eliminating boost creep through mbc???

[91-gsx]

i was wondering if i could eliminate boost creep by making the little hole on the mbc a little bigger, what are your thoughts?
thank you for the replies in advance

 

[DGajre777]

Creating a boost leak by making a small hole in a MBC is not a way to eliminate boost creep. If you want to get rid of boost creep, try porting the turbine housing, manifold and the o2 housing.

 

[91-gsx]

all mbc, i believe, have a vent hole. im not saying im gonna make one, im saying they come with one and it might be beneficial to make it a little bit bigger. that way when the boost spikes past the pre set limit the hole is big enough to vent more of it out. anybody else think this might work or has anybody tried it?

 

[Quasimondo]

The MBC has absolutely nothing to do with boost creep. You can run a line directly from the compressor outlet to the wastegate and still end up with creep.

Boost creep, in a nutshell, is when the wastegate opening is not large enough to properly bypass the turbine on the turbo. If the turbine is not bypassed, then boost cannot be properly controlled. You have two options to fix your problem:

1. Port the wastegate opening to allow more exhaust to flow through.
2. Switch to an external wastegate.

Porting, when properly done usually works out fine. Switching to an external wastegate is expensive, but will definitely cure your boost creep issues.

Search up 'boost creep' for a more detailed explaination from one of the wisemen.

 

[tominatortwo]

ya what he said.

 

[oldman]

i was wondering if i could eliminate boost creep by making the little hole on the mbc a little bigger, what are your thoughts?
thank you for the replies in advance

I know where you're going this, not only it's a bad idea if it would work, it will not work. Assuming you have a ball/spring type mbc, the function of the bleeder hole is to relief wastegate pressure when boost falls under the setting and the ball moves back to it's original position. Without this hole, pressure air will be trapped between your mbc and actuator causing the wastegate to never close. Making the hole larger will result in bleeding off more pressure off the signal to the wastegate resulting in a higher boost level, you can achieve the same thing by raising the boost via the mbc knob, you're effectively trying to convert your ball/spring type mbc into a bleeder type. Raising the boost level has always been a back door solution to curing minor cases of boost creep (the higher the boost level, the later the spool rpm, the less time to creep), the issue here is having a adequate fuel system to support the higher boost level.

I believe your intension is to create a boost leak to control boost creep. Not only it's a terrible idea, to make it work you would have to create this leak before the mbc not after, a 2g bov does a real good job in hiding boost creep. I would much rather see you restrict the exhaust flow, also another bad idea but not as bad as yours. Like already mentioned by Quasimondo above, porting and externals are the only two effective solutions. I prefere porting vs. external because it's free, improves spool and flow at the same time, no noise or high engine temperature .....etc. but most of all, it's a great way to become intimate with your forced induction system. Here are a couple of article/thread that covers exactly where and how much to port. Good luck.

http://www.dsmtuners.com/forums/showthread.php?t=186525
http://www.dsmtuners.com/forums/showthread.php?t=191447

 

[91-gsx]

thanks for the info, but i am not trying to create a boost leak. i know that it very bad, i was under the impression that the hole in the mbc was to bleed off any extra pressure once you have reached your boost level, and it helped smooth things out for the wastegate to open as well... but maybe i was misinformed, but definately do not want to just create a stupid boost leak or restrict my exhaust, that is why i bought the cutout obviously. i also wrongly thought that if i made the hole bigger that once it reached the desired boost and was ready to spike, that the bigger hole would bleed it off too quickly and just in time for the wastegate to do its job. but the real problem is in the housing and the wastegate hole not showing. thanks for the info though. one other question, have any of you ever run open o2 housing? if yes, from experience please, what did you spike to. i am curious because i have the 14b set at 19psi already, do you think it will go way past that?

 

[oldman]

but maybe i was misinformed, but definately do not want to just create a stupid boost leak or restrict my exhaust, that is why i bought the cutout obviously.

You were misinformed there again. In helping many try to solve their boost creep, I have yet to see one cut out setup that worked. Without properly cut out the o2 housing to match the turbine, it can also cause turbulence.

one other question, have any of you ever run open o2 housing? if yes, from experience please, what did you spike to. i am curious because i have the 14b set at 19psi already, do you think it will go way past that?

Boost spike and boost creep are two different things. spike is when boost shoot past the setting then immediately settle back down to the setting. If you're asking about an o2 dump, it's another one of those half ass solutions that will only cure minor case of creep at best. Porting isn't as difficult as it seems so don't be afraid, it's actually addictive once you get started.

 

[91-gsx]

i would do the porting but i would rather just leave the turbo alone because i am thinking of upgrading it soon. what do you mean if the cutout is not matched to the o2 housing, o you mean like having the cutout in a 2.5" tube but the cut out is actually something like 2 3/8"? oldman i have a o2 housing and it does not have a dump, i have heard the dump will help a little, and that they are obnoxiously loud, so i went for the recirculation of exhaust. plus i would rather just dump the whole exhaust... . well even with my restrictive exhaust, i get only boost spike not creep and only like 1-2 psi, so it nothing for me to worry about. i was actually just to ask if boost creep and spike where 2 different things, . i guess they are. so boost creep would be the boost surpassing your preset limit using the mbc and actually staying there without coming back down like spiking?
thanks for the info

 

[oldman]

what do you mean if the cutout is not matched to the o2 housing, o you mean like having the cutout in a 2.5" tube but the cut out is actually something like 2 3/8"?

I'm saying you must port the stock cast o2 housing so the inlet divider area becomes a mirror image of the cutout on the turbine housing, you will not be able to do the required porting on a tubular o2.

well even with my restrictive exhaust, i get only boost spike not creep and only like 1-2 psi, so it nothing for me to worry about.

Boost spike is a mbc/actuator problem nothing to do with exhaust what so ever. If you're tapping the BOV line as your pressure source to you mbc, switch it to the turbo compressor housing and keeping all vacuum hoses as short as possible in and out of the mbc will most likely help if not solve your boost spike.

i was actually just to ask if boost creep and spike where 2 different things, . i guess they are. so boost creep would be the boost surpassing your preset limit using the mbc and actually staying there without coming back down like spiking?

No, that would "all out boost" or "out of control boost". Boost creep is when boost hits the setting first, pause for half a second, then slowly CREEPS up as rpm increases.

thanks for the info

You're welcome.

 

[91-gsx]

I'm saying you must port the stock cast o2 housing so the inlet divider area becomes a mirror image of the cutout on the turbine housing, you will not be able to do the required porting on a tubular o2.

i do not understand what you are talking about, i want to put the cutout right where the bend is like this here(bottom pic), and this cutout is different then the other ones, the end where the cutout is, is bigger then 2.5" so that it is a true 2.5" all the way through. i have a tubular o2 housing that is 2.5" and a downpipe that starts out as 2.5" and then goes to 3" after the flew section. so i do not know what part you are saying will not match up.
http://www.dsmtuners.com/forums/showpost.php?p=1648070&postcount=13 pic of the way i want my cutout to look.

Boost spike is a mbc/actuator problem nothing to do with exhaust what so ever. If you're tapping the BOV line as your pressure source to you mbc, switch it to the turbo compressor housing and keeping all vacuum hoses as short as possible in and out of the mbc will most likely help if not solve your boost spike.

i have read that the best place to tap is the bov line because it is the pressure that your engine is actually seeing.

No, that would "all out boost" or "out of control boost". Boost creep is when boost hits the setting first, pause for half a second, then slowly CREEPS up as rpm increases.

o i see, but wouldnt the mbc stop it from creeping as well as the wastegate, anyway i do not have this problem.

 

[oldman]

i do not understand what you are talking about, i want to put the cutout right where the bend is like this here(bottom pic), and this cutout is different then the other ones, the end where the cutout is, is bigger then 2.5" so that it is a true 2.5" all the way through. i have a tubular o2 housing that is 2.5" and a downpipe that starts out as 2.5" and then goes to 3" after the flew section. so i do not know what part you are saying will not match up.
http://www.dsmtuners.com/forums/showpost.php?p=1648070&postcount=13 pic of the way i want my cutout to look.

Nevermind, I thought you were talking about a turbine housing cut out like the ones SBR sell.

i have read that the best place to tap is the bov line because it is the pressure that your engine is actually seeing.

What you read is not always the truth. This would be true if the boost gauge pressure source is also moved. Since you will be tuning your mbc according your boost gauge which is meassuring the intake manifold pressure, where you tap the pressure surce for your mbc to meassure the manifold becomes a non issue. Tapping off the compressor housing will however help prevent boost spike due to short route pipping and prevent over-boosting the turbo in the case of boost leaks. You especially do not want to tap off the BOV if you have a bleeder type mbc like the TurboXS unit which will result in sucking in un-metered and un-filtered air through the bleeder valve when the system is in vacuum.

o i see, but wouldnt the mbc stop it from creeping as well as the wastegate, anyway i do not have this problem.

No, the only way to use mbc against boost creep is to turn up the boost. The higher the boost setting, the less likelyhood of boost creep. Obviously turning up the boost will require additional supporting mods.

 

[91-gsx]

Nevermind, I thought you were talking about a turbine housing cut out like the ones SBR sell.

never seen them, which one is that?

You especially do not want to tap off the BOV if you have a bleeder type mbc like the TurboXS unit which will result in sucking in un-metered and un-filtered air through the bleeder valve when the system is in vacuum.

i do not think that it would suck in anything big enough to screw you over, but the other reasons you gave me are good enough for me to switch back to the boost source on the comp housing.

do you think that i will encounter any problems with the cutout where i want it, like boost creep or spiking above average?
thanks for the help oldman

 

[oldman]

never seen them, which one is that?

I did a quick search and didn't find the pics but basically it was their attemp to control boost creep by offering porting service in which they port out the divider between the wastegate path and the main path on the outlet of your turbine housing, not a very successful attemp I might add.

do you think that i will encounter any problems with the cutout where i want it, like boost creep or spiking above average?

I think you should be fine. Like I said before, boost spike is a mbc/actuator related and boost creep is mostly turbine housing related.

thanks for the help oldman

You're welcome.