 PM   #19
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right now it's a 2.5" to 2.75"

however my cat and catback is 2.25"

the muffler is also a dual exit with dual 2" outlets.


so I have absolutely the worst setup for flow, as it progressively gets smaller.

I did minor headwork and have shaved about 500RPM off my spoolup time.

I have a 3" on the way, so I'm excepting to see even better results. Hopefully something like 20rwhp at the same boost level.
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Old 10-09-2007, 02:47 PM   #20
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that would be great success...
are you gonna do a write up on your head-work?
did you do it yourself or at a machine shop, i hear a lot of people saying they did it at home, but have no info to back it up, etc...
i have a spare motor, so i may want to experiment myself with some headwork
let me know if you did it yourself

I did minor headwork and have shaved about 500RPM off my spoolup time
thats impressive
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