boost control

[greg donovan]

is it possible to set up a MBC that is only "on" during WOT?

so that at any time other than WOT the car is at the stock boost level. i am envisioning some type of switch and a solenoid or something like that.

or do i need to pony up the dough for a EBC?

[vrg3]

Anything's possible.

This would be pretty straightforward. Stick a solenoid in there that's triggered by throttle position. There are a few different "dual stage" MBCs out there, and this is kind of like that.

So, for example, you could use a stock pressure exchange solenoid. Connect its outlet to the wastegate actuator. Connect the compressor outlet nipple to a tee. One side of the tee goes to the PES's primary inlet, and the other side of the tee goes to the MBC inlet. The MBC outlet goes to the PES's secondary inlet. Then you just rig a little circuit to trigger the PES when the throttle opens wide. The simplest way is to mount a microswitch under the gas pedal. Slightly more complex but more elegant might be a simple comparator and a transistor to drive the solenoid.

[greg donovan]

when i get around to modding the car after i get hoses and what not replaced we will have to talk about this again.

i dont need near fuel cut levels of boost all the time.

[vrg3]

Yeah... Most people just suggest dealing with it by being judicious with the throttle.

But it'd be kind of nice not to be strangling the engine and overworking the compressor all the time.

A while back I had envisioned a boost controller that would incorporate a modified throttle linkage. Basically, the ratio of the pulley would be doubled, so when the pedal was halfway down, the throttle plate would be fully open. Beyond that, the signal from the TPS would be used to control boost pressure, which up until that point was limited to wastegate-controlled levels.

[greg donovan]

judicious throttle application is always a good option and much easier and cheaper.

i understand the overworking the compressor part of your statement but do not have a total grasp on the strangling part. im sure once you explain it it will seem obvious. i have a bit more to learn a bout forced induction engines as you can see.

[vrg3]

Well, having the throttle partly closed means you're choking off airflow, right? You're kind of chasing your own tail by making the compressor produce pressure and then restricting flow with the throttle plate to reduce that pressure.

[azn2nr]

i have a turbosmart dual stage and its kinda like that. not exatly but kinda. you could get one like it and set it up on a tps swich so that it would use it as a swich instead of the actual swich that it come with.

most of the time i dont get full boost unless im wot anyway, i do get ptfb sometimes but not verry ofen. mostly when the car is in the wrong gear compared to throtle imput

[greg donovan]

Well, having the throttle partly closed means you're choking off airflow, right? You're kind of chasing your own tail by making the compressor produce pressure and then restricting flow with the throttle plate to reduce that pressure.

i think i understand that.

essentially have more throttle and less boost rather than less throttle and more boost?

[vrg3]

Yep.

[free5ty1e]

I was thinking about this too -

I can easily write firmware for the PSoC that trips at an adjustable voltage level (TPS) and either activates or deactivates a solenoid. This solenoid would bypass the MBC and directly apply boost to the wastegate - the path of least resistance, thereby giving wastegate boost until the solenoid is closed (by the TPS reading tripping the comparator), at which point you'd have MBC boost.

I've got some old Ford fuel injectors lying around, is there any reason why I couldn't just use one of them for the bypass solenoid...? It'd be either full open or full closed, no duty cycles involved...

[vrg3]

I was thinking you'd want a three-way solenoid, but using just a two-way one to bypass the MBC seems like it ought to work too... Or if it's a bleeder-type MBC then the solenoid could just open or close off the bleed.

Will fuel injectors work reliably without a continuous flow of fuel to cool them?

[IronMonkeyL255]

They might.

Under these conditions, they'd only be asked to to open occasionally, instead of the thousands of times per second they are being asked to as fuel injectors.

[free5ty1e]

Yeah, obviously a ball-and-spring style MBC would be recommended for the bypass method I suggested. I only ask about the fuel injector thing because I have a few of them available to me to use.

So ya think using a fuel injector for this application would kill the injector, staying open for long periods of time...?

[vrg3]

I don't know for sure. It's possible. But if you have them lying around it couldn't hurt to try.

What's the injector's flow capacity? It wouldn't be too restrictive or anything like that, right?

[free5ty1e]

good question, lol.... no idea, a friend brought them home from work. Yeah, I hadn't thought about them being too restrictive... the lines for my boost control are 1/4" -- I doubt the injector opens that wide