Big 16g set at 21 psi but falls to 20 psi then 17-18 psi by redline

I have an external wastegate and an MBC. My boost leak tester is not setup yet, but I would like some idea as to whether or not this is typical before I get started.

Thanks

 

Also, this guys issue seems almost like mine!

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[GVR4_1057]

Could be pre turbo exhaust leak. /ubbthreads/images/graemlins/dunno.gif

 

All the 16gs I've ever had would never hold boost to redline.

 

[belize1334]

My s16g held 20+ to redline no problem.

 

Thanks for all of the thoughts...boost leak test coming one day but no so sure that it will help! /ubbthreads/images/graemlins/dunno.gif

 

[belize1334]

A boost leak will cause the turbo to have to move more air to maintain the psi that you're asking for. Since a 16g can only hold about 24psi to redline, a boost leak could easily drop that figure down to 18psi or so. It may not be the problem but it certainly could be. You'd also be running rich if that were the case. Do you have a wideband? Another possible issue is leaking BOV which could also diminish peak boost but wouldn't cause the rich issue if recirculated.

 

Wow, thanks for explaining this to me. I have a wideband and I am running 10.2:1 AFR at WOT...but this is after changing the injectors from 450cc to 650cc and upping the boost. I compensated for the injector size/deadtime in Tuner Pro though. I am not so sure 10.2:1 is pig rich...definitely not optimal but not sure if it meets what you have in mind.

The car ran 10.8:1 AFR not too long ago with 450s @ 16 psi. No other changes were made in tuner pro since then FYI.

How much pressure drop would I expect with the large ETS FMIC I am running?

Also, I am running a BOV that I crushed and measured with a handheld vacuum pump to not open at less than 21 hg so I would guess that I am ok there unless something else weird is going on.

Could you also expand on this a little bit more. "A boost leak will cause the turbo to have to move more air to maintain the psi that you're asking for. Since a 16g can only hold about 24psi to redline, a boost leak could easily drop that figure down to 18psi or so."

Are you saying that since a 16g can only hold boost to 24 psi by default that it would no longer be capable of holding 24 psi due to a boost leak? I guess I don't understand the in's and out's of that part. /ubbthreads/images/graemlins/frown.gif

 

[cheekychimp]

What he is saying is that you are losing pressure post turbo. If you have set your boost controller to give you 21 psi that is the maximum amount of boost the turbo will be able to give before the wastegate opens. If you are losing pressure post turbo, obviously the manifold is never going to see the entire 21 psi perhaps only the 17-18 psi you are getting. It is 'feasible' that by increasing boost to 24 psi you 'might' end up seeing 21 psi at the manifold but if the leak is large enough it is quite likely even doing this will not net you the results you want, apart from which it is a band aid solution and a bad one at that since it would cause you to run rich, which you have already confirmed to be the case.

Do the boost leak test!

 

[belize1334]

The issue I'm describing is a result of the fact that your 16g can only flow so-much-air. On a 2.0L engine, it should be able to hold 23psi or so to redline. But, if you put it on, say, a 2.3L engine which consumes more air to begin with, it may only be able to support 18psi to redline. So, suppose you have a big boost leak or your bov isn't sealing correctly. Then not only is the engine consuming air... but also you're wasting air out the leak. That means that the turbo has to move MORE air then it normally would for a nice tight 2.0L. This is going to reduce the boost level that it can support.

As an exaggerated example. Suppose that you pulled the bov off and didn't seal the flange. You'd have a MASSIVE leak where the bov used to be. Now there's no back pressure from the engine and all the air is fee to just flow right out to atmosphere. The turbo would NEVER build ANY boost. It would overspin and push a sh*t TON of air against zero restriction and you'd get 0 psi, all the way to redline.

Find the leak...

 

/ubbthreads/images/graemlins/grin.gif Thanks for explaining all of this to me. Good information!

 

Well the problem is still happening. I forgot that I posted this here. Could you all please visit this thread?

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Thanks for the brains everyone! /ubbthreads/images/graemlins/grin.gif