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Old 02-03-2011, 12:02 PM   #1
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Default boost creep question

So I'm running an internal gate on my 3076 and get a little creep. I know I know "we told you so, bla bla bla", but its really not that bad and I'm not at all regretting going IWG.

The creep is not major, and not over a big area of the rpm range: between 5-6k and 2 psi.
So I hit 14psi, then it slowly creeps up to 15.8-16psi from 5-5300, stays there til 6 then drops back down to 14 all the way to redline.

My question is this: will raising the boost so that my target is 16 everywhere more or less stabilize my boost and mask/hide/get rid of the creep?

I'm thinking yes, since apparently 16psi is the least amount of boost the internally gated turbo can produce between 5-6 due to iwg flow limitation. (I did port/polish it btw and enlarged the opening to as big as it can possibly be).

Wanted to get your opinions.

PS: forgot to mention I'm using an MBC.

Last edited by 18psi; 02-03-2011 at 12:13 PM.
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Old 02-03-2011, 12:19 PM   #2
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Quote:
Originally Posted by 18psi View Post
My question is this: will raising the boost so that my target is 16 everywhere more or less stabilize my boost and mask/hide/get rid of the creep?

I'm thinking yes, since apparently 16psi is the least amount of boost the internally gated turbo can produce between 5-6 due to iwg flow limitation.
I think your logic is sound.
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Old 02-03-2011, 12:55 PM   #3
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I say you're going to get 16psi, with a spike to 18. What's your wastegate source?
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Old 02-03-2011, 12:57 PM   #4
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/\ See that is what I'm afraid of. What makes you say that though? I want to know how my logic is flawed and try to figure this out.

Wastegate source is intake manifold with an mbc plumbed in.

Like I've said before it doesn't really bother me enough to go ewg or re-do **** majorly, but if there's an easy fix I'm all for it.
Hitting the dyno in a couple days and just wanted to see if I can get this sorted out before I do.
Would an EBC or 3port BCS be an option? Make target 16 before and after the creep and just zero it out from 5-6 keeping it at 16?
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Old 02-03-2011, 01:02 PM   #5
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I thought directly pre-TB was the ideal location.

I'd think that trying to shove more boost through a hole would cause it to back up even more. Unless there's some trickery flow stuff going on I don't understand. Try turning it down, see if it gets better or worse.
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Old 02-03-2011, 01:08 PM   #6
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True but I always had the signal coming off the mani and never had any problems.

If you take a look at my BUILD THREAD you can see a log of what I'm talking about.
Sorry can't hotlink pics at work.
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Old 02-03-2011, 01:23 PM   #7
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Why don't you just turn up the boost and give it a try? It's only a few pounds and you're built...
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Old 02-03-2011, 01:35 PM   #8
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Quote:
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I thought directly pre-TB was the ideal location.
It's largely a matter of opinion as to directly pre-TB vs. post-TB. The one you want to avoid is pre-IC, however that leads to boost sag, not boost creep.

Going post-TB should have relatively little effect on stability of boost, other than that you're likely to see a sharp boost spike when transitioning from, say, 75% throttle to 100% throttle. The real "issue" is that, when you are running at heavy load but using the throttle to maintain something less than target boost, the boost controller will be trying like hell to achieve the target (against the partially closed throttle) and will thus be running with the WG fully closed, making unnecessary heat and restriction. But again, this is a part-throttle phenomenon, not a WOT condition.
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Old 02-03-2011, 01:52 PM   #9
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Quote:
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I'd think that trying to shove more boost through a hole would cause it to back up even more. Unless there's some trickery flow stuff going on I don't understand.
Not so much that, you're bleeding off exhaust. Sounds like what he has is a fully open WG trying to lose enough exhaust to keep his lower boost from 5-6k, and instead getting 16 psi. If he turned it up to 16, then I'd think the fully open WG in that scenario would have the same "problem". Still probably get the sag at the end though, from 6k "all the way" to redline. lol.

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But again, this is a part-throttle phenomenon, not a WOT condition.
Nailed it, Joe. But I think the part-throttle is a bit more important for a street car, since that's so much of its operation. Extra heat, noise, wear, etc.
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Old 02-03-2011, 02:07 PM   #10
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with wastegate pressure only (which was supposed to be about 8psi) i would creep to about 13psi at the very top of the rev range. When I added the boost controller set for 12 psi, I would spike to 15psi and boost cut at about 4300rpm.

This on internally gated 2560
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Old 02-06-2011, 04:42 AM   #11
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Ok so I have made a few observations tonight:

1) turning up the MBC results in the same boost curve, but higher up, so it doesn't solve anything.

2) Richening up the afr's up top REDUCED the boost sag past 6300

Its weird as hell: if I run 11.5-11.8 afr past 6300, boost starts to slowly taper from 16psi @6k to 13.9 at redline.
Richening it to 11.0:1 past 6300 caused it to stay at mid/low 15's from 6300 all the way to redline.


Now, next question is this: should I run it rich and make up for the small power loss with the higher boost or should I get the afr's back up to upper 11's and let the boost sag? Which is the lesser of two evils?
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Old 02-06-2011, 05:56 AM   #12
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Quote:
Originally Posted by curly View Post
I say you're going to get 16psi, with a spike to 18.
Called it!!

I had this exact problem with 9ish psi on my setup and a compressor housing sourced IWG.

Just for ***** and giggles, put your wastegate source pre-tb and see what happens. Can't hurt.
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