legacycentral bbs

I was just curious if anyone had any links, or write-ups on a DIY boost controller. I've seen them before, but I'm looking for something that's already been done and is fairly reliable. I know about the drawbacks of using a MBC vs. an EMC, but I currently don't have the funds for an EBC. Igg, I know you made one up recently, what'd you use? And anyone else that's gone through this, could you guys chime in and let me know what you're using. TIA.

-Brian

Iggdawg used a bleed valve, i believe. in my opinion, bleed valves suck! i would go ball/spring mbc. many people on www.nasioc.com have done this custom for a wrx. might want to check there.

YEah. as far as boost control goes, this bleed valve does suck. HOWEVER, the boost it gives and the reliability/lack of spiking I've had has more comined unsuck than the valve has suck. not only that, but I made it from parts anyone could scrounge from their house. I work as IT at a biotech lab, so finding silicone tube and fittings is no problem .

it bleeds off measured air which is it's only problem. currently I'm working on a nice little 15 cent mod to play with the O2 sensor during closed loop mode that'll make up for it and help with the part throttle/full boost problem.

I'd say go with a ball/spring valve for a MBC. but in all honesty, go for a EBC. MBCs have issues. they allow for full boost at part throttle which can get EGTs to rise quickly. I believe the quote is "you can run rich all the time, but you can only run lean once." there's also increased backfiring from unburned fuel in the exhaust. I'm not a WRC car, so I don't need ALS . also, there's some hesitation at full boost and part throttle which I'm currently trying to figure out. All those aside tho, as long as you know to watch your EGTs and A/F ratio (or at least be aware that funkyness happens and make provisions to see that no problems occur), making a bleed or ball type MBC is dirt cheap and wicked easy.

the next best thing IMO is a BoostMonkey type EBC. one of the guys on NASIOC makes them and sells them for around $120. much cheaper than other EBCs. and I've seen the electronics involved in these EBCs vs. other brands. it's light years ahead. and MUCH more robust. there were some issues early on but those were all ironed out long ago.

Lord knows I spent a while looking around at MBCs. I'm cheap and I had to find a way to feed my power habit. go to www.nasioc.com , hop into the forums, and look for "DIY boost controller" . there's one post with a title like "DIY two stage boost controller" that leads to an outside page. go to that page, and find the way back to the main turbo page of his. there's instructions for a simple bleed valve. basically, you remove the FBC completely. connect the turbo outlet line and the wastegate line from the FBC with a tee fitting. on the 3'rd nipple ( i said nipple ) attach a short line with a check valve to prevent it from sucking vacuum. lastly, attach a valve of some sort. ball valve, needle valve, whatever you want. as long as it has a 3/16ths or so opening. I get 0.065 MPa / 10-ish lbs of boost very consistantly with no spiking to speak of. sometimes it'll spike to 0.07. It is dependant on temperature, so if the temp varries a lot between day and night you might be under the hood a lot.

anyways, any mroe questions feel free to ask.

Mabey you shoud pipe the bleed air back into the intake (after the air flow meter but before the turbo), this might stop the rich running etc.

thought about that, but I'd have to cut a new bung to do it properly. also, I could use the extra richness for partial throttle I guess. MBCs allow for full boost under partial throttle. that being bad, every bit of extra richness I can get is good.

Shouldn't the computer compensate for extra boost ?. It has a pressure sensor to calculate how much fuel to add dependant on the boost. The only trouble that would arise is if the sensor was bottomed out (ie the high boost has pushed the sensor to its stops) however this is probably not likely at 10 psi.

The ECU only uses the pressure sensor for 1) fuel cutoff, 2) boost-dependent ignition retard, 3) boost-dependent mixture richening, and 4) closed-loop boost control.

Fueling is determined primarily using the MAF sensor.

Another issue with an MBC, in addition to the full-boost-at-part-throttle issue, is that it allows full boost in all gears. Our stock ECUs only allow wastegate-limited boost (about 6psi) in first gear to try to protect the gearbox. Some might see this as a drawback and some as an advantage, but it's important to be aware of it.

The autotrannies don't have to worry about full boost in 1st so much as the MTs. most of the WRX guys go to drag strips regularly and launch their autos at 3K RPMs with no issue. there's only been one grenading to date and that was a center diff problem.

back to the full-boost-part-throttle thing... The FBC uses the throttle position sensor to determine how much (up to full boost) it should allow. when you cut it out of the mix, boost is no longer a function of throttle position in any capacity. that's where the problem lies.

Oh, right, automatics... Yeah, they ought to be okay. It will still affect transmission life, but it's not as big a deal as with the manuals.

Yes, the factory setup controls boost based on the TPS. This is also what the Boost Monkey does, I believe; it has two levels of boost that it allows, and switches between them based on a TPS threshold. It wouldn't be too hard to rig something similar up using two ball-and-spring valves, a very simple op-amp circuit, and a solenoid valve.

just to add to this thread and to teh suck of MBCs... it gets really irritating to try and keep it out of part-throttle-full-boost. I can either be in 0-20% throttle or 80-100% throttle. I'm either cruising along and generally keeping up with traffic, or tearing pavement. I can't just cruise by someone when passing... I have to rocket by. Sometimes I want to take this thing off just so I can drive normally again :rolleyes: . at least until I get a boostmonkey and an intercooler.

-IggDawg