another MBC question.

That spinning thing that makes all of the cool noises. OE and Aftermarket.

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dillonr92
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another MBC question.

Post by dillonr92 »

I just want good solid boost.(ive read installing a MBc cleans things up a bit and eliminates problems like the BCS clicking, [which happens alot] and the only 5lbs of boost problem, [this Has only happened once for me]...I also read the vf11 dosnt do much in higher boost ranges so no need to crank it past 11 or 12) IF I INSTALL A MBC ON STOCK VF11. .with only these mods---desnork.coffecup.diamomd coil.ngk plugs. Duralast plugwires..............Will i get better spool .feel more solid power.less hesitation. Better response ??
92 SS winestone red. td04 - FMIC. RWD 5 spd swap/LSD.dead...
94 LEGACY GT RAISED ROOF WAGON, fozzy lift hydro clutch/91SS 5speed/VLSD..#5.NEW FuLL DRiFT SLuT 93SS winestone,RS 5speed RWD. Welded rear, td04, fmic, 17x9 +20
mike-tracy
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Re: another MBC question.

Post by mike-tracy »

I don't think you'll be able to notice any spool up difference in as turbo that small, and a 22t. If you had a td05, maybe. Thats my opinion.
1992 Legacy SS 5mt, build in progress
Josh Colombo wrote: Mon Jan 14, 2002 10:23 am Wait....I'm confused now.
Legacy777
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Re: another MBC question.

Post by Legacy777 »

If you don't have an intercooler, don't bother upping the boost.
Josh

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James614
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Re: another MBC question.

Post by James614 »

What Josh said. You'll make a lot more heat and almost no extra power
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.
dillonr92
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Re: another MBC question.

Post by dillonr92 »

K but i will be ok if i leave the boost. At 10 . At least thats were my gauge hits. I just wanna delete the BCS
92 SS winestone red. td04 - FMIC. RWD 5 spd swap/LSD.dead...
94 LEGACY GT RAISED ROOF WAGON, fozzy lift hydro clutch/91SS 5speed/VLSD..#5.NEW FuLL DRiFT SLuT 93SS winestone,RS 5speed RWD. Welded rear, td04, fmic, 17x9 +20
free5ty1e
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Re: another MBC question.

Post by free5ty1e »

Stock setup @ 10psi ought to be fine. 12psi may be pushing it without an appropriately-installed intercooler and/or larger Walbro 255lph fuel pump, but then you can probably push it to 13-14psi (and at this point you will need a Fuel Cut Defender of some sort to prevent the ECU from saying "NO" after 3 seconds of 13+ psi). Beyond this I wouldn't try to push the stock VF11 turbo much. Gonna start pumping out superheated plasma instead of air and that's not gonna help anything except uncontrolled detonation.

Also, it sounds like you may be now or in the past have been running "regular" octane gasoline (or perhaps have another fuel-related issue). The ECU limits boost to 5-6psi (wastegate boost) when it detects less-than-premium fuel in the system. Going to a MBC may allow you higher boost levels but this is "fixing the symptom and not the cause." The ECU also limits boost to wastegate level from enough knock that it can't correct around.

Especially before cranking the boost up (which you should stop doing around 11psi for several reasons, the main one being the lack of intercooler), I'd heavily recommend turning your efforts towards getting the stock boost control to "behave" -- this is an indication that your ECU is happy with the rest of the setup and you can probably turn your attention to power modifications again :) Once you're regularly running 9psi of solid stock boost levels on every WOT pull, then is the time for a MBC.

To answer your question though, even with my little stock VF11 I noticed the spool difference between MBC and stock BCS. The nice thing about the MBC is that it keeps the wastegate completely closed during spoolup, the stock BCS allows a tiny tiny amount of waste gas by and slows spoolup. What's more, I believe the stock BCS attempts to smooth out things by slowly opening the wastegate as levels closer and closer to the target level are reached - so you should notice better spoolup. (anyone need to correct me here? This is what I've concluded from my experiences...)

Reference thread with relevant discussion on this starts about here: viewtopic.php?f=25&t=46609&p=402245
-Chris
91SS 4EAT stock
91SS 5MT awaiting engine rebuild and VF36...
92SS 4EAT - RIP :(
94SS 5MT4.11+rLSD 289k km: RobTune550,TD05-16g @ 18psi,FMIC,3"TBE,Forester lift
cj91legss
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Re: another MBC question.

Post by cj91legss »

As far as I can tell, that was a pretty good way to put things. The only thing I would like to add to your conclusion is that regular unleaded isn't the only reason the ecu limits boost to 5 PSI. There are several trouble codes that will cause the ecu to go in to limp mode (cutting boost at 5Psi.)
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dillonr92
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Re: another MBC question.

Post by dillonr92 »

Thank you all for the information
92 SS winestone red. td04 - FMIC. RWD 5 spd swap/LSD.dead...
94 LEGACY GT RAISED ROOF WAGON, fozzy lift hydro clutch/91SS 5speed/VLSD..#5.NEW FuLL DRiFT SLuT 93SS winestone,RS 5speed RWD. Welded rear, td04, fmic, 17x9 +20
free5ty1e
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Re: another MBC question.

Post by free5ty1e »

cj91legss wrote:As far as I can tell, that was a pretty good way to put things. The only thing I would like to add to your conclusion is that regular unleaded isn't the only reason the ecu limits boost to 5 PSI. There are several trouble codes that will cause the ecu to go in to limp mode (cutting boost at 5Psi.)
Good point; not just low octane fuel and knock / knock sensor issues cause the limp mode. Those are just where I'd start. They're common issues.

I wanted to add some downsides to the MBC option, just so you are aware of them:

1) Typical MBCs are too simple to really "regulate" boost well. The resulting boost level is highly dependent on engine load. How this manifests: Full boost in 1st gear will be probably a couple PSI LOWER than full boost in 5th gear. Even with a Dawes Devices Hybrid MBC (very decent inexpensive MBC btw), I was seeing probably 13-14 PSI in 1st gear, and 17-18 PSI in 5th gear. You may be able to alleviate this a bit by running the MBC between the intake manifold and wastegate instead of turbo compressor outlet and wastegate, but you will then probably suffer from boost spiking as that is too long of an air circuit to regulate in this fashion. There are also dual-stage boost controllers (TurboXS?) that get pretty fancy mechanically to try and get around this regulation issue, but at that point you are approaching the cost of an EBC setup which would be far better at regulation AND give you a setting to adjust in your cab.

2) If you get an MBC without a center bleed hole (not entirely certain of the technical name for this), your wastegate can remain OPEN between quick shifts / blowoffs. The stock BCS relieves pressure on the wastegate in this situation, allowing it to close much quicker and promotes quicker spoolup for the following shift. (I can only imagine, I've never confirmed this, but I do feel the difference between shifts as I recently went from my MBC back to the stock BCS to troubleshoot some other issues.) I remember seeing an MBC with this feature on this board somewhere but don't have it handy. Anyone know off-hand?
-Chris
91SS 4EAT stock
91SS 5MT awaiting engine rebuild and VF36...
92SS 4EAT - RIP :(
94SS 5MT4.11+rLSD 289k km: RobTune550,TD05-16g @ 18psi,FMIC,3"TBE,Forester lift
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