Sr20 loosing boost after 5500rpm Gt3076r @20psi

[joe_nismo]

I'm running a gt3076r with 72lb injectors, 300z maf, and jwt tune to match. Internal gate spring at 15psi
I decided to throw a isis mbc on there and cranked it up to 20ish psi.

The problem. It rises to 20psi and holds, but after 5500rpm the boost starts falling and by 6500 I have around 10psi on the guage. If I take the mbc off it reads 13-14 steady.
Any clues other than what I suspect? Mbc is faulty.

[ultimateirving]

Edited.

Nvm

[joe_nismo]

I notice absolutely zero hiccups or issues. It feels more like a smooth bleed at the wc. But how could that happen?

[ultimateirving]

I notice absolutely zero hiccups or issues. It feels more like a smooth bleed at the wc. But how could that happen?

Is there any chance the wastegate (or actuator) is loose or letting exhaust gasses by ?

[joe_nismo]

Wouldn't the wg leak at a lower pressure? I wonder if the mbc is withholding pressure up to a certain point and then dumping all of it down the line causing the wg to open wide

[Bleakley]

Sounds like your mbc does not have a bleed? EDIT: Wait, I do not think that is your problem.. But I will leave this up..

If you suspect it is faulty, here is what I will be running: http://nxsmotorsports.com/content/manual-boost-controllers
I have heard of other people running these. And have heard nothing but superb results..

[cbeuglas]

I am running one and love it.

[ultimateirving]

Wouldn't the wg leak at a lower pressure? I wonder if the mbc is withholding pressure up to a certain point and then dumping all of it down the line causing the wg to open wide

That is kinda of the theory. Depending on the mbc it's probably opening once it reaches the 20psi and then it might not have the gusto to keep that psi to redline.

The fact that your wg pressure holds boost better is what throws me off.

[joe_nismo]

I might just have a bad mbc. Only easy way to tell is to throw a known good one on there and see if it behaves the same way. The wg is from a 2871 that the rod was slightly modified to fit on the gt30. Being from a smaller turbo shouldn't cause any issue right? Pressure is pressure. Apparently this is a common mod so I hope not.

[bmaddock]

Where is your boost gauge located? You could move that around to figure out where the boost leak is. In other words, if you're seeing boost lost at the compressor vs boost lost at the manifold, it might give you a better idea of where it's escaping.


But judging by what you've posted, sounds like it could be the MBC. That should be simple to boost leak test out of the car with a compressor and some vacuum line.

[joe_nismo]

Boost guage is at the throttle body.. If only I had an air compressor :/

I'm not sure what you mean by 'the fact your wg holds boost better throws me off'

[bmaddock]

Err thinking about it some more, if you're truly only seeing 10psi after 5500rpm despite your 15psi wastegate spring and 20psi MBC....I would think that means your wastegate is leaking.

But what ssedtohavs said, the fact that the wastegate holds boost without the MBC is confusing. At 20psi and 5500+rpm, there could be enough exhaust flow out of the turbine housing to pull open the wastegate. I presume you're internally gated?

I would try a 20psi wastegate spring if you can borrow from a friend or what not.

[bmaddock]

Oh sweet, you're in Richmond too!? I don't have a 20psi wastegate spring but I do have another MBC you can try. We should meet up

[ultimateirving]

Ok this dude is just a spammer and copy pasted my post.
If you have someone who will let you borrow or use a mbc try And swap it out and test it.

The fact that your wg pressure holds boost better is what throws me off.http://goo.gl/0AtosF

[Mikester]

My theory: 720cc injectors, Z32MAFS & 3076 with JWT tune is a solid setup. You threw a ghetto mod (ISIS MBC) suited better for OEM T25/28 setups & got what you paid for. A system pushing well over 1.0-1.2bar of boost should really have a solid, proven EBC in there. Recommend you yank it before something goes boom.