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Discussion Starter · #1 ·
So as of tonight I finally have a TBE, a 255HP, and a K&N Drop-In on order. After all this is installed I plan on getting tuned and flashed. For boost control, I'm leaning towards keeping the stock BCS and having the boost level tuned in my flash. The reasons I'm leaning towards the BCS as opposed to the MBC are:

I do not plan on changing boost levels often. I do not plan on going to the drag strip often. I do not plan on dumping 110 octane into my fuel tank and cranking up the boost for a few glorifying blasts down the old 1320. It's a street car. When I race it, I plan to race it in full street trim, "as is". I'd like to have my tuner set boost to a relaible 20-21-22 psi and leave it there. Also, I don't like the idea of using my boost gage to set my boost. How accurate is my boost gage reading? Who knows. 2 psi can be a big difference when setting max boost levels. It seems to me that setting the desired boost levels in the stock boost control maps in the stock ecu might be a more accurate way of setting boost. I dunno, maybe it doesn't make much of a difference. Lastly, I like the idea of using OEM hardware to control my boost for reliability reasons. Again, maybe I'm being anal and a MBC would be just as reliable.

My question is, would you guys recommend using a MBC for boost control and if so why? Just looking to cover all my bases and make sure there isn't anything big I'm missing here. Does anyone know how boost is controlled in the stock ecu settings anyway? Is it just a engine speed/engine load map like a fuel or ignition map is? Or simpler than that maybe. I'm guessing there has to be a pressure sensor somewhere that reads intake manifold pressure? Help a brother out. Sorry for the long post. Thanks again in advance.
 

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That's the problem. People think that with a flash, the tuner just chooses the boost from a dropdown list or something, but it's not like that at all. They can't set your boost at all. The tuners who don't recommend MBCs use boost hose modifications with restrictor pills to force the BCS to regulate the boost at a different level. This is not direct control like people seem to think. Because of this, the boost is set based on the boost gauge anyway...or whatever boost sensor the tuner uses. For Dynoflash, when he custom tunes, he hooks up his MAP sensor to read true boost, then tunes and adjusts accordingly. The vast majority of us use our boost gauge. It's not a perfect science, but it's good enough unless the gauge is way off. I pay attention to Al's map sensor logs when he tunes me and compare them with what my boost gauge says. Down at sea level, my gauge was 1psi high.

I still recommend an MBC for direct control. The whole "I want to race in full street trim" is definitely overrated. I do that...put down a good time...then toss in the race gas for some huge power gains and better times. That makes it fun. I race to race, not just to see what my car can do on the street, because I can't do any racing on the street. That part is entirely up to you, but I do understand not caring that much about the occasional race gas run...that's why I got alky so that I could be in full race mode 24/7.
 

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Hey Warr,

You are correct in your thinking...... if you are talking about a DSM where the solenoid is open all the time unless there is knock in which case it closes limiting you to WG spring pressure.

But the EVO is set up like the Subaru's with a WG solenoid duty cycle VS RPM map that Al is able to adjust for different boost levels. He can't get much more than stock pressure in the mid range, but he can reduce the high RPM tapper substantially. Go ahead and ask him about it.

This is one of the areas where your DSM knowledge does not directly transfer over to the EVO :)

Keith

PS: I also think you should go with a MBC by the way. Spool up is always better with an inturupter style boost controler (ball and spring MBC) than it is with a bleader type boost control (stock solenoid, cheap MBC)
 

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Discussion Starter · #5 ·
Fourdoor said:
PS: I also think you should go with a MBC by the way. Spool up is always better with an inturupter style boost controler (ball and spring MBC) than it is with a bleader type boost control (stock solenoid, cheap MBC)
OK, yeah that makes total sense to me. With a bleader type I guess the wastegate would always see at least some boost, whereas with interrupter type it sees zero boost until the spring encounters enough force to lift it off its seat, right? Therefore spool up will be better because the wastegate is staying completely closed for longer, right? I didn't know the stock BCS was bleader type with a duty cycle. I thought it was a gate that was either completely open or completely closed.

Anyways, thanks for the advice. I think I will get a MBC then.
 

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just wondering, what mbc do you guys suggest? and i probably shouldn't get one until after i get my tbe right? and the walbro 255 after all that?
 

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I've had no problems with my Dejon Tool. It is starting to show some rust though, but it's only $50.
Yea, exhaust first. If you like to flog the car for lengths at a time then get the 255 pump. Then go ahead with the boost controller. :thumb:
 

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jluckyp said:
just wondering, what mbc do you guys suggest? and i probably shouldn't get one until after i get my tbe right? and the walbro 255 after all that?
The Forge UNOS and Hallman Pro are considered the two best. I give the Forge the nod, though, because it has a ratcheting knob that lets you know exactly how far you've turned it, because it clicks each time. It makes it very easy to remember how far you've gone or how far you need to go from minimum if it ever gets tampered with. I also use the feature when switching from pump gas to race gas and need to change boost, etc.

You can get it before or after those mods - that's not the problem. You just need to make sure you get the proper COMBINATION of mods before you're done. On an VIII, your stage 1 mods should include:

- TBE
- MBC + boost gauge
- BOV (recirculating only)
- Walbro 255
- Flash (or other type of tune)
 

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what would be a good price for the forge unos? and can it be installed inside the cabin for easier adjustment? also what do you guys think of the greddy profec b II ebc? not worth the money and not necessary is what i would assume since u all use an mbc. thanks for answering my many questions.
 

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$80-90. No, it is not an in-cabin unit, but that is by no means necessary. You don't need to change your boost while you're driving. The only time you change your boost is when you initially install it and when you want to crank it up on race gas when racing. If you have to put in race gas, then changing the boost under the hood is no issue.

I think the Greddy is expensive, complicated, and by no means needed for basic boost control.
 
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