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Old 07-28-2008, 07:14 PM   #1
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Default Max boost over WG spring pressure with MBC?

I seem to have hit a brick wall boost wise at 15psi, apparently that is as far as my MBC will allow me to go. I completely forgot that I have a 4psi spring in it from day one going turbo. I am going to order a new spring anyways, but I got to wondering, whats the general max above WG spring pressure a MBC will allow? I would have thought it was more than 10psi, or maybe I have leak somewhere, but it holds steady at 15psi and I have checked the car over for leaks. 15psi is starting to feel like stock
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Old 07-28-2008, 07:19 PM   #2
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That is not a generic answer. It is one which will differ from Turbo to Turbo.

I had a T3/T4 60 Trim with a Stage 3 Exhaust Wheel and .63 AR and it would not boost over 18psi even with a Wastegate with no vacuum line. Exhaust Back Pressure was so high it was opening the gate! The Turbo wheels were just sized from and did not work on the BP.

Switched out to a 50 Trim and ran 30psi on the same Manifold and setup!

A lot of the big boost folks will run CO2 to help with this when using an EWG. If you are internal you might find a helper spring will help a little, or even a stiffer 15psi spring from your external gate.
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Old 07-28-2008, 07:36 PM   #3
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ive seen helper springs on quite a few cars, and it works great...extremely cheap too
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Old 07-28-2008, 08:00 PM   #4
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Sorry should have been more specific on the turbo. Its a T3/T4E 50t .48 .60, Tial 38mm external gate. WG vacuum source is run directly from the manifold after the TB, nothing else is on the line other than the MBC of course. I guess I am just wondering if that seems somewhat accurate, or if that is a red flag of a problem that I am not seeing.
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Old 07-28-2008, 08:21 PM   #5
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Should be fine. How big is your downpipe? I'd install a larger spring 12-15 psi is my best guess!

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Old 07-28-2008, 09:09 PM   #6
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I <3 actively involved sponsors
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Old 07-29-2008, 02:22 AM   #7
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Quote:
Originally Posted by [email protected] View Post
Should be fine. How big is your downpipe? I'd install a larger spring 12-15 psi is my best guess!
2.5" open downpipe, ends 3' after the turbo

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