Can I lower boost with a MBC?

04SexTI · 11-12-2012, 11:58 PM

I have an 06 STI that I bought modded from the previous owner. It is currently tuned to 21 psi and uses a MBC for boost control. My question is, is it safe to turn the boost down to say about 18 psi by adjusting the MBC, or would I also need to get the car tuned again since the current tune is set to 21 psi?

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Black94Snake · 11-13-2012, 12:48 AM

You'll be fine, just turning it down.

OC_Nooby · 11-13-2012, 01:12 AM

lower away, it can only get safer.

04SexTI · 11-13-2012, 02:00 AM

Great, just what I was hoping for. Thanks for the help guys.

Bamofo · 11-13-2012, 08:02 AM

Depends on who tuned it.. In some cases tuners only do it for a small variance of 1-2 psi.... unless they tuned it for stages like 10,15,21 psi then you could hit AFR's that arent desirable as well as too much/too little timing.

the suicidal eggroll · 11-13-2012, 10:47 AM

Quote:

Originally Posted by Bamofo

Depends on who tuned it.. In some cases tuners only do it for a small variance of 1-2 psi.... unless they tuned it for stages like 10,15,21 psi then you could hit AFR's that arent desirable as well as too much/too little timing.

This

Some tuners just set the car to target boost and get the car running correctly there, while the other parts of the table haven't been touched. Lowering the boost could throw you into an untuned region of your map, if so then anything could happen...too much timing, too little timing, too much fuel, too little fuel, etc.

If the car was tuned properly for all conditions up to and including the final target boost, then you'd be fine, but there's no guarantee that it was.

OC_Nooby · 11-13-2012, 01:10 PM

Quote:

Originally Posted by the suicidal eggroll

This

Some tuners just set the car to target boost and get the car running correctly there, while the other parts of the table haven't been touched. Lowering the boost could throw you into an untuned region of your map, if so then anything could happen...too much timing, too little timing, too much fuel, too little fuel, etc.

If the car was tuned properly for all conditions up to and including the final target boost, then you'd be fine, but there's no guarantee that it was.

You guys are correct. Hopefully the tuner did tune the timing map but you wouldn't know until you looked at the map.

NSFW · 11-13-2012, 07:12 PM

Just for the record: Tuners who don't tune for part-throttle suck at their job.

Cars that can't run safely at part-throttle are time bombs.

the suicidal eggroll · 11-13-2012, 08:37 PM

Quote:

Originally Posted by NSFW

Just for the record: Tuners who don't tune for part-throttle suck at their job.

Indeed they do, but it happens...a lot

NSFW · 11-13-2012, 11:17 PM

I don't doubt it.

Bamofo · 11-14-2012, 06:00 PM

Quarter throttle and full throttle with less boost are different stories though :-) whats fun is tuning the newer STI's and setting up different boost maps for I, S and S# then having to tune it all those times. But when its done... holy crap does it make it fun :-)

NSFW · 11-15-2012, 04:55 AM

Quote:

Originally Posted by Bamofo

Quarter throttle and full throttle with less boost are different stories though :-)

How so?

If the ECU crosses through the same cells in the same tables, with the same MAF, same RPM, same load... what difference are you referring to?

Black94Snake · 11-15-2012, 06:43 AM

Quote:

Originally Posted by NSFW

How so?

If the ECU crosses through the same cells in the same tables, with the same MAF, same RPM, same load... what difference are you referring to?

Full throttle for me is ~3.5 load, where quarter and half are significantly less...

Seems like it would make a difference to me.

BlazeRex · 11-15-2012, 09:56 AM

Quote:

Originally Posted by Black94Snake

Full throttle for me is ~3.5 load, where quarter and half are significantly less...

Seems like it would make a difference to me.

I think what's being discussed here is whats the difference between lets say 2.5 load at full throttle with low boost, or 2.5 load high boost at partial throttle.

I personally havent noticed a measurable difference, but in theory the two conditions would be slightly different from one another (more heat and pumping loss at higher boost, lower throttle).

Bamofo · 11-15-2012, 02:01 PM

If you turn down the boost say 2psi or 3psi to run it "safer" you might go from hitting the normal 3.5 down to a peak of 3 now. at half throttle you may only see the 2 load range... i think they are different in tuning... when i think of 1/4 thorttle i think of just barely in boost... my setup may be different then others but... that's all i ment. We are all agreeing here anyways. :-)

04SexTI · 11-15-2012, 04:53 PM

Thank you guys for all the great information. I decided that I will just leave it alone for now use my foot to control the boost. Although, I will slightly be adjusting it lower since its getting colder, thus causing the boost to creep up slightly.

NSFW · 11-15-2012, 11:13 PM

Quote:

Originally Posted by BlazeRex

I think what's being discussed here is whats the difference between lets say 2.5 load at full throttle with low boost, or 2.5 load high boost at partial throttle.

Exactly.

Obviously if the load is different, that matters.

That's not the point.

The point is that the very same boost levels (and the load cells) that you get at part-throttle can be achieved at WOT if you play with WGDC or an MBC. And I don't see why you'd need to retune for the difference.

If I remember right, WOT pulls at 30% throttle give me exactly the same boost as WOT pulls at 100% throttle and 0% WGDC. I actually did some experimentation to figure that out, because I figure it doesn't matter what the WGDC is boost levels lower than whatever you get with 0% WGDC, or at throttle levels lower that whatever it takes to make that much boost.

Black94Snake · 11-16-2012, 06:52 AM

Quote:

Originally Posted by NSFW

WOT pulls at 30% throttle give me exactly the same boost as WOT pulls at 100% throttle and 0% WGDC.

Wait... What?

Methinks this statement needs a revision.

the suicidal eggroll · 11-16-2012, 10:16 AM

Quote:

Originally Posted by NSFW

WOT pulls at 30% throttle

*head explodes*

jthatch12 · 11-16-2012, 10:34 AM

Quote:

Originally Posted by NSFW

If I remember right, partial throttle and full throttle give me exactly the same amount of boost.....blah.. blah.. blah

that sounds better but still doesn't make sense lol

NSFW · 11-19-2012, 02:37 AM

WOT pulls at 30% is, um, wrong.

I just meant "pulls" at 30% throttle. Or, 30%OT pulls, I guess?

I got curious one day, and revised my DBW tables to cap them at progressively lower throttle openings until I got down to WG boost levels, and 30% was it. So with my foot to the floor, the throttle plate went to 30%, and I got 10 or 11 psi, which is the same boost I get with WOT (really WOT this time) and 0% WGDC.

That's with an ATP 3076 and the IWG and actuator that it came with. I'm sure it would vary with different turbos and WGs and WG springs.

Am I making sense yet?

11-12-2012, 11:58 PM	#1
04SexTI Scooby Newbie Member#: 278236 Join Date: Mar 2011 Chapter/Region: International Location: The dirty south Vehicle: '06 sti varies with the seasons	Can I lower boost with a MBC? I have an 06 STI that I bought modded from the previous owner. It is currently tuned to 21 psi and uses a MBC for boost control. My question is, is it safe to turn the boost down to say about 18 psi by adjusting the MBC, or would I also need to get the car tuned again since the current tune is set to 21 psi? * Registered users of the site do not see these ads.

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11-13-2012, 12:48 AM	#2
Black94Snake NASIOC Supporter Member#: 274499 Join Date: Feb 2011 Chapter/Region: NESIC Location: RI Vehicle: 2007 CGM VF'd WRX 12.9 @ 105mph	You'll be fine, just turning it down.

11-13-2012, 01:12 AM	#3
OC_Nooby Scooby Specialist Member#: 311781 Join Date: Feb 2012 Location: Canada Vehicle: 2003 WRX w STI V8	lower away, it can only get safer.

11-13-2012, 02:00 AM	#4
04SexTI Scooby Newbie Member#: 278236 Join Date: Mar 2011 Chapter/Region: International Location: The dirty south Vehicle: '06 sti varies with the seasons	Great, just what I was hoping for. Thanks for the help guys.

11-13-2012, 08:02 AM	#5
Bamofo Scooby Specialist Member#: 159743 Join Date: Sep 2007 Location: Plymouth Ma Vehicle: 07 STI Limited TurboMike Tuned 2.35	Depends on who tuned it.. In some cases tuners only do it for a small variance of 1-2 psi.... unless they tuned it for stages like 10,15,21 psi then you could hit AFR's that arent desirable as well as too much/too little timing.

11-13-2012, 07:12 PM	#8
NSFW Scooby Guru Member#: 140444 Join Date: Feb 2007 Chapter/Region: NWIC Location: Near Seattle, WA Vehicle: 05 Stage Free LGT ATP 3076, 6MT, AVO FMIC	Just for the record: Tuners who don't tune for part-throttle suck at their job. Cars that can't run safely at part-throttle are time bombs.

11-13-2012, 11:17 PM	#10
NSFW Scooby Guru Member#: 140444 Join Date: Feb 2007 Chapter/Region: NWIC Location: Near Seattle, WA Vehicle: 05 Stage Free LGT ATP 3076, 6MT, AVO FMIC	I don't doubt it.

11-14-2012, 06:00 PM	#11
Bamofo Scooby Specialist Member#: 159743 Join Date: Sep 2007 Location: Plymouth Ma Vehicle: 07 STI Limited TurboMike Tuned 2.35	Quarter throttle and full throttle with less boost are different stories though :-) whats fun is tuning the newer STI's and setting up different boost maps for I, S and S# then having to tune it all those times. But when its done... holy crap does it make it fun :-)

11-15-2012, 02:01 PM	#15
Bamofo Scooby Specialist Member#: 159743 Join Date: Sep 2007 Location: Plymouth Ma Vehicle: 07 STI Limited TurboMike Tuned 2.35	If you turn down the boost say 2psi or 3psi to run it "safer" you might go from hitting the normal 3.5 down to a peak of 3 now. at half throttle you may only see the 2 load range... i think they are different in tuning... when i think of 1/4 thorttle i think of just barely in boost... my setup may be different then others but... that's all i ment. We are all agreeing here anyways. :-)

11-15-2012, 04:53 PM	#16
04SexTI Scooby Newbie Member#: 278236 Join Date: Mar 2011 Chapter/Region: International Location: The dirty south Vehicle: '06 sti varies with the seasons	Thank you guys for all the great information. I decided that I will just leave it alone for now use my foot to control the boost. Although, I will slightly be adjusting it lower since its getting colder, thus causing the boost to creep up slightly.

11-19-2012, 02:37 AM	#21
NSFW Scooby Guru Member#: 140444 Join Date: Feb 2007 Chapter/Region: NWIC Location: Near Seattle, WA Vehicle: 05 Stage Free LGT ATP 3076, 6MT, AVO FMIC	WOT pulls at 30% is, um, wrong. I just meant "pulls" at 30% throttle. Or, 30%OT pulls, I guess? I got curious one day, and revised my DBW tables to cap them at progressively lower throttle openings until I got down to WG boost levels, and 30% was it. So with my foot to the floor, the throttle plate went to 30%, and I got 10 or 11 psi, which is the same boost I get with WOT (really WOT this time) and 0% WGDC. That's with an ATP 3076 and the IWG and actuator that it came with. I'm sure it would vary with different turbos and WGs and WG springs. Am I making sense yet?