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Old 02-17-2009, 01:56 AM   #1
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Default GT3076R Boost Creep?

So, in my quest for big power (see this thread), I am looking at a bigger turbo. I have pretty much decided on something around the GT3076 range. I am very interested in this turbo from ATP because of the t25 flange.

My main concern is boost creep. I have a gt2860rs now and I am creeping about 5psi past wastegate pressures (creeping from 10psi to 15psi.) This is with a BEGi 2.75" separated gasses downpipe and straight pipe after that. I would like to stick with an internally gated turbo if at all possible. However, if I'm going to have to switch to an externally gated setup then, I'm going to have to change from my current BEGi log style manifold to one with a flange for the external wastegate. If I'm going to change my manifold, I might as well go with a T3 flange. If I'm going to go with a T3 flange I might as well go with a different turbo. Changing all this stuff is expensive.

Does anyone have any thoughts or suggestions?
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Old 02-17-2009, 02:00 AM   #2
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EWG, T3, MBC, FTW. Internal gates suck.
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Old 02-17-2009, 02:01 AM   #3
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I'd suggest on an ewg for sure. With that big of a turbo you really dont want to take the risk of possible boost creep. That said, if you want big turbo and no creep either port the **** out of wg, get bigger flapper, or run a restrictive exhaust. with something the size of your planned turbo, I just dont understand not getting an ewg though

also: if you're going for big turbo/powerful setup/big numbers why are you building it "around" a shitty t25 flanged log manifold? **** man, if you're going big do it right. tubular mani, ewg, the works
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Old 02-17-2009, 02:10 AM   #4
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Yeah, you're right. I should just go with the right manifold.
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Old 02-17-2009, 02:22 AM   #5
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Nother suggestion. Get a weld ell 4:1 manifold. Build one or buy one, but it's the manifold for what you're trying to do. I bought this FM thing and modifilested it into a FM3 with big bolts, but it still sucks. Well, not sucks, but I have:

At least 10 hours of drilling, taping, cutting, grinding, etc on it
Paid a welder 40 bucks to weld a flange on it
Paid 118 for the manifold
Factor in my time and I should have just bought a damn S5 from Bell. But really the only reason I did this was because I thought (hahahahah) that this would be faster and easier. hehe. As much time and money as I have in this, I could have just as well built a damn 4:1 weld ell manifold and have a better setup. Sigh....

CLIFFS:
Do **** right the first time
I got 35.8% thermal efficiency for a FWH Rankine cycle on problem 5
Don't buy a turbo that's way to big. If you want 400whp, don't buy a 600whp turbo, etc. A GT3271 might be the right turbo for your goals if 400whp is the upper limit. Besides a GT3271 is a good bit cheaper too. And if you sell some of your old **** you'll recoup some of your money for the new stuff.

CLIFFS for CLIFFS
Make sure you get the right stuff the first time.
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Old 02-17-2009, 02:34 AM   #6
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Ex WG or go home.
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Old 02-17-2009, 11:37 AM   #7
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there are two things that cause boost creep.

wastegates that are too small for the turbo
and turbos that are too big for the wastegate.
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Old 02-17-2009, 12:08 PM   #8
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Quote:
Originally Posted by patsmx5 View Post
Nother suggestion. Get a weld ell 4:1 manifold. Build one or buy one, but it's the manifold for what you're trying to do. I bought this FM thing and modifilested it into a FM3 with big bolts, but it still sucks. Well, not sucks, but I have:

At least 10 hours of drilling, taping, cutting, grinding, etc on it
Paid a welder 40 bucks to weld a flange on it
Paid 118 for the manifold
Factor in my time and I should have just bought a damn S5 from Bell. But really the only reason I did this was because I thought (hahahahah) that this would be faster and easier. hehe. As much time and money as I have in this, I could have just as well built a damn 4:1 weld ell manifold and have a better setup. Sigh....

CLIFFS:
Do **** right the first time
I got 35.8% thermal efficiency for a FWH Rankine cycle on problem 5
Don't buy a turbo that's way to big. If you want 400whp, don't buy a 600whp turbo, etc. A GT3271 might be the right turbo for your goals if 400whp is the upper limit. Besides a GT3271 is a good bit cheaper too. And if you sell some of your old **** you'll recoup some of your money for the new stuff.

CLIFFS for CLIFFS
Make sure you get the right stuff the first time.
Hmm, i know a guy that i can get to do the welding for a very good price. I could buy the pieces and have him put it together. Hell, we could even do the downpipe as well. A T3 flanged turbo is the way i should go. I would like to stay with BB though.
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Old 02-17-2009, 01:55 PM   #9
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By no means am I an expert but here is what has been explained to me in my research of my planned 3071R. Yes external waste gates help along with porting but here are a few that were pointed out with my planned build.

1. Boost creep is exaggerated by larger exhaust.

2. Boot creep is an issue with larger turbo run at low pressures.

From what I am reading in your thread you have a 2860 with the BEGI 2.75 exhaust and you are trying to keep the boost at 10 psi. That 10psi limit is why you are having the creep issue. You are in search of big power but still only planning 18psi on a much larger turbo. My uneducated guess is that the 3076 will flow enough air to support well over 450 hp with +20psi boost.
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Old 02-17-2009, 02:02 PM   #10
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If you are going with an ATP turbo I believe they make an exhaust housing with an outlet for an external wastegate already plumbed in. That would save you from needing a new manifold or welding. I have no idea if it would fit in a miata but worth a look. I think it is available on this size turbo.
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Old 02-17-2009, 02:20 PM   #11
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Special Turbine Housing T25-EWG-44: atpturbo.com

The only issue is the wastegate is going to be at 12o'clock with the Begi cast manifold. Might not fit.
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